Room Temperature Excitonic Structure in Li-doped CsPbBr3 Nanocrystals Via Two Photon Absorption

This talk investigates the nonlinear photoluminescence (PL) response of CsPbBr3 nanocrystals (NCs) embedded in a Cs2PbBr6 matrix under 800 nm excitation. X-ray diffraction (XRD) confirms a cubic phase for all samples. Linear absorption spectra for both doping levels yield consistent electronic bandgaps; Li incorporation does not measurably shift the band edge, indicating that Li acts primarily as a passivator of surface and impurity states rather than a lattice substituent.

Across fluences of 0.509 mJ cm⁻²–20.37 mJ cm⁻², the room-temperature PL shows pronounced excitonic structure, departing from the single-Gaussian line shape often reported. At low fluence, log–log fits of peak intensity versus fluence give slopes near 2, consistent with two-photon absorption as the dominant excitation pathway. At higher fluence, we observe spectral narrowing and threshold-like behavior indicative of optical gain/amplified spontaneous emission (ASE), with lower apparent thresholds in Li-doped samples. Together, the unchanged band edge and the PL gain behavior establish a stable, room-temperature platform for nonlinear and gain-enabled photonics.