Phonon properties of and photoluminescence

We have investigated phonon properties of some crystals with characteristic light emission properties by using measurements of far-infrared absorption and photoluminescence in order to discuss a correlation between them. It has been found that there is a systematic correlation between phonon states and light emission efficiency and that the phonons above the energy of more than ∼44 meV may be effectively coupled to the optical indirect transition for the IR light emission from crystals.