EFFECT OF PRESSURE ON AMORPHOUS EU(OH)3 - A LUMINESCENCE STUDY

Luminescence from the D-5(0) --> F-7(0,1,2,4) transitions in the Eu3+ ion in amorphous Eu(OH)(3) was investigated as a function of pressure up to 8 GPa. The spectral characteristics were correlated with various aspects of the ''structure'' of amorphous Eu(OH)(3) and used to discuss the effect of pressure on this material. It was found that pressure induced a decrease in the covalency of the Eu-O bond, a decrease in the Eu-O bond distance, and an increase in the number of non-equivalent Eu3+ ion sites. Discontinuities in the shift of peak positions, the width of the luminescence peak from the D-5(0) --> F-7(0) transition, the intensity ratios, and the crystal-field parameters between 4 and 5 GPa suggested that a phase transition occurred within this pressure range. Compression of amorphous Eu(OH)(3) results in both the shortening of the Eu-O bond distance and an increase in the number of non-equivalent Eu3+ ion sites, which leads to greater non-uniformity in amorphous Eu(OH)(3) under pressure.