Abstract
Effects of illumination on the spectra obtained from chromium-doped GaP crystals using a new technique of thermally-detected (TD) absorption spectroscopy are described. Photo-induced effects in TD EPR are also investigated on the same samples. It is shown that the spectra identified as due to Cr2+ centres decrease in intensity in both types of experiment, and that the spectra attributed to Cr3+ increase by a smaller amount in the absorption experiments. The photo-induced changes in TD EPR are difficult to measure. However, they are consistent with the deduction that the same Cr3+ centre is seen in both types of experiments, providing an experimental correlation between the two sets of measurements.