摘要
在团簇近似的基础上,利用分子动力学和密度泛函计算相结合的手段,在Y_2O_3:Eu^(3+)中研究了随Li^+掺杂浓度的变化,缺陷形成情况以及C_2位处Y—O键长的变化对电子态密度的影响。结果表明,随着Li^+掺杂浓度的增加,与C_2格位相关团簇的Y—O键平均键长出现了增加-减小-增加的变化趋势,这可能是引起此类材料发光强度随Li^+浓度出现类似变化的原因。
Yttrium oxide is one of the scintillation material used in X-ray imaging, in order to improve the light output of doped rare earth ions, Li^＋ is always codoped with the luminescent center. However the mechanism for this codoping approach is still not quite clear research work shows the enhance effects of Li^＋ doping except the common explanation of flux effect. Further is related with concentration of Li^＋ and the lattice constants, but the implication of this kind of relationship is still not clear. Based on the model of cluster approximation, the influence of Li^＋ doped concentration on defects formation and the effect of the change of Y--O bond length on electronic density of states are studied with molecular dynamics and density functional simulation with software package （ADF2005）. Since the clusters we chosen are relatively small in order to save simulation time, charge the results of former simulation are adopted for the cluster value. The value of cluster charge is further readjusted so that the cluster with least bonding energy is used for discussion, by this way we can eliminate partly the effect caused by dangling bond. Furthermore, the simulation result by cluster approximation is compared with that of the supercell methods. From these results we can draw conclusion that the methods we adopted in the simulation is reliable. The results shows that firstly the Li^＋ tender to occupy the interstitial position around the C2 site, which producing the stretching of the Y--O bond, thus lower the phonon energy of the sample, and increase the quantum efficiency of the material, by this way the light yield of the sample is improved. From the results of simulation, with the increase of Li^＋ , the length of Y--O bond for C2 sites changes with the tendency of decrease-increase-decrease, which may explain the similar emission change via Li^＋ concentration for this type of material, thus explained the two maximum peaks in the Li^＋ concentration-light yield curve. The stretching of the Y--O bond may also cause the narrowing of the band gap, which might be the cause of small shift of the absorption spectrum.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2007年第5期693-698,共6页
Chinese Journal of Luminescence
基金
上海市科委基础研究重点项目(05JC14062)
高等学校优秀青年教师教学科研奖励计划(JRS-2002-123)
上海市教育委员会曙光计划(02SG19)
上海市科委自然科学基金(05ZR14123)
同济大学理学基金
