OPTICAL MODULATION TECHNIQUES IN EPR FOR STUDIES OF LUMINESCENT MATERIALS.

The rare earch oxysulfides are currently of interest due to their high luminescence efficiency and interesting thermal properties. A major problem in the description of the luminescence process is the sequential thermal quenching of the luminescence exhibited by the oxysulfides doped with rare earths. Due to this current interest, a study was undertaken to observe the effects of ultraviolet radiation on the EPR spectrum of the materials. The Tb**3** plus spectrum consists of four strong hyperfine resonances between 3 and 4 KG at K-band microwave frequencies and when the magnetic field is parallel to the c-axis of the crystal. This spectrum is taken at 1. 5 degree K and the lines vanish at approximately 20 degree K. The g-values of the Tb**3** plus site are g parallel equals 4. 404 and g (perpendicular) equals 0. There is also a set of six less intense equally spaced lines in the spectrum. These are due to Pr** plus **3 ions, which exists in the sample as an unintentional impurity.