Multinary semiconductor quantum dots (QDs) composed of low toxic elements have been intensively investigated as an alternative to conventional binary Cd- and Pb-based QDs. Recently, we reported that colloidally synthesized Ag-In-Ga-Se (AIGSe) QDs exhibited a sharp band-edge emission peak (fwhm = 100 ~ 200 meV), the wavelength of which was tunable in near-IR wavelength region from ca. 680 to 900 nm by changing the In/Ga ratio in QDs.¹ However the optimum photoluminescence quantum yield (PL QY) was moderate, 14%, even after removing the surface defects by coating of AIGSe cores with GaS_x shell (AIGSe@GaS_x). In this study, we focused on the water content in the reaction solvent, which was recently reported to affect the formation of surface defects in PbS QDs². The formation of GaS_x shell layer in the presence of a small amount of water increased the PL QY of AIGSe core without changing the PL peak shape.
AIGSe QDs were prepared by the thermal decomposition of corresponding metal salts and selenourea in a hot organic solvent. Thus-prepared AIGSe QDs used as a core and the precursors of Ga(acac)₃ and selenourea for GaS_x shell were dissolved in oleylamine (OLA) containing a small amount of water, followed by heating at 300 ^oC. The content of water in OLA was controlled in the H₂O/Ga³⁺ between 0.06 and 20.
The average size of AIGSe@GaS_x QDs was almost constant at 5.7 nm, regardless of the water content. A sharp band-edge PL peak appeared at 800 nm and the PL intensity varied depending on the H₂O/Ga³⁺ratio in preparation. The PL QY showed a volcano-type dependence on the H₂O/Ga³⁺ ratio, in which the maximum value of 30 % was obtained at H₂O/Ga³⁺ = 0.2. Furthermore, by treating the optimized QDs with trioctylphosphine, we were able to remove the remaining surface defects to increase the PL QY to 62%.
[1] T. Kameyama, et al., ACS Appl. Nano Mater. 2020, 4, 32750. [2] D. Zherebetsky, et al., Science. 2014, 344, 1380.

Chisato Muto

Appearances