Nanoparticles of wide band gap II-VI compounds doped with transition metal or rare earth ions are perspective fluorescence labels for applications in biology and medicine. For this application nanoparticles should efficiently emit light, which was rather unexpected for parity and often spin forbidden 3d-3d and 4f-4f intra-shell transitions. However, in nanoparticles efficiency of intra-shell transitions is enhanced. Mechanisms of emission enhancement will be discussed, based on our recent results for Mn doped nanoparticles of ZnS and CdS. Two effects will first be discussed - quantum confinement imposed on free carriers, which enhances spin dependent interactions of free carriers with impurities and increased rate of host to impurity transfer.

Passivation of surface states is important to limit rates of nonradiative transitions. We show that this can be achieved by doping of nanoparticles. Nanopowders of ZnO n-type doped with aluminium were studied to demonstrate such possibility. We show that intensity of light emission increases with an increasing Al fraction in ZnO nanopowders.

This work was partly supported by grant no. 1 P03B 090 30 of MEiN granted for the years 2006-2008.