AbstractThis paper describes the characteristics of the luminescence centers observed in the various photoluminescence (PL) and photoluminescence excitation (PLE) spectra of hexagonal InxGa1−xN microcrystals, synthesized by the nitridation of sulfide in the In concentration range of 2%<x<6%. The grown crystals showed macroscopic and microscopic inhomogeneity. A series of component bands expressed by Gaussian functions with discrete peak energies selected from the frequently observed peaks in the PL spectra and full width at half maximum obtained from the narrowest PL bands were fitted well to observed broad emission bands. As some of the peak energies of the component bands coincide with those of the bands that are attributed to the decay of excitons at the localized states caused by the In content fluctuation in the literature, we concluded the luminescence center for the component bands also originates from the fluctuation of the In contents. Although the In contents of the samples determined by the X ray diffraction method were compatible the gap energies from the PLE measurements were different. The PLE spectra showed that the Stokes shifts were large and the gap energies were irrelevant to the emission band peaks. The excitation bands for the emission bands in the range of 2.8 to 2.48 eV were located at 3.36, 3.26, and 3.21 eV. These results indicate that the states of the luminescence center are localized and the energy levels are discrete. To obtain the microscopic structure of the localized states in InxGa1−xN, we propose the isoelectronic atom cluster model comparable with Te clusters in ZnSeTe.