Preparation of Uncapped CdSe^sub x^Te^sub 1-x^ Nanocrystals with Strong Near-IR Tunable Absorption

Semiconducting nanocrystals with near-infrared (NIR) photosensitivity are appealing materials for application as photodetectors and in medical diagnostics. Herein, we report the preparation of composition-tunable, uncapped CdSe^sub x^Te^sub 1-x^ (x = 0 to 1) nanocrystals by simple mechanical alloying. The resulting ternary CdSe^sub x^Te^sub 1-x^ (x = 0.25, 0.5, 0.75) nanocrystals with average sizes smaller than 10 nm have zincblende crystal structure, instead of the wurtzite structure commonly obtained by wet chemical routes, and show strong NIR absorption even beyond 1400 nm. While a linear relationship between the lattice parameter and the chemical composition (Se/Te ratio) is observed, indicating the formation of homogeneous alloys, the bandgap energy of the three ternary samples is found to be substantially lower than that of binary CdSe or CdTe nanocrystals, and lower than any ternary CdSeTe reported so far. Existence of a small number of tellurium metal defects in the CdSe^sub x^Te^sub 1-x^ (x = 0.25, 0.5, 0.75) nanocrystals is confirmed by x-ray diffraction and Raman spectroscopy. Both the optical bowing effect and tellurium metal-induced defects of the mechanically alloyed samples are believed to cause the strong NIR photosensitivity.[PUBLICATION ABSTRACT]