Two temperature-dependent energy transfers in CdTe nanocrystal films

In order to obtain the influence of two temperature-dependent energy transfers (the one Energy Transfers (ET) from band edge to defect states in one nanocrystal and the other energy transfers from different size nanocrystals) on fluorescence emission intensity of CdTe nanocrystals, the fluorescence emission spectra of CdTe nanocrystals films at temperature from 78 to 300 K were investigated. The results of the experiment show that the fluorescence emission spectra of CdTe nanocrystals films exhibit band edge emission centered at about 520 nm and defect fluorescence emission centered at about 605 nm, and the fluorescence intensity presents different change regularity with temperature increasing. At the first stage of temperature(78~140 K), for the green-emitted CdTe NCs, large size ones have fewer defect sites and the fluorescence emission efficiency is higher than the small size ones. The energy transfers from small size ones to large, resulting in increasing of the band edge fluorescence emission intensity. At the second temperature stage(140~300 K), the defect and band edge fluorescence emission intensity gradually decreases. Therefore, the ET rates with temperature are prominent at the first stage of temperature and subordinate at the second temperature stage, compared to the nonradiative recombination rates. To further prove the influence of ET on the fluorescence emission intensity, the CdTe NC films were dried under vacuum conditions, which could avoided the atmospheric oxidation and therefore had fewer defects on the NCs surface. CdTe NCs were put in PEG matrix film in order to reduce the ET rates from different size nanocrystals. Fluorescence emission intensities of as-prepared CdTe NC films were decreased with temperature at the first stage and coincided with the variations of ET rates with temperature. ©, 2015, Chinese Optical Society. All right reserved.