抄録
Luminescence and its excitation spectra are investigated on TlBr and TlCl single crystals. The luminescence spectra of both halides consist of three characteristic emissions, a broad emission band and two kinds of narrow emission lines. The highest energy emission line is ascribed to the resonance emission of the direct exciton. The low energy threshold of the excitation spectra is interpreted as the contribution from the indirect interband transition, In TlBr, an oscillatory phonon structure is observed above this threshold, from which the indirect-exciton energy is estimated to be 2.630±0.005 eV. A similar edge in TlCl is supposed to lie around 3.20 eV. The sharp emission lines appearing below this indirect edge are attributable to the radiative recombination of the indirect exciton bound to some impurities. Discussions are presented on the radiative decay of these direct and indirect excitons in thallous halides.
