Anti-Stokes photoluminescence in colloidal semiconductor quantum dots

We report anti-Stokes photoluminescence (photon energy up-conversion) from size-quantized CdSe and InP nanocrystalline colloids. The observed up-conve rsion is highly efficient and occurs at very low excitation intensities. Wi th low temperatures the intensity of the up-converted photoluminescence dec reases while that of the usual Stokes photoluminescence increases; the up-c onverted photoluminescence is also restricted to energies corresponding to the band gaps of the quantum dots that are present in the colloid ensemble. The anti-Stokes photoluminescence is explained by a model that involves su rface states. (C) 1999 American Institute of Physics. [S0003-6951(99)03033- 8].