EFFECT OF DILATATIONAL STRAIN ON THE SELF-TRAPPED EXCITON LUMINESCENCE OF ALKALI-HALIDES

The effect of dilatational strain on the self-trapped exciton (STE) luminescence of alkali halides is investigated at 11 K by using thin crystals grown inside a narrow gap of the quartz cell. In strained NaBr, new luminescence is found to appear around 3.13 eV in addition to the well-known π emission. This luminescence has an excitation threshold at the absorption band associated with spin-triplet exciton states, and exhibits a long lifetime of 103 µs. The same emission band can be produced by causing electrons to recombine with VK centers. It is pointed out that an expansion of the lattice parameter leads to an STE configuration of low symmetry, from which the 3.13 eV luminescence occurs. It is further proved that the dilatational strain has a considerable effect on the STE luminescence in RbI, but not in KBr. These results are discussed in terms of the off-center model for the STE. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.