Excitonic emissions and above-band-gap luminescence in the single-crystal perovskite semiconductors CsPbBr3 and CsPbCl3

The ternary compounds CsPbX3 (X = Br or Cl) have perovskite structures that are being considered for optical and electronic applications such as lasing and gamma-ray detection. An above-band-gap excitonic photoluminescence (PL) band is seen in both CsPbX3 compounds. An excitonic emission peak centered at 2.98 eV, similar to 0.1 eV above the room-temperature band gap, is observed for CsPbCl3. The thermal quenching of the excitonic luminescence is well described by a two-step quenching model, yielding activation energies of 0.057 and 0.0076 eV for high-and low-temperature regimes, respectively. CsPbBr3 exhibits bound excitonic luminescence peaks located at 2.29 and 2.33 eV that are attributed to recombination involving Br vacancy centers. Activation energies for thermal quenching of the excitonic luminescence of 0.017 and 0.0007 eV were calculated for CsPbBr3. Temperature-dependent PL experiments reveal unexpected blueshifts for all excitonic emission peaks in CsPbX3 compounds. A phonon-assisted step-up process leads to the blueshift in CsPbBr3 emission, while there is a contribution from band-gap widening in CsPbCl3. The absence of significant deep level defect luminescence in these compounds makes them attractive candidates for high-resolution, room-temperature radiation detection.