A mechanism for the upconversion of 1.06‐mgr;m radiation to 0.873 mgr;m in LaCl3 : Nd is described. The 1.06‐mgr;m radiation is absorbed by4I13/2→4F7/2,2S3/2transitions and 0.873‐mgr;m radiation is emitted by2S3/2,4F7/2→4I11/2transitions of the Nd3+ions. The temperature dependence of the intensity response is a function of (a) the population density of the4I13/2level at high temperatures, (b) the trap density of the4I11/2level at low temperatures, and (c) the quantum efficiency of radiative transitions from theAlevel. The multiphonon transitions from the populatedAlevel reduce the radiative transitions to zero at approximately 365 °K, whereas the multiphonon transitions do not appreciably affect the radiative transitions at lower temperatures. By postulating that electrons are thermally present in the ground state of the Nd3+ions of the LaCl3 : Nd prepared by vapor chemical deposition, the model is in agreement with experimental data.
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