Fast resonant nonradiative energy transfer in alexandrite

Abstract

We measured the R-line fluorescence ( 2E → 4A 2) under site-selective dye laser excitation via pseudo-Stark R-line components in a modulated external electric field, and hence the kinetics of 2E-energy transfer among the Cr 3+ ions in mirror (C s) sites in alexandrite at T = 2 K were studied. Fast (microsecond range) resonant nonradiative 2E-energy transfer was observed. This shows that during the metastable 2E-state lifetime τ R = 2.4 ms the electronic 2E-excitations can perform many jumps over the Cr 3+(C s) ion ensemble. This result correlates directly with the results of four-wave mixing experiments [1,2], indicating the existence of long-range spatial diffusion of 2E excitation among the Cr 3+ (C s) ions.