PICOSECOND NONRADIATIVE PROCESSES IN NEODYMIUM-DOPED CRYSTALS AND GLASSES - MECHANISM FOR THE ENERGY-GAP LAW

We present measurements of the (4)G(7/2) emission lifetime for 26 Nd-d oped crystals and glasses, including phosphates, silicates, oxides, ga rnets, apatites, and fluorides. The fluorescent decays were found to r ange from 70 ps to 41 ns, depending on the host medium. We show that t he (4)G(7/2) emission lifetime is correlated to the I-4(11/2) relaxati on time to within a factor of two, by comparing the present results wi th previous directly-determined I-4(11/2) lifetimes. This (4)G(7/2) - I-4(11/2) correlation is useful because the I-4(11/2) state is the ter minal level for the common 1.06 mu m Nd-laser transition, while the (4 )G(7/2) emission time can be measured in a relatively straightforward manner. A model of nonradiative decay based on dipole-dipole energy tr ansfer is developed and found to be supported by our data. It allows i ndependent calculation of the parameters of the energy gap law, in add ition to fitting the nonradiative lifetime data. (C) 1998 Elsevier Sci ence B.V. All rights reserved.