Near-Band-Edge Optical Responses of ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbCl}}_3$ Single Crystals: Photon Recycling of Excitonic Luminescence

The determination of the band gap and exciton energies of lead halide perovskites is very important from the viewpoint of fundamental physics and photonic device applications. By using photoluminescence excitation (PLE) spectra, we reveal the optical properties of ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbCl}}_3$ single crystals in the near-band-edge energy regime. The one-photon PLE spectrum exhibits the $1s$ exciton peak at 3.11 eV. On the contrary, the two-photon PLE spectrum exhibits no peak structure. This indicates photon recycling of excitonic luminescence. By analyzing the spatial distribution of the excitons and photon recycling, we obtain 3.15 eV for the band gap energy and 41 meV for the exciton binding energy.

Figure 1

(a) 1-PLE and (b) 2-PLE spectral maps for the $\mathrm{MA}{\mathrm{PbCl}}_3$ single crystal. $E_1$ and $E_2$ correspond to the excitation laser energy during 1- and 2-PLE measurements, respectively.

Figure 2

The PL spectra (red data points) for (a) the single crystal and (b) the thin film, under one-photon excitation with energies close to the band edge of $\mathrm{MA}{\mathrm{PbCl}}_3$. For comparison, the PL spectrum for an excitation of the thin film with $E_1=3.50\mathrm{eV}$ is shown with the blue curve.

Figure 3

The PL spectra for (a) the single crystal and (b) the thin film, under two-photon excitation with energies close to half of the band gap of $\mathrm{MA}{\mathrm{PbCl}}_3$.

Figure 4

(a) 1-PLE and (b) 2-PLE spectra of the $\mathrm{MA}{\mathrm{PbCl}}_3$ single crystal for different monitor wavelengths. The inset indicates the monitoring wavelength with a representative PL spectrum.

Figure 5

(a) Comparison of PL and PLE spectra of the $\mathrm{MA}{\mathrm{PbCl}}_3$ single crystal for one- and two-photon excitation conditions. (b) The one-photon (blue) and two-photon (red) absorption spectra, as calculated from the PLE spectra. The continuous line is the fitting result using Elliott’s formula.