Chalcopyrite-type CuInS 2 -based alloyed fluorescent nanocrystals (NCs), which contain no regulated heavy metal ions, were synthesized by heating an organometallic solution to demonstrate optical property tunability. Introduction of Zn into the CuInS 2 system enhanced their photoluminescence (PL) intensity. The resultant particles were 3-6 nm; they varied with experimental conditions and were discrete and colloidally stable. The band-gap energy and PL wavelength of Zn-Cu-In-S (ZCIS) NCs varied with Zn content and particle size. Their PL was controllable within 570-800 nm by altering the band-gap energy. Furthermore, indium substitution with gallium was shown to control band-gap energy toward ∼3.1 eV, 500 nm of PL wavelength. In addition, ZnS coating of this nanocrystal can approximately double the PL strength. Finally, surface treatment with mercaptoundecanoic acid dispersed hydrophilic ZCIS NCs into water.

The size dependent optical band gap of the less-toxic ternary I-III-VI2 chalcopyrite-type semiconductor quantum dots (QDs), CuInS2, CuInSe2, CuGaS2, CuGaSe2, AgInSe2, AgGaS2, and AgGaSe2, were evaluated using the finite-depth-well effective mass approximation calculation. From the comparison of the calculation result with the experimental values for the CuInS2 case, it was shown that the calculation was highly valid to predict the size dependent optical gap of the ternary semiconductor QDs. The optical band gap of the above seven I-III-VI2 QDs covers a wide wavelength range from the near-infrared to ultraviolet. It has been shown that the I-III-VI2 semiconductor QDs have a significant potential as alternatives to the highly toxic cadmium-containing II-VI semiconductor QDs and they are applicable to the wide range of light emitting devices and solar cells.

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.