Persistent spectral hole-burning and hole-filling in CuBr semiconductor nanocrystals

Persistent spectral holes (p-SHs) are induced in the Z(1,2) excitonic absor ption band of CuBr nanocrystals (NCs) in glass by selective excitation with nanosecond dye-laser pulses at low temperatures. The effect can be observe d only in samples containing NCs with mean radius smaller than about 5 nm. The kinetics of p-SHs growth and the long-time relaxation (spontaneous hole -filling) after burning are studied. The burning process may be described a s the first order dispersive reaction, which proceeds through a phonon-assi sted tunneling between different excited states of the NC/matrix system. Th e same model apply in the backward reaction (hole-filling) but the tunnelin g takes place between different ground states of the NC/matrix system and t he reaction rate is much lower. The photoproduct of persistent spectral hol e-burning reaction is a charged NC which energy states are modified by the Stark effect. The quantum efficiency of burning reaction is quite high 4x10 (-3) (mean rate constant is 4x10(7) s(-1)) while the rate of spontaneous HF reaction is very low (0.5 s(-1)). (C) 1999 American Institute of Physics. [S0021-9606(99)70144-3].