Optical traits of neodymium-doped new types of borate glasses: Judd-Ofelt analysis

Optical traits of neodymium-doped new types of borate glasses: Judd-Ofelt analysis

Journal Pre-proof Optical traits of neodymium-doped new types of borate glasses: Judd-Ofelt analysis A.U. Ahmad, S. Hashim, S.K. Goshal PII: S0030-4...

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Journal Pre-proof Optical traits of neodymium-doped new types of borate glasses: Judd-Ofelt analysis A.U. Ahmad, S. Hashim, S.K. Goshal

PII:

S0030-4026(19)31413-5

DOI:

https://doi.org/10.1016/j.ijleo.2019.163515

Reference:

IJLEO 163515

To appear in:

Optik

Received Date:

28 June 2019

Accepted Date:

1 October 2019

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Optical traits of neodymium-doped new types of borate glasses: Judd-Ofelt analysis A.U. Ahmada,c, S. Hashima , S.K. Goshalb,* Department of Physics, Faculty of Science, Universiti Teknologi Malaysia 81310 UTM Skudai, Johor, Malaysia. a

b Advanced Optical Materials Research Group & Laser Centre, Department of Physics, Faculty

of Science, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia Department of Integrated Science, Jigawa State College of Education, PMB 1002, Gumel, Nigeria. c

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author

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* Corresponding

Abstract

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Improvement in the optical properties of rare earth ions activated inorganic glasses is one of the challenges in materials science. Driven by this idea a new series of borate glass activated with varying concentrations of neodymium ions (Nd3+) were prepared using the melt-quenching technique. Such glasses were characterized by various analytical tools to determine the Nd3+ contents dependent spectroscopic attributes. Furthermore, Judd-Ofelt intensity parameters of Nd3+ were evaluated. XRD pattern of as-quenched samples confirmed their amorphous nature. FTIR spectra of glasses revealed the bonds stretching and vibration of different borate functional groups. UV-Vis spectra of glasses displayed twelve absorption bands accompanied by hypersensitive transition positioned at 581 nm which were used to calculate the oscillator strengths. Judd-Ofelt parameters for all glasses disclosed a similar trend of Ω4 > Ω6 > Ω2. Proposed glass hosts were found to be effective for the enhancement of spectroscopic quality factor of Nd3+ as much as 1.2603, suggesting their usefulness in photonics devices. Keywords: Absorption spectra, Borate glass, Judd-Ofelt parameters, Neodymium, Optical traits. Introduction

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1.

Rare earth ions (REIs) activated inorganic glasses due to their enticing optical traits are indisputably prospective for technological applications especially in optoelectronics and solids state laser [1], [2]. Moreover, enhanced transition, the acceptability of RE elements, wide bandwidth, cost-effectiveness, and easy fabrication make them relatively more attractive [3]. Glass (host) compositions together with the selected modifiers play a significant role in the achievement of improved absorption and emission characteristics of doped REIs [4]. Amongst all binary and ternary inorganic glasses, borate systems are preferred because of their several notable properties including excellent glass forming

ability, high transparency, relatively low melting temperature, high thermal stability, and good rare earth ions solubility [5]–[7]. On top, borate glasses containing alkali metal resist atmospheric moisture and accept a high amount of transition metals wherein the transparency spread from near UV through visible to the middle infrared spectral region [8].

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Lithium as glass modifier can reduce the hygroscopicity and stabilize the glass by introducing non-bridging oxygen (NBO) that forms the color centers. It has been established that strontium improves the optical and structural traits of lithium modified borate glass [9]. Besides, zinc is added to lithium borate glass in order to improve the glass strength and electron emission capability [10]. Included zinc in borate glass structure acts as either a network former or a network modifier. In the network former mode it incorporates in the network of the glass as zinc bonded covalently with four ions of oxygen (ZnO4) however, as modifier it forms dangling bonds and non-bridging oxygen by breaking the B-O-B bond [7].

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Neodymium-doped glasses have diverse applications in photonic devices [11], solid states and microchip lasers, planar waveguides [12], ultra-violet radiations absorber in halogen lamp, refractory glasses due to their good hardness and chemical durability and filters for band rejection [13]. Neodymium-doped borate glass in the presence of lithium, strontium, zinc or combination of two elements have been extensively studied [5], [6], [11], [13]–[20]. However, neodymium-doped borate glass in combination with lithium strontium and zinc is rarely studied. In this view, we synthesized new type of borate glasses with varying concentration of Nd2O3 (in the range of 0 to 2) using the melt-quenching method. The influence of changing Nd3+ ions concentration on the optical and physical properties of the glasses was analyzed via different characterizations. Activation of the studied glasses by Nd3+ could produce excellent optical absorption, emission and better quality factor (𝜒) than those reported in other hosts including phosphate [21] [22] [23], tellurite [24] and fluoroborate [25] glasses. Results were compared and discussed with reported studies in the literature. 2.

Experimental details

2.1

Glass preparation

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Melt-quenching method was used to prepare Nd3+ activated LSZB glasses (six samples) with molar compositions of 20Li2CO3 – 5SrO – 5ZnO – (70-x) B2O3 – xNd2O3 (where x = 0. 0.4, 0.8, 1.2, 1.6 and 2.0 mol%). In each batch composition, about 20 g of the analytical grade powder of Li2CO3, SrO, ZnO, B2O3 and Nd2O3 was thoroughly mixed using an agate mortar and the homogenous mixture of the glass constituents was placed in a crucible before being transferred in an electric furnace (operated at 1200 oC) for 1 h at an ambient condition. The melts were quenched onto a brass plate and annealed at 300 oC for 3 h before cooled down to room temperature to avoid embrittlement of the glass due to thermal strain. Depending on the Nd2O3 contents, prepared glasses were coded as LSZBN0, LSZB0.4, LSZBN0.8, LSZBN1.2, LSZBN1.6, and LSZBN2.0.

2.2

Characterizations

𝑆(𝑖)

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𝑆. 𝐸𝑖 =

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Rigaku smartlab X-ray diffractometer (XRD) coupled with diffraction software was used to confirm the amorphous nature of as-quenched samples. The diffractometer operated at 40 kV with Cu Kα radiation of wavelength (λ)  0.154 Å in the angular scan (2θ) range of 0 to 100o at the interval of 0.02. Local structure (so-called functional groups) of the glasses was probed using FTIR (Perkin Elmer Spectrometer) spectral measurement where KBr pelleting was utilized. A mixture of the glass powder and potassium bromide (KBr) was mixed using 120 MPa to form a transparent tiny pellet. Abbe refractometer with a filter of diameter (D) 1:589 nm was used to measure the refractive index of the samples. The error related to the refractive index measurement was calculated using standard deviation expression[22], [26]: √𝑛

(1)

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where 𝑆. 𝐸𝑖 is the standard error of the mean, 𝑆(𝑖) is the standard deviation of the mean and n is the number of repeated experiments.

𝛼 𝛼−𝛽

(𝜌𝛽 − 𝜌𝛼 ) + 𝜌𝛼

lP

𝜌 =

re

Archimedes principle was employed to determine the studied glass density (ρ) wherein toluene served as the immersion fluid. Precisa digital balance (model XT220A) with the uncertainty of ± 0.001 was used in the weighting of the samples. The relation for density becomes: (2)

ur na

where α and β are respectively the weights of the glass samples in the air and in the toluene (inert immersion fluid) and 𝜌𝛽 = 0.8669 g/cm3. The molar volume ( 𝑉𝑚 ) of each glass sample was evaluated from the average molecular weight, molar fraction and density of the samples using the expression [27]: 𝑉𝑚 =

∑𝑖 𝑥𝑖 𝑀𝑖 𝜌

(3)

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where M, ρ, and x are respectively the molecular weight, density, and the mole fraction of each glass component i. Nd3+ ions concentration in the studied samples was estimated via[28]: 𝑁𝑖 =

𝑚𝑜𝑙% 𝑜𝑓 𝑁𝑑3+ . 𝑁𝐴 𝑥 𝜌 𝑀𝑎𝑣

(4)

where Mav is the average molecular mass of the studied glass. Polaron radius (rp), inter-atomic distances (ri) and field strengths (F) were calculated by means of the following relations[29]:

1 3

𝜋

𝑟𝑝 (Å) = 0.5 (6𝑁 )

(5)

𝑖

1

𝑟𝑖 (Å) =

1 3 (𝑁 ) 𝑖

(6)

𝑍

(7)

𝐹(𝑐𝑚−1 ) =

𝑟𝑝2

where 𝑍 is the molar mass of the rare earth (Nd).

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The dielectric constant (ε), reflection loss (R), molar refractivity (Rm) and electron polarizability (αm) were evaluated using the refractive index of the as-prepared glasses via the following equations [30]: 𝜀 = 𝑛2

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𝑛−1 2

𝑅 = (𝑛+1)

𝑛2 −1

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𝑅𝑚 = (𝑛2 +1) × 𝑉𝑚 3

𝛼𝑚 = (4.𝜋.𝑁 ) × 𝑅𝑚

(9) (10) (11)

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𝐴

(8)

𝛼(𝜔) =

𝛼𝑜 (ℎ(𝜔)𝑣−𝐸𝑔 )

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UV-VIS-NIR spectrometer (UV-3600 plus) was used to measure the optical absorption of the as-prepared glasses in the range of 300-900nm. The energy band gaps were determined via[9]: 𝑟

ℎ(𝜔)𝑣

(12)

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where α is the absorption coefficient and is a function of photon energy ℎ𝜗, 𝛼𝑜 is an energy independent constant called band tailing parameter and the exponent r for direct (r=2) and indirect (r=1/2) band gaps. The area under the absorption bands was used to evaluate the experimental oscillator strength (fexp) using [31]: 𝑓𝑒𝑥𝑝 = 4.318 × 10−9 ∫ 𝜀(𝜗)𝑑𝜗

(13)

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where 𝜀(𝜗) is the band molar absorptivity at wave number 𝜗. The theoretical oscillator strength (fcal) of absorption to excited from the ground state was obtained from [26]: 8𝜋 2 𝑚𝑐

𝑓𝑐𝑎𝑙 = 2ℎƮ(2𝐽+1)

(𝑛2 −1) 9𝑛

2

∑Ʈ=2,4,6 Ω𝜆 Ι⟨(𝑆, 𝐿)𝐽|𝑈 Ʈ|(𝑆 ′ 𝐿′ )𝐽′ ⟩Ι2

(14)

where |𝑈 Ʈ | is the doubly reduced matrix elements obtained from [32]. Fit quality between 𝑓𝑒𝑥𝑝 and 𝑓𝑐𝑎𝑙 which is determined by the root means square deviation δrms was expressed as (Hehlen et al, 2013):

∑(𝑓𝑒𝑥𝑝 −𝑓𝑐𝑎𝑙 )

𝛿𝑟𝑚𝑠 = (

(𝑥−𝑦)

1 2 2

)

(15)

where x and y are the transitions considered and the number of Ω𝜆 parameters respectively. 3.

Results and discussions

3.1.

Structural characteristics

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The amorphous nature of the lithium strontium zinc borate doped with different mol% of neodymium (LSZBN) was confirmed using x-ray diffraction (XRD). Fig. 1 depicts the pattern of the XRD which indicates broad hump but no sharp peak or reflection, these indeed confirmed that the samples are non-crystalline[35].

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Intensity (a.u.)

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LSZBN1.2 LSZBN0.0

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20

40 60 2(Degree)

80

100

Fig. 1. XRD pattern of two selected glasses without and with Nd3+ doping. Fig. 2 displays the FTIR spectra of the studied glasses showing the presence of various function group in the glass network [11], [36]. Six distinguished regions are generally observed in these borate glasses: (a) 467 cm-1 assigned to O–B–O bond bending and O–Cation vibration [36], (b) 698 cm-1 is allotted to Bending vibration of B-O-B linkage [37], (c) 1073 cm-1 is allocated to B–O bond stretching of tetrahedral BO4 units [11], (d) 1234 cm-1 was due

to B-O was stretching of [BO3]3+ unit in meta borate chain and ortho borates [36], (e) 1405 cm-1 and 1628 cm-1 were respectively given to B–O stretching of trigonal BO3 and O-H vibration of water group [29]. Fig. 2 shows the spectra of the lithium strontium zinc borate and 1.2mol% Nd3+ doped lithium strontium zinc borate.

467

698

800

1073 1234 1628 1405

1200 1600 -1 Wavenumber (cm )

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Absorbance (a.u.)

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LSZBN0.0 LSZBN1.2

2000

Fig. 2 FTIR spectra of two selected glasses without and with Nd3+ doping. Physical properties

The physical properties of all the prepared glasses are enlisted in Table 1.

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3.2.

Table 1: Physical properties of the prepared glasses Physical parameters

Glass with different Nd2O3 contents

73.8302

74.8976

75.9651

2.3968

2.4421

2.4734

2.5566

2.5277

2.4982

30.3588

30.2322

30.2812

29.7129

30.475

31.2624

0.7968

1.5910

2.4321

3.1618

3.8526

3.0679

-p

78.0999

1.6024

1.3910

1.2745

1.1933

3.9760

3.4515

3.1625

2.9608

1.4737

2.3368

3.1020

3.6937

4.2139

1.7526

1.7514

1.7535

1.7535

1.7521

3.0717

3.0674

3.0749

3.0749

3.0700

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5.0067

1.7515

re

2.0178

77.0325

ro

72.7628

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Average molecular weight Mav(g) Density, ρ (±0.0023 gcm-3) Molar vol, Vm (±0.0288 cm3) Nd3+ ion conc, Ni (±0.0035 ×1022 ioncm-3) Polaron radius, rp (Ǻ) Inter–ionic distance ri (Ǻ) Field strength, F (×1017 cm-2) Refractive index, n (±0.0019) Dielectric const., Ɛ (±0.0067)

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LSZBN0.0 LSZBN0.4 LSZBN0.8 LSZBN1.2 LSZBN1.6 LSZBN2.0

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The average molecular weight of the samples increases with the addition of Nd2O3. This is obvious as the Nd2O3 with a higher molecular weight (336.4782) replaces B2O3 with a lower molecular weight (69.6202). Changes in the density of the glass can be related to the geometrical configuration, cross-link density, interstitial spaces sizes, co-ordination number and the refractive index which may eventually affect the optical band gaps of the glass system [11][30]. In the present glass the density increases from 2.3968 to 2.5566 and then declined to 2.4982 through 2.5277, the increased in the first instance could be due to the replacement of B2O3 by the Nd2O3 which has higher molecular weight [38]. While the decrease in the density in the last two samples could be attributed to the formation of Non-bridging oxygen (NBO) atoms in the glass matrix [5]. The trend of the refractive index of the glass samples is in tandem with the pattern of the glass density. The trend of Molar volume and fluctuation

of its values is attributed to the nature of the glass density and modifying effect of neodymium ions by forming interstitial gaps with NBO in the matrix of the glass [39]. The concentration of ions increases with the dopant concentration, which is obvious. The Polaron radius and Inter ionic distance decreased as the neodymium ions increased, this can be attributed to the overcrowding of the dopant in the glass [40] 3.3.

Optical absorption spectra

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Fig. 3 depicts the absorption spectra of LSZBN glasses within the range of 300 to 950 nm. The spectra show twelve different strong asymmetric peaks with dissimilar broadening correspond to transition from 4I9/2 to (4D1/2 4D5/2 4D3/2), 2P1/2, 4G11/2, 2K15/2, 4G9/2, 4G7/2, 4G5/2, 2H11/2, 4F9/2, (4F7/2 4S3/2), 4F5/2 and 4F3/2, these energy transitions correspond to the wavenumber (cm-1) (28694, 28409, 28328), 23310, 21763, 21142, 19531, 19084, 17212, 16000, 14749, 13486, 12516, 11474 respectively. The absorption spectra and the transitions herein are similar to those reported by [22], [41]. The first three absorption bands are due to the effects of Nd3+ ions and the glass host [39]. The hypersensitive transition was observed at 581 nm which correspond to wavenumber 17212 cm-1, it satisfies the selection rule|𝛥𝑆| = 0, |𝛥𝐿| ≤ 2, |𝛥𝐽| ≤2 being the most intense peak [42]. The bonding environment of ligand and ion plays a key role in deciding the hypersensitive transition intensity [6]. The intensities of the experimental oscillator strength substantiate the hypersensitive of transition from 4I9/2 to 4G5/2.

LSZBN0.0 LSZBN0.4

G5/2

LSZBN1.2

G9/2

LSZBN1.6

ro F3/2

4

re

600 Wavelength (nm)

900

lP

300

4

-p

F9/2

K15/2

2

2

P1/2

4

4

G7/2

G11/2

F5/2

F7/2+4S3/2

H11/2

2

4

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LSZBN2.0

4

D1/2+4D3/2+4D5/2

4

LSZBN0.8

4

I9/2

4

Absorbance (a.u.)

4

Fig. 3. Absorption spectra of the studied glasses 3.4.

Optical band gap and Urbach energy

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The optical band gap in the amorphous materials can be explored using the UV absorption spectra of the system. Electromagnetic waves interact with the electrons in the valence band and elevate them to the conduction band [43]. The Indirect and direct optical band gaps and Urbach energy were determined using Eqs. (13). Tauc’s plot was employed to plot the values of (𝛼ℎ𝑣)0.5, (𝛼ℎ𝑣)2 and Inα against photon energy (ℎ𝑣) for Indirect, direct optical band gap and Urbach energy respectively. The α is the absorption coefficient which 𝐴 can be calculated from the relation 𝛼 = 2.303 presented first by Thutpalli and Tomlin 𝑑

[44]. The band gaps and Urbach were determined by extra-polating the linear part of the plot to meet the ℎ𝑣 axis, as depicted in Fig. 4 and the inverse of the slope of the linear part of the plot of 𝐼𝑛𝛼 against (ℎ𝑣). The values of the direct and indirect band gaps, as well as that of the Urbach, were enlisted in Table 2. With the increase in the concentration of Nd3+ ions in the glasses, more of the ions are incorporated in the glasses structure. Such structural changes with the incorporation of Nd ions affect the values of the optical band gap of the glass system. The structure of the glass changes with the incorporation of Nd3+ ions which also affects the

values of the optical band gaps. The band gaps of the glasses were decreased with increased in Nd3+ ions but slightly increased at 1.2 mol% of Nd3+ ions and the decreased as shown in Fig. 5, this pattern agrees well with the density of the studied glass. In glasses, non-bridging oxygen (NBO) have higher negative charges than bridging oxygen (BO) therefore, converting the bridging oxygen (BO) to non-bridging oxygen (NBO) has the effect of decreasing the valence band and consequently decrease the energy of the optical band gap [45]. Increasing NBO in the glass leads to the increase of in the localized electrons which resulted in the higher donor centers in the glass system. The high donor centers in the glass matrix have directly reduced the energy of the band gap [45].

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In amorphous material, there is no long-range order which resulted in the tailing of the density of states. Disorder effect of a glassy material can be understood from the edge of the fundamental absorption in the Urbach (Exponential) region. Absorption coefficient increased when the band gap energy is more than incidence photon energy, and these resulted in the decay of the density of localized states exponentially into a gap and edge called the Urbach energy [46]. Urbach energy is a measure of the degree of disorder in the amorphous and crystalline system and it corresponds to the localized state's width. Materials with higher Urbach energy are more likely to transform bands that are weak to defects [45]. In the studied glasses, LSZBN1.2 has the highest Urbach energy that explains the highest absorption and other optical traits.

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Table 2. Nd3+ concentration dependent Urbach energy, indirect and direct band gap energy of the glasses Parameters

LSZBN0.4 LSZBN0.8 LSZBN1.2 LSZBN1.6 LSZBN2.0

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Indirect band gap, (±0.0117 3.4080 eV) Direct band gap (±0.0406 3.8959 eV) Urbach energy (± 0.0014 0.3077 eV)

3.4442

3.4361

3.4108

3.4101

3.8973

3.9034

3.9036

3.9021

0.3068

0.3145

0.3113

0.3071

LSZBN1.2 (a)

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2

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(hv)2 (eV.cm)2

4

3.8

4.0 hv (eV)

4.2

4.4

lP

re

3.6

-p

0

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LSZBN1.2

(b)

0.6

Jo

(hv)1/2 (eV.cm)1/2

1.2

0.0 3.4

3.6

3.8 4.0 hv (ev)

4.2

4.4

Fig. 4. Tauc’s plots depicting a) direct and b) indirect optical band gap for LSZBN1.2 glass

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3.9

3.6

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3.6

-p

(hv)1/2(eV.cm)1/2

3.9

4.2

(hv)2eV.cm)2

Indirect optical band gap Direct optical band gap

3.3

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0.8 1.2 1.6 Nd2O3 concentration (mol%)

2.0

lP

0.4

3.3

Fig. 5. Nd3+ ions concentration dependent indirect and direct optical band gaps of glasses 3.5.

Nephelauxetic ratio and bonding parameter

𝜐

𝛽 = 𝜐𝑐

𝑎

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(16)

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The nephelauxetic ration of the samples was determined from the wave number of a given Nd3+ transition in the studied sample and the wavenumber of the same transition in aqua from the Carnall table [25], [32]. The nephelauxetic ratio and bonding parameters were determined using [47]

̅ 1−𝛽 ̅ )𝑥 𝛽

𝛿=(

100

(17)

∑𝑛 𝛽 where 𝛽̅ = 𝑁 , 𝜐𝑐 and 𝜐𝑎 are the wavenumbers in the studied sample and aqua respectively

and N is the number of transitions. Table 3 outlines the values of nephelauxetic ratio (β) and the parameter of bonding (δ), the later indicates the nature of bonding between a rare earth and the surrounding environment. The Positive sign of δ designates covalent interaction

between Nd3+ ions and the nearby ligand while negative shows ionic interaction [39], [47]. In this research the sign of δ is negative as shown in the Table 3, this indicates that the bond between the Nd and the surrounding environment is relatively ionic. Table 3: Values of β and δ for proposed glasses Parameters 𝛽 𝛽̅ 𝛿

LSZBN0.8 12.0115 1.0010 -0.0957

LSZBN1.2 12.0029 1.0002 -0.0239

LSZBN1.6 12.0111 1.009 -0.0927

Judd-Ofelt Intensity parameters

LSZBN2.0 12.0115 1.0010 -0.0961

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5.6.

LSZBN0.4 12.0137 1.0011 -0.1144

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Judd-Ofelt formalism is used to obtain trivalent rare earth ions absorption transition in the glass systems. According to the Judd-Ofelt model, the intensities of the transition from the ground state to excited were determined from the Judd-Ofelt parameters ( Ω2 , Ω4 𝑎𝑛𝑑 Ω6 ) which depends on the host materials and they can also be used to explain the bonding, symmetry and the host material stiffness [23], [47]. The Ω2 depends on the material composition and the local structure and it specifies asymmetric and the covalency of Nd3+ ions [35]. In the present material relative low value of Ω2 indicates the bond between the Nd3+ and surrounding ligands is less covalent which agrees with the result of bonding parameter presented in table.3. The Ω4 𝑎𝑛𝑑 Ω6 depend on the bulk characters and rigidity of the prepared glasses [35]. The strengths spectroscopic quality factor (𝜒 = Ω4 ⁄Ω6 ) were observed to range from 1.1403 to 1.2603 which is far better than those reported for other glass systems [24] [21] [25] [22] [23]. The values of the Ω2 , Ω4 and Ω6 and the quality factor are presented in Table 4. The Nd3+ ions dependent Judd-Ofelt parameters was presented in Fig. 6.

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Table 4: Caparison of the values of Judd-Ofelt parameters and quality factor of the present glasses with others reported in the literature. Glass code

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LSZBN0.4 LSZBN0.8 LSZBN1.2 LSZBN1.6 LSZBN2.0 ZnO-Li2O-Na2OP2O5 [22] 50P2O5-30ZnO20SrO [23]

𝛀𝟐

0.2950 0.2664 0.4459 0.2340 0.1378 0.51552.2208 0.2339

𝛀𝟒

1.1283 1.1053 1.4217 0.7038 0.4527 0.13580.2408 0.6437

𝛀𝟔 0.9688 0.8770 1.1348 0.6172 0.3937 1.08814.0142 0.9598

𝝌=

𝛀𝟒 𝛀𝟔

1.1646 1.2603 1.2528 1.1403 1.1498

Tend Ω4 > Ω6 > Ω2 Ω4 > Ω6 > Ω2 Ω4 > Ω6 > Ω2 Ω4 > Ω6 > Ω2 Ω4 > Ω6 > Ω2 Ω6 > Ω2 > Ω4 Ω6 > Ω4 > Ω2

1.98

0.88

1.83

Ω2 > Ω6 > Ω4

1.897

0.820

1.834

Ω2 > Ω6 > Ω4

0.2339

0.6437

0.9598

Ω6 > Ω4 > Ω2

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Nd3+ doped barium bismuth tellurite glasses [24] Phosphate glass 3000 ppmNd3+/Yb3+ [23] Phosphate glass 30000 ppmNd3+/Yb3+ [23]

ro

1.5

-p

 

lP

re

1.0

0.5

ur na

 (10-20cm2)



0.4

0.8 1.2 1.6 Nd2O3 concentartion (mol%)

2.0

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Fig. 6. Nd3+ ions concentration dependent Judd-Ofelt intensity parameters The oscillator strength characterized the absorption band intensity and it is a function of the area under the absorption band [31]. The oscillator strengths (calculated and experimental) for the electric dipole transition from initial to final states were determined using the absorption spectrum via Eqs. 13 and 14 respectively. The deviation between experimental and calculated oscillator strength was ascertain using Eqs.15. This is to establish the best fit of the Judd-Ofelt parameter. The values of the spectral intensities (calculated and experimental) and the root means square deviation were enlisted in table 5.

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Table 5. Experimental (fexp) and calculated (fcal) oscillator strengths (10-6) and root mean square deviation of glasses. LSZBN0.4 fexp fcal

LSZBN0.8 fexp fcal

LSZBN1.2 fexp fcal

LSZBN1.6 fexp

4D1/2,4D5/2, 4D3/2

1.5621

0.9544

1.0935

0.281

1.1689

0.968

0.587

0.4802

0.4102

0.3086

2P1/2

0.0762

0.1101

0.05586

0.1077

0.0773

0.1387

0.0325

0.0688

0.0204

0.0441

4G11/2

0.0556

0.0341

0.0485

0.0319

0.0819

0.0411

0.0325

0.0215

0.0198

0.0137

2K15/2

0.1409

0.0476

0.1205

0.044

0.19

0.5697

0.0873

0.0301

0.0524

0.0192

4G9/2

0.2256

0.2435

0.1648

0.2319

0.3824

0.2999

0.1796

0.1536

0.1036

0.0982

4G7/2

0.5355

0.5376

0.5591

0.5146

0.7522

0.676

0.3579

0.3432

0.2205

0.2185

4G5/2

2.3342

1.495

2.2126

1.418

3.135

2.0126

1.5956

1.0235

0.9905

0.6346

2H11/2

0.0359

0.024

0.0291

0.0221

0.0491

0.0287

0.018

0.0152

0.0118

0.0097

4F9/2

0.1216

0.0859

0.1147

0.0789

0.1922

0.1023

0.0816

0.0546

0.0494

0.0348

4F3/2

𝜹𝒓𝒎𝒔

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fcal

LSZBN2.0 fexp fcal

1.5000

1.0617

1.3755

0.9643

1.7572

1.2478

0.9466

0.6743

0.6045

0.43

1.7262

0.9315

1.566

0.8694

2.0486

1.1235

1.0883

0.5883

0.6968

0.3759

0.4851

0.2908

0.4791

0.2627

0.7621

0.3402

0.3736

0.1851

0.2316

0.1178

0.1398

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4F5/2

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4F7/2, 4S3/2

ro

Transition

0.2253

0.1863

0.0976

0.0600

4.

Conclusion

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For the first time, Neodymium activated lithium strontium zinc borate glasses were prepared via melt quenching technique and characterized. The effects of varying Nd3+ ions concentration on the physical, optical and structural properties were determined. FTIR spectra revealed six distinguished regions with different borate functional groups. Of the twelve-absorption band, 581 nm was assigned to the hypersensitive transition. With increasing of dopant concentration in the glasses, the optical band gaps for both direct and indirect transition were first reduced and then increased at 1.6 Nd3+ mol% before being decreased. The trend of Judd-Ofelt parameters followed the trend of Ω4 > Ω6 > Ω2 for all the glasses with relatively higher quality factor compared to many other glasses reported earlier. Glass containing 1.2 mol% of Nd3+ disclosed highest Judd-Ofelt parameters and its quality factor was higher, indicating practical applications.

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Acknowledgments

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The financial support from UTM and Ministry of Malaysian Higher Education (MoHE)

References

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