Emission Spectra of Erbium in the Scheelite Structure

Abstract

Erbium exhibits luminescent emission from excited states at 15 300, 18 400, and 24 500 cm—1 in calcium tungstate at room temperature and at 77°K. At room temperature, emission from thermally excited states at 18 830, 19 080, and 19 200 cm—1 is also prominent. At high erbium concentrations, the above spectra are essentially quenched at room temperature and new spectral lines which appear to originate from electronic levels just below the 18 400- and 24 500-cm—1 states are seen. However, at 77°K, emission from the 15 300, 18 400- and 24 500-cm—1 states is again strong and emission associated with levels just below these is no longer observed. There is no evidence of exchange coupling preferentially quenching the higher-energy emission states as in the cases of Tb3+ and Eu3+. This and the temperature dependencies observed suggest that thermal coupling to the lattice is the main factor responsible for quenching the emission of Na0.5 Er0.5 WO4.