[en] We report on the use of thermoluminescence and radioluminescence to monitor first order phase transitions. The luminescence signals not only offer information on the mechanisms of the relaxation processes, including changes in charge trapping energies and emission spectra, but also provide unique, sharply defined, temperature signals to act as temperature calibration standards for thermoluminescence. The wider implications of the method are mentioned, including the inverse problem of detection of phase transitions. (author)