Concentration dependent spectroscopic properties of Sm3+ doped borophosphate glasses

Concentration dependent spectroscopic properties of Sm3+ doped borophosphate glasses

Accepted Manuscript Concentration dependent Spectroscopic properties of Sm3+ doped borophosphate glasses R. Vijayakumar, K. Marimuthu PII: DOI: Refere...

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Accepted Manuscript Concentration dependent Spectroscopic properties of Sm3+ doped borophosphate glasses R. Vijayakumar, K. Marimuthu PII: DOI: Reference:

S0022-2860(15)00256-2 http://dx.doi.org/10.1016/j.molstruc.2015.03.022 MOLSTR 21406

To appear in:

Journal of Molecular Structure

Received Date: Revised Date: Accepted Date:

13 January 2015 6 March 2015 13 March 2015

Please cite this article as: R. Vijayakumar, K. Marimuthu, Concentration dependent Spectroscopic properties of Sm3+ doped borophosphate glasses, Journal of Molecular Structure (2015), doi: http://dx.doi.org/10.1016/ j.molstruc.2015.03.022

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Concentration dependent Spectroscopic properties of Sm3+ doped borophosphate glasses R.Vijayakumar, K.Marimuthu Department of Physics, Gandhigram Rural University, Gandhigram-624302, India Abstract A new series of Sm3+ doped borophosphate glasses 50B2O3+20Li2CO3+10ZnO +9SrCO3+(11–x)P2O5+xSm2O3 (x = 0.1, 0.25, 0.5, 1 and 2 in wt%) have been prepared by following melt quenching technique. The structural and optical properties of the prepared glasses were characterized through XRD, FTIR, absorption, luminescence and decay spectral measurements. The XRD spectrum exhibit broad diffusion at lower angles which reveal the amorphous nature and the presence of various functional groups such as P‒O‒P bonds, B−O vibrations in BO3 units and P‒OH and B‒OH bonds in the title glasses were confirmed through the FTIR spectra. The nature of the metal-ligand bonding and the electronic band structure has been investigated using the absorption spectra. The Judd-Ofelt (JO) intensity parameters (Ω2, Ω4 and Ω6) were evaluated from the JO theory using the refractive index and the experimental oscillator strength values. The emission spectra exhibit four emission bands in the visible region corresponding to the 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2 transitions by monitoring an excitation wavelength at 403 nm. The emission spectra have been characterized through Commission International de I’Eclairage (CIE) 1931 chromaticity diagram to explore the dominant emission from the studied glasses. The radiative parameters such as transition probability (AR), branching ratios (R) and stimulated emission cross-section (

) were obtained

for the emission transitions using JO parameters and the results were discussed and compared with the reported literature. Keywords: Absorbance, Bonding parameters, Judd-Ofelt parameters, Radiative properties, Decay curves, CIE diagram *

Corresponding author. Tel.: +91 451 2452371; Fax: +91 451 2454466.

E-mail address: [email protected] 1. Introduction Glasses containing trivalent rare earth (RE) ions are promising luminescent materials for optical detectors, sensors, lasers, color displays and light emitting diode device applications due to their intense emissions in the visible and near infrared region. The transitions between the 4f 1

electronic states of the RE ions provide excitation and emission spectra of the optical materials sensitive to the ligand field environment, structure, phonon energy of the host and symmetry around the RE ion site. The absorption and luminescence spectra of the RE doped glasses when compared to the crystals deserves much attention in spectroscopic as well as in technological point of view [1,2]. A thorough investigation on the spectroscopic properties of RE doped glasses is essential to design new efficient optical devices or to improve the performance of the existing devices for optoelectronic applications because it provides valuable information about the important parameters like energy level structure, transition probabilities, lifetime and stimulated emission cross-section which contribute to the optical gain of the RE doped optical devices. It is essential to find an appropriate host for RE ion doping due to its crucial role in the development of efficient optical devices because of the fact that the absorption and emission spectral intensities exhibit considerable dependency on the ligand field environment around the RE ion site. The phosphate glasses are useful for the fabrication of solid state batteries and solid state ionics due to their peculiar properties like high refractive index, low melting and glass transition temperatures, high thermal expansion coefficient and high transparency to UV and far infrared radiations etc., The borate based glasses are suitable for RE 3+ ion doping because of their important properties like larger RE ion solubility, high transparency and high thermal stability. However, pure borate and phosphate glasses are not stable and their properties differ from the mixed borophosphate glasses. Since the phosphate based glasses possess less chemical durability and high hygroscopic nature which inturn limits its applicability in the fabrication of opto-electronic devices [3,4]. The addition of B2O3 improves the chemical durability of the phosphate glasses by changing the glass network along with the formation of new cross-linked BOP bonds [5]. In order to avail the advantages of both phosphate and borate networks it is combined together to attain good optical quality glasses for optoelectronic applications. The Sm3+ doped optical materials are more attractive compared to the other RE ions incorporated materials due to their practical importance in the applications of color display devices, solid state lasers and high-dose measurements in the medical radiation dosimetry etc., The Sm3+ ions 4f6 electronic configuration exhibit four intense emission bands in the visible region corresponding to the 4G5/26H5/2, 6H7/2, 6H9/2 and 6H11/2 transitions. Among them, the reddish orange emission around 602 nm corresponding to the 4G5/26H7/2 transition of the Sm3+ 2

ion is useful for high density optical storage and undersea communication applications [6]. Further, this reddish orange emission band does not get affected by the multiphonon nonradiative decay because of the fact that the energy difference between the emission level and the next lower level (~7250 cm–1) is very much higher than the phonon energy of the borate glasses [7] which increases the flexibility of Sm3+ ions doped optical materials for many applications. Considerable work has been carried out on Sm3+ doped glasses quite recently. The spectroscopic and laser properties of Sm3+ doped lithium fluoroborate glasses were investigated by Swapna et al. [6]. Sooraj Hussain et al. [8] have analyzed the luminescence behavior of Sm3+ ions activated borophosphates glasses. The absorption and emission spectra of Sm3+ ions doped borophosphate glasses were analyzed and reported by Aruna et al. [9]. The optical properties of Sm3+ doped cadmium bismuth borate glasses were characterized by Sailaja et al. [10]. The concentration dependent structural and optical properties of Sm3+ doped borophosphate glasses were examined by Hongbin Liang et al. [11]. The spectroscopic properties of Sm3+ ions doped borophosphate glasses deserves much importance due to their versatile applications in the field of optoelectronics. Considering the practical importance it is proposed to synthesis Sm3+ doped borophosphate glasses and study their structural and spectroscopic properties by varying the RE ion concentration. The XRD spectra have been recorded to confirm the amorphous nature and the presence of various functional groups in the studied glasses were explored through the FTIR spectral analysis. The Judd-Ofelt (JO) intensity parameters (Ω2, Ω4 and Ω6) derived from the absorption bands were used to obtain the radiative properties such as transition probability (AR), branching ratios (R) and stimulated emission cross-section (

) from the luminescence spectra

which are useful for the fabrication of new solid state laser devices and the results were discussed and compared with the similar reported literature. 2. Experimental In the present study, Sm3+ doped borophosphate glasses have been prepared by employing melt quenching technique following the procedure reported in literature [12]. The high purity (99.99%) analytical grade chemicals such as H 3BO3, Li2CO3, ZnO, Sr2CO3, 2[NH4H2PO4] and Sm2O3 were used as raw materials and the detailed compositions and sample codes are as follows. ZSBP0.1Sm : 50B2O3+20Li2CO3+10ZnO+9SrCO3+10.9P2O5+0.1Sm2O3 3

ZSBP0.25Sm : 50B2O3+20Li2CO3+10ZnO+9SrCO3+10.75P2O5+0.25Sm2O3 ZSBP0.5Sm : 50B2O3+20Li2CO3+10ZnO+9SrCO3+10.5P2O5+0.5Sm2O3 ZSBP1Sm

: 50B2O3+20Li2CO3+10ZnO+9SrCO3+10P2O5+1Sm2O3

ZSBP2Sm

: 50B2O3+20Li2CO3+10ZnO+9SrCO3+9P2O5+2Sm2O3

The refractive indices of the studied glasses were measured at sodium wavelength (5893A°) using Abbe refractometer and 1-bromonapthalene was used as the contact liquid. The density measurements were made following Archimedes principle using xylene as an immersion liquid. The absorption spectral measurements were made employing JASCO V570 spectrometer in the wavelength region 350–1700 nm with a spectral resolution of ± 0.1 nm. The luminescence spectral measurements were made using Perkin-Elmer LS55 spectrophotometer in the wavelength region 535–735 nm with a spectral resolution of ± 0.1 nm. Jobin-Yvon Fluorolog-3 Spectrofluorometer was employed to measure the decay curves of the studied glasses using xenon flash lamp as an excitation source. All these spectral measurements were carried out at room temperature (RT) only. The physical properties of the prepared glasses have been calculated and presented in table 1. 3. Results and Discussion 3.1. Structural analysis 3.1.1. XRD and FTIR spectral analysis The XRD pattern of the prepared glasses exhibit broad diffused scattering at lower angles without any sharp peaks thus confirms the amorphous nature and as a representative case XRD pattern of the ZSBP0.5Sm glass is shown in figure 1. The FTIR spectra of the prepared ZSBPxSm glasses recorded in the region 4004000 cm−1 are shown in figure 2. The observed band positions and their assignments corresponding to the various fundamental stretching vibrations of borate and phosphate groups are presented in table 2. The band observed at 574 cm−1 is due to the bending vibrations of O‒P‒O bonds and the presence of symmetric vibrations of P‒O‒P chains in the prepared glasses have been confirmed through the band centered at around 724 cm−1 [13]. The band observed at 1037 cm−1 is ascribed to the symmetric stretching vibrations of BO4 and PO4 units. The band at 1390 cm−1 in the IR spectra is caused by the B−O bond vibrations in BO3 units and also due to the P=O linkage [14]. The band around 1628 cm−1 is assigned to the vibrations of O‒H, P‒OH and B‒OH bonds [13]. The band observed around 2856‒2931 cm−1 is due to the presence of hydrogen bond in the 4

prepared glasses. The presence of fundamental stretching of OH groups in the prepared glasses has been confirmed through the band observed at 3438 cm−1. 3.2. Optical properties 3.2.1. Absorption spectra and bonding parameters The UV-Vis-NIR optical absorption spectra of the prepared glasses have been recorded in the wavelength region 350–1700 nm and as a representative case absorption spectrum of the ZSBP2Sm glass is shown in figure 3. The absorption spectra exhibit twelve absorption bands centered at around 360, 374, 402, 415, 437, 473, 937, 1073, 1223, 1368, 1472 and 1582 nm corresponding to the various excited states such as

4

D3/2,

6

P7/2, 4L15/2+4L13/2+4F7/2+6P3/2,

4

M19/2+6P5/2, 4G11/2+4M17/2+4F5/2, 4I13/2+4I11/2 +4M15/2 +4I9/2, 6F11/2, 6F9/2, 6F7/2, 6F5/2, 6F3/2+6H15/2 and

6

F1/2 respectively from the 6H5/2 ground state and the band assignments were made based on the

reported literature [12]. The absorption band assignments and the corresponding band positions of the prepared ZSBPxSm glasses are presented in table 3. From the absorption spectra it is observed that the intensity of the bands observed in the NIR region are found to be more intense compared to the bands in the UV-Vis region because of the fact that the transitions from the 6H5/2 ground state to the excited states such as 6FJ (J=11/2, 9/2, 7/2, 5/2, 3/2 and 1/2) and 6H15/2 are spin allowed |S|=0 [15]. Among the observed transitions,

6

H5/2→6F1/2,

6

F3/2 transitions are

hypersensitive in nature which obey the selection rules |S|=0, |L|2 and |J|2 and are sensitive to the ligand field environment around the RE ion site. Due to the overlapping of 4f electronic orbitals of the RE ions with the oxygen orbitals caused by the Nephelauxetic effect the RE ions exhibit shift in their energy level positions when doped into the glass matrices. This change in RE ion energy level positions gives an idea about the nature of the bonding between RE-ligand and oxygen. The metal-ligand bonding nature has been evaluated from the Nephelauxetic ratios () and bonding parameter (δ) studies. The Nephelauxetic ratio (=c/a) is defined as the ratio of wave number of a particular RE ion transition (c) to the corresponding aquo-ion transition (a). The δ values can be calculated using the below given expression [16], 

1 



100

(1)

where,  is the average value of the Nephelauxetic ratios (). The calculated  and δ values of the studied glasses are presented in table 3 and the negative sign of the δ values specify the ionic nature of the Sm−O bond in the title glasses. Generally, interactions of network former with the 5

surrounding oxygen ions determine the strength of the covalency between RE 3+–O. Due to the difference in electro negativity of the two network formers, the interaction of phosphate ions with the surrounding oxygen is stronger compared to the boron and it controls the polarization of oxygen upon Sm3+ ions. In the present study, there exist two network formers (P5+ and B3+) and the decreasing P2O5 content enhances the interaction of oxygen atoms with the Sm3+ ions which leads to have slight monotonic decrease in ionicity of the Sm−O bond in the prepared glasses [17]. The addition of Sm2O3 content into the glass matrix causes only a slight deviation in the energy level positions of the Sm3+ ions which has been observed from the average Nephelauxetic ratio values that exhibit minor changes as is presented in table 3. 3.2.2. Band gap and Urbach’s energy studies When electromagnetic radiations interact with the electrons in the valence band, then the electrons in the valence band reaches the conduction band by absorbing the photons of energy higher than the band gap energy of the material. This type of transitions occurs in crystalline and non-crystalline materials at the fundamental absorption edge directly or through phonon assistance called direct/ indirect allowed transitions [18]. The electronic band structure of the RE doped materials can be studied through the optical absorption spectra. The absorption coefficient α( ) as a function of photon energy (h ) can be expressed using Mott and Davis theory [19] as, (2) where, h is the photon energy, B is the band tailing parameter, E g is the optical band gap energy and n is an index number and it can be (n=1/2) for direct allowed transitions and (n=2) for indirect allowed transitions respectively. The direct and indirect band gap (Eg) values of the prepared glasses were obtained by extrapolating the linear region of the Tauc’s plot as shown in figure 4 and the calculated values are presented in table 4. Both direct and indirect band gap values increases with the increase in Sm3+ ion concentration and the addition of Sm3+ ions produces structural changes in the studied glasses which leads to have change in the Eg values. At the same time, fall in P2O5 content attribute to the decrease in non-bridging oxygens in the prepared glasses thus shift the valence band in the direction opposite to the conduction band and the same may be the reason for the increase in Eg values [19]. The increasing band gap values is the evidence for decreasing ionicity of Sm3+–O bond in the prepared glasses [20] and the trend coincide with the results obtained from bonding parameter values.

6

When photons having energy less than that of band gap energy, the absorption coefficient at the fundamental edge follows exponential decay of the localized states which is extended into the forbidden band gap [19]. The width of the tail of the localized states called Urbach energy gives the degree of disorderliness and defects in the prepared glasses. At lower absorption region ( <104), the absorption coefficient exhibit exponential variation to the photon energy and follows the Urbach rule given by [21],

 h       0 exp    E  where,

0

(3)

is a constant and ΔE is the Urbach’s energy. The ΔE values of the prepared glasses

were calculated by taking the reciprocal of the slope at the linear region of the Urbach curves obtained by plotting ln against the photon energy. The Urbach energy values of the studied glasses are presented in table 4 and it is observed from the table that the Urbach energy values decreases with the increase in Sm3+ ion content in the prepared glasses. Insert of figure 4 shows the comparison between the direct band gap and Urbach energy of the studied glasses and it is observed from the figure that the Urbach energy varies inversely with the band gap values. The fall in ΔE values signify that the prepared glasses possess minimum defects because of the fact that weak bonds with lower Urbach energies could not be converted into defects. Further, lower Urbach energy values lead to have lesser disorderliness in the studied glasses facilitating long range order. 3.2.3. Oscillator strength and Judd-Ofelt analysis The experimental oscillator strength (ƒexp) is the strength of the absorption transition and is calculated from the integrated area under the absorption bands using the below given expression,

2.303mc2 f exp  ( )d  4.318  109   ( )d 2  Ne

(4)

where, m is the mass of an electron, c is the velocity of light, N is the Avagadro number, e is the charge of an electron and ε() is the molar absorptivity of the band at a wave number  (cm1). The calculated oscillator strength (ƒcal) of the electric dipole transitions from the ground state (J) to the excited state (’J’) within the 4f configuration can be obtained using JO theory [22,23] from the following expression,

7

2  8 2 mc   n 2  2   ' ' f cal =  .      2 , 4 , 6   J U  J   3h2 J  1  9n 





2

(5)

where h is the planck’s constant, J is the total angular momentum of the ground state, n is the refractive index of the prepared glasses, Ω  (λ=2, 4 and 6) are the JO intensity parameters and 2

║U2║ , ║U4║

2

and ║U6║

2

are the doubly reduced square matrix elements and their values

were chosen from the reported literature [24]. The JO intensity parameters were obtained from the absorption spectra by taking the least square fitting approximation between the experimental and calculated oscillator strengths [22,23]. The ƒexp and ƒcal values along with the root mean square (σrms) deviation values are presented in table 5. The lower σrms values indicate the quality of the fit between ƒexp and ƒcal values and the validity of the JO theory. The Ω2 intensity parameter is mainly affected by the asymmetry of the ligand field environment around the RE3+ ions as well as the covalency of the RE–O bond. The Ω4 and Ω6 parameters are related to the bulk properties such as viscosity and rigidity of the RE–O bond in the RE3+ doped glasses [25]. The calculated JO intensity parameters of the prepared glasses along with the reported Sm3+ glasses are presented in table 6. The JO intensity parameters of all the prepared glasses follow the trend as Ω4> Ω6 >Ω2 similar to the reported glasses [26–30]. It is observed from table 6 that the Ω2 value decreases upto 0.5wt% of Sm3+ ion content beyond that increases similar to the reported Sm3+ doped borate glass [31]. Generally, both the covalency of the metal-ligand bond and the asymmetry of the ligand field environment around the RE 3+ ion site contribute together for the determination of Ω2 values. But, Ω2 intensity parameter exhibit less dependency on the covalency and is highly sensitive to the asymmetry of the ligand field environment [32,33]. The structure of the borophosphate glass consists of strongly distorted network as a result of three network formers such as [BO3] trihedra, [BO4] tetrahedra and [PO4] tetrahedra groups [17]. Initially, Sm3+ ions are located in a higher asymmetrical ligand field and the asymmetry decreases upto 0.5wt% Sm2O3 content as P2O5 content decreases which may be due to the reduction in the formation of [PO4] tetrahedra groups. Further, asymmetry of the RE 3+ ion site is related to the Sm−O bond length and polarizability of the surrounding oxygens. At higher Sm2 O3 content, the ligand atoms (oxygen atoms) located around the Sm3+ ions are highly affected and hence there is a fall in average Sm−O bond length in the prepared glasses which exhibit strong field around the Sm3+ ion site [34]. Consequently, symmetry of the ligand field around the Sm3+ ion site becomes lower and in turn leads to have slight increase in the Ω2 values at higher Sm3+ 8

ion concentration. The spectroscopic quality factor (Ω4/Ω6) of the prepared glasses has been obtained in order to characterize the optical quality and stimulated emission of the prepared glasses. The calculated (Ω4/Ω6) values of the studied Sm3+ doped borophosphate glasses are found to be higher than the reported Borophosphate [8], LBTAF [26], Lead borate [30] glasses and lower than the KTFB [27], B3TS[28], 1SmPbFB [29] glasses. The higher (Ω4/Ω6) values specify the fact that the studied glasses possess good optical quality and are suitable for photonic applications. 3.2.4. Fluorescence dynamics and Radiative properties The excitation spectra of the prepared glasses have been recorded in the wavelength region 325500 nm monitoring an excitation wavelength at 598 nm and as a representative case excitation spectrum of the ZSBP0.5Sm glass is shown in figure 5. The excitation spectra exhibit six excitation bands at around 344, 373, 403, 437, 465 and 472 nm corresponding to the transitions 6H5/2→4H9/2, 6H5/2→4D1/2, 6H5/2→4F7/2, 6H5/2→4G9/2, 6H5/2→4I13/2 and 6H5/2→4I11/2 respectively. It is observed from figure 5 that the band at 403 nm attributed to the 6H5/2→4F7/2 transition possess higher intensity compared to all other excitation bands and the same may be used as an excitation wavelength to record the luminescent spectra. The luminescence spectra of the present glasses have been recorded in the wavelength region 535 735 nm and are shown in figure 6. The emission spectra exhibit four emission bands at around 561, 598, 644 and 709 nm corresponding to the

4

G5/26H5/2,

4

G5/26H7/2,

4

G5/26H9/2 and

4

G5/26H11/2 transitions

respectively. Among them the emission band attributed to the 4G5/26H7/2 transition exhibit reddish-orange emission due to the mixed magnetic-electric dipole transitions and possesses maximum intensity. The intensity ratio can be defined as the ratio of the intensities of the electric dipole (ED) to the magnetic dipole (MD) transitions and is used to examine the symmetry around the Sm3+ ion site. In the present study, the intensity ratio has been measured as a ratio between the intensity of the 4G5/2→6H9/2 (ED) transition to the 4G5/2→6H5/2 (MD) transition. The intensity ratio values are found to be 3.19, 3.18, 2.96, 2.95 and 2.69 corresponding to the ZSBP0.1Sm, ZSBP0.25Sm, ZSBP0.5Sm, ZSBP1Sm and ZSBP2Sm glasses respectively. The decreasing intensity ratio values indicate the fact that the Sm3+ ions are surrounded by higher symmetrical environment in the studied glasses. The JO intensity parameters (Ω2, Ω4, Ω6) and refractive index were used to obtain the radiative parameters like transition probability (AR), branching ratios (R), effective line width 9

(∆λeff), and stimulated emission cross-section ( 4

) for the emission transitions such as

G5/2→6H5/2, 6H7/2, 6H9/2 and 6H11/2 using JO theory [22,23]. The radiative properties for the

emission transitions corresponding to the ZSBP0.5Sm glass were presented in table 7 along with the reported Sm3+ doped glasses [3537]. The higher branching ratio and stimulated emission cross-section value is the characteristics feature to obtain lasing action. The branching ratio value corresponding to the 4G5/2→6H7/2 transition of the studied ZSBP0.5Sm glass is found to be 50% thus indicates that effective laser action can be achieved. From the tabulated results, it is observed that the mixed magnetic-electric dipole transition (4G5/2→6H7/2) possess maximum stimulated emission cross-section than the other transitions and is found to be higher compared to the reported CdBiB [35], TZKCSm10 [36], A2 [2] and LiPbFP [37] glasses. The optical gain (  PE ×exp) and gain bandwidth (  PE ×∆λeff) are the essential parameters for the fabrication of

efficient optoelectronic devices. The (  PE ×exp) and (  PE ×∆λeff) values of the 4G5/2→6H7/2 transition is found to be 14.29, 16.28, 13.69, 8.92, 3.57 (×1025cm2s) and 69.92, 86.35, 96.23, 88.94, 90.39 (×1022 nmcm2) corresponding to the ZSBP0.1Sm, ZSBP0.25Sm, ZSBP0.5Sm, ZSBP1Sm, ZSBP2Sm glasses respectively. Among the studied glasses, 4G5/2→6H7/2 transition of the ZSBP0.5Sm glass exhibit higher A, R,  PE and gain bandwidth values and the same can be used as a potential active medium in solid state lasers for reddish-orange emission centered at 598 nm. 3.2.5. CIE chromaticity coordinates In order to explore the emission color of the present Sm3+ doped glasses, emission spectra were characterized using CIE 1931 chromaticity diagram. Using CIE 1931 chromaticity diagram, the composition of any color can be illustrated in terms of three primary colors such as blue, green and red. The spectral color can be obtained by adding three artificial colors called tristimulus values (X, Y and Z). The chromaticity coordinates (x, y, z) were calculated by taking the ratios of the X, Y, Z of the emission light to the sum of the three tristimulus values [7,38] . In general, color chromaticity coordinates (x,y,z) are calculated using the below given expressions x=

(6)

10

y=

(7)

z=

(8)

The standard x, y coordinates (where x=0.33 and y=0.33) corresponding to the location of the white light emission is always situated at the center of the CIE 1931 chromaticity diagram. The (x, y) values of the prepared glasses were calculated from the emission spectra and the values are found to be (0.598, 0.387), (0.602, 0.389), (0.604, 0.391), (0.604, 0.389) and (0.581, 0.382) corresponding to the ZSBP0.1Sm, ZSBP0.25Sm, ZSBP0.5Sm, ZSBP1Sm and ZSBP2Sm glasses respectively. The CIE 1931 diagram for the Sm3+ doped borophosphate glasses is presented in figure 7 and it is observed from the figure that the x,y coordinates were mostly located in the orange-red region of the CIE 1931 diagram. This indicates the fact that the reddish-orange emission can be achieved with the prepared Sm3+ doped borophosphate glasses. 3.2.6. Decay curve analysis and Quantum efficiency The luminescence decay profile corresponding to the 4G5/2 level of the Sm3+ doped borophosphate glasses have been recorded monitoring an excitation at 403 nm and emission at 598 nm and the same is shown in figure 8. The decay curves of the present glasses exhibit single exponential behavior for lower concentration (0.1wt% of Sm3+ ion content) and turn to nonexponential behavior due to the ion-ion interaction which takes place between the nearby Sm3+ ions at higher concentration. The experimental lifetime of the prepared glasses have been obtained by using single and non-exponential fitting methods and can be expressed as [39], =

(single exponential)



(9)



(non-exponential)

(10)

where It and I0 are the luminescence intensities at time t and at t=0 respectively, τ is the lifetime of the excited state. 1 and 2 are the lifetimes of the two channels involving decay processes, A1 and A2 are decay constants. The experimental lifetime (exp) values of the non-exponential decay curves were obtained by using the below given expression, (11) The obtained experimental lifetime values of the present glasses are found to be 1.9904, 1.8206, 1.5108, 1.0005 and 0.4033 ms corresponding to the ZSBP0.1Sm, ZSBP0.25Sm, ZSBP0.5Sm,

11

ZSBP1Sm and ZSBP2Sm glasses respectively. The exp values of the ZSBPxSm glasses gradually decreases as the Sm3+ ion content increases and it may be due to the efficient energy transfer process which takes place between the Sm3+ ions either by cross-relaxation or by multiphonon non-radiative decay [1,40]. The energy transfer by multiphonon relaxation is negligible for the present Sm3+ doped glasses due to the large energy gap (7250 cm1) between the 4G5/2 level and the next lower level which is very much higher than the phonon energy of the host. Therefore, energy transfer between Sm3+ ions occurs mainly due to the cross-relaxation mechanism. In RE3+ doped glasses, cross-relaxation arises between two nearby RE3+ ions when their absorption and emission levels are separated by equal amount of energy. During the crossrelaxation, donor ions in the higher excited state give part of its energy to the ground state ion (acceptor) and bring it to the metastable state. Finally, both the donor and acceptor ions come to the ground state by means of non-radiative decay. The energy level diagram of the Sm3+ ions and the potential cross-relaxation channels are shown in figure 9. In the present study, energy of the donor emissions such as

4

G5/2→6F5/2,

4

G5/2→6F7/2,

4

G5/2→6F9/2 and

4

G5/2→6F11/2 are

approximately equal to the energy of the acceptor absorptions such as 6H5/2→6F11/2, 6H5/2→6F9/2, 6

H5/2→6F7/2 and 6H5/2→6F5/2 respectively. The donor ions (Sm3+ ions) in the excited state (4G5/2)

transfers part of its energy to the acceptor ions (Sm3+ ions) in the ground state (6H5/2) and bring them to the 6F5/2, 6F7/2, 6F9/2 and 6F11/2 metastable states. Later, the ions in the metastable states relax to the ground state non-radiatively. The rate of energy transfer by cross-relaxation can be represented as [40],

 The





(12)



values of the present glasses are found to be 258, 296, 364, 673 and 1929 s1 analogous

to the ZSBP0.1Sm, ZSBP0.25Sm, ZSBP0.5Sm, ZSBP1Sm and ZSBP2Sm glasses respectively. Thus the increase in energy transfer rate is due to the large difference between the calculated and experimental lifetime values. The quantum efficiency (η) can be defined as the ratio of number of photons emitted to the number of photons absorbed. For rare earth ions, it is the ratio between the experimental and the radiative lifetimes of the excited state 4G5/2 and can be expressed as,

η=

100

(13)

The calculated η values of the prepared glasses are given in table 8 and it is observed that the η values are found to decrease as the concentration of the Sm3+ ions increases due to the 12

efficient energy transfer between the Sm3+ ions (donor and acceptor ions) in the studied glasses. For the present case, the energy transfer process takes place between the donor and acceptor ions can be explained by fitting the decay curves into IH model (Inokuti-Hirayama model) [41] using the expression,   t  t I (t )  I 0 exp   Q    0  0

  

3/ S

    

(14)

where t is the time after excitation, 0 is the intrinsic decay time of the donors (without acceptor ions) and S can have values as 6, 8 and 10 depending upon the dipole-dipole (DD), dipolequadrupole (DQ) and quadrupole-quadrupole (QQ) interactions respectively. Then, Q is the energy transfer parameter and can be written as,

Q

4  3  1   N 0 R03 3  S

(15)

where, N0 is the acceptor ion concentration per cubic centimeter which is roughly equal to the RE ion concentration, the (x) function is equal to 1.77 for DD, 1.43 for DQ and 1.3 for QQ interactions respectively and R0 is the critical transfer distance equal to the decay rate (o1) of the donor ions. The donor-acceptor interaction parameter (CDA) can be obtained using the below given expression, (16)



The decay curves of the prepared Sm3+ doped borophosphate glasses have been well fitted to the IH model for S=6 compared to S=8 and S=10 which confirms the fact that the energy transfer process is mainly due to the dipole-dipole interaction which takes place between the Sm3+ ions in the prepared glasses. The Q, R0 and CDA values were determined from the IH fitted curves of the studied glasses and are presented in table 8. Of all the studied glasses, ZSBP2Sm glass exhibit higher Q, R0 and CDA values similar to the reported Sm3+ doped glasses [26,42,43]. The emission spectra of the prepared glasses show that the luminescence intensity increases upto 0.5wt% of Sm3+ ion content and then decreases due to luminescence quenching. In RE doped materials, luminescence quenching occurs as a result of efficient energy transfer which takes place between RE3+–RE3+ ions. The non-exponential behavior becomes stronger when the Sm3+ ion content exceeds 0.5wt% and is due to the energy transfer process which takes place between the nearby Sm3+ ions. This non-radiative energy migration process gives rise to luminescence quenching in 13

the prepared glasses [44,45]. The Q, R0 and CDA values are found to be more for higher Sm3+ ion content thus indicates the occurrence of efficient energy transfer process in the prepared glasses. Considering these energy transfer parameters, luminescence intensity and the CIE color coordinates can be optimized by adjusting the Sm3+ ion concentration for orange LED’s and visible laser applications. 4. Conclusion The amorphous nature was confirmed through the XRD spectral measurements. The presence of various stretching and bending vibrations of different borate and phosphate networks have been identified from the FTIR spectra. The ionic nature of the Sm3+ metal ligand bonding have been explored from the absorption spectral measurements and the ionicity decreases due to the decrease in P2O5 content because of the fact the polarization of oxygen upon Sm3+ ions is higher. The Eg values are found to increase with the Sm3+ ion content due to the fall in nonbridging oxygens in the prepared glasses which shift the valence band in the downward direction. The Urbach energy is inversely proportional to the band gap values and the lower ΔE values indicate the minimum defects and less disorderliness in the title glasses. The lower Ω2 intensity parameter values and the decreasing intensity ratio values prove that Sm3+ ions are located in a higher symmetrical environment and the same is further confirmed through the more ionic nature of the SmO bond. The 4G5/2→6H7/2 transition of the ZSBP0.5Sm glass exhibit higher A, R,  PE and gain bandwidth values and can be used as a potential active medium for the fabrication of visible lasers. The x,y coordinates of the studied glasses passes through the reddish-orange region in the CIE 1931 diagram and are suitable for orange LED and visible laser applications. The decay profile of the studied glasses exhibit single exponential behavior for lower Sm3+ ion concentration and becomes non-exponential for higher Sm3+ ion content. The non-exponential decay curves were well fitted to the IH model for S=6 confirming the fact that the energy transfer occurs between Sm3+ ions is mainly due to dipoledipole interactions.

14

References [1] K. Swapna, Sk. Mahamuda, A. SrinivasaRao, T. Sasikala, L. Rama Moorthy, J. Lumin. 146 (2014) 288–294. [2] Fakhra Nawaz, Md. Rahim Sahar, S.K. Ghoshal, Asmahani Awang, Ishaq Ahmed, Physica B 433 (2014) 89–95. [3] N. Kiran, C.R.Kesavulu, A.SureshKumar, J.L.Rao, Physica B 406 (2011) 1897–1901. [4] Aliff Rohaizada, Rosli Hussina, Nur Aimi Syaqilah Aziza, Royston Uninga, Nur Zu Ira Boharia, Jurnal Teknologi, 62 (2013) 119–122. [5] K. Srinivasulu, I. Omkaram, H. Obeid, A. Suresh Kumar, J. L. Rao, J. Phys. Chem. A 116 (2012) 3547−3555. [6] K. Swapna, Sk.Mahamuda, A. Srinivasa Rao, T. Sasikala, D. Haranath, G. Vijaya Prakash, Spectrochim. Acta Part A 125 (2014) 53−60. [7] Sd. Zulfiqur Ali Ahamed, C. Madhukar Reddy, B. Deva Prasad Raju, Spectrochim. Acta Part A 103 (2013) 246−254. [8] N. Sooraj Hussain, V. Aruna, S. Buddhudu, Mater. Res. Bull. 35 (2000) 703–709. [9] V. Aruna, N. Sooraj Hussain, and S. Buddhudu, Mater. Res. Bull. 33 (1998) 149–159. [10] S. Sailaja, C. Nageswara Raju, C. Adinarayana Reddy, B. Deva Prasad Raju, Young-Dahl Jho, B. Sudhakar Reddy, J. Mol. Struct. 1038 (2013) 29–34. [11] Hongbin Liang, Qinghua Zeng, Ye Tao, Shubin Wang, Qiang Su, Mater. Sci. Eng. B 98 (2003) 213−219. [12] K. Maheshvaran, K. Linganna, K. Marimuthu, J. Lumin. 131 (2011) 2746–2753. [13] Ming Hua Wan, Poh Sum Wong, Rosli Hussin, Hendrik O. Lintang, Salasiah Endud, J. Alloys Compd. 595 (2014) 39 45. [14] S. Kumar, P. Vinatier, A. Levasseur, K.J. Rao, J. Solid State Chem. 177 (2004) 1723−1737. [15] Sd. Zulfiqar Ali Ahamed, C. Madhukar Reddy, B. Deva Prasad Raju, Spectrochim. Acta Part A 103 (2013) 246–254. [16] S.P. Sinha, Complexes of the Rare Earths, Pergamon, Oxford, 1966. [17] Xian Feng, Changhong Qi, Fengying Lin, Hefang Hu, J. Am. Ceram. Soc. 82 (1999) 3471– 3475. [18] M.A. Marzouk, J. Mol. Struct. 1019 (2012) 80–90. [19] Fouad El-Diastya and Fathy A. Abdel Wahab, J. Appl. Phys. 100 (2006) 093511-093511-7. 15

[20] Li-Hua Zheng, Xin-Yuan Sun, Ri-Hua Mao, Hao-Hong Chen, Zhi-Jun Zhang, Jing-Tai Zhao, J. Non–Cryst. Solids 403 (2014) 1–4. [21] F. Urbach, Phys. Rev. 92 (1953) 1324–1325. [22] B.R. Judd, Phys. Rev. 127 (1962) 750–761. [23] G.S. Ofelt, J. Chem. Phys. 37 (1962) 511–520. [24] W.T. Carnall, P.R. Fields, K. Rajnak, J. Chem. Phys. 49 (1968) 4424–4442. [25] S. Babu, A. Balakrishna, D. Rajesh, Y.C. Ratnakaram, Spectrochim. Acta Part A 122 (2014) 639–648. [26] B.C. Jamalaiah, J. Suresh Kumar, A. Mohan Babu, T. Suhasini, L. Rama Moorthy, J. Lumin. 129 (2009) 363–369. [27] M. Jayasimhadri, L.R. Moorthy, S.A. Saleem, R.V.S.S.N. RaviKumar, Spectrochim. Acta Part A 64 (2006) 939–944. [28] K. Maheshvaran, K. Linganna, K. Marimuthu, J. Lumin. 131 (2011) 2746–2753. [29] S. Arunkumar, K. Marimuthu, J. Alloys Compd. 565 (2013) 104–114. [30] Priyanka Srivastava, S.B. Rai, D.K. Rai, Spectrochim. Acta Part A 60 (2004) 637–642. [31] D. Rajesh, A. Balakrishna, Y.C. Ratnakaram, Opt. Mater. 35 (2012) 108–116. [32] K. Linganna, Ch. Srinivasa Rao, C.K. Jayasankar, J. Quant. Spect. Radiat. Trans. 118 (2013) 40–48. [33] S. Babu, A. Balakrishna, D. Rajesh, Y.C. Ratnakaram, Spectrochim. Acta Part A 122 (2014) 639–648. [34] M. Chandra Shekhar Reddy, B. Appa Rao, M.G. Brik, A. Prabhakar Reddy, P. Raghava Rao, C.K. Jayasankar, N. Veeraiah, Appl. Phys. B 108 (2012) 455–461. [35] S. Sailaja, C. Nageswara Raju, C. Adinarayana Reddy, B. Deva Prasad Raju, Young-Dahl Jho, B. Sudhakar Reddy, J. Mol. Struct. 1038 (2013) 29–34. [36] T. Sasikala, L. Rama Moorthy, A. Mohan Babu, Spectrochim. Acta Part A 104 (2013) 445– 450. [37] S. Babu, A. Balakrishna, D. Rajesh, Y.C. Ratnakaram, Spectrochim. Acta Part A 122 (2014) 639–648. [38] K.V. Krishnaiah, K.U. Kumar and C.K. Jayasankar, Mater. Express 3 (2013) 61−70. [39] V. Naresh, S. Buddhudu, J. Lumin. 147 (2014) 63–71. [40] C. Madhukar Reddy, G.R. Dillip, K. Mallikarjuna, Sd. Zulifiqar Ali Ahamed, B. Sudhakar Reddy, B. Deva Prasad Raju, J. Lumin. 131 (2011) 1368–1375. [41] M. Inokuti, F. Hirayama, J. Chem. Phys. 43 (1965) 1978

.

[42] T. Sasikala, L. R. Moorthy, A. M. Babu, Spectrochim. Acta Part A 104 (2013) 445–450. 16

[43] B.C. Jamalaiah, M.V. Vijaya Kumar, K. Rama Gopal, Opt. Mater. 33 (2011) 1643–1647. [44]

[45] Joanna Pisarska, J. Phys.: Condens. Matter 21 (2009) 285101 285101-6.

17

Figure 1: XRD spectrum of the ZSBP0.5Sm glass

18

ZSBP2sm

% Transmittance

ZSBP1sm ZSBP0.5sm

ZSBP0.25sm

ZSBP0.1sm

400

800

1200

1600

2000

2400

2800

3200

3600

-1

Wavenumber (cm ) Figure 2: FTIR spectra of the Sm3+ doped borophosphate glasses

19

6

F7/2

4

L15/2,4L13/2,4F7/2,6P3/2

6 6

D3/2

350

4 6

P7/2

4

F9/2

4

I13/24,I11/24,M

F5/2 6

4

F3/26,H15/2

G11/2, M17/2, F5/2

M19/2,6P5/2

4

4 15/2 9/2

,I

4

Absorption coefficient (cm)

ZSBP2Sm

6

F1/2

6

F11/2

400

450

500

1000

1200

1400

1600

Wavelength (nm)

Figure 3: UV-Vis-NIR absorption spectrum of the ZSBP2Sm glass

20

h(cm-1 eV)

0.45

3.45

0.40

0.35

3.40

Urbach energy (eV)

Band gap energy(eV)

3.50

0.30 3.35

0.25 0.0

0.5

1.0

1.5

2.0

3+

Sm ion concentration (wt%)

ZSBP0.1Sm ZSBP0.25Sm ZSBP0.5Sm ZSBP1Sm ZSBP2Sm

3.2

3.3

3.4

3.5

3.6

h(eV) Figure 4: Tauc’s plot of the Sm3+ doped borophosphate glasses [Inset shows the comparison of band gap and Urbach energy]

21

Excitation intensity (a.u)

6H 5/2

4F 7/2

emi = 598 nm

4D 1/2

4I 11/2 4I 13/2 4G 9/2

4H 9/2 350

400

450

Wavelength (nm)

Figure 5: Excitation spectrum of the ZSBP0.5Sm glass

22

500

exc

403nm

6H 9/2

4G 5/2

6H 11/2

6H 5/2 ZSBP2Sm ZSBP1Sm ZSBP0.5Sm ZSBP0.25Sm ZSBP0.1Sm

550

600

650

700

A

Figure 6: Luminescence spectra of the Sm3+ doped borophosphate glasses

23

Luminescence Intensity (a.u)

6H 7/2

Green

White

Figure 7: CIE 1931diagram of the Sm3+ doped borophosphate glasses

24

ZSBP0

.1Sm

.25Sm

ZSBP

0.5Sm

ZSBP

1Sm

S=10 ln intensity (a.u)

ln intensity (a.u)

ZSBP0

S=8 ZSBP2Sm

ZSB

P2Sm

S=6 0

1

2

3

4

Time (ms)

0

1

Time (ms)

2

3

Figure 8: Decay profile of the of the Sm3+ doped borophosphate glasses [Inset shows the IH fit of the ZSB2Sm glass]

25

4 6

D3/2 P7/2 6 P3/2 6 P5/2 4 P5/2 4 I9/2,4I11/24,M 15/2 4 I13/2 4 G 4 7/2 F 4 3/2 G5/2

25000

709 nm

598 nm 644 nm

15000

561 nm

403 nm

Energy (cm1)

20000

A

B

C D

10000

6

F11/2 6

F9/2 F7/2

6

6

6

F1/2

H13/2 H11/2 6 H9/2 6 H7/2 6 H5/2 6

6

5000

6 F5/2,F3/2,,6H15/2

0 Emission

Cross-relaxation

Figure 9: Energy level diagram of the Sm3+ ions in borophosphate glasses

26

Table 1: Physical properties of the Sm3+ doped borophosphate glasses Physical Properties Density ρ (g/cm3) Refractive index nd (589.3 nm) RE ion concentration N(1020 ions cm3) Polaron radius rp (A°) Inter ionic distance ri (A°) Field strength F (1014 cm–2) Electronic polarizability e(10–22 cm3) Molar refractivity Rm (cm3) Dielectric constant () Reflection losses R (%)

ZSBP 0.1Sm 3.291 1.587 0.451 11.32 28.09 0.380 17.796 1.531 2.518 5.148

27

ZSBP 0.25Sm 3.199 1.604 1.092 8.43 20.92 0.685 7.523 1.612 2.573 5.380

ZSBP 0.5Sm 3.128 1.606 2.121 6.75 16.77 1.067 3.883 1.654 2.579 5.407

ZSBP 1Sm 3.079 1.602 4.121 5.41 13.44 1.661 1.988 1.671 2.566 5.353

ZSBP 2Sm 3.249 1.622 8.477 4.26 10.57 2.687 0.992 1.626 2.631 5.627

Table 2: The observed FTIR band positions (in cm1) and their assignments of the Sm3+ doped borophosphate glasses Band positions Serial Band assignments ZSBP ZSBP ZSBP ZSBP ZSBP No. 0.1Sm 0.25Sm 0.5Sm 1Sm 2Sm 1 586 574 574 574 574 Bending vibrations of O–P–O bonds 2 710 724 725 714 725 Symmetric vibrations of P–O–P chains Symmetric stretching of the BO4 and PO4 3 1050 1045 1048 1035 1037 groups Vibrations of B–O bond in BO3 units and 4 1388 1396 1392 1392 1390 the P=O linkage 5 1617 1636 1635 1620 1628 (OH), POH and BOH vibrations 6 2859 2857 2856 2856 2856 Hydrogen bonding 7 2920 2929 2934 2931 2931 8 3449 3439 3448 3438 3438 Fundamental stretching of OH group

28

Table 3: The energy level positions (cm1) and bonding parameters ( and δ) of the Sm3+ doped borophosphate glasses Transitions 4

D3/2 P7/2 4 L15/2+4L13/2+4F7/2+ 6P3/2 4 M19/2+6P5/2 4 G11/2+4M17/2+4F5/2 4 I13/2+4I11/2+4M15/2+4I9/2 6 F11/2 6 F9/2 6 F7/2 6 F5/2 6 F3/2+6H15/2 6 F1/2 6

δ

ZSBP 0.1Sm 24987 21207 9302 8185 7322 6798 6308 1.0119 1.176

ZSBP 0.25Sm 26835 24949 24024 22865 21211 10649 9321 8174 7314 6794 6322 1.0097 0.961

29

ZSBP 0.5Sm 27867 26842 24906 24114 22934 21181 10633 9300 8173 7304 6785 6316 1.0091 0.899

ZSBP 1Sm 27824 26844 24924 24076 22870 21163 10620 9304 8182 7305 6797 6329 1.0089 0.884

ZSBP 2Sm 27793 26766 24890 24086 22880 21129 10675 9320 8175 7308 6790 6322 1.0088 0.871

Aquo-ion [24] 27700 26750 24950 24050 22700 21100 10500 9200 8000 7100 6630 6400 -

Table 4: Optical band gap (Eopt), band tailing parameter (B) of the corresponding direct (n=1/2) and indirect (n=2) allowed transitions and Urbach’s energy (∆E) of the Sm3+ doped borophosphate glasses Glass code ZSBP0.1Sm ZSBP0.25Sm ZSBP0.5Sm ZSBP1Sm ZSBP2Sm

n=1/2 Eg (eV) B (cm2ev) 3.34 772.59 3.35 757.16 3.42 713.09 3.44 831.69 3.49 1055.57

30

Eg (eV) 3.11 3.13 3.21 3.24 3.34

n=2 B (cm2ev) 5.52 5.31 5.95 6.79 6.81

ΔE (eV) 0.4518 0.3962 0.3893 0.3276 0.2742

Table 5: Experimental and calculated oscillator strengths (×106) and root mean square deviation (σrms) of the Sm3+ doped borophosphate glasses Transition 4

D3/2 P7/2 4 L15/2+4L13/2 +4F7/2+ P3/2 4 M19/2+6P5/2 4 G11/2+4M17/2+4F5/2 4 I13/2+4I11/2+4M15/2+4I9/2 6 F11/2 6 F9/2 6 F7/2 6 F5/2 6 F3/2+6H15/2 6 F1/2 N σrms 6

ZSBP0.1Sm fexp fcal -

ZSBP0.25Sm ZSBP0.5Sm ZSBP1Sm ZSBP2Sm fexp fcal fexp fcal fexp fcal fexp fcal 1.556 0.990 1.203 1.549 0.632 1.364 1.245 1.598

4.829 3.311 5.686 4.179 5.962 4.541 5.782 4.303 5.089 4.701 2.082 1.739 3.085 1.241 0.917 0.125

0.610 2.021 2.964 1.597 0.809 0.155

7  0.820

0.740 0.000 0.333 0.191 1.424 0.847 2.282 0.463 2.528 2.811 4.005 4.014 1.673 1.988 1.082 0.942 0.052 0.105 10  0.818

31

0.572 0.000 0.343 0.205 1.746 0.907 0.341 0.495 2.894 3.010 4.385 4.322 1.825 2.159 1.145 1.013 0.053 0.099 11  0.553

0.304 0.000 0.180 0.182 1.842 0.798 0.337 0.435 2.748 2.661 3.815 3.889 1.742 2.056 1.146 0.975 0.028 0.105 11  0.608

0.201 0.000 0.179 0.212 1.979 0.938 0.413 0.515 3.037 3.123 4.515 4.476 2.055 2.244 1.250 1.073 0.031 0.132 12  0.389

Table 6: Judd-Ofelt parameters (Ωλ×1020 cm2) and Spectroscopic quality factor (Ω4/Ω6) of the Sm3+ doped borophosphate glasses along with the reported Sm3+ doped glasses

Glass code

JO Parameters

Ω4/Ω6

Trends of Ωλ

References

Ω2

Ω4

Ω6

ZSBP0.1Sm

0.438

2.908

2.289

1.270

Ω4> Ω6 >Ω2

Present

ZSBP0.25Sm

0.255

3.607

3.159

1.142

Ω4> Ω6 >Ω2

Present

ZSBP0.5Sm

0.231

3.924

3.382

1.160

Ω4> Ω6 >Ω2

Present

ZSBP1Sm

0.258

3.742

2.981

1.255

Ω4> Ω6 >Ω2

Present

ZSBP2Sm

0.324

3.814

3.357

1.161

Ω4> Ω6 >Ω2

Present

B2O3–TeO–P2O5–Li2O3

0.934

1.131

0.956

Ω4> Ω6 >Ω2

[8]

LBTAF

0.27

2.52

2.47

1.184 1.020

Ω4> Ω6 >Ω2

[26]

KTFB

0.15

2.44

1.76

1.380

Ω4> Ω6 >Ω2

[27]

B3TS

0.372

2.980

1.867

1.590

Ω4> Ω6 >Ω2

[28]

1SmPbFB

0.316

3.289

1.918

1.706

Ω4> Ω6 >Ω2

[29]

B2O3–PbO–Li2O

0.845

3.513

3.540

0.992

Ω4> Ω6 >Ω2

[30]

32

Table 7: Peak wavelength (λp, nm), effective linewidth (∆λeff, nm), radiative transition probability (A, s–1), stimulated emission cross-section (  PE ×10–21cm2), experimental and calculated branching ratio (βR) corresponding to the 4G5/2 emission transitions of the ZSBP0.5Sm glass with the reported Sm3+ doped glasses Transitions

4

4

4

4

G5/26H5/2

G5/26H7/2

G5/26H9/2

G5/26H11/2

λp ∆λeff Α

ZSBP 0.5Sm 561 9.169 22.10

CdBiB [33] 563 12.71 23.68

TZKCSm10 [34] 567 11.66 47.82

A2 [2] 563 26 39.15

LiPbFP [36] 564 120

 PE

1.2358

0.65

1.35

6.1

βR(Exp) βR(Cal) λp ∆λeff Α

0.1094 0.0753 598 10.611 146.25

0.17 0.04 600 21.33 325.11

0.17 0.08 603 14.64 232.76

0.29 3.31 598 17 535.61

0.18 0.23 601 177

 PE

9.0678

6.95

6.68

7.61

8.1

βR(Exp) βR(Cal) λp ∆λeff Α

0.5010 0.5050 644 10.686 59.03

0.43 0.57 646 18.89 101.40

0.56 0.38 649 17.03 199.43

45.35 643 17 449.63

0.61 0.34 647 145

 PE

4.9168

3.29

6.60

8.54

7.4

βR(Exp) βR(Cal) λp ∆λeff Α

0.3228 0.2098 709 12.204 34.71

0.32 0.17 708 22.71 67.47

0.25 0.33 711 23.57 57.24

41.88 706 24 156.71

0.21 0.28 708 49

 PE

3.6819

2.62

1.97

3.07

3.2

βR(Exp) βR(Cal)

0.0666 0.1201

0.06 0.11

0.01 0.09

13.26

0.01 0.09

Parameters

33

Table 8: The calculated and experimental lifetimes (ms), quantum efficiency η (%), energy transfer parameter (Q), critical transfer distance R0 (×108 m) and donor-acceptor interaction parameter CDA (×1040cm6/s) of the Sm3+ doped borophosphate glasses

Parameters

ZSBP0.1Sm

ZSBP0.25Sm

ZSBP0.5Sm

ZSBP1Sm

ZSBP2Sm

τcal (ms)

4.103

3.954

3.362

3.062

1.819

τexp(ms)

1.990

1.821

1.511

1.001

0.403

η

49%

46%

45%

33%

22%

Q



0.1442

0.5599

1.2144

2.8391

Ro



5.6272

7.0887

7.3533

7.6741

CDA



0.2118

0.8464

1.0545

1.3625

34

6H 7/2

exc

403nm

6H 9/2

4G 5/2

6H 11/2

6H 5/2 ZSBP2Sm ZSBP1Sm ZSBP0.5Sm ZSBP0.25Sm ZSBP0.1Sm

550

600

650

700

A

35

Luminescence Intensity (a.u)

Graphical abstract

Highlights  Lower ΔE values indicate that the title glasses possess minimum defects and less disorderliness.  Lower Ω2 and intensity ratio confirm that Sm3+ ions are located in a higher symmetrical environment  4G5/2→6H7/2 transition of ZSBP0.5Sm glass exhibit higher A, R,  PE ,  PE ×∆λeff useful for visible lasers  x, y coordinates of the title glasses were located in the reddish-orange region of CIE 1931 diagram  Energy transfer process occurs between the Sm3+ ions is mainly due to dipole-dipole interactions

36