On the distribution of energy between the Tm 3F4 and Ho 5I7 manifolds in Tm-sensitized Ho luminescence

Abstract A theory on the distribution of energy between the Tm 3 F 4 and Ho 5 I 7 manifolds in Tm-sensitized Ho materials is presented. A rate equation approach is utilized to arrive at an expression for the temperature-dependent equilibrium constant, Θ. Experimental support for this calculation is obtained by two different experimental procedures. Approximations used in the theory and the limits of applicability are also discussed. In the course of the development of the theory, a distinction is made between low and high excitation regimes, and criterion for applicability are given. Equations for the fractional population of Tm and Ho ions of the total excited state population in the low excitation density limit are derived in the context of the present theory, which differ from those widely used in the literature.