Radiationless Transitions and Excited-State Absorption in Tunable Laser Materials

摘要

A coordinated experimental and theoretical investigation of fluorescencequenching and excited-state absorption was conducted on the chromium-doped halide elpasolites K2NaGaF6, K2NaScF6 and Cs2NaYC16, and on the laser-active T10(l) color center in KC1. Luminescence lifetime measurements on Cs2NaYC16:Cr3+ revealed a linear pressure dependence of the activation energy for thermal fluorescence quenching which was accurately predicted by a semi-empirical theoretical model incorporating quadratic coupling to an asymmetric mode. An ab-initio theoretical model, based on embedded-cluster and lattice-statics and dynamics calculations, accounted very well for optical and vibrational properties of these materials, but still needs refinement for reliable prediction of thermal quenching behavior. Two-photon excitation spectroscopy helped to explain broad-band excited-state absorption. Embedded-cluster calculations on laser-active color centers are in progress, with encouraging preliminary results. Non-radiative transitions, transition metals, chromium, tunable lasers, high pressure, luminescence, color centers.