InP nanocrystals via surfactant-aided hydrothermal synthesis

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In the presence of surfactant, potassium stearate, quantum-confined InP nanocrystals (NCs) were hydrothermally synthesized in aqueous ammonia. Powder x-ray diffraction (XRD) patterns give the zinc blende phase of InP with lattice constant a=5.8377±8×10−4 Å. Transmission electron microscopy (TEM) micrographs show that the as-prepared InP NCs are spherical secondary particles (120 nm) consisting of spherical nanocrystals and rod-like nanocrystals grown in the direction perpendicular to the [111] direction, which is different from those grown by solution–liquid–solid process. X-ray photoelectron spectra indicate that the nanocrystals have a stoichiometric ratio of In:P=1.2:1 and their surfaces are capped with stearate ions. Powder XRD, TEM images, Raman spectra, optical absorption and photoluminescence spectra of InP NCs grown with surfactant were compared with those of the InP NCs grown without surfactant, and it indicated that the as-prepared InP NCs via surfactant-aided synthesis are quantum confined: their transverse optical and longitudinal optical vibration modes exhibit frequency redshifting and asymmetric broadening which is consistent with the phonon confinement model of nanoparticles. Compared with bulk values, InP NCs exhibit a band-edge emission band centered at 1.81 eV (685 nm) with a blueshift of 0.44 eV at 300 K. A wide distribution in size and the two-morphology nature of the NCs resulted in featureless absorption spectra and broadening of the emission band. The formation mechanism of the InP NCs is discussed and attributed to an in situ decomposition process of an indium polyphosphide amorphous precursor.