Up-conversion luminescence in GaSe nanocrystals

Optical properties of GaSe crystals have been investigated at wide temperature range from 10 to 300 K by help of reflection, absorption, and wavelength modulated reflection, and transmission spectra. Received data were compared with measured photoluminescence spectra. Three excitonic series were found out. The parameters of excitonic serie for С1-V1 bnads were determined. The longitudinal-transversal splitting of excitonic polariton ground states were determined. The doublet character of the transversal excitonic polariton mode (ωТ) was found out. The ground (n = 1) and excited (n = 2,3 … Eg) states of two high-energy excitonic series caused by C2–V1 and С3-V1 bands had been recognized, and its parameters were determined. The up-conversion of luminescence from high-energy excitonic levels (Е > 3 eV) was studied. The electrons were excited from V1 (Г1) to C1 (Г6) and C2 (Г5) bands with further transitions to higher energy levels С3-С6. So the luminescence from the excitonic levels of C3-С6 bands towards valence bands takes place. The band model in the Brillouin zone centerwas constructed based on the obtained data.