Reabsorption artifacts in measured excited-state lifetimes of solids

The effect of repeated radiative energy transfer on the observed excited-state lifetime tau(obs) Of a luminescent species in a solid is studied by Monte Carlo simulations. Increasing the sample path length, the reabsorption coefficient, or the luminescence quantum yield significantly lengthens tau(obs), relative to its intrinsic value tau(0). This effect is additionally amplified by total internal reflection. Room-temperature lifetimes of F-2(5/2) in YAG:1%Yb3+ and I-4(11/2) in YLF:5%Er3+ were measured in a spherically refractive-index-matched geometry, yielding the low values of 0.9489 +/- 0.0006 and 3.75 +/- 0.01 ms, respectively. It is concluded that lifetimes obtained from non-refractive-index matched experiments are usually significantly overestimated. The technique presented is easily applicable to room-temperature excited-state lifetime measurements of many luminescent solids. (C) 1997 Optical Society of America.