Anti-Stokes photoluminescence in CsPbBr3 caused by resonant multiple-phonon absorption

Abstract

Cesium lead bromide nanocrystals, in contrast to most other materials, exhibit near-unity photoluminescence quantum yields (PLQY). When excited below the band gap, they absorb the photons and show anti-Stokes photoluminescence (ASPL), emitting higher energy, band-gap photons. Simultaneous existence of near-unity PLQY and ASPL can be used to optically cool these materials. In this talk, I will report near-unity ASPL efficiencies in CsPbBr₃ nanocrystals and attribute it to resonant multiple-phonon absorption by polarons. The theory explains paradoxically large efficiencies for intrinsically disfavored, multiple-phonon-assisted ASPL in nanocrystals.