Lifetime measurements with the pinhole method in presence of radiation trapping: I--theoretical model

This paper reports a new theoretical model for the evaluation of the results of the so-called pinhole method for the measurement of the upper level lifetime in doped optical materials exhibiting radiation trapping effects due to resonant reabsorption of the emitted fluorescence. The model correctly predicts that the fluorescence decay has a double exponential behavior with two time constants, with the shorter one near the intrinsic decay time of the upper level, with a correction depending on the effect of the short range reabsorption. As a consequence, a new method is proposed for the data analysis and the interpretation of the results with respect to the previous literature.