方波激发下Ho^(3+)上转换绿色发光粉的激发机理

Dynamic Process of Green Upconversion Emission from Ho^(3+) Under Square Wave Excitation

采用溶胶-凝胶法制备了BaGd2ZnO5:Yb3+,Ho3+的发光材料,测量了样品在不同激发密度下的上转换光发射光谱。用方波调制的971 nm LD激光激发样品得到上转换绿光发射的上升和衰减变化曲线,通过建立Ho3+离子5F4(5S2)和5I6能级及Yb3+离子2F5/2能级的速率方程,并利用速率方程对绿光的上升和衰减过程进行拟合,确定了Yb3+离子2F5/2能级寿命及Ho3+离子5F4(5S2)和5I6的能级寿命,并证实在Ho3+离子能级粒子数布居趋于稳定时,Yb3+→Ho3+的能量传递是Ho3+离子5F4(5S2)能级粒子的主要布居途径,而激发态吸收对粒子布居数的贡献较小。

Yb3+ and Ho3+ codoped BaGd2ZnO5 phosphors were synthesized by using the sol-gel method.The upconversion emission spectra of BaGd2ZnO5∶Yb3+,Ho3+ phosphors were measured under the excitation of 971 nm LD laser at different excitation density.Under the excitation of 971 nm LD laser modulated by a square wave signal,the excited and decay processes of green upconversion luminescence in Yb3+/Ho3+ codoped BaGd2ZnO5 were observed by an oscilloscope.The rate equations of energy level 5F4(5S2),5I6 with Ho3+ ion and energy level 2F5/2 with Yb3+ ion were built to analyze the upconversion mechanism in Yb3+/Ho3+ codoped system,then the rate equation of the energy level 5F4(5S2) with Ho3+ ion was used to fit this processe in order to determine the lifetime of the energy levels.When excitation is steady,the population of 5F4(5S2) energy level with Ho3+ ion mainly come from the energy transfer from Yb3+ to Ho3+,and the effect of excited state absorption was able to be ignored.