Quantification of the Optical Properties of Perovskite Nanocrystals Using a Combination of Polarized Resonance Synchronous and Polarized Anti-Stokes, On-Resonance, and Stokes-Shifted Spectroscopy

Abstract

Reliable quantification of the optical properties of perovskite nanocrystals (PNCs) is necessary for rational PNC design and applications in optoelectronics. Presented herein is the experimental evaluation of the photon scattering, absorption, and on-resonance fluorescence (ORF) cross sections of lead halide PNCs. Four CsPbX3 (X = Cl, Br, or I) PNCs fabricated through anion exchanges with the same parent PNC CsPbCl3 were studied using UV–vis, fluorescence, polarized resonance synchronous spectroscopic (PRS2), and the polarized anti-Stokes-shifted, on-resonance, and Stokes-shifted (PAOS) spectroscopic methods. All of the PNCs exhibit strong ORF in the wavelength region where the PNC absorption and fluorescence spectra overlap. The PNC optical properties under resonance excitation and detection conditions differ in different wavelength regions. They are simultaneous light absorbers and scatterers in the wavelength region shorter than the blue-edge wavelength of the PNC ORF peak; simultaneously, photon absorbers, scatterers, and emitters in the wavelength region where the PNC is ORF active; and light scatterers alone in the wavelength region longer than the red-edge wavelength of the PNC ORF peak. The PNC peak ORF wavelength and absorption extinction cross section increase with increasing fraction of heavy halides. However, the ORF cross section and quantum yield (QY) of the iodide-containing PNCs are several folds lower than those of their counterpart iodide-free PNCs. The effects of sample aging on the PNC optical properties have been quantified in terms of PNC absorption, scattering, and ORF cross sections and ORF QY. In addition to providing a series of quantitative information not accessible before, we anticipate that the devised methodology will be extended to fluorescent nanomaterials for which the existing tools are inadequate for decoupling the complex interplay among light UV–vis absorption, scattering, and fluorescence emission that can concurrently occur under the same excitation and detection conditions.