Exciton luminescence spectra in CuCI, CuBr, and C u I microcrystals of a few nm in size which are ernbedded in alkali-halide matrices are studied under selective excitation a t the exciton absorption bands inhomogcncously broadened by the size distribution. The size-quantized cxciton states are found to split into various components. From the analysis of the splitting on the basis of the sizequantization of the cxciton translational motion in the microcrystals of thin plateleta, the Z, exciton translational maw, the Luttinger parameters, and k-linear terms for the Zl,2 excitons are derived in these compounds.Les spectres de luminescence excitonique de microcristaux de CuCl, CuBr e t de CuI ayant, des dimensions de quclques nm enfouia dans des matrices de halogbnurea alcalins sont Btudib par excitation sBlectivc dans la bande d'absorption excitonique, celle-ci Btant Blargie de figon inhomoghe & cause dc la distribution en dimension des microcristaux. On obscrvo une sbparation en diffbrentes composantes des Btats excitoniques quantifies en dimension. A partir de I'analyse de cette separation des niveaux nous obtcnons la masse translationnelle de l'exciton Z,, les paramBtrcs de Luttinger do l'exciton ct les tcrmes linthire en k des exciton Zl,2 dans ces trois compods.
IntroduetionQuantum-size effects upon electronic excited states have been optically studied in semiconductors with the use of thin films [l to 41, quantum well structures [5], small colloidal crystallites [6 t o 81, microcrystals embedded in solid matrices [9 to 131, and bare microcrystals prepared by the gas-evaporation method [ 141. Excitons in GaAs quantum wells have been most extensively studied, where various fine structures due t o splitting8 of the electronic excited states have been found [5]. However, the Coulomb interaction energy between the electron and the hole inside the excitons is rather small compared with the confinement energies both for electron and hole, and hence, the electron-hole confinement picture is plausible [15].On the other hand, little is known about the quantum-size effect on excitons having large effective Rydberg constant, in which exciton confinement, in other words, quantization of exciton translational motion, is expected to be plausible [la, 161. Recently, Ekimov e t al. have performed optical studies in spherical microcrystals of CuCl dispersed in a transparent silicate glass matrix [ll]. On the basis of the exciton confinement picture, they have explained the energy positions and the profiles of absorption and luminescence spectra of the free exciton bands. However, in their experiments no information has been obtained about the splitting of the size-quantized cxciton states.In our preceding paper 1171 size and shape of CuCl microcrystals embedded in KaCl and KC1 matrices have been studied together with their correlation with exciton confinement. The crystalline shape has been found to be not spherical but somewhat flat, and from the analysis of the relation between the crystalline size and the blue shift I) Send...
