Temperature Dependence of Raman and Photoluminescence Spectra of Ternary Alloyed CdSe 0.3 Te 0.7 Quantum Dots

The Raman and photoluminescence spectra of ternary alloyed CdSe 0.3 Te 0.7 quantum dots (QDs) have been studied at temperatures between 84 K and 293 K. The average diameter of QDs is about 5.1 nm. The temperature dependence of the longitudinal optical (LO) phonon frequencies and the phonon band width was analyzed and the anharmonic constants relating to various high-order phonon processes was determined. While the three-phonon processes plays a dominant role in the temperature-dependent shift of the LO-phonon frequencies, the four-phonon processes contribute to the increase of the phonon linewidth with increasing temperature. The photoluminescence (PL) spectra were used to study the temperature dependence of the bandgap, the linewidth and the integrated PL intensity. At low temperatures below about 120 K, the PL linewidth decreases and the PL intensity increases as temperature increases. This temperature behavior can be ascribed to the exciton fine structure.