Colloidal CuInS 2 nanocrystals were synthesized in a hot organic solvent containing surfactant molecules. The CuInS 2 phase was controlled by the ligand species of the metallic monomers. When the metallic monomers were coordinated with trioctylphosphite, the resulting CuInS 2 had a chalcopyrite or zincblende phase. When the metallic monomers were coordinated with hexadecylamine or oleylamine, the thermodynamically metastable wurtzite phase appeared. The experimental results indicated that the obtained phase was predominantly determined by the growth rate of the nanocrystals. The bond strength between the metallic monomers and ligand molecules and steric size of the ligand molecules influenced the growth rate. The CuInS 2 nanocrystals showed photoluminescence in the near-infrared region. Its energy was far from the optical energy band gap; the luminescence was attributable to the electron-hole recombination via deep defect levels. In the photoluminescence spectrum of the CuInS 2 /ZnS core/shell nanocrystals, a band near the optical energy band gap, whose Stokes' shift was ∼50 meV, appeared. The band was suggested to be attributable to the defect-related emission from CuInS 2 -ZnS alloy formed at the interfaces between the core CuInS 2 and shell ZnS.

Chalcopyrite-type CuInS 2 NCs was synthesized by the hot-soap method. Mixed solutions, CuI and InCl 3 dissolved in the mixture of the tri-octylphosphite and 1-octadecene and the sulfur dissolved in tri-phenylphosphite, were used as source solutions; the hexadecylamine was additionally mixed as a surfactant before the reaction. It was observed that the product CuInS 2 NCs structurally transformed from the chalcopyrite(CP)-or zincblende(ZB)-to the wurtzite(WZ)-type depending on the amount of the surfactant and a storage time after the surfactant addition. Very weak photoluminescence in the nearinfrared region was observed for the CP-or ZB-type NCs. This band was attributable to the electronhole recombination via defect levels. No photoluminescence was detected for the wurtzite-type NCs.ternary I-III-VI 2 semiconductor, CuInS 2 , nanocrystal, structure transformation, photoluminescence Single nanometer-sized semiconductors, so-called semiconductor nanocrystals (NCs) have attracted much attention because of their unique properties depending on crystal size. The widening of energy band gap with decreasing crystal size is one of the remarkable properties. For the CdSe, which possess direct transition and 1.76 eV of energy band gap, the emission derived from the exciton recombination shifted from red to blue-green with decreasing crystal size from 5 nm to 3 nm [1] . Because the excitonic emission is essentially bright, it is expected that the semiconductor NCs are applied to flat panel displays and bio tags as phosphor materials. However, because the CdSe is extremely toxic, it is difficult to use for the practical applications. The development of semiconductor NCs applicable to practical use is necessary.Chalcopyrite-type (CP-type) CuInS 2 is a direct transition semiconductor with 1.54 eV energy band gap and consists of lower toxic elements. There are a few reports about the synthesis of CuInS 2 NCs [2][3][4][5][6] . According to these studies, highly crystallized CuInS 2 NCs enough to be observed excitonic emission have not been obtained.In the present study, we have developed a novel synthesis method of colloidal CuInS 2 NCs based on pyrolysis of organometallic complexes in organic solvent with a surfactant. During the synthesis, we observed a crystal structural transformation depending on the amount of the additional surfactant and a preserved time after the surfactant addition. We discuss the effect of the surfactant hexadecylamine in the formation reaction of CuInS 2 NCs and their luminescence properties.