Photoluminescence upconversion in colloidal CdTe quantum dots

Efficient photoluminescence (PL) up-conversion has been observed in colloidal CdTe quantum dots with an energy gain of as high as 360 meV. Compared with the normal PL, the peak energy of this up-converted PL (UCPL) shows a redshift of about 80 meV, and the corresponding radiative lifetime becomes nearly twice as long. This UCPL is attributed to the carrier recombination involving surface states mainly through a thermal excitation process.