Synthesis temperature-dependent optical properties of ZnS-shell formation on InP nanoparticles

In this work reports the controlled synthesis and physical property characterization of nanoparticles of InP/ZnS type with core/shell structure obtained by the colloid chemistry method called "single-step procedure without precursor injection" at different synthesis temperatures. Varying the reaction temperature from 100 to 320 °C was possible to control the formation of the ZnS-shell on InP nanoparticles. Colour changes in the colloid dispersions were clearly observed according to the reaction temperature. The InP/ZnS nanoparticles chemical stoichiometry was determined by Energy-dispersive X-ray spectroscopy, demonstrating that with the increase of the reaction temperature the particles are obtained with a better stoichiometric ratio. The X-ray-diffraction analysis reveals that InP/ZnS nanoparticles showed zinc blende crystalline phase that was confirmed by High-resolution transmission electron microscopy. The average particle sizes (2-10 nm) were estimated by the Wang equation, which are confirmed analysing the grain average diameter by transmission electron microscopy measurements. The particles sizes indicate a high quantum confinement because of they are lower than the Bohr excitonic radius of InP. The obtained semiconductor nanoparticles presented crystalline structure InP-core/ZnS-shell, uniformity in size and exhibit a dependence of emission in the range of 450-650 nm measured by UV-Vis spectroscopy, which allowed obtaining the band gap of the nanostructures. The value of the bandgap could be tuned from 3.73 to 2.38 eV through the variation of the synthesis temperature. The emission peak in InP core quantum dots varied as a function of quantum dots size, ranging in the 2.61-2.17 eV region. The InP/ZnS nanoparticles present a high passivation for samples synthetized at 300 °C.