Using radiation intensity dependence on excitation level for the analysis of surface plasmon resonance effect on ZnO luminescence

Abstract

For the analysis of ZnO luminescence the system of rate equations (SRE) was proposed. It contains a set of parameters that characterizes processes participating in luminescence: zone-zone excitation, excitons formation and recombination, formation and disappearance of photons and surface plasmons (SP). It is shown that experimental ZnO microstructure radiation intensity dependence on photoexcitation level can be approximated by using SRE. Thus, the values of these parameters can be estimated and used for luminescence analysis. This approach was applied for the analysis of ZnO microfilms radiation with different thickness of Ag island film covering. It was revealed that the increase of cover thickness leads to the increase of losses and decrease of probability of photons to SP conversion. In order to take into account visible emission, rate equations for levels populations in band-gap and for corresponding photons and SP were added to SRE. By using such SRE it is demonstrated that the form of visible luminescence intensity dependence on excitation level (P) like P1/3, as obtained elsewhere [1], is possible only in case of donor-acceptor pairs existence. The proposed approach was applied for consideration of experimental results obtained in [5-8] taking into account their interpretation of these results based on assumption about transfer of electrons from defect level in ZnO band-gap to metal and then to conduction band in ZnO. Results of performed calculations using modified SRE revealed that effects observed in these papers can exist under only low pumping level. This result will be experimentally checked later.