Synthesis of Quaternary Semiconductor Nanocrystals with Tunable Band Gaps

Dispersible quaternary Cu1.0GaxIn2-xS3.5 and Cu1.0InxTl2-xS3.5 nanocrystals were successfully prepared by a toluene-thermal and a hot-injection approach and characterized using UV-vis spectroscopy, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). UV-vis absorption spectra of Cu1.0GaxIn2-xS3.5 nanocrystals revealed that the band gaps of alloyed nanocrystals can be precisely adjusted in the range of 1.43 to 2.42 eV by increasing the indium content. From XRD analysis, the lattice parameters of Cu1.0GaxIn2-xS3.5 nanocrystals decreased linearly with an increase in the Ga/(Ga + In) ratio in accordance with Vegard's law, which confirmed that alloyed nanocrystals have a homogeneous structure. Alloyed Cu1.0GaxIn2-xS3.5 and Cu1.0InxTl2-xS3.5 nanocrystals have a narrow size distribution according to TEM analysis results. Moreover, it was found that oleylamine played an important role in the formation quaternary homogeneous Cu1.0GaxIn2-xS3.5 and Cu1.0InxTl2-xS3.5 nanocrystals due to eliminating the reactivity difference of copper, gallium, and indium as well as thallium precursors.