Mixed Crystallization Effects on the Optical Properties of Multilayer Alkali Halide Films

The optical properties and X-ray diffraction of the MI-MBr and MI-MCl (M=K, Rb) multilayer (ML) films were investigated. The excitonic absorption spectra of the MI-MBr ML films with layers thinner than 10 nm (layers in a film were of equal thickness) showed a blue shift, while those of the MI-MCl ML films did not. The luminescence spectra and the X-ray diffraction profiles of the thin-layered KI-KBr ML films were very similar to those of the mixed crystal, indicating close similarity of crystallographic structure. Thus, the observed blue shift of the excitonic absorption for the thin-layered MI-MBr ML films seems to originate from the interlayer mixed crystallization grown by diffusion in the boundary region between layers, but not from the quantum-confinement effect.