Excitonic relaxation processes in solid rare gases

Abstract

Recent experiments of our group on excitonic energy transfer and relaxation processes in doped and undoped solid rate gases are reviewed. The samples studied were vapor deposited films, mainly solid Ar and Kr doped with Ag or Au atoms. X-ray irradiation and selective VUV-excitation were used for exciton generation. Excitonic relaxation processes during and after exciton generation were monitored via the fluorescence of self-trapped and impurity- trapped excitons as well as via thermally stimulated luminescence and conductivity measurements after irradiation, respectively. Exciton diffusion lengths, diffusion constants, and trapping rates at impurities are determined by comparing the emission yield spectra of impurity and self-trapped exciton emission. By identifying the impurity states being excited during exciton trapping we could show that in all systems studied the dominating exciton capture process is the one yielding the lowest excess energy to be dissipated into the crystal. Impurity trapping of excitons partly leads to the production of free charge carriers, which can be captured in shallow traps. The glow curves of impurity luminescence and conductivity during thermal annealing clearly reveals the existence of intrinsic and extrinsic electron and hole traps. Binding energies of these traps are evaluated from the data.