纳米晶体ZnS：Mn2+发光寿命异常减缩机理的探讨

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.

DISCUSSION ON THE MECHANISM OF PHOTOLUMINESCENCE OF NANOCRYSTAL ZnS：Mn2+

It's beyond common understanding that the luminescent lifetime of ⁴T₁→⁶A₁ transition of Mn²⁺ 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 Mn²⁺ 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 ⁴T₁ state of Mn²⁺ and certain excited state of host whose energy is slightly higher than ⁴T₁ state of Mn²⁺,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.