Excitonic emissions and above-band-gap luminescence in the single-crystal perovskite semiconductorsCsPbBr3andCsPbCl3

The ternary compounds $\mathrm{CsPb}{X}_{3}$ ($X=\mathrm{Br}$ 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 $\mathrm{CsPb}{X}_{3}$ compounds. An excitonic emission peak centered at 2.98 eV, $\ensuremath{\sim}0.1$ eV above the room-temperature band gap, is observed for $\mathrm{CsPbC}{\mathrm{l}}_{3}$. 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. $\mathrm{CsPbB}{\mathrm{r}}_{3}$ 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 $\mathrm{CsPbB}{\mathrm{r}}_{3}$. Temperature-dependent PL experiments reveal unexpected blueshifts for all excitonic emission peaks in $\mathrm{CsPb}{X}_{3}$ compounds. A phonon-assisted step-up process leads to the blueshift in $\mathrm{CsPbB}{\mathrm{r}}_{3}$ emission, while there is a contribution from band-gap widening in $\mathrm{CsPbC}{\mathrm{l}}_{3}$. The absence of significant deep level defect luminescence in these compounds makes them attractive candidates for high-resolution, room-temperature radiation detection.