Optical properties of PbS nanocrystal quantum dots at ambient and elevated pressure.

We investigated pressure-dependent changes in the optical properties of PbS nanocrystal quantum dots (NQD) by combining X-ray scattering and optical absorption spectroscopy in a diamond anvil cell. We discovered that the excitonic absorption peak vanishes as the NQD crystal structure reversibly undergoes the pressure-induced phase transition from rock-salt to orthorhombic structure. In the rock-salt phase, the pressure coefficient ∂E(g)/∂P of PbS NQD is negative and decreases in magnitude with decreasing NQD size.