Cross relaxation and upconversion coefficients of the mid-infrared transitions of Pr3+:LaCl3

Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (upsilon < 10(-4) cm(-1)) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3-7.2 mu m spectral range are discussed. (C) 1997 American Institute of Physics.