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Photoluminescence studies of Terbium doped Calcium Aluminate nanophosphors (CaAl2O4: Tb) synthesized by sol-gel method.
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 4283–4289
www.materialstoday.com/proceedings
I3C4N
Photoluminescence studies of Terbium doped Calcium Aluminate nanophosphors (CaAl2O4: Tb) synthesized by sol-gel method. M. Freedaa *, T.D. Subashb a
Assistant Professor, Ponjesly College of Engineering, Nagercoil, Tamil Nadu, India b Assistant Professor, Holy Grace Academy of Engineering, Trissur, Kerala, India
Abstract This paper presents Photoluminescence studies of Terbium doped Calcium Aluminate nanophosphor (CaAl2O4: Tb), prepared by sol-gel method. The prepared nanophosphor was characterized by using techniques such as XRD (X-ray diffraction), SEM (Scanning electron microscopy), DRS (Diffuse reflectance spectroscopy), PL (Photoluminescence). XRD analysis confirmed, the monoclinic structure, the particle size was found to be 31 nm and is determined by W-H plot method. The optical bandgap (Eg) is found to be 2.7 eV. PL emission is obtained at 395nm, 535 nm corresponds to blue region, green region of the spectrum for 800nm excitation. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Conference Committee Members of International Conference on Computing, Communication, Nanophotonics, Nanoscience, Nanomaterials and Nanotechnology. Keywords: XRD; SEM; PL; W-H plot; sol-gel method.
* Corresponding author. Tel.: +91 8675983137 E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Conference Committee Members of International Conference on Computing, Communication, Nanophotonics, Nanoscience, Nanomaterials and Nanotechnology.
4284
M. Freeda, T.D. Subash/ Materials Today: Proceedings 4 (2017) 4283–4289
1. Introduction Aluminates are more chemically stable, environmentally friendly [1] and they can be easily produced costeffectively. Therefore the study of the preparation and characterization of aluminates based phosphors is growing rapidly. Scientists and researchers are conducting research in search for suitable host lattices that can be used to prepare phosphors for solid state lighting. The host must, among other things, be chemically and thermally stable. Alkali earth aluminates with a general formula MAl2O4 (M = Ba, Ca or Sr) are widely used as hosts for trivalent rare-earth (Dy3+, Nd3+, etc) and divalent europium (Eu2+) ions for the preparation of light emitting materials (phosphors) with persistent luminescence. Phosphors such as SrAl2O4: Eu2+, CaAl2O4:Eu2+ and BaAl2O4:Eu2+ phosphors, co-activated with different rare-earths (Dy3+, Nd3+, Pr3+) have been reported [2]. Rare earth and non-rare earth inorganic phosphors are widely used in a variety of applications, such as lamp industry, radiation dosimetry, X-ray imaging and color display [3].Various aluminates are used as host for doping rare earth ions in luminescent applications. Several reports dealing with the luminescence studies of SrAl2O4, BaAl2O4 and MgAl2O4 are available in the literature [4, 5]. Alkaline earth aluminates doped with Eu2+ exhibit luminescent properties in the blue/green visible range relating to the host lattice[6,17] It is also known that co-doping with other rare earth ions (Dy3+, Nd3+, Tm3+) extends the lifetime of the persistent luminescence and the intensities of these materials due to the existence of long-lived trap levels[6–8, 9, 10,11-17]. 2. Experimental Starting Materials 98.5 wt. % of 2M Calcium acetate [(CH3COO) 2 Ca.2H2O>98.5%], 1 wt. % of 2 M Aluminium acetate [C4H6AlO4.4H2O>99%], 0.5 wt. % of 2M Terbium nitrate,
Calcium acetate
Aluminium acetate
Terbium nitrate
Mixing in 2 - methoxy ethanol Continuous stirrering
Ammonia Heating at 40 ˚C
Sol Gel Dried at 80 ˚C Grinding into powder 5 to 6 hrs
Annealed at 900 ˚C
Fig.1. Flowchart for the Preparation of Tb - Doped Calcium Aluminate phosphors.
M. Freeda, T.D. Subash / Materials Today: Proceedings 4 (2017) 4283–4289
4285
Starting materials were dissolved in 25 ml of 2-methoxy ethanol with continuous stirring by magnetic stirrer for 5 minutes individually. All the solutions were mixed and the mixture was magnetically stirred for 15 min. at room temperature. For 15 minutes, Acetic acid and ethylene glycol in the ratio of 1:1 was added to the above solution and stirred. Dropwise, Ammonia was then added to the above mixture to attain pH value of 10.3. It was observed that the solution became sol. The sol was heated at 40 ºC while being mechanically stirred with a magnetic stirrer. On further heating, the sol turned into a viscous gel. The gel was aged for 2 hr and then dried at 80 ºC for about 5 hr. The resulting material was well grinded and annealed at 900 ºC for 2hr; we get white coloured Tb-doped CaAl2O4 nanopowder (Figure 1). 3. Results and discussions 3.1. X-ray diffraction analysis The XRD pattern of the prepared CaAl2O4: Tb synthesized by sol-gel process at annealing temperature of 900 °C is shown in fig. 2. All the diffraction peaks in figure 2 are in good agreement to the pure monoclinic phase structure of CaAl2O4. Furthermore, a small amount of doped rare earth ion, Tb has almost no effect on CaAl2O4 phase composition.
Counts CAOTb
400
300
200
100
0 20
30
40
50
60
70
Position [°2Theta] (Copper (Cu))
Fig.2. XRD Pattern of Tb - Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5%.
W.H plot is shown in Figure 3. According to the Williamson Hall method, the particle size was estimated from the y-intercept, of the fit using (Williamson and Hall plot) β cosθ = [𝐾λ/D] + [4 ε sinθ]
M. Freeda, T.D. Subash/ Materials Today: Proceedings 4 (2017) 4283–4289
4286
A plot is drawn with 4sinθ along the x-axis and β cosθ along the y-axis for as prepared nano-particles as shown in Figure 3. From the linear fit to the data, the crystalline size was estimated from the y-intercept, of the fit, the particle size was found to be 31 nm.
0.015 Equation
Tb
y=a+b
Adj. R-Squa 0.05919 Value
Standard Err
J
Intercept 0.0044
0.00106
J
Slope
0.00275
-0.004
βCosθ
0.010
0.005
0.000
0.1
0.2
0.3
0.4
0.5
0.6
4Sinθ Fig.3. W - H plot of Tb - Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5%.
3.2. SEM analysis Figure 4 shows the SEM micrograph of the prepared sample CaAl2O4: Tb with two different magnifications. It reflects the agglomerate particle nature of the powder.
Fig.4. SEM Image of Tb -Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5%.
M. Freeda, T.D. Subash / Materials Today: Proceedings 4 (2017) 4283–4289
4287
3.3. Diffuse reflectance spectroscopic analysis Figure 5(a) shows the diffuse reflectance spectrum of the CaAl2O4:Tb. Diffuse reflectance Spectroscopy (DRS) is a simple, but powerful spectroscopic tool to estimate the band gap energy (Eg) of powder samples. Kubelka Munk function F(R) provides the theoretical descriptions of diffuse reflectance spectroscopy. The intensity of the diffused reflectance spectrum is effectively expressed by Kubelka Munk function F(R) by the relation [18-20],
F (R ) =
(1 − R ) 2 2R
where, R is the absolute diffuse reflectance (Kubelka-Munk function)[21-23]. a
Fig.5. (a) Diffuse reflectance spectra of Tb doped CaAl2O4
b
(b) Plot of (F(R)*hυ) 2 vs. photon energy hυ of Tb doped CaAl2O4
Figure 5(b) shows the plot with hυ along x-axis and [F(R)*h υ] 2 along y-axis. The band gap (Eg) of the prepared samples is estimated by extrapolating the straight line in the graph to the wavelength axis. The optical bandgap (Eg) is found to be 2.7 eV. 3.4. Photoluminescence analysis Figure 6 shows the emission spectra of the Tb doped CaAl2O4 nanophosphors measured at room temperature for 800 nm excitation. The photoluminescence emission spectra consist of two emission peaks at 395nm, 535nm, corresponds to blue region, green region of the spectrum.
M. Freeda, T.D. Subash/ Materials Today: Proceedings 4 (2017) 4283–4289
4288
500
Intensity
400
300
200
100
0 350
375
400
425
450
475
500
525
550
wavelength (nm) Fig.6. PL Emission Spectrum of Tb - Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5% for 800 nm.
4. Conclusions The CaAl2O4: Tb phosphors were successfully synthesized by sol-gel method. Characterizations like XRD, SEM, DRS, photoluminescence (PL) were studied. The XRD pattern of synthesized CaAl2O4: Tb phosphor matched well with standard data. All the diffraction peaks in are in good agreement to the pure monoclinic phase structure of CaAl2O4. Furthermore, a small amount of doped rare earth ion, Tb has almost no effect on CaAl2O4 phase composition. The particle size was found to be 31 nm. SEM micrograph of the prepared sample CaAl2O4: Tb shows the agglomeration of particle nature of the powder. The optical bandgap (Eg) is found to be 2.7 eV. The photoluminescence emission spectra consist of two emission peaks at 395nm, 535nm, corresponds to blue region, green region of the spectrum.
References Mothudi BM, Ntwaeaborwa OM., Pitale SS and Swart HC 2010 Journal of Alloys and Compounds 508 262. Eeckhout KV, Philippe FS and Poelman D 2010 Materials 3 2536. Yamamoto H, Okamoto S, Kobayashi H. Cr3+ doping optimization of CaAl2O4:Eu2+ blue phosphor. J. Lumin., 2002, 100:325. Yingliang, L.; Dexiong, F.; Peihui, Y. Preparation of phosphors MAl2O4: Eu2+ (M=Ca, Sr, Ba) by microwave heating technique and their phosphorescence, Rare Metals, 2000, 19(4), 297. [5] Kinsman, K. M. ; Mc Kittrick, J. ; Slizky, E, ; Hesse, K. Phase development and luminescence in chromium doped Yttrium aluminum garnet (YAG :Cr) phosphors. J. Am. Ceram. Soc., 1994, 77 (11), 2866. [6] K.Van den Eeckhout, P. F. Smet, D. Poelman, Materials 2010, 3, 2536–2566. [7] J. Holsa, H. Jungner, M. Lastusaari, J. Niittykoski, J. Alloys Compd. 2001, 323–324, 326–330. [8] H. Ryu, K. S. Bartwal, Open Appl. Phys. J. 2009, 2, 1–4. [9] T. Aitasalo, J. Holsa, H. Jungner, J. - C. Krupa, M. Lahtinen,M. Lastusaari, J. Legendziewicz, J. Niitykoski, J. Valkonen, Radiat. Eff. Defects S. 2003, 158, 309–313. [10] L.T. Chen, C. - S. Hwang, I - L. Sun, I. - G. Chen, J. Lumin.2006, 118, 12–20. [1] [2] [3] [4]
M. Freeda, T.D. Subash / Materials Today: Proceedings 4 (2017) 4283–4289 [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
4289
H. Lange, Luminescent Europium Activated Strontium Aluminate,US patent number 3,294, 699, date of patent Dec 27,1966. T. Aitasalo, J. Holsa, H. Jungner, M. Lastusaari, J. Niittykoski, J. Phys. Chem. B 2006, 110, 4589–4598. T. Matsuzawa, Y. Aoki, N. Takeuchi, Y. Murayama, J. Electrochem. Soc. 1996, 143, 2670–2673. H. Takasaki, S. Tanabe, T. Hanada, J. Ceram. Soc. Jpn 1996,104, 322–326. T. Aitasalo, J. Holsa, H. Jungner, M. Lastusaari, J. Niittykoski,M. Parkkinen, R. Valtonen, Opt. Mater. 2004, 26, 113 – 116. Z. Qiu, Y. Zhou, M. Lu, A. Zhang, Q. Ma, Acta Mater. 2007, 55, 2615–2620. C. Zhao, D. Chen, Mater. Lett. 2007, 61, 3673–3675. P. D. Fochs, Proc. Phys. Soc. (London) B69 (1956) 70. J.E. Van Haecke, P.F. Smet, D. Poelman Luminescent characterization of CaAl2S4: Eu powder, Journal of Luminescence 126 (2007) 508– 514. Mohammad Ziyauddin, Nameeta Brahme, D.P. Bisen, R.S. Kher Photoluminescence (PL) and Thermoluminescence (TL) studies of γ- irradiated CaAl2O4: Eu2+ phosphor synthesized by combustion technique. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 - 0056 Volume: 02 Issue: 05 (Aug-2015) 873-876. Paul Kubelka, J. Oct. Soc. Am., 38 (1948) 448. D. Barcelo, Modern Fourier Transform Infrared Spectroscopy, Wilson&Wilson’s, 2001. A. B. Murphy, Solar Energy Mater., Solar Cells, 91(20).
ScienceDirect Materials Today: Proceedings 4 (2017) 4283–4289
www.materialstoday.com/proceedings
I3C4N
Photoluminescence studies of Terbium doped Calcium Aluminate nanophosphors (CaAl2O4: Tb) synthesized by sol-gel method. M. Freedaa *, T.D. Subashb a
Assistant Professor, Ponjesly College of Engineering, Nagercoil, Tamil Nadu, India b Assistant Professor, Holy Grace Academy of Engineering, Trissur, Kerala, India
Abstract This paper presents Photoluminescence studies of Terbium doped Calcium Aluminate nanophosphor (CaAl2O4: Tb), prepared by sol-gel method. The prepared nanophosphor was characterized by using techniques such as XRD (X-ray diffraction), SEM (Scanning electron microscopy), DRS (Diffuse reflectance spectroscopy), PL (Photoluminescence). XRD analysis confirmed, the monoclinic structure, the particle size was found to be 31 nm and is determined by W-H plot method. The optical bandgap (Eg) is found to be 2.7 eV. PL emission is obtained at 395nm, 535 nm corresponds to blue region, green region of the spectrum for 800nm excitation. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Conference Committee Members of International Conference on Computing, Communication, Nanophotonics, Nanoscience, Nanomaterials and Nanotechnology. Keywords: XRD; SEM; PL; W-H plot; sol-gel method.
* Corresponding author. Tel.: +91 8675983137 E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Conference Committee Members of International Conference on Computing, Communication, Nanophotonics, Nanoscience, Nanomaterials and Nanotechnology.
4284
M. Freeda, T.D. Subash/ Materials Today: Proceedings 4 (2017) 4283–4289
1. Introduction Aluminates are more chemically stable, environmentally friendly [1] and they can be easily produced costeffectively. Therefore the study of the preparation and characterization of aluminates based phosphors is growing rapidly. Scientists and researchers are conducting research in search for suitable host lattices that can be used to prepare phosphors for solid state lighting. The host must, among other things, be chemically and thermally stable. Alkali earth aluminates with a general formula MAl2O4 (M = Ba, Ca or Sr) are widely used as hosts for trivalent rare-earth (Dy3+, Nd3+, etc) and divalent europium (Eu2+) ions for the preparation of light emitting materials (phosphors) with persistent luminescence. Phosphors such as SrAl2O4: Eu2+, CaAl2O4:Eu2+ and BaAl2O4:Eu2+ phosphors, co-activated with different rare-earths (Dy3+, Nd3+, Pr3+) have been reported [2]. Rare earth and non-rare earth inorganic phosphors are widely used in a variety of applications, such as lamp industry, radiation dosimetry, X-ray imaging and color display [3].Various aluminates are used as host for doping rare earth ions in luminescent applications. Several reports dealing with the luminescence studies of SrAl2O4, BaAl2O4 and MgAl2O4 are available in the literature [4, 5]. Alkaline earth aluminates doped with Eu2+ exhibit luminescent properties in the blue/green visible range relating to the host lattice[6,17] It is also known that co-doping with other rare earth ions (Dy3+, Nd3+, Tm3+) extends the lifetime of the persistent luminescence and the intensities of these materials due to the existence of long-lived trap levels[6–8, 9, 10,11-17]. 2. Experimental Starting Materials 98.5 wt. % of 2M Calcium acetate [(CH3COO) 2 Ca.2H2O>98.5%], 1 wt. % of 2 M Aluminium acetate [C4H6AlO4.4H2O>99%], 0.5 wt. % of 2M Terbium nitrate,
Calcium acetate
Aluminium acetate
Terbium nitrate
Mixing in 2 - methoxy ethanol Continuous stirrering
Ammonia Heating at 40 ˚C
Sol Gel Dried at 80 ˚C Grinding into powder 5 to 6 hrs
Annealed at 900 ˚C
Fig.1. Flowchart for the Preparation of Tb - Doped Calcium Aluminate phosphors.
M. Freeda, T.D. Subash / Materials Today: Proceedings 4 (2017) 4283–4289
4285
Starting materials were dissolved in 25 ml of 2-methoxy ethanol with continuous stirring by magnetic stirrer for 5 minutes individually. All the solutions were mixed and the mixture was magnetically stirred for 15 min. at room temperature. For 15 minutes, Acetic acid and ethylene glycol in the ratio of 1:1 was added to the above solution and stirred. Dropwise, Ammonia was then added to the above mixture to attain pH value of 10.3. It was observed that the solution became sol. The sol was heated at 40 ºC while being mechanically stirred with a magnetic stirrer. On further heating, the sol turned into a viscous gel. The gel was aged for 2 hr and then dried at 80 ºC for about 5 hr. The resulting material was well grinded and annealed at 900 ºC for 2hr; we get white coloured Tb-doped CaAl2O4 nanopowder (Figure 1). 3. Results and discussions 3.1. X-ray diffraction analysis The XRD pattern of the prepared CaAl2O4: Tb synthesized by sol-gel process at annealing temperature of 900 °C is shown in fig. 2. All the diffraction peaks in figure 2 are in good agreement to the pure monoclinic phase structure of CaAl2O4. Furthermore, a small amount of doped rare earth ion, Tb has almost no effect on CaAl2O4 phase composition.
Counts CAOTb
400
300
200
100
0 20
30
40
50
60
70
Position [°2Theta] (Copper (Cu))
Fig.2. XRD Pattern of Tb - Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5%.
W.H plot is shown in Figure 3. According to the Williamson Hall method, the particle size was estimated from the y-intercept, of the fit using (Williamson and Hall plot) β cosθ = [𝐾λ/D] + [4 ε sinθ]
M. Freeda, T.D. Subash/ Materials Today: Proceedings 4 (2017) 4283–4289
4286
A plot is drawn with 4sinθ along the x-axis and β cosθ along the y-axis for as prepared nano-particles as shown in Figure 3. From the linear fit to the data, the crystalline size was estimated from the y-intercept, of the fit, the particle size was found to be 31 nm.
0.015 Equation
Tb
y=a+b
Adj. R-Squa 0.05919 Value
Standard Err
J
Intercept 0.0044
0.00106
J
Slope
0.00275
-0.004
βCosθ
0.010
0.005
0.000
0.1
0.2
0.3
0.4
0.5
0.6
4Sinθ Fig.3. W - H plot of Tb - Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5%.
3.2. SEM analysis Figure 4 shows the SEM micrograph of the prepared sample CaAl2O4: Tb with two different magnifications. It reflects the agglomerate particle nature of the powder.
Fig.4. SEM Image of Tb -Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5%.
M. Freeda, T.D. Subash / Materials Today: Proceedings 4 (2017) 4283–4289
4287
3.3. Diffuse reflectance spectroscopic analysis Figure 5(a) shows the diffuse reflectance spectrum of the CaAl2O4:Tb. Diffuse reflectance Spectroscopy (DRS) is a simple, but powerful spectroscopic tool to estimate the band gap energy (Eg) of powder samples. Kubelka Munk function F(R) provides the theoretical descriptions of diffuse reflectance spectroscopy. The intensity of the diffused reflectance spectrum is effectively expressed by Kubelka Munk function F(R) by the relation [18-20],
F (R ) =
(1 − R ) 2 2R
where, R is the absolute diffuse reflectance (Kubelka-Munk function)[21-23]. a
Fig.5. (a) Diffuse reflectance spectra of Tb doped CaAl2O4
b
(b) Plot of (F(R)*hυ) 2 vs. photon energy hυ of Tb doped CaAl2O4
Figure 5(b) shows the plot with hυ along x-axis and [F(R)*h υ] 2 along y-axis. The band gap (Eg) of the prepared samples is estimated by extrapolating the straight line in the graph to the wavelength axis. The optical bandgap (Eg) is found to be 2.7 eV. 3.4. Photoluminescence analysis Figure 6 shows the emission spectra of the Tb doped CaAl2O4 nanophosphors measured at room temperature for 800 nm excitation. The photoluminescence emission spectra consist of two emission peaks at 395nm, 535nm, corresponds to blue region, green region of the spectrum.
M. Freeda, T.D. Subash/ Materials Today: Proceedings 4 (2017) 4283–4289
4288
500
Intensity
400
300
200
100
0 350
375
400
425
450
475
500
525
550
wavelength (nm) Fig.6. PL Emission Spectrum of Tb - Doped CaAl2O4 with wt. % of Al as 1%, and wt. % of Tb as 0.5% for 800 nm.
4. Conclusions The CaAl2O4: Tb phosphors were successfully synthesized by sol-gel method. Characterizations like XRD, SEM, DRS, photoluminescence (PL) were studied. The XRD pattern of synthesized CaAl2O4: Tb phosphor matched well with standard data. All the diffraction peaks in are in good agreement to the pure monoclinic phase structure of CaAl2O4. Furthermore, a small amount of doped rare earth ion, Tb has almost no effect on CaAl2O4 phase composition. The particle size was found to be 31 nm. SEM micrograph of the prepared sample CaAl2O4: Tb shows the agglomeration of particle nature of the powder. The optical bandgap (Eg) is found to be 2.7 eV. The photoluminescence emission spectra consist of two emission peaks at 395nm, 535nm, corresponds to blue region, green region of the spectrum.
References Mothudi BM, Ntwaeaborwa OM., Pitale SS and Swart HC 2010 Journal of Alloys and Compounds 508 262. Eeckhout KV, Philippe FS and Poelman D 2010 Materials 3 2536. Yamamoto H, Okamoto S, Kobayashi H. Cr3+ doping optimization of CaAl2O4:Eu2+ blue phosphor. J. Lumin., 2002, 100:325. Yingliang, L.; Dexiong, F.; Peihui, Y. Preparation of phosphors MAl2O4: Eu2+ (M=Ca, Sr, Ba) by microwave heating technique and their phosphorescence, Rare Metals, 2000, 19(4), 297. [5] Kinsman, K. M. ; Mc Kittrick, J. ; Slizky, E, ; Hesse, K. Phase development and luminescence in chromium doped Yttrium aluminum garnet (YAG :Cr) phosphors. J. Am. Ceram. Soc., 1994, 77 (11), 2866. [6] K.Van den Eeckhout, P. F. Smet, D. Poelman, Materials 2010, 3, 2536–2566. [7] J. Holsa, H. Jungner, M. Lastusaari, J. Niittykoski, J. Alloys Compd. 2001, 323–324, 326–330. [8] H. Ryu, K. S. Bartwal, Open Appl. Phys. J. 2009, 2, 1–4. [9] T. Aitasalo, J. Holsa, H. Jungner, J. - C. Krupa, M. Lahtinen,M. Lastusaari, J. Legendziewicz, J. Niitykoski, J. Valkonen, Radiat. Eff. Defects S. 2003, 158, 309–313. [10] L.T. Chen, C. - S. Hwang, I - L. Sun, I. - G. Chen, J. Lumin.2006, 118, 12–20. [1] [2] [3] [4]
M. Freeda, T.D. Subash / Materials Today: Proceedings 4 (2017) 4283–4289 [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
4289
H. Lange, Luminescent Europium Activated Strontium Aluminate,US patent number 3,294, 699, date of patent Dec 27,1966. T. Aitasalo, J. Holsa, H. Jungner, M. Lastusaari, J. Niittykoski, J. Phys. Chem. B 2006, 110, 4589–4598. T. Matsuzawa, Y. Aoki, N. Takeuchi, Y. Murayama, J. Electrochem. Soc. 1996, 143, 2670–2673. H. Takasaki, S. Tanabe, T. Hanada, J. Ceram. Soc. Jpn 1996,104, 322–326. T. Aitasalo, J. Holsa, H. Jungner, M. Lastusaari, J. Niittykoski,M. Parkkinen, R. Valtonen, Opt. Mater. 2004, 26, 113 – 116. Z. Qiu, Y. Zhou, M. Lu, A. Zhang, Q. Ma, Acta Mater. 2007, 55, 2615–2620. C. Zhao, D. Chen, Mater. Lett. 2007, 61, 3673–3675. P. D. Fochs, Proc. Phys. Soc. (London) B69 (1956) 70. J.E. Van Haecke, P.F. Smet, D. Poelman Luminescent characterization of CaAl2S4: Eu powder, Journal of Luminescence 126 (2007) 508– 514. Mohammad Ziyauddin, Nameeta Brahme, D.P. Bisen, R.S. Kher Photoluminescence (PL) and Thermoluminescence (TL) studies of γ- irradiated CaAl2O4: Eu2+ phosphor synthesized by combustion technique. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 - 0056 Volume: 02 Issue: 05 (Aug-2015) 873-876. Paul Kubelka, J. Oct. Soc. Am., 38 (1948) 448. D. Barcelo, Modern Fourier Transform Infrared Spectroscopy, Wilson&Wilson’s, 2001. A. B. Murphy, Solar Energy Mater., Solar Cells, 91(20).