Influence of alloying on the optical properties of IV-VI nanorods

The synthesis and structural and optical characterization of PbSe _xS _1-x and PbSe/PbSe _xS _1-x nanorods with a diameter between 2 and 4.5 nm and a length of 10 to 38 nm is reported. The energy band gap of the nanorods exhibits a pronounced variation upon the change in diameter and composition, with a minor influence on lengths beyond 10 nm. The photoluminescence spectrum of the nanorods is composed of a dominant band, accompanied by a satellite band at elevated temperatures. The dominant band shows an exceptionally small band gap temperature coefficient and negligible extension of the radiative lifetime at cryogenic temperatures compared with the photoluminescence processes in PbSe nanorods and in PbSe _xS _1-x quantum dots with similar band gap energy. A theoretical model suggests the occurrence of independent transitions from a pair of band-edge valleys, located at the L points of Brillouin zone, related to the dominant and satellite emission processes. Each valley is four-fold degenerate and possesses a relatively small electron-hole exchange interaction.