Photoluminescence and thermoluminescence behavior of Gd doped Y2O3 phosphor

Photoluminescence and thermoluminescence behavior of Gd doped Y2O3 phosphor

G Model IJLEO-55166; No. of Pages 5 ARTICLE IN PRESS Optik xxx (2014) xxx–xxx Contents lists available at ScienceDirect Optik journal homepage: www...

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G Model IJLEO-55166; No. of Pages 5

ARTICLE IN PRESS Optik xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Optik journal homepage: www.elsevier.de/ijleo

Photoluminescence and thermoluminescence behavior of Gd doped Y2 O3 phosphor Vikas Dubey a,b,∗ , Sadhana Agrawal b , Jagjeet Kaur c a b c

Department of Physics, Bhilai Institute of Technology Raipur, New Raipur, Chhattisgarh, India Department of Physics, National Institute of Technology, Raipur, Chhattisgarh, India Department of Physics, Government V.Y.T.PG. Autonomous College, Durg, Chhattisgarh 91001, India

a r t i c l e

i n f o

Article history: Received 9 November 2013 Accepted 8 June 2014 Available online xxx Keywords: Photoluminescence Thermoluminescence CIE techniques

a b s t r a c t The present paper reports the synthesis and characterization photoluminescence and thermoluminescence studies of Gd3+ doped Y2 O3 phosphors. The effect of variable concentration of europium on photoluminescence (PL) and thermoluminescence (TL) behavior are also studied. The samples were prepared by solid state synthesis technique which is suitable for large scale production of phosphors. The starting materials used for sample preparation are ZrO2 and Gd2 O3 and CaF2 used as a flux. The prepared sample was characterized by X-ray diffraction technique (XRD). The surface morphology of prepared phosphor was determined by field emission gun scanning electron microscopy (FEGSEM) technique. The diffraction pattern was measured by transmission electron microscopy (TEM) with selected area diffraction pattern. All prepared phosphor with variable concentration of Gd3+ (0.2–2 mol%) was studied by photoluminescence analysis it is found that the excitation spectra of prepared phosphor shows broad excitation centered at 249 and 254 nm with few shoulder weak peaks at 275, 308 and 315 nm. The excitation spectra with variable concentration of Gd3+ show strong peaks at 613 nm for 254 nm excitation. For 275 nm excitation strong peaks found at 468, 567, 578 and 608 nm. For recording TL glow curve every time 2 mg phosphor was irradiated by UV 254 nm source and fixed the heating rate at 6.7 ◦ C s−1 . Sample shows well resolved peak at 97 ◦ C for 2 mol% of Gd3+ . Trapping parameters are calculated for every recorded glow curve. © 2014 Elsevier GmbH. All rights reserved.

1. Introduction Since a short-wavelength UV light of mercury vapour plasma is commonly used as an excitation source in most commercially available lamps, the optimization of luminescence quantum efficiency of phosphors is required for the 254 nm excitation in the fluorescent light products [1]. Nevertheless, the disposing of the used vapour junk causes environmental contamination. Recent investigation on deep violet light-emitting devices and lasers quite possibly provides an alternative excitation in the range of 340–400 nm [2–8]. Yttrium sesquioxide (Y2 O3 ) ceramics have been intensively investigated for different technological purposes. For decades, yttrium oxide has been an important material in the ceramic industry, from being a constituent of ceramic super-conductors [9], to well-known YSZ ceramics [10]. Y2 O3 is used in electronic applications as a part

∗ Corresponding author at: Department of Physics, Bhilai Institute of Technology Raipur, New Raipur, Chhattisgarh, India. Tel.: +91 09826937919. E-mail address: [email protected] (V. Dubey).

of metal–oxide–semiconductor hetero structures in Metal Oxide Semiconductor (MOS) transistors [11]. It also plays an important role in the preparation of novel light-emitting materials [12,13]. Host materials with a wide band gap are attractive for optical applications in the visible and UV spectral ranges [14,15], because the rare earths can emit within its optical window and do not suffer of quenching effects inherent to semiconductor hosts [16,17]. The present paper reports the synthesis of Y2 O3 phosphor with variable concentration of gadolinium (0.2–2 mol%). All samples was prepared by solid state reaction techniques and characterized by XRD, FEGSEM, TEM, PL and TL studies. The particle size of prepared phosphor was calculated by Scherer’s formula. The average particle size of prepared phosphors found in the range 70–100 nm. All sample shows cubic structure of Y2 O3 . There is no impurity phase found due to the concentration of gadolinium. FEGSEM study shows the surface morphology of prepared phosphor. The obtained sample shows an intense blue, greenish and red-white emission (ranging from 400 to 650 nm), under a wide range of UV light excitation (220–400 nm). The PL spectra recorded for different concentration of gadolinium. The PL emission intensity increases with increasing

http://dx.doi.org/10.1016/j.ijleo.2014.06.175 0030-4026/© 2014 Elsevier GmbH. All rights reserved.

Please cite this article in press as: V. Dubey, et al., Photoluminescence and thermoluminescence behavior of Gd doped Y2 O3 phosphor, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.175

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(222)

XRD D Pattern of Y2O3:G Gd ICDD D card No. - 89-5591 (440) (6 622)

1.5mol% Gd

Intensity (a.u.)

(400)

1 mol% Gd

0.5mol% Gd 20

40



60

80

100

Fig. 1. Powder XRD pattern of Y2 O3 : Gd (0.5–1.5 mol%) doped phosphor.

Fig. 2. FEGSEM image of Y2 O3 :Gd (1.5 mol%).

the gadolinium concentration up to 1.5 mol% after that the intensity decreases due to concentration quenching occurs. The results indicate that Y2 O3 :Gd (1.5%) phosphors can be selected as a potential candidate for LED application (Ex.275) as well as for Fluorescent lamp phosphor as well as Compact fluorescent lamps (Ex.254). Spectrophotometric determination was done for PL emission in Commission Internationale de I’Eclairage (CIE) technique. The optimized sample was studied by TL glow curve with variable UV dose at fixed concentration of Gd and fixed heating rate.

Y2 O3 , after the diffraction peaks as well indexed based on the ICDD No. 89-5591. This reveals that the structure of Y2 O3 is cubic [18,26].

2. Experimental To prepare Y2 O3 with gadolinium (0.2–2 mol%) consists of heating stoichiometric amounts of reactant mixture is taken in alumina crucible and is fired in air at 1300 ◦ C for 4 h in a muffle furnace. Every heating is followed by intermediate grinding using agate mortar and pestle. The Gd activated Y2 O3 phosphor was prepared via high temperature modified solid state diffusion. The starting materials were as follows: Y2 O3 , Gd2 O3 and CaF2 (as a flux) in molar ratio were used to prepare the phosphor [18,26]. The sample was characterized using photoluminescence (PL), thermoluminescence (TL), XRD, FEGSEM and HRTEM. The XRD measurements were carried out using Bruker D8 Advance X-ray diffractometer. The X-rays were produced using a sealed tube and the wavelength of X-ray was 0.154 nm (Cu K-alpha). The X-rays were detected using a fast counting detector based on Silicon strip technology (Bruker LynxEye detector). Observation of particle morphology was investigated by FEGSEM (field emission gun scanning electron microscope) (JEOL JSM-6360). The photoluminescence (PL) emission and excitation spectra were recorded at room temperature by use of a Shimadzu RF-5301 PC spectrofluorophotometer. The excitation source was a xenon lamp. Thermally stimulated luminescence glow curves were recorded at room temperature by using TLD reader I1009 supplied by Nucleonix Sys. Pvt. Ltd., Hyderabad. The obtained phosphor under the TL examination is given UV radiation using 254 nm UV source [19–21,27–29].

3.1. FEGSEM and HRTEM Field emission gun scanning electron microscopy and high resolution transmission electron microscopy images are shown in Figs. 2 and 3. From the images that confirms the formation of phosphor. The prepared sample shows a compact distribution over the surface and good connectivity between grains. Similarly the HRTEM SAED (selected area electron diffraction) pattern image is the diffraction pattern that is similar as XRD pattern. The particles had a narrow size distribution, a rugby-like shape and a diameter of 70–100 nm. Some agglomerates formation occurs in the papered sample. 4. Photoluminescence study Fig. 4 shows the PL excitation spectra of prepared phosphor (Y2 O3 :Gd), excitation spectra recorded at 613 nm excitation. Peaks found 249, 254, 275, 308 and 315 nm. The band near 254 nm is known to be a charge transfer (CT) process that is related to the excitation of an electron from the oxygen 2p state to a Gd3+ 4f state. The emission spectrum of phosphors was recorded by excitations with, 254 and 275 nm. The emission peaks found at 400–650 nm range (Figs. 5 and 6) more intense peaks at 468, 567, 574, 608 and 618 nm. Its shows that the all emission belongs in visible region and useful for potential candidate for LED (Light Emitting Diode) application (Ex.275) as well as for FL (Fluorescent Lamp) and Compact Fluorescent Lamp (CFL) (Ex.254 nm).

3. Results and discussion The prepared phosphor materials were analyzed by PXRD to reveal phase compositions and the particle size (Fig. 1). The crystallite size was calculated from the PXRD pattern following the Scherer equation D = 0.9/ˇ cos ␪. Here, D is the crystallite size for the (hkl) plane,  is the wavelength of the incident X-ray radiation [CuK˛ (0.154056 nm)], ˇ is the full width at half maximum (FWHM) in radians, and  is the diffraction angle for the (hkl) plane. From the PXRD pattern, it was found that the prominent phase formed is

Fig. 3. HRTEM image of Y2 O3 :Gd.

Please cite this article in press as: V. Dubey, et al., Photoluminescence and thermoluminescence behavior of Gd doped Y2 O3 phosphor, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.175

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Y O :Gd monitored at 613 nm 50

249 254 nm

Intensity (arb. units)

40

275 nm

30

20

10

0 200

308nm 315 nm

220

240

260

280

300

320

340

360

380

400

420

Wavelength (nm)

Fig. 4. PL Excitation spectra of Y2 O3 :Gd doped phosphor monitored with 613 nm.

700

1.5mol% Gd 613nm

600

2 mol% Gd

500

Intensity (a.u.)

0.2mol% Gd 0.5mol% Gd 1mol% Gd 1.5mol% Gd 2mol% Gd

1mol% Gd

400

613nm 300

200

0.5mol% Gd 613nm

100

0.1mol% Gd

0 400

450

500

550

600

650

Fig. 7. TL glow curve of Y2 O3 :Gd Phosphor with the variation of UV exposure time (5–20 min).

Wavelength (nm)

Fig. 5. PL emission spectra of Y2 O3 :Gd (0.2–2 mol%) doped phosphor monitored with 254 nm.

It is very interesting results found from PL emission spectra at 254 nm excitation (Fig. 5). The effect of variable concentration of gadolinium on PL study shows linear response with doing concentration up to 1.5 mol% of Gd3+ after that concentration quenching occurs and PL intensity decreases with increasing the dopant concentration. So the optimized concentration is 1.5 mol% of Gd in Y2 O3 host. A different observation in PL emission spectra was found for 275 nm excitation (Fig. 6). All peaks found in visible region (468, 567, 583, 608 and 618 nm) these all peaks indicate that the single host with single dopant shows composed white light so it may be useful for white light emitting diode (WLED) application. 4.1. Thermoluminescence study The glow curve is characteristic of the different trap levels that lie in the band gap of the material. A reliable dosimetric study of a thermoluminescent material should be based on a good knowledge Y2O3 (Gd 1%) Excitation at 275nm 468

50

567

of its kinetic parameters that include trap depth (E), order of kinetics (b) and frequency factor (s). The study of relatively deep trapping defect-states in various phosphors, as well as TL dating of solid state materials, is closely related to the position of the trapping levels within the forbidden gap. Although there are various methods to obtain the number of glow peaks in the complex glow curves and their kinetic parameters that best describe the peaks [22]. To gain some idea of the characteristic glow curves of the synthesized Y2 O3 :Gd3+ samples, the TL glow curves were obtained by heating samples from 50 up to 400 ◦ C at a heating rate of 6.7 ◦ C s−1 . The glow curves of synthesized Y2 O3 :Gd (Fig. 7) with the variation of UV exposure time 5–20 min. Prominent peak found at 95 ◦ C and sample shows the second order kinetics which is determined by shape factor. The values of kinetic parameters for Y2 O3 :Gd (1 mol%) is given in Table 1. The peak shape factor for the TL glow curve of the prepared phosphor was found to be ∼0.5 for maximum peaks. For variable concentration of Gd3+ in Y2 O3 host in thermoluminescence glow curve shows very good interesting result. The TL intensity increase with increasing the concentration of Gd3+ up to 1.5 mol% thereafter the intensity decreases due to concentration quenching occurs. Here the optimized TL is Y2 O3 :Gd3+ (1.5 mol%) which is suitable for dosimetric application on TL.

608

Intensity (arb. units)

450

482

574

493

40

4.2. Determination of kinetic parameters

30

583 20

618

10

0 400

450

500

550

600

650

Wavelength (nm)

Fig. 6. PL emission spectra of Y2 O3 :Gd doped phosphor monitored with 275 nm.

The TL glow curve is related to the trap levels lying at different depths in the band gap between the conduction and the valence bands of a solid. These trap levels are characterized by different trapping parameters such as trap depth, order of kinetics, and frequency factor [25,30–34]. The loss of dosimetry information stored in the materials after irradiation is strongly dependent on the position of trapping levels within the forbidden gap which is known as trap depth or activation energy (E). The mechanism of recombination of detrapped charge carriers with their counter parts is known

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Table 1 shape factor (), activation energy (E) and frequency factor (s) of UV irradiated Y2 O3 :Gd (1 mol%). UV min

T1

Tm

T2



ı

ω

 = ı/ω

Activation energy (E) eV

Frequency factor (s) s−1

5 min 10 min 15 min 20 min

70 70 70 76

97 95 95 101

134 128 130 131

27 25 25 25

37 33 35 30

64 58 60 55

0.57 0.56 0.58 0.54

0.67 0.71 0.71 0.73

2 × 1010 1 × 1011 1 × 1011 1 × 1011

Fig. 8. Representative diagram of different parameters used in the glow-curve shape method [24].

as the order of kinetics (b). The frequency factor (s) represents the product of the number of times an electron hits the wall and the wall reflection coefficient, treating the trap as a potential well. Thus, liable dosimetry study of thermoluminescent material is based on its trapping parameters. Here each of the glow curves analyzed based on glow curve shape method [23] (Fig. 7). The order of kinetic of glow curves was calculated by measuring symmetry (geometrical) factor g ∼ 0.5 (Fig. 8). The values of , ı and ω are calculated, where ‘’ is the lowtemperature half width of the glow curve i.e.  = Tm − T1 , ‘ı’ is the high-temperature half width of the glow curve i.e. ı = T2 − Tm and ‘ω’ is the full width of the glow peak at its half height i.e. ω = T2 − T1 . From the value of geometrical factor it is clear that the glow peaks obey the general order kinetics. The trap depth also known as the activation energy of the luminescence centers is calculated using Chen’s equation [23]



E˛ = C˛

2 kB Tm ˛



− b˛ (2Tm )

(1)

where kB is Boltzmann constant. Tm is peak temperature. The constant C˛ and b˛ were also calculated by the Chen’s equation. The mean activation energy was found to be ∼0.67 and ∼0.73 eV for 95 and 101 ◦ C and value of frequency factor lies in between 2 × 1010 and 1 × 1011 s−1 . The CIE coordinates were calculated by Spectrophotometric method using the spectral energy distribution of the Y2 O3 :Gd sample (Fig. 9). The color co-ordinates for the Gd doped sample are x = 0.42 and y = 0.32 (these coordinates are very near to the white light emission). Hence this phosphor having excellent color tenability from white light emission. 5. Conclusion Y2 O3 :Gd doped phosphor synthesized by modified solid state reaction method. XRD pattern confirms that synthesized sample shows cubic structure. The crystallites size was found to be 70–100 nm range. XRD studies confirm the phosphors are in single phase and nano crystallites. FEGSEM images show the formation of phosphors. The PL emission was observed in the range 400–650 nm for the Y2 O3 phosphor doped with Gd. Excitation spectrum found at 254 and 275 nm. Sharp peaks found around 468, 569, 574, 608 and 618 nm with high intensity. The present phosphor can act as

Fig. 9. CIE coordinates depicted on 1931 chart of Gd (1 mol%) doped Y2 O3 phosphor.

single host for white light emission in display devices. The CIE 1931 chromaticity coordinates much closer to the equal-energy whitelight. Thermoluminescence glow curve shows linear response with dose which indicate that the prepared sample may be useful for TL dosimetry application. Also the trapping parameters are calculated for variable UV dose for single glow peak. All samples show the second order of kinetics. For the variable concentration Gd in TL study shows linear response and the concentration quenching occurs for 2 mol% of Gd3+ . So the optimized TL is Y2 O3 :Gd3+ (1.5 mol%) which is suitable for dosimetric application on TL. References [1] Y. Sato, N. Takahashi, S. Sato, Full-color fluorescent display devices using a nearUV light-emitting diode, Jpn. J. Appl. Phys. 35 (Pt 2) (1996) 838. [2] N. Ohashi, N. Ebisawa, T. Sekiguchi, I. Sakaguchi, Y. Wada, T. Takenaka, H. Haneda, Yellowish-white luminescence in codoped zinc oxide, Appl. Phys. Lett. 86 (091) (2005) 902. [3] X.Q. Piao, T. Horikawa, H. Hanzawa, K. Machida, Characterization and luminescence properties of Sr2 Si5 N8 :Eu2+ phosphor white light emitting-diode illumination, Appl. Phys. Lett. 88 (161) (2006) 908. [4] J.K. Park, C.H. Kim, S.H. Park, H.D. Park, S.Y. Choi, Application of strontium silicate yellow phosphor for white light-emitting diodes, Appl. Phys. Lett. 84 (2004) 1647. [5] R.J. Xie, N. Hirosaki, M. Mitomo, K. Takahashi, K. Sakuma, Highly efficient whitelight-emitting diodes fabricated with short-wavelength, Appl. Phys. Lett. 88 (101) (2006) 104. [6] R. Xie, N. Hirosaki, K. Sakuma, Y. Yamamoto, M. Mitomo, Eu2+ doped Ca-␣SiAlON: a yellow phosphor for white light-emitting diodes, Appl. Phys. Lett. 84 (2004) 5404. [7] N. Sagawa, T. Uchino, Visible luminescence from octadecylsilane monolayers on silica surfaces: time-resolved photoluminescence characterization, Appl. Phys. Lett. 87 (251) (2005) 923. [8] B. Liu, C. Shi, Z. Qi, Potential white-light long-lasting phosphor: Dy3+ doped aluminate, Appl. Phys. Lett. 86 (191) (2005) 111. [9] P. Regnier, M. Sapin, C. Thomas de Montpreville, On the substitution of Y2 O3 with ZrO2 in the synthesis of YBa2 Cu3 O7 , Supercond. Sci. Technol. 2 (1989) 173. [10] M. Boaro, J.M. Vohs, R.J. Gorte, Synthesis of highly porous yttria-stabilized zirconia by tape-casting methods, J. Am. Ceram. Soc. 86 (2003) 395. [11] J.J. Chambers, G.N. Pearson, Physical and electrical characterization of ultrathin yttrium silicate insulators on silicon, J. Appl. Phys. 90 (2001) 918. [12] F. Vetrone, J.-C. Boyer, J.A. Capobianco, A. Speghini, M. Bettinelli, Concentration dependent near infrared-to-visible upconversion in nanocrystalline and bulk Y2 O3 :Er3+ , Chem. Mater. 15 (2003) 2737. [13] A. Konrad, U. Herr, R. Tidecks, F. Kummer, K. Samwer, Luminescence of bulk and nanocrystalline cubic yttria, J. Appl. Phys. 90 (2001) 3516.

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Please cite this article in press as: V. Dubey, et al., Photoluminescence and thermoluminescence behavior of Gd doped Y2 O3 phosphor, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.175