The structural transition behavior of CdSe/ZnS core/shell quantum dots under high pressure

The structural phase transition of CdSe/ZnS core/shell quantum dots (QDs) has been studied by in situ angle-dispersive X-ray diffraction under high pressure up to 53.6 GPa. The CdSe core transforms from wurtzite to rock-salt structure near 6.3 GPa and then to Cmcm or distorted Cmcm structure probably occurs at 45.1 GPa which has not been observed in CdSe nanomaterials before. The critical pressure from wurtzite to rock-salt and the bulk modulus of rock-salt phase are much higher than those for bulky and uncapped nanoparticle CdSe. The released sample can be kept in rock-salt phase for a certain time, verified by photoluminescence (PL) spectra, quite different from the reversible transition for pure CdSe. A reasonable interpretation of the experimental phenomena is given by comparing the bulk modulus of the core and shell and studying the stress sate of the core after decompression. Our study suggests that capping a hard shell is an effective approach to quench the high pressure phase of nanomaterial with a reversible phase transition. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim