Whispering gallery mode micro-lasing in CsPbI3 quantum dots coated on TiO2 microspherical resonating cavities.

Whispering gallery mode (WGM) lasing in CsPbI3 quantum dots (QDs) coated on TiO2 spherical microcavities is demonstrated. The photoluminescence emission from a CsPbI3-QDs gain medium strongly couples with a TiO2 microspherical resonating optical cavity. Spontaneous emission in these microcavities switches to a stimulated emission above a distinct threshold point of 708.7 W/cm2. Lasing intensity increases three to four times as the power density increases by one order of magnitude beyond the threshold point when the microcavities are excited with a 632-nm laser. WGM microlasing with quality factors as high as Q∼1195 is demonstrated at room temperature. Quality factors are found to be higher for smaller TiO2 microcavities (∼2 µm). CsPbI3-QDs/TiO2 microcavities are also found to be photostable even after continuous laser excitation for 75 minutes. The CsPbI3-QDs/TiO2 microspheres are promising as WGM-based tunable microlasers.

Sublattice Distortion Enabled Strong Interplay between Phonon Vibrations, Electron-Phonon Coupling, and Self-Trapped Excitonic Emissions in Cs2Ag1-xNaxBiCl6 Double Perovskites.

Sublattice distortion resulting from alloying compositionally distinct double perovskites is shown to influence photoluminescence emission in Cs2Ag1-xNaxBiCl6 (0 < x < 1). The end members show negligible photoluminescence, whereas interestingly the alloys exhibit broad photoluminescence. These emissions are attributed to self-trapped excitons (STE) resulting from sublattice distortions arising due to the mismatch in [AgCl6]5- and [BiCl6]3- octahedra. Change in sublattice distortions plays significant role in the formation and recombination of STEs. The STE emission intensity and quantum yield greatly depend on x, with highest intensity observed for x = 0.75, consistent with a large change in sublattice found at this x. Variation in photoluminescence properties with composition follows a similar trend as that of bandgap and phonon vibrational changes observed due to sublattice distortion. Temperature-dependent phonon vibrations and photoluminescence studies reveal a giant electron-phonon coupling. A strong synergy between STE emissions, electron-phonon coupling, bandgap, and phonon vibrations in double perovskites with sublattice distortions is demonstrated.