Thermal Shifts in the Energy Levels of LaF_3:Nd^3+*

Abstract

We have measured the temperature dependence of the linewidths and positions for a number of transitions in the spectrum of LaF3:Nd3+. As the temperature increases, all lines broaden because of relaxation and Raman scattering of phonons. Relative to the ground state, all observed levels shift to lower energies as the temperature increases. Most lines show the usual shifts to the red. All these effects are qualitatively attributable to lattice vibrations. In general, the level shifts increase for the higher levels so that, ordinarily, line shifts are to the red with increasing temperatures. However, because of irregularities of the magnitudes of the level shifts, a few lines show shifts to the blue with increasing temperature, over some temperature ranges.