Luminescence mechanisms: from single crystals to nanocrystals

Larisa Grigorjeva ,  Donats Millers 

Institute of Solid State Physics, University of Latvia, 8 Kengaraga, Riga LV-1063, Latvia

Abstract

According to considerable progress in the synthesis of nanocrystals the investigation of luminescence properties of these systems became actual. The overview of luminescence models (excitonic, activator and defect associated) in bulk materials and nanocrystals will be presented.
The excitonic luminescence is very sensitive to grain size and the quantum confinement effect of exciton luminescence (as well as absorption) was observed in a numerous semiconductor nano systems. The decay time of the excitonic luminescence is short (in subnanosecond region at RT) and together with the luminescence intensity enhancement due to quantum effects the commercial interest (fast scintillators or/and displays) will be satisfy.
The luminescence of defect states (donor-acceptor recombination or free electron/hole recombination on charged traps) in nanocrystals as a rule are associated with surface states. The role of nonradiative recombinations due to surface defects will be observed in luminescence decay times and luminescence yield decreasing with grain size decreasing. The surface effects of nanocrystals embedded in matrix can strongly differ from those for free standing nanocrystals since interface layer between nanocrystal and matrix play an important role. These surface and interface states changes during the thermal annealing of system. The luminescent properties of material are an efficient indicator of these changes due to the luminescence high sensitive to any modification of defect states.
The results of investigations of doped nanocrystals show that impurity ions are incorporated at surface and near surface states mainly. The luminescence quenching due the efficient association of impurity (like surface aggregates) and the growths of probability of nonradiative transitions in local impurity centers will be observed.



 

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Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium F, by Larisa Grigorjeva
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 18:44
Revised:   2009-06-08 12:55