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Photoluminescence of orthorhombic and cubic single crystals

The photoluminescence of orthorhombic and cubic crystals has been studied with the use of a deuterium lamp or synchrotron radiation as the light source. The spectra of orthorhombic samples exhibit a single band at 2.07 eV, while the spectra of cubic samples show an intense band at 4.10 eV, accompanied by some other bands depending on the sample. These two main bands are stimulated only under exciton-band excitation. No luminescence is detected when both crystals are excited with photons in the band-to-band region. The present results are compared with earlier data for and which have the orthorhombic structure. The relaxation processes of excitons and electron-hole pairs in lead halides are discussed.