Available online at www.sciencedirect.com
Physics Procedia 29 (2012) 62 – 64
The Int. Conf. on Luminescence & Optical Spectroscopy of Condensed Matter 2011
Long lasting Red Phosphoresce and Photostimulated Luminescence in Ca2SnO4:Sm3+ Phosphor Xuhui Xu,Yu Gong, Wei Zeng, Yuhua Wang, * Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Lanzhou, 730000, China Received 25 July 2011; accepted 25 August 2011 , Abstract Long-lasting red phosphorescence and photostimulated luminescence in Ca2SnO4:Sm3+ were observed. The decay patterns of afterglow and thermoluminescence curves demonstrate that introduction of Gd3+ can increase the number of shallow traps and deep traps. PACS: 78.20.-e Long-lasting phosphor, photostimulated, luminescence,
thermoluminescence
1. Introduction Long afterglow phosphors have been of great interest for applications as displays in dark environment.[1,2] Until now, intense green and blue afterglow phosphors have been commercially available with better chemical stability over sulfides.[3,4] However, long wavelength emitting long afterglow phosphor, whose persistent time last longer than 2h, is still in great scarcity. Therefore, there is a strong desire for the development of long afterglow phosphors with long wavelength emissions in recent years. In addition, some rare earth ion activated long afterglow phosphors are applicable for erasable optical storage.[5] Light energy is stored in these materials by exposing it to x-rays, ultraviolet or visible light and is released through photostimulated luminescence (PSL) by infrared excitation.[6] In this paper, we report the observation of long lasting red phosphorescence and PSL in Ca2SnO4:Sm3+ and Ca2SnO4:Sm3+,Gd3+ phosphors. The decay patterns of afterglow and thermoluminescence (TL) curves in the two phosphors are comparably studied. The effect of co-doped Gd3+ on phosphorescence and PSL is investigated. 2. Experimental Section Ca2-x-ySnO4:Smx3+, Gdy3+ (x=0.0025, y=0, 0.00125) were prepared by a solid-state reaction. Analytical reagent grade CaCO3 (99%), SnO2 (99 %), Sm2O3 (99.99%) and Gd2O3(99.99%) were employed as reactants. The phases of samples were identified by X-ray powder diffraction (XRD) with Ni-filtered CuK radiation at a scanning step of 0.02º in the 2 range from 10º to 80 º. Emission spectrum was recorded on a FLS-920T spectrometer. Afterglow decay curves were measured with a PR305 long afterglow instrument after the sample was irradiated by artificial light (1000±5% lux) for 10min. The thermoluminescence(TL) curves were measured with a FJ-427A TL meter (Beijing Nuclear Instrument Factory). The sample weight was kept constant (0.002 g). Prior to the measurements, powder samples were first exposed for 20 min to standard artificial daylight (1000 lux), then heated from room temperature to 180 °C with a rate of 1 K/s. 3. Results and discussion Figure.1 shows the XRD pattern and crystal structure of Ca2SnO4 host. As shown in fig.1, all the observed peaks can be indexed to the pure phase of Ca2SnO4, indicating the high purity and crystalline of the sample in this work.
* Corresponding author. Tel.: +86 -931- 891-2772; fax: +86 -931 -891-3554. E-mail address:
[email protected]
1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the organizing committee represented by Stephen C. Rand and the guest editors. doi:10.1016/j.phpro.2012.03.693
Xuhui Xu et al. / Physics Procedia 29 (2012) 62 – 64
63
Ca2SnO4 belongs to the Sr2PbO4-type structure.[7] In this structural types, SnO6 octahedra are connected in lowdimensional form; SnO6 octahedra are linked sharing edges with each other and forming one-dimensional chains in Ca2SnO4.
Figure.1 Crystal structures of Ca2SnO4. Emission spectra of Ca2SnO4:Sm3+ and Ca2SnO4:Sm3+,Gd3+ excited by 254nm excitation source are shown in Fig.2, all emission peaks exhibit the characteristic emission of Sm3+. The co-doping Gd3+ dose not make any noticeable variation of the emission of the phosphor.
Figure.2 Emission spectra of Ca2SnO4:Sm3+ and Ca2SnO4:Sm3+,Gd3+ excited by 254nm excitation source A very important result of our present work is that the red long afterglow can be observed in Ca2SnO4:Sm3+ with naked eye in the dark clearly. In addition, as shown in Figure.3, the persistent time of Ca2SnO4:Sm3+,Gd3+ (3h) has been observed to increase, comparing with Ca2SnO4:Sm3+ (1h). The thermoluminescence curves (Figure.3 insert) demonstrate that introduction of Gd3+ can increase the number of shallow traps and deep traps. Accordingly, the enhancement of the red afterglow in Ca2SnO4:Sm3+, Gd3+ could be ascribed to more appropriate traps created by the incorporation of Gd3+. The presence of deep stable traps(T2) in Ca2SnO4:Sm3+ able to immobilize the energy permanently at room temperature, since the TL bands at 424k remained the original intensity after a delay of 72h in dark. Taking into account these finding and considerations, it can be concluded that Ca2SnO4:Sm3+ fulfill the requirements of either a long-afterglow phosphor or a photostimulated (storage) phosphor.[8]
64
Xuhui Xu et al. / Physics Procedia 29 (2012) 62 – 64
Figure.3 The aftergow decay curves of Ca2SnO4:Sm3+ (black) and Ca2SnO4:Sm3+, Gd3+ (red). Insert: the thermoluminescence curves of Ca2SnO4:Sm3+ (black) and Ca2SnO4:Sm3+, Gd3+ (red). Conclusion Red long afterglow was obtained from Ca2SnO4:Sm3+ and Ca2SnO4:Sm3+,Gd3+ prepared via a solid state reaction. The introduction of Gd3+ can increase the number of appropriate traps (T1), which is responsible for the intense red afterglow. The presence of deep stable traps (T2) in Ca2SnO4:Sm3+ able to immobilize the energy permanently at room temperature, which indicates that Ca2SnO4:Sm3+ fulfill the requirements of either a long-afterglow phosphor or a photostimulated (storage) phosphor. Acknowledgment This work is supported by the National Natural Science Foundation of China (No. 10874061), the National Science Foundation for Distinguished Young Scholars (No. 50925206), and the Research Fund for the Doctoral Program of Higher Education (No. 200807300010). Reference [1] Xu, C. N.; Watanabe, T.; Akiyama, M.; Zheng, X. G., Direct view of stress distribution in solid by mechanoluminescence. Appl Phys Lett, 74, 2414 (1999). [2] Aizawa, H.; Katsumata, T.; Takahashi, J.; Matsunaga, K.; Komuro, S.; Morikawa, T.; Toba, E., Fiber-optic thermometer using afterglow phosphorescence from long duration phosphor. Electrochemical and Solid-State Letters, 5, H17 ˄2002˅. [3] Matsuzawa, T.; Aoki, Y.; Takeuchi, N.; Murayama, Y., A New Long Phosphorescent Phosphor with High Brightness, SrAlO: Eu, Dy. J Electrochem Soc, 143, 2670 (1996). [4] Xu, X.; Wang, Y.; Li, Y.; Gong, Y., Effects of Pr3+ Doping on the Optical Properties of Eu and Nd Co-Doped CaAl2O4-Based Phosphor. Electrochemical and solid-state letters, 13 (5) (2010). [5] Zych, E.; Trojan-Piegza, J.; Hreniak, D.; Strek, W., Properties of Tb-doped vacuum-sintered LuO storage phosphor. J Appl Phys, 94, 1318 (2003). [6] Kinoshita, T.; Yamazaki, M.; Kawazoe, H.; Hosono, H., Long lasting phosphorescence and photostimulated luminescence in Tb-ion-activated reduced calcium aluminate glasses. J Appl Phys, 86, 3729 (1999). [7] Yamashita, T.; Ueda, K., Blue photoluminescence in Ti-doped alkaline-earth stannates. J Solid State Chem, 180 (4), 1410-1413 (2007). [8] Trojan-Piegza, J.; Zych, E.; Ho lsa , J.; Niittykoski, J., Spectroscopic Properties of Persistent Luminescence Phosphors: Lu2O3: Tb3+, M2+ (M= Ca, Sr, Ba). The Journal of Physical Chemistry C, 113 (47), 20493-20498 (2009).
