The phenomenon of photon avalanche, which involves both an excited state absorption process from a metastable level and a cross relaxation energy transfer process responsible for the large increases in population of this metastable level, has been investigated in ${\mathrm{LaCl}}_3:{\mathrm{Pr}}^{3+}.$ In this paper, we report on the intensity dependence of both the steady-state fluorescence and the temporal evolution of the avalanche signal as a function of temperature (80 K to room temperature). Comparisons are made between experimental results and mathematical models based on a six-level system described by a series of coupled rate equations combined with the propagation of a Gaussian beam. We develop a model with only one adjustable parameter, the excited state absorption cross section, which provides a good description of all of our experimental data. We have estimated values of the excited state absorption cross section for the various ${}^3{\overrightarrow{{\mathrm{H}}_5}}^3{\mathrm{P}}_0$ pumping transitions at different temperatures.

• Received 3 May 2000

DOI:https://doi.org/10.1103/PhysRevB.62.10790