Absorption and Luminescence of (Br⁻)₂-Centers in NaCl:Br

Abstract

Luminescence due to Br⁻-ions in NaCl has been investigated at liquid nitrogen temperature by varying the amount of Br⁻-ions from 1×10⁻³ to 1.4×10⁻² mole fraction. Two emission bands, having their maxima at about 4.0 eV and 5.15 eV, were observed with UV-light excitation. The 4.0 eV luminescence is known to enhance linearly with increasing Br⁻-ion concentration. Ratio of the intensity of the 5.15 ev luminescence to that of the 4.0 eV luminescence was found to vary in proportion to the Br⁻-ion concentration, suggesting that the intensity of the 5.15 eV luminescence varies with square of Br⁻-ions concentration. This means that the 5.15 eV luminescence is caused by (Br⁻)₂-center. Presence of the absorption band of (Br⁻)₂-center was also confirmed in the low energy side of the absorption band due to Br⁻-ion monomer.