Controlling the Electronic Energy Structure of ZnS–AgInS₂ Solid Solution Nanocrystals for Photoluminescence and Photocatalytic Hydrogen Evolution

Abstract

Simultaneous control of the size and chemical composition is an advantageous strategy to obtain the desired photochemical properties of multinary semiconductor nanocrystals, ZnS-AgInS2 solid solution ((AgIn) x Zn2(1–x)S2, ZAIS) nanocrystals (NCs), being different from conventional binary nanocrystals. The energy gap (E g) of ZAIS NCs was enlarged with a decrease in particle size due to the quantum size effect or with an increase in ZnS content in the ZAIS solid solution. The levels of the conduction band edge and valence band edge, determined by photoelectron spectroscopy in air, were shifted more negatively and more positively, respectively, with an increase in E g. A volcano-type dependence was observed between the PL quantum yield (QY) and the size of ZAIS NCs, in which the optimal PL QY for each x value was obtained at a similar particle size around 5–6 nm, except for x = 1.0, and maximum QY was recorded to be 79% for ZAIS NCs prepared with x = 0.5. The photocatalytic activity for H2 evolution was also greatly dependent on both the size and the chemical composition of ZAIS NCs, and then the highest activity was observed for ZAIS NCs having an average diameter of about 4.2–5.5 nm and E g of 2.3–2.4 eV. This can be reasonably explained by the enlargement of the driving force to reduce protons in the solution with a negative shift of the conduction band edge of ZAIS NCs and by the quenching of photoexcited ZAIS NCs with an increase in the amount of surface defect sites and/or with the formation of deeper trap sites along with a decrease in the particle size.

Single-particle spectroscopy of I–III–VI semiconductor nanocrystals: spectral diffusion and suppression of blinking by two-color excitation

“…[1][2][3][4][5][6] Tunable band gap (E g ), large extinction coefficient and low toxicity make them potential alternatives to II-VI semiconductor NCs. As prepared NCs of AgInS 2 often show poor photoluminescence (PL) quantum efficiency.…”

Nanostructure Engineering of Size-Quantized Semiconductor Particles for Photoelectrochemical Applications

“…Figure 10a shows the time course of H 2 evolution of spherical ZAIS nanoparticles of x = 0.5 with different sizes. 50 With elapse of light irradiation time, the amount of H 2 evolved linearly increased, while the H 2 evolution rate (R(H 2 )) was remarkably dependent on particle size. The relationship between R(H 2 ) and particle size is shown in Fig.…”

“…One strategy is to regulate the reactivity of individual metal precursors by adding one or more kinds of surface modifiers, such as alkylamines and thiols, or by using a mixture of different metal salts as a precursor instead of a single precursor. 50 Thermal reaction of a mixture of corresponding metal acetates with thiourea was carried out in a mixture solution of OLA and 1-dodecanthiol (DDT) at 250°C, with the ratio of Ag + :In 3+ :Zn 2+ being fixed to x:x:2(1 ¹ x). The average size (d ave ) of ZAIS nanoparticles with x = 0.5 decreased from 8.5 to 3.9 nm with an increase of DDT concentration in the preparation from 0 to 8.7 vol%.…”

“…Similar optical tunability was observed for other kinds of Ag-based solid solution nanoparticles, Ag-In-Ga-S 51,52 and ZnCu-Ag-In-S particles. 53 Figure 9 shows E CB and E VB of multinary semiconductor nanoparticles as a function of E g , 50,54,55 determined by photoemission yield spectroscopy in air or by photoelectrochemical measurement. The electronic energy structure of ZAIS particles was significantly dependent on both their chemical composition and particle size.…”

“…The electronic energy structure of ZAIS particles was significantly dependent on both their chemical composition and particle size. 50 Even when either of these two parameters was modified, the potentials of E CB and E VB were shifted more negatively and more positively, respectively, with an increase in E g . Other multinary solid solution nanoparticles of ZnS-AgInSe 2 54 and ZnS-Cu 2 SnS 3 55 also exhibited similar changes in the electronic energy structure as a function of E g .…”