The peak shift and evolution of upconversion luminescence from CsPbBr3 nanocrystals under femtosecond laser excitation

The luminescent characteristics of CsPbBr3 nanocrystals in n-hexane are investigated by the use of steadystate/time-resolved photoluminescence and transient absorption spectroscopy. Compared with normal luminescence, a redshift of the upconversion luminescence (UCL) spectrum under 800 nm femtosecond laser excitation is observed. Time-resolved PL and TA spectroscopy under near-infrared femtosecond laser excitation demonstrate that the full width at half maximum and peak position are changed at various delay times, suggesting the existence of more than a single excited state. It is found that UCL is composed of a photoinduced surface-trapping and a band-edge excitonic state, causing the observed biexponential dynamics. We conclude that the redshift of the emission peak is caused by the relative change in luminescent intensity between excitonic and trapping states.