Highly intense, long persistent Sr4Al14O25:Eu2+,Dy3+ blue-green phosphor with different B3+, Eu2+, Dy3+, and Ag+ contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H2 in N2. The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ~40？mol% H3BO3 showed dense and pure Sr4Al14O25 phase with higher emission intensity, but in the samples containing less than 20？mol% H3BO3 mixed phases consisting of Al2O3, SrAl12O19 and SrAl2O4 were observed, while in higher H3BO3 content, SrAl2B2O7 phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4？at.% of Eu and 8？at.% of Dy, and 3？at.% Ag exhibited the maximum initial intensity of 5170？mcd·m？2 and the longest persistency of greater than 30 hours over the value of 5？mcd·m？2, higher than the commercial products and applicable for various display applications involving indoor as well as outdoor uses. 1. Introduction Phosphor materials with long afterglow is a kind of energy storing materials that can absorb UV-visible light from sun light, and gradually release the absorbed energy in the darkness at a certain wavelength [1]. Among the various phosphors, ZnS-based materials doped with Cu or Mn ions were first prepared and applied for various fields [2]; however, the luminescent intensity of these phosphors are not bright enough and the afterglow time is short. Therefore, some radio-active elements such as Co and Pm had to be codoped into the ZnS-matrix so as to prolong the afterglow time. Compared to sulfide-based phosphors, oxide-based phosphors have been recognized as the efficient host materials because of their high quantum efficiency [3], chemical stability, no radio-active radiations, environmental capability, and long persistence of phosphorescence [4]. As far as the development of phosphor is concerned, Eu2+ ions were used frequently as an activator ion for various host lattices. This occurs because the 4f7 electron configuration of the Eu2+ ion shows efficient luminescence owing to the 4f → 5d transition, and the luminescence colors or wavelengths change widely from near UV to red regions depending on the nature of host lattice [5]. As a new phosphor, strontium aluminates doped with Eu divalent ion (SAE) have been investigated as an efficient phosphor that
References
[1]
C. K. Chang, L. Jiang, D. L. Mao, and C. L. Feng, “Photoluminescence of 4SrO·7Al2O3 ceramics sintered with the aid of B2O3,” Ceramics International, vol. 30, no. 2, pp. 285–290, 2004.
[2]
Y. Lin, Z. Tang, and Z. Zhang, “Preparation of long-afterglow Sr4Al14O25-based luminescent material and its optical properties,” Materials Letters, vol. 51, no. 1, pp. 14–18, 2001.
[3]
B. Smets and G. Hoeks, “2SrO·3Al2O3:Eu2+ and 1.29(Ba,Ca)O, 6Al2O3:Eu2+. Two new blue-emitting phosphors,” Journal of the Electrochemical Society, vol. 136, no. 7, pp. 2119–2123, 1989.
[4]
W. Jia, H. Yuan, L. Lu, H. Liu, and W. M. Yen, “Phosphorescent dynamics in SrAl2O4:Eu2+, Dy3+ single crystal fibers,” Journal of Luminescence, vol. 76-77, pp. 424–428, 1998.
[5]
W. B. Lm, Y. L. Kim, H. S. Yoo, and D. Y. Jeon, “Luminescent and structural properties of ( )3MgSi2O8:Eu2+: effects of ba content on the Eu2+ site preference for thermal stability,” Inorganic Chemistry, vol. 48, no. 2, pp. 557–564, 2009.
[6]
R. Zhong, J. Zhang, X. Zhang, S. Lu, and X. J. Wang, “Red phosphorescence in Sr4Al14O25:Cr3+, Eu2+, Dy3+ through persistent energy transfer,” Applied Physics Letters, vol. 88, no. 20, Article ID 201916, 2006.
[7]
D. Haranath, P. Sharma, H. Chander, A. Ali, N. Bhalla, and S. K. Halder, “Role of boric acid in synthesis and tailoring the properties of calcium aluminate phosphor,” Materials Chemistry and Physics, vol. 101, no. 1, pp. 163–169, 2007.
[8]
V. Bachmann, C. Ronda, O. Oeckler, W. Schnick, and A. Meijerink, “Color point tuning for (Sr,Ca,Ba)Si2O2N2:Eu2+ for white light LEDs,” Chemistry of Materials, vol. 21, no. 2, pp. 316–325, 2009.
[9]
G. Blasse and B. C. Grabmair, Luminescence Materials, Springer, Berlin, Germany, 1994.
[10]
T. Aitasalo, J. H？ls？, H. Jungner et al., “Effect of temperature on the luminescence processes of SrAl2O4:Eu2+,” Radiation Measurements, vol. 38, no. 4–6, pp. 727–730, 2004.
[11]
T. Aitasalo, P. Dereń, J. H？ls？ et al., “Persistent luminescence phenomena in materials doped with rare earth ions,” Journal of Solid State Chemistry, vol. 171, no. 1-2, pp. 114–122, 2003.
[12]
H. N. Luitel, T. Watari, T. Torikai, and M. Yada, “Luminescent properties of Cr3+ doped Sr4Al14O25: Eu/Dy blue-green and red phosphor,” Optical Materials, vol. 31, no. 8, pp. 1200–1204, 2009.
[13]
E. Nakazawa, Y. Murazaki, and S. Saito, “Mechanism of the persistent phosphorescence in Sr4Al14O25: Eu and SrAl2O4: Eu codoped with rare earth ions,” Journal of Applied Physics, vol. 100, no. 11, Article ID 113113, 2006.
[14]
Y. Lin, Z. Tang, Z. Zhang, and C. Nan, “Influence of co-doping different rare earth ions on the luminescence of CaAl2O4-based phosphors,” Journal of the European Ceramic Society, vol. 23, no. 1, pp. 175–178, 2003.
[15]
G. W. Scherer, Relaxation in Glasses and Composites, John Wiley & Sons, New York, NY, USA, 1986.
[16]
D. Wang, M. Wang, and G. Lü, “Synthesis, crystal structure and X-ray powder diffraction data of the phosphor matrix 4SrO·7Al2O3,” Journal of Materials Science, vol. 34, no. 20, pp. 4959–4964, 1999.
[17]
Z. X. Yuan, C. K. Chang, D. L. Mao, and W. Ying, “Effect of composition on the luminescent properties of Sr 4Al14O25:Eu2+, Dy3+ phosphors,” Journal of Alloys and Compounds, vol. 377, no. 1-2, pp. 268–271, 2004.
[18]
C. Chang, Z. Yuan, and D. Mao, “Eu2+ activated long persistent strontium aluminate nano scaled phosphor prepared by precipitation method,” Journal of Alloys and Compounds, vol. 415, no. 1-2, pp. 220–224, 2006.
[19]
G. F. J. Garlick, Luminescent Materials, Oxford University Press, 1949.
[20]
S. D. Han, K. C. Singh, T. Y. Cho et al., “Preparation and characterization of long persistence strontium aluminate phosphor,” Journal of Luminescence, vol. 128, no. 3, pp. 301–305, 2008.
[21]
M. L. Ruiz-González, P. Escribano, J. B. Carda, and M. Marchal, “Planar defects in a precursor for phosphor materials: SrAl2？xBxO4 ( ),” Journal of Materials Chemistry, vol. 12, no. 4, pp. 1128–1131, 2002.
[22]
Y. T. Yu and B. G. Kim, “Effects of adding B2O3 as a flux on phosphorescent properties in synthesis of SrAl2O4: (Eu2+, Dy3+) phosphor,” Korean Journal of Chemical Engineering, vol. 20, no. 5, pp. 973–976, 2003.
[23]
A. Nag and T. R. N. Kutty, “The mechanism of long phosphorescence of SrAl2？xBxO4 ( ) and Sr4Al 14？xBxO25 ( ) co-doped with Eu2+ and Dy3+,” Materials Research Bulletin, vol. 39, no. 3, pp. 331–342, 2004.
[24]
M. Peng, Z. Pei, G. Hong, and Q. Su, “Study on the reduction of Eu3+ to Eu2+ in Sr4Al14O25: Eu prepared in air atmosphere,” Chemical Physics Letters, vol. 371, no. 1-2, pp. 1–6, 2003.
[25]
Q. Li, J. Zhao, and F. Sun, “Energy transfer mechanism of Sr4Al14O25:Eu2+ phosphor,” Journal of Rare Earths, vol. 28, no. 1, pp. 26–29, 2010.
[26]
D. Wang, Q. Yin, Y. Li, and M. Wang, “Concentration quenching of Eu2+ in SrO·Al2O3:Eu2+ phosphor,” Journal of Luminescence, vol. 97, no. 1, pp. 1–6, 2002.
[27]
C. Zhao and D. Chen, “Synthesis of CaAl2O4:Eu,Nd long persistent phosphor by combustion processes and its optical properties,” Materials Letters, vol. 61, no. 17, pp. 3673–3675, 2007.
[28]
P. Dorenbos, “Mechanism of persistent luminescence in Eu2+ and Dy3+ codoped aluminate and silicate compounds,” Journal of the Electrochemical Society, vol. 152, no. 7, pp. H107–H110, 2005.
[29]
A. Nag and T. R. N. Kutty, “Role of B2O3 on the phase stability and long phosphorescence of SrAl2O4:Eu, Dy,” Journal of Alloys and Compounds, vol. 354, no. 1-2, pp. 221–231, 2003.
[30]
Y. Lin, Z. Tang, and Z. Zhang, “Preparation of long-afterglow Sr4Al14O25-based luminescent material and its optical properties,” Materials Letters, vol. 51, no. 1, pp. 14–18, 2001.
[31]
N. Suriyamurthy and B. S. Panigrahi, “Effects of non-stoichiometry and substitution on photoluminescence and afterglow luminescence of Sr4Al14O25:Eu2+, Dy3+ phosphor,” Journal of Luminescence, vol. 128, no. 11, pp. 1809–1814, 2008.
