Effects of nanocrystal shape and size on the temperature sensitivity in Raman thermometry

The effects of CdSe nanocrystal (NC) shape and size on the temperature sensitivity of the Raman shift have been investigated, for the interest of Raman thermometry using NCs. For spherical CdSe NCs of diameters 2.8 nm, 3.6 nm, and 4.4 nm, the temperature sensitivities are -0.0131 cm(-1)/K, -0.0171 cm(-1)/K, and -0.0242 cm(-1)/K, respectively. This trend indicates that as the diameter increases, the effect of increasing phonon anharmonicity dominates over the effect of the decreasing thermal expansion coefficient. On the other hand, triangular NCs with a size of 4.2 nm and elongated NCs of a dimension of 4.6 nm by 14 nm show temperature sensitivities of -0.0182 cm(-1)/K and -0.0176 cm(-1)/K, respectively. This trend indicates that in non-spherical shape NCs, the effect of decreasing thermal expansion coefficient dominates over the effect of slightly increasing phonon anharmonicity. The selection of NCs for Raman thermometry should depend on the specific requirements of temperature sensitivity, spatial resolution, and response time. (C) 2013 AIP Publishing LLC.