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High temperature solid state synthesis and photoluminescence behavior of Eu3+ doped GdAlO3 nanophosphor
Accepted Manuscript High Temperature Solid State Synthesis and Photoluminescence behavior of Eu3+ doped GdAlO3 nanophosphor Kanchan Upadhyay, Raunak Kumar Tamrakar, Vikas dubey PII: DOI: Reference:
S0749-6036(14)00458-3 http://dx.doi.org/10.1016/j.spmi.2014.11.030 YSPMI 3507
To appear in:
Superlattices and Microstructures
Received Date: Accepted Date:
7 November 2014 26 November 2014
Please cite this article as: K. Upadhyay, R.K. Tamrakar, V. dubey, High Temperature Solid State Synthesis and Photoluminescence behavior of Eu3+ doped GdAlO3 nanophosphor, Superlattices and Microstructures (2014), doi: http://dx.doi.org/10.1016/j.spmi.2014.11.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
High Temperature Solid State Synthesis and Photoluminescence behavior of Eu3+ doped GdAlO3 nanophosphor Kanchan Upadhyay a , Raunak Kumar Tamrakar b and Vikas dubeyc a
Department of Chemistry, Shree Shankayacharya School, hudco, (C.G.), India
b
Department of Applied Physics, Bhilai Institute of Technology (Seth Balkrishan Memorial), Near Bhilai House, Durg (C.G.) Pin-491001, India
c
Department of Applied Physics, Bhilai Institute of Technology (Seth Balkrishan Memorial), Raipur, India Corresponding: [email protected], [email protected] Ph :-+919827850113 Abstract:-
Gadolinium monoaluminate is successfully synthesized by the high solid state reaction method. The method is suitable for large scale production and its eco friendly method of synthesis any phosphor. The high temperature synthesis techniques have some advantages for enhance the efficiency of luminescence. Sample prepared with variable concentration of europium (0.5 to 6mol%) after the all prepared sample were characterized by X-ray diffraction technique (XRD) and transmission electron microscopic (TEM) technique. The ƉĂƌƚŝĐůĞ ƐŝnjĞ ǁĂƐ ĞǀĂůƵĂƚĞĚ ďLJ ^ĐŚĞƌĞƌ͛Ɛ ĨŽƌŵƵůĂ ĂŶĚ ĨŽƵŶĚ Ăƚ 55.16nm and having orthorhombic phase. The surface morphology of prepared phosphor was determined by TEM and it shows good connectivity with grain and formation of nano sized crystal. The photoluminescence with variable concentration of europium shows very good excitation and emission spectra. The excitation spectra monitored at 612nm excitation and excitation found with broad peaks at 266nm with shoulder peak at 274nm. The emission spectra monitored at 266nm and it shows all peaks in visible region (583, 594, 599, 613 and 630nm) with intense peak at 613nm (red emission). The intensity of PL spectra increases with increasing the concentration of europium, up to 5mol% after this concentration intensity decreases due to concentration quenching occurs. The spectrophotometric determination was determined by &RPPLVVLRQ,QWHUQDWLRQDOHGH,¶(FODLUDJH &,( technique. Keywords: GdAlO3: Eu3+, XRD, TEM, Solid state Synthesis, Photoluminescence; CIE, phosphor. 1. Introduction:-
During the last few decades, rare-earth-activated phosphors have led to a revolution in lighting industry. Now in the present day high efficient phosphor with higher lifetime as well as eco friendly qualities are basic requirement for environment. Therefore Mercury free phosphors with high efficacy under excitation with ultraviolet radiation and excellent physical and chemical stability ware foremost requirements for good lamp phosphors with better future environment [1]. Gadolinium based materials are having remarkable application in different fields of the biological, medical and optical applications [2-6]. GdAlO3 is an ortho-aluminate crystal. It is a hard crystal of high density, which shows fast luminescence behavior under excitations [7]. The rare-earth aluminates RAlO3 are a potential class of host material for rare earth ions to give light emission [8-11]. It is well known that rare-earth-ion-doped, activated phosphors have attracted considerable research interest due to their excellent luminescent properties. Because the 4f electrons of rare-earth ions are shielded by outer 5s2 and 5p6 electrons, the intra 4f±4f emission spectra of rare-earth ions are characterized by narrow lines with high color purity [12,13]. Due to, the remarkable narrow-band emission properties of Eu3+, Tb3+, Dy3+ and Tm3+ ions have been utilized to the maximum extent in the development of efficient phosphors for lamps, plasma display panels and also for light-emitting diodes [14]. All of these, it is well known that Eu3+ is an excellent candidate to produce red color LED's. Eu3+ must be doped into a lattice to emit luminescence upon excitation. Eu3+-doped phosphor are very interesting materials for luminescence applications due to its red emission [15-20]. In the present work, GdAlO3: Eu3+- doped phosphors were prepared via a solid-statereaction method to examine the potential for their utility as luminescence phosphors with different color emission at each exciting wavelength. 2.Experimental methods:2.1 Synthesis of Eu3+ doped GdAlO3 phosphors: - The Eu3+ doped GdAlO3 phosphors with different concentration of doping (0.5, 1, 2, 3, 4, 5 and 6mol %) were prepared via high temperature modified solid state reaction method. Gadolinium nitrate [Gd(NO3)3], aluminum nitrate [Al(NO3)3], europium nitrite [Eu(NO3)3], purchased from Sigma Aldrich and boric acid used as flux were taken as starting raw materials in stoichiometric amount. After being ground thoroughly by using an agate, mortar-pestle by dry grinding for near about 45 minutes, to ensure the best homogeneity and reactivity, powder was put in alumina crucible, and heated in a muffle furnace at 1000 °C for 2 hour[4].
2.2 Instrumentation details:
The samples were characterized at the Inter University
Consortium (IUC) Indore for X-ray diffraction. X-ray diffraction was used for phase identification and crystallite size calculation. XRD data were collected over the range 20ʹϳϬȗ at room temperature. The XRD measurements were carried out using a Bruker D8 Advance X-ray diffractometer. The X-rays were produced using a sealed tube, and the wavelength of the 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 Lynx Eye detector).The excitation and emission spectra were recorded using RF5301 spectrophotofluorometer. 3. Result and discussion :(I)XRD Results:- The crystalline structure of the powders was analyzed by X-ray diffraction (XRD). Fig 1 is the XRD pattern of GdAlO3: Eu3+(4 ŵŽůйͿƉŚŽƐƉŚŽƌƐŽĨϮɽ range from 200 to 700. The crystalline size is calculated using ^ĐŚĞƌĞƌ͛Ɛ formula [21-23] DсŬʄͬĐŽƐɽ͕ where k is the ^ĐŚĞƌĞƌ͛Ɛ constant ;Ϭ͘ϵϰͿ͕ʄŝƐƚŚĞǁĂǀĞůĞŶŐƚŚŽĨy-ray (1.54060 A0) , B is the full-width at half maxima͕ɽŝƐƚŚĞragg angle of the XRD big peak. The average particle size was found around 55.16nm. Nanophosphors can be indexed to orthorhombic phase of GdAlO3 (JCPDS No. 46-0395) without impurity peaks [24]
3.2 Fourier transformation infrared spectroscope (FTIR) results of GdAlO 3: Eu3+ (4 mol %) Nanophosphor:- Figure 2 shows the FTIR spectra of solid state synthesized GdAlO3: Eu3+(4 mol %) phosphor. A strong absorption peak at 549.86 cm-1 corresponds to Gd-O vibrational modes. The band at 471.86 attributed to the Eu-O stretching [18, 19].
3.3 Scanning Electron Microscope results of GdAlO3: Eu3+ (4 mol%) nanophosphor:- The SEM micrographs of GdAlO3: Eu3+( 4mol%) phosphor show the crystallites with regular shape and contain several voids and pores (Fig. 3). It can be observed that the crystallites have uniform shape and size. This was believed to be related to the uniform distribution of temperature. 3.4 Transmission Electron Microscope results of GdAlO3: Eu3+( 4mol%) phosphor:- From TEM picture (Fig. 7a) the particle size varies from 45 to 55nm, which was in good agreement to those obtained by ^ĐŚĞƌĞƌ͛ƐĨŽƌŵƵůĂ͘ (III) Photoluminescence (PL) Spectra:-
The Excitation spectrum of GdAlO3:Eu3+ was observed by monitoring the 5D0ĺ7F2 transition of Eu3+at 613 nm emission. It exhibits a broad excitation peak at 266 nm with a shoulder peak at 274nm is caused by the charge transfer band (CTS) originates due to transition from 2p orbital of O2íto 4f orbital of Eu3+ (figure 5). The emission spectra of GdAlO3:Eu3+ was recorded under 266 nm excitation. The phosphor shows characteristic emission bands of Eu3+ in visible region. The most intense peak was found at 613nm, weak bands were present within orange-red region at 583nm, 594nm, 599 and in red region at 630nm. For all the assynthesized samples, the spectra show the emission of Eu3+ ions which corresponds to the 5
D0ĺ 7FJ transitions (J=0,1,2,3). The emission signals at 583nm, 594nm , 599nm, 613nm
and 630nm were corresponds to the 5D0ĺ7F0, 5D0ĺ7F1, 5D0ĺ7F1, 5D0ĺ7F2 and 5D0ĺ7F3 respectively [25,26]. , The transitions 5D0ĺ7F1 and 5D0ĺ7F3 are magnetic dipole transitions and independent from the surrounding of Eu 3+ ion. The strong red signal due to the , 5D0ĺ 7
F2 transition corresponds to the electric dipole transition and strongly affected by the
surroundings of Eu3+ ion [27]. From the emission spectrum it is clearly observed that the emission intensity of magnetic dipole was lower than that of electric dipole transition, due to this Eu3+ ions occupy a low symmetry site in GdAlO3 host [5]. Both magnetic dipole transition and electric dipole transition transitions are shown in the emission spectra. If the magnetic dipole transition 5D0Æ7F1 having the weak intensity then Eu3+ ions in host lattice occupies an inversion centre. If the emission intensity of magnetic dipole transition was lower than that of electric dipole transition, which indicates that Eu 3+ ions occupied without an inversion symmetric centers in the host. Mechanism: The down conversion mechanism of the prepared phosphor is due to cooperative energy transfer from Gd3+ to nearby Eu3+ ions using defects state as intermediate. This energy transfer results in emission in visible region. The ground state of Gd 3+ ion 8S7/2 absorbs the UV light of 266 nm and excites to its CTB or 6I7/2 excited energy state. The excited state of Gd3+ 6I7/2 populates 6P7/2 by non radiative decay. The energy transfer to the nearby Eu 3+ ion from 6P7/2 level of Gd3+ ion and non radiatively transfer to the lower crystal field levels of the Eu3+ ion which are responsible for the visible emissions of the phosphor. The energy transfer process may be either due to non-radiative transition of Oí ions or a phonon assisted direct energy transfer to Eu3+ that represent the transitions related to Oí ĺEu3+. Once some Eu3+ ions are excited on the level L the energy can be released by phonon-assisted back-transfer (EBT) Eu3+ ĺO2í, or a fast non-radiative relaxation from upper Eu 3+ level L to the lower
5
D0 energy level. Then, when the Eu3+ ions are in 5D0 energy level, it undergoes various
radiative and non-radiative and radiative decay 5 D0 ĺ7Fj (j =0, ..., 6}). The radiative decay results in orange red emission by the prepared phosphor. It can also undergoes a cross relaxation process (5D0, 7Fj) ĺ(7Fj, 5D0) between two Eu3+ ions,(CR)[19]. Effect of Eu3+ concentration: The emission spectra of GdAlO3:Eu
3+
phosphor was recorded as a function of Eu 3+ ion
concentration to determine the effect of Eu3+ ion concentration on emission spectra recorded under 266 nm excitation. The increase in Eu3+ ion concentration do not change the peak positions, whereas the intensity of emission peaks increases with increasing Eu 3+ ion concentration. The intensity increases up to 5 mol% of Eu 3+ above this concentration of Eu3+ ion quenching in intensity was observed. The initial increase in emission intensity may be due to increases in CR process between to nearby Eu3+ ions due to decrease in interioninc distances between dopant ions [29]. Later the decrease in intensity is due to concentration quenching. CIE coordinate: The CIE coordinates were calculated by Spectrophotometric method using the spectral energy distribution of the GdAlO3:Eu3+ (1.75%) sample (Fig 8). The colour co-ordinates for the Eu3+ doped sample are x=0.566 and y=0.393 (these coordinates are very near to the red light emission). Hence this phosphor having excellent color tenability from red light emission. The results indicate that GdAlO3:Eu3+ (1.75%) phosphors can be selected as a potential candidate for FL (Fluorescent Lamp) and Compact Fluorescent Lamp (CFL) (Ex.266).However, the relative intensity of the emission bands which provide the fundamental colours balance for red-light emission was achieved with the 0.5 mol% sample with the spectrum (Fig. 8 ) providing the CIE 1931 chromaticity coordinates much closer to the equal-energy red-light. If one increases the activator concentration even further, the emission intensity commences to decrease owing to concentration quenching. This concentration quenching is due to the increase in the ion±ion interaction provoked by the shorter distance between interacting activators as the concentration increases. The fluorescence light spectral profile as a function of the activator concentration was examined and the results indicated that the chromaticity coordinates of the overall emission light changed resulting in different colours of the overall emission light, for different concentrations as can be observed [5].
Conclusion: GdAlO3:Eu3+ doped phosphor synthesized by solid state synthesis method. XRD pattern confirms that synthesized sample shows orthorhombic structure. The crystallites size was found to be 45 ± 55 nm range. XRD studies confirm the phosphors are in single phase and nano crystallites. The PL emission was observed in the range 400- 650nm ranges with intense red emission centred at 613nm peak for the GdAlO3 phosphor doped with Eu3+. Excitation spectrum found at 266nm. Broad intense peaks found around 594 and 613 with high intensity. The results indicate that GdAlO3:Eu3+ (5%) phosphors can be selected as a potential candidate for FL (Fluorescent Lamp) and Compact Fluorescent Lamp (CFL) (Ex.266). The electric dipole transition ( 5D0Æ7F2) dominants the magnetic dipole transition (5D0Æ7F1) in PL emission spectra of GdAlO3:Eu3+ doped phosphor. Reference:1. Shionoya S. , Yen W.,Phosphor Handbook,CRC Press,New York,1998,p.389. 2. Tamrakar, R. K., Bisen, D. P., & Brahme, N. (2014). Characterization and luminescence properties of Gd2O3 phosphor. Research on Chemical Intermediates, 40, 1771-1779 3. Tamrakar R. K., Bisen D. P., Sahu I. P., and Brahme N.(2014),, UV and gamma ray induced thermoluminescence properties of cubic Gd2O3:Er3+ phosphor, Journal of Radiation
Research
and
Applied
Sciences,(2014),
http://dx.doi.org/10.1016/
j.jrras.2014.07.003 4. Tamrakar, R. K., Bisen, D. P., Robinson, C. S., Sahu, I. P., & Brahme, N. (2014). Ytterbium doped gadolinium oxide (Gd2O3:Yb3+) phosphor: topology, morphology, and luminescence behaviour in Hindawi Publishing Corporation. Article ID 396147 Indian
Journal
of
Materials
Science,
7.
Accepted
4
February
2014,
http://dx.doi.org/10.1155/2014/396147. 5. Chan W. C. W. and Nie S. 0 ³4XDQWXP GRW ELRFRQMXJDWHV IRU XOWUDVHQVLWLYH QRQLVRWRSLFGHWHFWLRQ´Science 281, 2016±2018,1998. 6. Tamrakar R. K., Bisen D. P., Upadhyay K. and Bramhe N., Effect of Fuel on Structural and Optical Characterization of Gd 2O3:Er3+ Phosphor, Journal of Luminescence and Applications (2014) Vol. 1 No. 1 pp. 23-29. 7. J.W.M. Verweij, M.Th. Cohen-Adad, D. Bouttet, H. Lautesse, B. Moine, C. Prdrini, Chemical Physics Letters 239 (1995) 51-55.
8. Liu XM, Yan LS, Lin J. J Phys Chem C 2009;113:8478±83. 9. Lu WC, Ma XH, Zhou H, Chen GT, Li JF, Zhu ZJ, et al. J Phys Chem C 2008;112: 15071±4. 10. Osiac E. J Alloys Compd 2002;341:263±6. 11. Seeta Rama Raju G, Park JY, Jung HC, Yang HK, Moon BK, Jeong JH, et al. Opt Mater, 2009, 31, 1210-1214 12. Yang WJ, Chen TM. Appl Phys Lett 2006;88:101903-3. 13. Tang YS, Hu SF, Lin CC, Bagkar NC, Liu RS. Appl Phys Lett 2007;90:151108±10. 14. Feldmann C., T. Jüstel, Ronda C.R. and Schmidt P. J. ,Inorganic Luminescent Materials: 100 Years of Research and Application, Advanced Functional Materials, Volume 13, Issue 7, pages 511±516, July, 2003 15. Walrand CG-, Binnemans K. In: Gschneidner KA, Eyring L, editors. Rationalization of Crystal-Field Parametrization Handbook on the Physics and Chemistry of Rare Earths. Amsterdam: North-Holland; 1996. 16. Xiaorui Dong, Zuoling Fu, Yingning Yu, Shuaibing Li, Zhenwen Dai, Materials Letters 74 (2012) 140±142. 17. Shilpa C. J., Akila Kadgathur Jayaram A. K., Dhananjaya N., Nagabhushana H., Prashantha S.C., Sunitha D. V., Sharma S. C., Shivakumara C., Nagabhushanam B.M." GdAlO3:Eu3+:Bi3+ nanophosphor: Synthesis and enhancement of red emission for WLEDs ", Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 550±558 18. E. De la Rosa, L.A. Diaz-Torres, P. Salas, R.A. Rodríguez, Opt. Mater. 27 (2005) 1320±1325.Jia, G.; Liu, K.; Zheng, Y.; Song, Y.; Yang, M.; You, H. Highly Uniform Gd(OH)3 and Gd2O3:Eu3+ Nanotubes: Facile Synthesis and Luminescence 3URSHUWLHV-3K\V&KHP& í 19. Meza Octavio, Villabona-E. G.,-Torres L. A, Desirena H., Rodríguez-Lopez J. L.,and Perez E., Luminescence Concentration Quenching Mechanism in Gd2O3:Eu3+. J. 3K\V&KHP$ í 20. Dubey V., Tiwari R., Pradhan M. K., Rathore G. S., Sharma C., and Tamrakar R. K. , Opticalbehaviour of cadmium and mercury free eco-friendly lamp nanophosphor for displaydevices, Results in Physics, Volume 4, 2014, Pages 63 21. Tamrakar R. K., Studies on Absorption Spectra of Mn Doped CdS Nanoparticles, (LAP Lambert Academic Publishing, VerlAg, (2012). ISBN 978-3-659-26222-7. 22. Tamrakar R. K. and Bisen D. P., Optical and kinetic studies of CdS:Cu nanoparticles Res Chem Intermed (2013) 39:3043±3048.
23. Tamrakar R. K. " UV-Irradiated thermoluminescence studies of bulk CdS with trap parameter, Research on chemical intermediates, (2013 ) DOI10.1007/s11164-0131166-4. 24. Wang P., Shanghai inst. of Ceramics, Chinese Academy of science, Shanghai, china, ICCD grant-in-Aid,(1994). 25. Yanhong Lia,b,_, Guangyan Hong, Journal of Luminescence 124 (2007) 297ದ301 26. Li-Ya Zhoua, _, WeiWanga, Jun-LiHuanga, QiPangb, Ling-HongYia, Meng-Lian Gongc, Jian-XinShi, Optik 121 (2010) 1516±1519 27. Krisjanis Smits, Larisa Grigorjev, Donats Millers, Anatolijs Sarakovskis, Agnieszka Opalinska, Janusz D. Fidelus, Witold Lojkowski, A. Emeline, G.V. Kataeva, A.S. Litke, A.V. Rudakova, V.K. Ryabchuk, N. Serpone, Langmuir 14 (1998) 5011±5022. 28. F. Vetrone, J. C. Boyer, J. A. Capobianco, A. Speghini and M. Bettinelli, R. Krsmanovic and S. Polizzi, Structural Investigation and Anti-Stokes Emission of Scandium Oxide Nanocrystals Activated with Trivalent Erbium, J. Electrochem. Soc., 152; H19-H24 (2005)
3+
GdAlO3 (4 % of Eu )
(020)
100000
Intensity (Arb. Units)
80000
(002)
60000
(022)
40000
(220) (310)
(133)
20000
20
25
30
35
40
45
T
50
55
60
Figure 1 XRD result of GdAlO3: Eu3+(4 mol %) phosphors
65
70
75
3+
FTIR spectra of GdAlO3: Eu ( 4mol%) 1.10
2950.07cm
Transmittance(%)
1.05
-1
1387.11cm
-1
1.00
0.95
471.86cm
-1
0.90
0.85
4000
549.86cm 3500
3000
2500
2000
1500 -1
Wavenumber (cm )
Figure 2. FTIR spectra of GdAlO3: Eu3+( 4mol%)
1000
-1
500
Figure 3. SEM Iamge of GdAlO3: Eu3+( 4mol%)
Figure 4. TEM Image of GdAlO3: Eu3+( 4mol%)
(266)
800
Ex=613nm
(274) 700
Intesnity (Arb. Units)
600 500 400 300 200 100 0 200
220
240
260
280
300
320
340
360
380
400
420
Wavelength(nm)
Figure 5. PL excitation spectra of GdAlO3: Eu3+(4 mol %) phosphors under 613nm
Intesnity (Arb. Units)
(613)
.5% Eu 1% Eu 2% Eu 3% Eu 4% Eu 5% Eu 6% Eu
1000
800
600
400
(594) (599)
(583)
200
(630)
0 550
575
600
625
650
Wavelength(nm)
Figure 6(a) PL Emission spectra of GdAlO3: Eu3+(0.5-6% mol %) phosphors for 266 nm excitation 1100
Peak Position
Intensity (Arb Units)
1000 900 800 700 600 500 400 .5% Er
1% Er
2% Er
3% Er 3+
Er
4% Er
5% Er
6% Er
in Mol%
Figure 6(b) Mol(%) concentration effect on PL spectra of GdAlO 3: Eu3+(0.5-6% mol %) phosphors
Figure 7. Energy level diagram of of GdAlO3: Eu3+
Figure 8 :CIE coordinates depicted on 1931 chart where X = 0.566 and Y = 0.393 (red emission O emission = 613nm) of Eu3+(5%) doped GdAlO3 phosphor
Table 1 Table1- Summary of diffraction angle, crystallite size and FWHM of GdAlO 3: Eu3+ (4 mol %) phosphor. S.No.
Eu3+in
2T T[°2Th.]
Intensity[cts]
FWHM [°2Th.]
D (particle size)
percent
1.
4%
24.70
60072
0.18
45.18
33.73
99685
0.19
43.69
41.00
38140
0.17
49.89
48.16
36835
0.16
54.39
55.50
20603
0.15
59.84
69.43
27318
0.18
56.85
Highlights 3+ 1. Solid state synthesis of Eu doped GdAlO3 nanophosphor. 3+ 2. Structural behaviour of Eu doped GdAlO3 nanophosphor. 3+ 3. Photoluminescent properties of Eu doped GdAlO3 nanophosphor.
S0749-6036(14)00458-3 http://dx.doi.org/10.1016/j.spmi.2014.11.030 YSPMI 3507
To appear in:
Superlattices and Microstructures
Received Date: Accepted Date:
7 November 2014 26 November 2014
Please cite this article as: K. Upadhyay, R.K. Tamrakar, V. dubey, High Temperature Solid State Synthesis and Photoluminescence behavior of Eu3+ doped GdAlO3 nanophosphor, Superlattices and Microstructures (2014), doi: http://dx.doi.org/10.1016/j.spmi.2014.11.030
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
High Temperature Solid State Synthesis and Photoluminescence behavior of Eu3+ doped GdAlO3 nanophosphor Kanchan Upadhyay a , Raunak Kumar Tamrakar b and Vikas dubeyc a
Department of Chemistry, Shree Shankayacharya School, hudco, (C.G.), India
b
Department of Applied Physics, Bhilai Institute of Technology (Seth Balkrishan Memorial), Near Bhilai House, Durg (C.G.) Pin-491001, India
c
Department of Applied Physics, Bhilai Institute of Technology (Seth Balkrishan Memorial), Raipur, India Corresponding: [email protected], [email protected] Ph :-+919827850113 Abstract:-
Gadolinium monoaluminate is successfully synthesized by the high solid state reaction method. The method is suitable for large scale production and its eco friendly method of synthesis any phosphor. The high temperature synthesis techniques have some advantages for enhance the efficiency of luminescence. Sample prepared with variable concentration of europium (0.5 to 6mol%) after the all prepared sample were characterized by X-ray diffraction technique (XRD) and transmission electron microscopic (TEM) technique. The ƉĂƌƚŝĐůĞ ƐŝnjĞ ǁĂƐ ĞǀĂůƵĂƚĞĚ ďLJ ^ĐŚĞƌĞƌ͛Ɛ ĨŽƌŵƵůĂ ĂŶĚ ĨŽƵŶĚ Ăƚ 55.16nm and having orthorhombic phase. The surface morphology of prepared phosphor was determined by TEM and it shows good connectivity with grain and formation of nano sized crystal. The photoluminescence with variable concentration of europium shows very good excitation and emission spectra. The excitation spectra monitored at 612nm excitation and excitation found with broad peaks at 266nm with shoulder peak at 274nm. The emission spectra monitored at 266nm and it shows all peaks in visible region (583, 594, 599, 613 and 630nm) with intense peak at 613nm (red emission). The intensity of PL spectra increases with increasing the concentration of europium, up to 5mol% after this concentration intensity decreases due to concentration quenching occurs. The spectrophotometric determination was determined by &RPPLVVLRQ,QWHUQDWLRQDOHGH,¶(FODLUDJH &,( technique. Keywords: GdAlO3: Eu3+, XRD, TEM, Solid state Synthesis, Photoluminescence; CIE, phosphor. 1. Introduction:-
During the last few decades, rare-earth-activated phosphors have led to a revolution in lighting industry. Now in the present day high efficient phosphor with higher lifetime as well as eco friendly qualities are basic requirement for environment. Therefore Mercury free phosphors with high efficacy under excitation with ultraviolet radiation and excellent physical and chemical stability ware foremost requirements for good lamp phosphors with better future environment [1]. Gadolinium based materials are having remarkable application in different fields of the biological, medical and optical applications [2-6]. GdAlO3 is an ortho-aluminate crystal. It is a hard crystal of high density, which shows fast luminescence behavior under excitations [7]. The rare-earth aluminates RAlO3 are a potential class of host material for rare earth ions to give light emission [8-11]. It is well known that rare-earth-ion-doped, activated phosphors have attracted considerable research interest due to their excellent luminescent properties. Because the 4f electrons of rare-earth ions are shielded by outer 5s2 and 5p6 electrons, the intra 4f±4f emission spectra of rare-earth ions are characterized by narrow lines with high color purity [12,13]. Due to, the remarkable narrow-band emission properties of Eu3+, Tb3+, Dy3+ and Tm3+ ions have been utilized to the maximum extent in the development of efficient phosphors for lamps, plasma display panels and also for light-emitting diodes [14]. All of these, it is well known that Eu3+ is an excellent candidate to produce red color LED's. Eu3+ must be doped into a lattice to emit luminescence upon excitation. Eu3+-doped phosphor are very interesting materials for luminescence applications due to its red emission [15-20]. In the present work, GdAlO3: Eu3+- doped phosphors were prepared via a solid-statereaction method to examine the potential for their utility as luminescence phosphors with different color emission at each exciting wavelength. 2.Experimental methods:2.1 Synthesis of Eu3+ doped GdAlO3 phosphors: - The Eu3+ doped GdAlO3 phosphors with different concentration of doping (0.5, 1, 2, 3, 4, 5 and 6mol %) were prepared via high temperature modified solid state reaction method. Gadolinium nitrate [Gd(NO3)3], aluminum nitrate [Al(NO3)3], europium nitrite [Eu(NO3)3], purchased from Sigma Aldrich and boric acid used as flux were taken as starting raw materials in stoichiometric amount. After being ground thoroughly by using an agate, mortar-pestle by dry grinding for near about 45 minutes, to ensure the best homogeneity and reactivity, powder was put in alumina crucible, and heated in a muffle furnace at 1000 °C for 2 hour[4].
2.2 Instrumentation details:
The samples were characterized at the Inter University
Consortium (IUC) Indore for X-ray diffraction. X-ray diffraction was used for phase identification and crystallite size calculation. XRD data were collected over the range 20ʹϳϬȗ at room temperature. The XRD measurements were carried out using a Bruker D8 Advance X-ray diffractometer. The X-rays were produced using a sealed tube, and the wavelength of the 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 Lynx Eye detector).The excitation and emission spectra were recorded using RF5301 spectrophotofluorometer. 3. Result and discussion :(I)XRD Results:- The crystalline structure of the powders was analyzed by X-ray diffraction (XRD). Fig 1 is the XRD pattern of GdAlO3: Eu3+(4 ŵŽůйͿƉŚŽƐƉŚŽƌƐŽĨϮɽ range from 200 to 700. The crystalline size is calculated using ^ĐŚĞƌĞƌ͛Ɛ formula [21-23] DсŬʄͬĐŽƐɽ͕ where k is the ^ĐŚĞƌĞƌ͛Ɛ constant ;Ϭ͘ϵϰͿ͕ʄŝƐƚŚĞǁĂǀĞůĞŶŐƚŚŽĨy-ray (1.54060 A0) , B is the full-width at half maxima͕ɽŝƐƚŚĞragg angle of the XRD big peak. The average particle size was found around 55.16nm. Nanophosphors can be indexed to orthorhombic phase of GdAlO3 (JCPDS No. 46-0395) without impurity peaks [24]
3.2 Fourier transformation infrared spectroscope (FTIR) results of GdAlO 3: Eu3+ (4 mol %) Nanophosphor:- Figure 2 shows the FTIR spectra of solid state synthesized GdAlO3: Eu3+(4 mol %) phosphor. A strong absorption peak at 549.86 cm-1 corresponds to Gd-O vibrational modes. The band at 471.86 attributed to the Eu-O stretching [18, 19].
3.3 Scanning Electron Microscope results of GdAlO3: Eu3+ (4 mol%) nanophosphor:- The SEM micrographs of GdAlO3: Eu3+( 4mol%) phosphor show the crystallites with regular shape and contain several voids and pores (Fig. 3). It can be observed that the crystallites have uniform shape and size. This was believed to be related to the uniform distribution of temperature. 3.4 Transmission Electron Microscope results of GdAlO3: Eu3+( 4mol%) phosphor:- From TEM picture (Fig. 7a) the particle size varies from 45 to 55nm, which was in good agreement to those obtained by ^ĐŚĞƌĞƌ͛ƐĨŽƌŵƵůĂ͘ (III) Photoluminescence (PL) Spectra:-
The Excitation spectrum of GdAlO3:Eu3+ was observed by monitoring the 5D0ĺ7F2 transition of Eu3+at 613 nm emission. It exhibits a broad excitation peak at 266 nm with a shoulder peak at 274nm is caused by the charge transfer band (CTS) originates due to transition from 2p orbital of O2íto 4f orbital of Eu3+ (figure 5). The emission spectra of GdAlO3:Eu3+ was recorded under 266 nm excitation. The phosphor shows characteristic emission bands of Eu3+ in visible region. The most intense peak was found at 613nm, weak bands were present within orange-red region at 583nm, 594nm, 599 and in red region at 630nm. For all the assynthesized samples, the spectra show the emission of Eu3+ ions which corresponds to the 5
D0ĺ 7FJ transitions (J=0,1,2,3). The emission signals at 583nm, 594nm , 599nm, 613nm
and 630nm were corresponds to the 5D0ĺ7F0, 5D0ĺ7F1, 5D0ĺ7F1, 5D0ĺ7F2 and 5D0ĺ7F3 respectively [25,26]. , The transitions 5D0ĺ7F1 and 5D0ĺ7F3 are magnetic dipole transitions and independent from the surrounding of Eu 3+ ion. The strong red signal due to the , 5D0ĺ 7
F2 transition corresponds to the electric dipole transition and strongly affected by the
surroundings of Eu3+ ion [27]. From the emission spectrum it is clearly observed that the emission intensity of magnetic dipole was lower than that of electric dipole transition, due to this Eu3+ ions occupy a low symmetry site in GdAlO3 host [5]. Both magnetic dipole transition and electric dipole transition transitions are shown in the emission spectra. If the magnetic dipole transition 5D0Æ7F1 having the weak intensity then Eu3+ ions in host lattice occupies an inversion centre. If the emission intensity of magnetic dipole transition was lower than that of electric dipole transition, which indicates that Eu 3+ ions occupied without an inversion symmetric centers in the host. Mechanism: The down conversion mechanism of the prepared phosphor is due to cooperative energy transfer from Gd3+ to nearby Eu3+ ions using defects state as intermediate. This energy transfer results in emission in visible region. The ground state of Gd 3+ ion 8S7/2 absorbs the UV light of 266 nm and excites to its CTB or 6I7/2 excited energy state. The excited state of Gd3+ 6I7/2 populates 6P7/2 by non radiative decay. The energy transfer to the nearby Eu 3+ ion from 6P7/2 level of Gd3+ ion and non radiatively transfer to the lower crystal field levels of the Eu3+ ion which are responsible for the visible emissions of the phosphor. The energy transfer process may be either due to non-radiative transition of Oí ions or a phonon assisted direct energy transfer to Eu3+ that represent the transitions related to Oí ĺEu3+. Once some Eu3+ ions are excited on the level L the energy can be released by phonon-assisted back-transfer (EBT) Eu3+ ĺO2í, or a fast non-radiative relaxation from upper Eu 3+ level L to the lower
5
D0 energy level. Then, when the Eu3+ ions are in 5D0 energy level, it undergoes various
radiative and non-radiative and radiative decay 5 D0 ĺ7Fj (j =0, ..., 6}). The radiative decay results in orange red emission by the prepared phosphor. It can also undergoes a cross relaxation process (5D0, 7Fj) ĺ(7Fj, 5D0) between two Eu3+ ions,(CR)[19]. Effect of Eu3+ concentration: The emission spectra of GdAlO3:Eu
3+
phosphor was recorded as a function of Eu 3+ ion
concentration to determine the effect of Eu3+ ion concentration on emission spectra recorded under 266 nm excitation. The increase in Eu3+ ion concentration do not change the peak positions, whereas the intensity of emission peaks increases with increasing Eu 3+ ion concentration. The intensity increases up to 5 mol% of Eu 3+ above this concentration of Eu3+ ion quenching in intensity was observed. The initial increase in emission intensity may be due to increases in CR process between to nearby Eu3+ ions due to decrease in interioninc distances between dopant ions [29]. Later the decrease in intensity is due to concentration quenching. CIE coordinate: The CIE coordinates were calculated by Spectrophotometric method using the spectral energy distribution of the GdAlO3:Eu3+ (1.75%) sample (Fig 8). The colour co-ordinates for the Eu3+ doped sample are x=0.566 and y=0.393 (these coordinates are very near to the red light emission). Hence this phosphor having excellent color tenability from red light emission. The results indicate that GdAlO3:Eu3+ (1.75%) phosphors can be selected as a potential candidate for FL (Fluorescent Lamp) and Compact Fluorescent Lamp (CFL) (Ex.266).However, the relative intensity of the emission bands which provide the fundamental colours balance for red-light emission was achieved with the 0.5 mol% sample with the spectrum (Fig. 8 ) providing the CIE 1931 chromaticity coordinates much closer to the equal-energy red-light. If one increases the activator concentration even further, the emission intensity commences to decrease owing to concentration quenching. This concentration quenching is due to the increase in the ion±ion interaction provoked by the shorter distance between interacting activators as the concentration increases. The fluorescence light spectral profile as a function of the activator concentration was examined and the results indicated that the chromaticity coordinates of the overall emission light changed resulting in different colours of the overall emission light, for different concentrations as can be observed [5].
Conclusion: GdAlO3:Eu3+ doped phosphor synthesized by solid state synthesis method. XRD pattern confirms that synthesized sample shows orthorhombic structure. The crystallites size was found to be 45 ± 55 nm range. XRD studies confirm the phosphors are in single phase and nano crystallites. The PL emission was observed in the range 400- 650nm ranges with intense red emission centred at 613nm peak for the GdAlO3 phosphor doped with Eu3+. Excitation spectrum found at 266nm. Broad intense peaks found around 594 and 613 with high intensity. The results indicate that GdAlO3:Eu3+ (5%) phosphors can be selected as a potential candidate for FL (Fluorescent Lamp) and Compact Fluorescent Lamp (CFL) (Ex.266). The electric dipole transition ( 5D0Æ7F2) dominants the magnetic dipole transition (5D0Æ7F1) in PL emission spectra of GdAlO3:Eu3+ doped phosphor. Reference:1. Shionoya S. , Yen W.,Phosphor Handbook,CRC Press,New York,1998,p.389. 2. Tamrakar, R. K., Bisen, D. P., & Brahme, N. (2014). Characterization and luminescence properties of Gd2O3 phosphor. Research on Chemical Intermediates, 40, 1771-1779 3. Tamrakar R. K., Bisen D. P., Sahu I. P., and Brahme N.(2014),, UV and gamma ray induced thermoluminescence properties of cubic Gd2O3:Er3+ phosphor, Journal of Radiation
Research
and
Applied
Sciences,(2014),
http://dx.doi.org/10.1016/
j.jrras.2014.07.003 4. Tamrakar, R. K., Bisen, D. P., Robinson, C. S., Sahu, I. P., & Brahme, N. (2014). Ytterbium doped gadolinium oxide (Gd2O3:Yb3+) phosphor: topology, morphology, and luminescence behaviour in Hindawi Publishing Corporation. Article ID 396147 Indian
Journal
of
Materials
Science,
7.
Accepted
4
February
2014,
http://dx.doi.org/10.1155/2014/396147. 5. Chan W. C. W. and Nie S. 0 ³4XDQWXP GRW ELRFRQMXJDWHV IRU XOWUDVHQVLWLYH QRQLVRWRSLFGHWHFWLRQ´Science 281, 2016±2018,1998. 6. Tamrakar R. K., Bisen D. P., Upadhyay K. and Bramhe N., Effect of Fuel on Structural and Optical Characterization of Gd 2O3:Er3+ Phosphor, Journal of Luminescence and Applications (2014) Vol. 1 No. 1 pp. 23-29. 7. J.W.M. Verweij, M.Th. Cohen-Adad, D. Bouttet, H. Lautesse, B. Moine, C. Prdrini, Chemical Physics Letters 239 (1995) 51-55.
8. Liu XM, Yan LS, Lin J. J Phys Chem C 2009;113:8478±83. 9. Lu WC, Ma XH, Zhou H, Chen GT, Li JF, Zhu ZJ, et al. J Phys Chem C 2008;112: 15071±4. 10. Osiac E. J Alloys Compd 2002;341:263±6. 11. Seeta Rama Raju G, Park JY, Jung HC, Yang HK, Moon BK, Jeong JH, et al. Opt Mater, 2009, 31, 1210-1214 12. Yang WJ, Chen TM. Appl Phys Lett 2006;88:101903-3. 13. Tang YS, Hu SF, Lin CC, Bagkar NC, Liu RS. Appl Phys Lett 2007;90:151108±10. 14. Feldmann C., T. Jüstel, Ronda C.R. and Schmidt P. J. ,Inorganic Luminescent Materials: 100 Years of Research and Application, Advanced Functional Materials, Volume 13, Issue 7, pages 511±516, July, 2003 15. Walrand CG-, Binnemans K. In: Gschneidner KA, Eyring L, editors. Rationalization of Crystal-Field Parametrization Handbook on the Physics and Chemistry of Rare Earths. Amsterdam: North-Holland; 1996. 16. Xiaorui Dong, Zuoling Fu, Yingning Yu, Shuaibing Li, Zhenwen Dai, Materials Letters 74 (2012) 140±142. 17. Shilpa C. J., Akila Kadgathur Jayaram A. K., Dhananjaya N., Nagabhushana H., Prashantha S.C., Sunitha D. V., Sharma S. C., Shivakumara C., Nagabhushanam B.M." GdAlO3:Eu3+:Bi3+ nanophosphor: Synthesis and enhancement of red emission for WLEDs ", Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 550±558 18. E. De la Rosa, L.A. Diaz-Torres, P. Salas, R.A. Rodríguez, Opt. Mater. 27 (2005) 1320±1325.Jia, G.; Liu, K.; Zheng, Y.; Song, Y.; Yang, M.; You, H. Highly Uniform Gd(OH)3 and Gd2O3:Eu3+ Nanotubes: Facile Synthesis and Luminescence 3URSHUWLHV-3K\V&KHP& í 19. Meza Octavio, Villabona-E. G.,-Torres L. A, Desirena H., Rodríguez-Lopez J. L.,and Perez E., Luminescence Concentration Quenching Mechanism in Gd2O3:Eu3+. J. 3K\V&KHP$ í 20. Dubey V., Tiwari R., Pradhan M. K., Rathore G. S., Sharma C., and Tamrakar R. K. , Opticalbehaviour of cadmium and mercury free eco-friendly lamp nanophosphor for displaydevices, Results in Physics, Volume 4, 2014, Pages 63 21. Tamrakar R. K., Studies on Absorption Spectra of Mn Doped CdS Nanoparticles, (LAP Lambert Academic Publishing, VerlAg, (2012). ISBN 978-3-659-26222-7. 22. Tamrakar R. K. and Bisen D. P., Optical and kinetic studies of CdS:Cu nanoparticles Res Chem Intermed (2013) 39:3043±3048.
23. Tamrakar R. K. " UV-Irradiated thermoluminescence studies of bulk CdS with trap parameter, Research on chemical intermediates, (2013 ) DOI10.1007/s11164-0131166-4. 24. Wang P., Shanghai inst. of Ceramics, Chinese Academy of science, Shanghai, china, ICCD grant-in-Aid,(1994). 25. Yanhong Lia,b,_, Guangyan Hong, Journal of Luminescence 124 (2007) 297ದ301 26. Li-Ya Zhoua, _, WeiWanga, Jun-LiHuanga, QiPangb, Ling-HongYia, Meng-Lian Gongc, Jian-XinShi, Optik 121 (2010) 1516±1519 27. Krisjanis Smits, Larisa Grigorjev, Donats Millers, Anatolijs Sarakovskis, Agnieszka Opalinska, Janusz D. Fidelus, Witold Lojkowski, A. Emeline, G.V. Kataeva, A.S. Litke, A.V. Rudakova, V.K. Ryabchuk, N. Serpone, Langmuir 14 (1998) 5011±5022. 28. F. Vetrone, J. C. Boyer, J. A. Capobianco, A. Speghini and M. Bettinelli, R. Krsmanovic and S. Polizzi, Structural Investigation and Anti-Stokes Emission of Scandium Oxide Nanocrystals Activated with Trivalent Erbium, J. Electrochem. Soc., 152; H19-H24 (2005)
3+
GdAlO3 (4 % of Eu )
(020)
100000
Intensity (Arb. Units)
80000
(002)
60000
(022)
40000
(220) (310)
(133)
20000
20
25
30
35
40
45
T
50
55
60
Figure 1 XRD result of GdAlO3: Eu3+(4 mol %) phosphors
65
70
75
3+
FTIR spectra of GdAlO3: Eu ( 4mol%) 1.10
2950.07cm
Transmittance(%)
1.05
-1
1387.11cm
-1
1.00
0.95
471.86cm
-1
0.90
0.85
4000
549.86cm 3500
3000
2500
2000
1500 -1
Wavenumber (cm )
Figure 2. FTIR spectra of GdAlO3: Eu3+( 4mol%)
1000
-1
500
Figure 3. SEM Iamge of GdAlO3: Eu3+( 4mol%)
Figure 4. TEM Image of GdAlO3: Eu3+( 4mol%)
(266)
800
Ex=613nm
(274) 700
Intesnity (Arb. Units)
600 500 400 300 200 100 0 200
220
240
260
280
300
320
340
360
380
400
420
Wavelength(nm)
Figure 5. PL excitation spectra of GdAlO3: Eu3+(4 mol %) phosphors under 613nm
Intesnity (Arb. Units)
(613)
.5% Eu 1% Eu 2% Eu 3% Eu 4% Eu 5% Eu 6% Eu
1000
800
600
400
(594) (599)
(583)
200
(630)
0 550
575
600
625
650
Wavelength(nm)
Figure 6(a) PL Emission spectra of GdAlO3: Eu3+(0.5-6% mol %) phosphors for 266 nm excitation 1100
Peak Position
Intensity (Arb Units)
1000 900 800 700 600 500 400 .5% Er
1% Er
2% Er
3% Er 3+
Er
4% Er
5% Er
6% Er
in Mol%
Figure 6(b) Mol(%) concentration effect on PL spectra of GdAlO 3: Eu3+(0.5-6% mol %) phosphors
Figure 7. Energy level diagram of of GdAlO3: Eu3+
Figure 8 :CIE coordinates depicted on 1931 chart where X = 0.566 and Y = 0.393 (red emission O emission = 613nm) of Eu3+(5%) doped GdAlO3 phosphor
Table 1 Table1- Summary of diffraction angle, crystallite size and FWHM of GdAlO 3: Eu3+ (4 mol %) phosphor. S.No.
Eu3+in
2T T[°2Th.]
Intensity[cts]
FWHM [°2Th.]
D (particle size)
percent
1.
4%
24.70
60072
0.18
45.18
33.73
99685
0.19
43.69
41.00
38140
0.17
49.89
48.16
36835
0.16
54.39
55.50
20603
0.15
59.84
69.43
27318
0.18
56.85
Highlights 3+ 1. Solid state synthesis of Eu doped GdAlO3 nanophosphor. 3+ 2. Structural behaviour of Eu doped GdAlO3 nanophosphor. 3+ 3. Photoluminescent properties of Eu doped GdAlO3 nanophosphor.