Photoluminescence of C₆₀ Single Crystals

The photoluminescence (PL) spectra of C₆₀ single crystals grown under double temperature gradient (DTG) and single temperature gradient (STG) techniques were investigated at room temperature. The results show that the PL emission intensity increases first and then decreases with increasing illuminated power density for the C₆₀single crystals grown by both DTG and STG techniques. Furthermore, one main peak with a shoulder peak can be clearly distinguished at low illumination, while only one main peak without the shoulder peak can be seen at high illumination. The main peak undergoes a continuous blue shift and broadening with the increase of illuminated power density. The difference of PL emission energy at the same illumination density of DTG and STG samples may correlated with the degree of both the orientational disorder of C₆₀ molecule and lattice perfectness. The Laue diffraction patterns show that the DTG sample has stronger strains and poorer crystalline quality than the STG sample.