Sensitivity of upconversion mechanisms to excitation laser wavelength in Er3+-doped YAG

A sensitive dependence of upconversion (UC) mechanisms on excitation wavelength in a rather small region of 0.5 nm near to the resonant absorption of 4F7/2 in Er3+(8.4 at%):YAG crystal has been observed and discussed. This kind of mechanism-sensitive UC luminescence comes from 2P3/2 which can be upconvertedly populated by both excited-stated absorption (ESA) and energy-transfer upconversion (ETU) processes. From a qualitative analysis, similar to the dependence of UC mechanisms on dopant concentration, the essence of this sensitivity reflects the influence of the interacting ion number on ETU. In order to give a quantitative description, we also performed a simulation for UC processes by rate equations, and the theoretical results attested the sensitivity as revealed in the experiment.