By means of localized time constant measurements, the fluorescent behavior for the principal transition of YAG:Nd emanating from the 4F3/2 state has been analyzed at room temperature as a function of concentration. It is found that the overall decay process is the superposition of multiexponential components over the concentration range of 0.9–1.6 at. % of Nd. The dependence of decay rate on excitation intensity was examined to register monomolecular kinetics for the case associated with each exponential decay process. From these results it is predicted that the YAG:Nd crystals are inhomogeneously broadened in nature similar to glass.
K. K. Deb, R. G. Buser, and J. Paul, "Decay kinetics of 4F3/2 fluorescence of Nd+3 in YAG at room temperature," Appl. Opt. 20, 1203-1206 (1981)