Abstract:
Anti-Stokes photoluminescence (ASPL), which is an up-conversion phonon-assisted process
of the radiative recombination of photoexcited charge carriers, was investigated in methylammonium
lead bromide (MALB) perovskite nanocrystals (NCs) with mean sizes that varied from about
6 to 120 nm. The structure properties of the MALB NCs were investigated by means of the scanning
and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. ASPL spectra of
MALB NCs were measured under near-resonant laser excitation with a photon energy of 2.33 eV
and they were compared with the results of the photoluminescence (PL) measurements under nonresonant
excitation at 3.06 eV to reveal a contribution of phonon-assisted processes in ASPL. MALB
NCs with a mean size of about 6 nm were found to demonstrate the most efficient ASPL, which is
explained by an enhanced contribution of the phonon absorption process during the photoexcitation
of small NCs. The obtained results can be useful for the application of nanocrystalline organometal
perovskites in optoelectronic and all-optical solid-state cooling devices.