纳米晶体ZnS∶Mn^(2+)发光寿命异常减缩机理的探讨

DISCUSSION ON THE MECHANISM OF PHOTOLUMINESCENCE OF NANOCRYSTAL ZnS∶Mn 2+

纳米晶体ＺｎＳ∶Ｍｎ２＋中Ｍｎ２＋粒子４Ｔ１→６Ａ１的发光寿命比晶体减缩了５个量级，这颇令人费解，因为通常解除自旋禁戒的磁作用远无如此强的效应．假定基质态的自旋不为零，且考虑了Ｍｎ２＋的ｄ电子和基质之间的交换库仑作用．若基质存在比Ｍｎ２＋的４Ｔ１激发态能量略高的某种激发态，则这种交换库仑作用将导致这两种激发态之间的混合，从而可解除发光能级弛豫中的自旋禁戒．这种混合随基质颗粒尺寸的减小而加强．我们并对此机制进行粗略的数值估计，给出了和实验相容的结果．

It′s beyond common understanding that the luminescent lifetime of 4T 1→ 6A 1 transition of Mn 2+ doped ZnS decrease drastically by 5 orders of maganitude from bulk to nanacrystal because the magnetic interactions which usuall relax the spin forbiddenness can not be so strong. In this paper, we present a possible mechanism involving in the exchange coulomb interaction between the d electrons of Mn 2+ and electrons of host. Assuming that the spin of the ground state of host is not zero, and that the exchange coulomb interaction cause mixing between the excited 4T 1 state of Mn 2+ and certain excited state of host whose energy is slightly higher than 4T 1 state of Mn 2+ , we found that the spin forbidden transition could be almost allowed. Morever, the mixing degree increases as the grain size of host decreases. A rough numerical estimation about this mechanism agrees with the results of experiment.