Photoluminescence of Band Gap States in AgInS2 Nanoparticles

AgInS2 nanoparticles of various sizes were synthesized over a range of reaction temperature from 120 to 180 degrees C. The band gap energies, obtained directly from photoluminescence spectra for the first time, were well correlated to the quantum confinement effects as a function of nanoparticle size, because the band gap shift was explained by the finite-depth-well effective mass approximation. The chalcopyrite and orthorhombic phases were observed to coexist in the AgInS2 nanoparticles, although the relative population of each phase depended on the reaction temperature and time. The band gap shift of each phase was comparable, which revealed that the size was the major determinant of the change in the band gap energy. The photodynamics of the band gap states exhibited emission-wavelength dependence, which further supported the coexistence of the two phases. The contributions of each phase in the time profiles matched the relative population of each phase observed in the steady-state photoluminescence spectra.