Transient Spectroscopy of Glass-Embedded Perovskite Quantum Dots: Novel Structures in an Old Wrapping

Abstract: Semiconductor doped glasses had been used by the research and engineering communities as color filters or saturable absorbers well before it was realized that their optical properties were defined by tiny specs of semiconductor matter known presently as quantum dots (QDs). Nowadays, the preferred type of QD samples are colloidal particles; however, there is still a number of applications that would benefit from the availability of high-quality glass-based QD samples. These applications include fiber optics, optically pumped lasers and amplifiers, and luminescent solar concentrators. Here we conduct optical studies of a new type of all-inorganic CsPbBr3 perovskite QDs fabricated directly in glasses by high-temperature precipitation. These samples are scattering free and exhibit excellent waveguiding properties. However, the presently existing problem is their low room-temperature emission quantum yields (QY) of only 1-2%. Here we investigate the reasons underlying the limited QY by conducting transient photoluminescence (PL) and absorption measurements across a range of temperatures from 20-300 K. We observe that the low-temperature PL QY of these samples can be as high as ~25%. However, it quickly drops with increasing temperature. Interestingly, experimental observations cannot be explained in terms of a thermally activated nonradiative rate but rather suggest the existence of two QD sub-ensembles of emissive and completely nonemissive particles. The temperature-induced variation in the PL efficiency is likely due to a structural transformation of the QD surfaces or interior leading to formation of trapping sites or nonemissive phases resulting in conversion of emissive QDs into nonemissive. Thus, future efforts on improving emissivity of glass-based perovskite QD samples might focus on approaches for extending the range of stability of the low-temperature up to room temperature.