Observations of unusual temperature dependent photoluminescence anti-quenching in two-dimensional nanosheets of ZnS/ZnO composites and polarization dependent photoluminescence enhancement in fungi-like ZnO nanostructures

Abstract

Hybrid semiconductor nanostructures which integrate the favourable characteristics of both the component materials are found recently to be attractive candidate materials for research investigations having interesting optical properties. Considering the fact that the temperature of the materials used in photo-luminescent devices may vary while using them in a real device, it is essential to study the performances of such materials at variable temperatures. But the photoluminescence (PL) emission capabilities of such materials above room temperatures have not been well investigated, yet. However, in this work we have reported temperature dependent unusual PL emission characteristics of 2D nanosheets of ZnS/ZnO composite in the temperature range of 273–333 K. The composite sample has been produced by annealing the organic-inorganic ZnS(ethylenediamine)0.5 nanosheets, which are obtained by solvothermal technique. The as-synthesized nanosheets and another thermally annealed product of ZnO nanostructures showed usual thermally quenched PL emissions, whereas luminescence temperature anti-quenching (LTAQ) effect has been found in the ZnS/ZnO composite nanosheets. The PL emission intensity has been enhanced up to 242% with a small temperature variation of 60 K. The LTAQ effect has been explained by using the Berthelot-type model. It has been found that the diffused oxygen present in the composite nanostructures is acting as trap centre and played the major role in LTAQ effect. The analyses of time resolved PL emission spectroscopy data also confirmed the presence of oxygen trap level within the band gap of the material. Further, enhanced PL emission from the synthesized fungi-like ZnO samples has also been reported under the excitation of polarised ultraviolet light.