The corresponding FPh, estimated from the Lorentz function-fitted steady-state PL spectra, decreases from 52 to 39% (Figure ). The fraction of the FPh to the total FPL increases modestly from 74 to 79% as the doping concentration increasing from 0.1 to 0.5 wt% and then drops 74% when the concentration reaches 2 wt%. Thus, the fraction of phosphorescence to the total photoluminescence stays essentially constant across this doping regime (Figure ).