Temperature dependence of electronic energy transfer in PbS quantum dot films

Colloidal PbS quantum dots dispersed as close-packed film and in polystyrene (PS) matrix are prepared and photoluminescence (PL) spectra are measured in the temperature range of 5-300 K. The integrated PL intensity of the close-packed film increases as the temperature is raised from 5 to 120 K, and then decreases to 300 K, while that of the PS film decreases monotonously. This abnormal behavior of the close-packed film can be explained by a thermally activated electronic energy transfer model, which is supported by time resolved PL measurements.