Characteristics of sensitized emission in laser crystals

Abstract

The effects of sensitization on the static and dynamic behavior of the luminescence emission of donors (D) and acceptors (A) in codoped laser crystals are investigated. In many cases the sensitization with transition-metal ions of the weakly absorbing rare-earth laser emitters leads to the modification of the spectral properties of both D and A ions, due to the mutual crystal-field perturbations. The main modifications of the spectral properties due to the change of symmetry and/or strength of the crystal field acting on these ions are discussed. Due to the discrete nature of perturbations, the D and A systems become inhomogeneous and they could be separated in several homogeneous subsystems connected with specific D-A pairs along with the subsystem of ``isolated'' ions. The selective modifications of the energy-transfer processes due to the mutual static perturbations are the main subject of this paper. A theoretical modeling of the donor and acceptor emission kinetics in such complex systems is presented, assuming a discrete random uniform noncorrelated distribution. An essential point in the theoretical treatment is the fact that for nearest D-A pairs a mixed interaction picture, with strong influences of short-range ion-ion interactions must be considered. The codoping can lead to selective behavior of acceptor emission for various subsystems as concerns the wavelength, the moment and peak instantaneous emission, and the character of the subsequent decay. The model is illustrated with data on the $^{3}$${\mathit{H}}_{4}$ ${\mathrm{Tm}}^{3+}$ emission in YAG sensitized with ${\mathrm{Cr}}^{3+}$ or ${\mathrm{Fe}}^{3+}$. \textcopyright{} 1996 The American Physical Society.