Controlled Synthesis and Optical Properties of Colloidal Ternary Chalcogenide CuInS2 Nanocrystals

Abstract

A facile method for the synthesis of size- and shape-controlled CuInS 2 semiconductor nanocrystals was developed by thermolysis of a mixed solution of CuAc, In(Ac) 3 (molar ratio of CuAc to In(Ac) 3 = 1:1) and dodecanethiol in noncoordinating solvent 1-octadecene (ODE) at 240 °C. CuInS 2 nanoparticles with size of 2 to ∼5 nm and nanorods with aspect ratio of 1 to ∼3 were obtained by adjusting the reaction parameters such as temperature and time. The as-prepared nanoparticles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, selected area electron diffraction spectroscopy, inductively coupled plasma atomic emission spectroscopy, UV−vis absorption, and photoluminescence (PL) spectroscopy. The nanoparticle solutions exhibit tunable absorption and PL spectra with the absorption edge ranging from 550 to 750 nm and PL emission peaks from 600 to 750 nm, indicating a strong size-dependent quantum confinement effect. Optical measurements of the CuInS 2 nanoparticles demonstrated that their optical properties are related to donor−acceptor defects, size-dependent quantum confined effects, and surface defects. The PL decay curve of CuInS 2 nanoparticles has a triple exponential characteristic with lifetimes of 4−12, 28−60, and 140−300 ns, respectively, and the PL emission with the longest lifetime (140−300 ns) occupied 40−80% of the PL emission of the samples. These results imply that the room-temperature PL emission of CuInS 2 nanoparticles involves three types of recombination: band exciton recombination, surface-related recombination, and donor−acceptor defects recombination. Among them, the PL emission from donor−acceptor defects occupied a large amount.