Elsevier

Microelectronics Journal

Volume 36, Issues 3–6, March–June 2005, Pages 546-548
Microelectronics Journal

Crystal size dependence of the persistent phosphorescence in Sr2ZnSi2O7: Eu2+, Dy3+

https://doi.org/10.1016/j.mejo.2005.02.067Get rights and content

Abstract

There has been considerable interest recently in materials which show prolonged persistent phosphorescence following short periods of excitation; the persistence has been reported in a large variety of phosphor materials including sulfides, oxides, and complex silicates and aluminates. The phosphorescence has generally been attributed to the presence of traps in most instances produced by a co-dopant ion. In this paper, we investigate the behavior of the persistent phosphorescence as a function of phosphor particle size and find that the persistence time increases as a function of decreasing particle size. The increase in time is attributable to an increase in surface trapping levels commensurate with changes in the surface to volume ratio in the phosphor particles.

Introduction

There has been a revival of interest in materials which evince a long persistent luminescence or phosphorescence [1], [2], [3], [4], [5], [6]. This phenomenon has been reported in a large variety of insulating materials and has most recently focused on doubly activated complex silicates and aluminates. For example, a commercially available material, Luminova, is an aluminate activated by Eu2+ and Dy3+; it is generally thought that the Dy3+ ion in this material creates hole traps which are ultimately responsible for the excitation of the Eu2+ phosphorescence observed. Rare earth doped nano-phosphors have been also prepared and their optical properties have been investigated in recent years, such as Gd2O3:Yb,Er and Gd2O3S:Yb,Er [7], ZnS:Eu [8], and Y2O3:Eu [9]. Spectral shifts have been observed due to the surface/size effects [1], [10]. In this paper, we have studied the behavior of the persistent phosphorescence decay as a function of particle size and find a functionality which is consistent with increase of traps as the surface to volume ratio increases with decreasing size. We report on this as well as the synthesis and optical properties of Sr2ZnSi2O7:Eu2+, Dy3+.

Section snippets

Experimental

The samples were prepared using a sol-gel procedure similar to that described by Jiang and coworkers [4]. In this procedure strontium and zinc acetates and tetraethoxysilane were used as starting materials and water and methanol were selected as solvents for all the salts. Europium and dysprosium chloride were obtained by reacting stoichiometric amounts of lanthanide oxides with hydrochloric acid. The dissolved salt solutions were stirred into the tetraethoxysilane solution and the mixture was

Results and discussion

Fig. 1 shows the X-ray diffraction patterns of the resulting gel powders for different annealing temperatures. This results show that the samples possess good crystallinity and that the material synthesized has the structure of the compounded Sr2ZnSi2O7 rather than the simpler Sr2SiO4. Through increased thermal mobility, the average phosphor particle size is found to increase with increased annealing temperature. The particle size dependence on temperature is illustrated in Fig. 2; as can be

Conclusions

In summary, we believe that this is the first study, though preliminary, of the dependence of persistent phosphorescence or afterglow properties of this class of phosphors to be carried out in nano-materials as a function of particle size. We have shown that it is possible to synthesize phosphor materials in a controllable way through the sol-gel technique and that materials grown in by this technique largely retain the optical properties of the bulk materials. The principal result from our

Acknowledgements

One of the authors (XJW) wishes to thank the supports from ‘One Hundred Talents Program’ of the Chinese Academy of Sciences and from the Cottrell College Science Awards of Research Corporation.

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