Mn²⁺-doped Zn–In–S quantum dots with tunable bandgaps and high photoluminescence properties

Abstract

In the present work, we reported the synthesis of Mn 2+ -doped Zn-In-S quantum dots (QDs) with high optical performance in a controlled manner. The effects of the temperature, the introduced ODE-S amount and Zn/In ratios in the raw materials, as well as the Mn 2+ doping concentrations on the photoluminescence (PL) properties of Mn 2+ -doped Zn-In-S QDs were investigated systematically. The resultant QDs exhibit tunable bandgaps ranged from 2.9 to 3.7 eV, well-resolved Mn 2+ d-d emission with a PL quantum yield (QY) of 56 % and a surprisingly long excited state lifetime up to ~4.2 ms, suggesting their excellent PL properties. Meanwhile, the initial high PL QY of the obtained Mn 2+ -doped Zn-In-S QDs in organics solvent could be preserved very well once they were transferred into aqueous media via ligand exchange. Furthermore, the as-synthesized QDs exhibit an excellent thermal stability up to 200 o C in a crude solution.. desired to develop cadmium-free alloy QDs with tunable bandgaps to meet the versatile applications.As a typical II-III-VI semiconductor, the "green" chalcogenide Zn-In-S materials have been extensively applied in catalysis, charge storage, and thermoelectric energy conversion, due to its high chemical stability and composition tunable optical bandgaps. 23-25 Furthermore, Shen et al pointed out that doping transition metals such as Cu, Mn into ZnIn 2 S 4 host could further improve their photocatalytic activity. 26,27 However, to date, most reported works were mainly focused on the Zn-In-S microcrystalline, suggesting that there remain material-and fabrication-related obstacles to obtain the small and uniform Zn-In-S QDs. 23, 25, 28 Until recently, Peng et al reported the growth of ZnIn 2 S 4 QDs with tunable sizes ranged from 2.1 to 9.2 nm and a high photocatalytic activity. 28 More recently, Zhang et al reported the optical properties of Cu doped Zn-In-S QDs, showing a high PL quantum yield (QY)and a composition-tunable PL emission over the entire visible spectral window and extending to the near-infrared spectral range. 29 However, to the best of our knowledge, little attention has been paid to the Mn 2+ -doped Zn-In-S NCs.Herein, we reported the growth of cadmium-free Mn 2+ -doped Zn-In-S QDs with high PL via a multi-step hot-injection strategy. The influences of various experimental variables on the growth and PL of the QDs, including the nucleation temperatures for the Mn:ZnInS core nanocluster, the amount of octadecene ODE-S, the Zn/In ratios, as well as Mn 2+ dopant concentration-dependent optical properties, 14 PL intensities increase rapidly and approach the highest one at ODE-S of 0.2 mmol, and then reduce with the further increase of ODE-S. In principle, when the S precursor is used in large excess, the cationic precursor should be consumed rapidly, and small-sized stable Mn:ZnInS nanoclusters would be the resultant products. On the other hand, the presence of additional excessive amount of ODE-S may result in the S-rich surface of the obtained Mn 2+ -doped Zn-In-S QDs, which allows the...

Robust and Stable Ratiometric Temperature Sensor Based on Zn–In–S Quantum Dots with Intrinsic Dual‐Dopant Ion Emissions

“…The Cu 2p spectrum splits into 2p3/2 (932.2 eV) and 2p1/2 (952.2 eV) peaks (Figure b), which are in good accordance with those reported in literatures, indicating that the Cu valence state in the Zn–In–S QDs is +1 . Similarly, the Mn 2p spectrum ( Figure c) splits into two peaks at 654.2 and 641.9 eV, implying that the Mn valence state is +2 . Figure d shows the typical In 3d spectrum, in which the strong peaks at 444.9 and 452.4 eV are assigned to the In 3d 3/2 and In 3d5/2, respectively, suggesting the In valence state is +3.…”

“…Figure b provides the representative UV–vis absorption and PL spectra of Cu and Mn codoped Zn–In–S QDs with various doping concentrations of Mn and Cu ions. As presented in Figure b, a broad absorption band is observed at ≈400 nm, which is similar to those in the previous works, and can be ascribed to the Zn–In–S host excitonic transition . The absorption spectra have no obvious sharp exciton absorption peak, which are related to both intrabandgap states and inhomogeneous composition distribution .…”

“…Now we come to the point about the PL mechanism of Cu and Mn codoped Zn–In–S QDs, which is the profound issue to realize the desired dual dopant emissions for the exploration of ratiometric temperature sensors. It is known that the host bandgaps of the QDs are dependent on Cu doping concentration, while the Mn ions emission can only be observed in the host with wide bandgap . In current case, the effect of Cu doping concentrations on the PL properties was investigated systematically to understand the exciton recombination mechanism in the Cu and Mn codoped Zn–In–S QDs, with a fixed Mn doping level of 2.5 mol%.…”

Curvature-dependent flexible light emission from layered gallium selenide crystals

“…chemical doping, [16][17][18] or by synthesizing the 2D semiconductors with different bandgaps. 4,13 Among those methods, strain engineering is more attractive and applicable when a exible optoelectronics device is under normally-operated condition.…”

Full‐visible spectrum emitting Zn–In–S:Cu/ZnS nanocrystals based on varying Cu concentrations and its application in white LEDs

“…According to previous reports, the dopant concentration also plays a vital role in the optical properties of d-NCs. [40][41][42] Thus, a series of Zn-In-S:Cu d-NCs samples with different nominal copper concentration (1%-40%) at same reaction condition were synthesized. Here, In/Zn was fixed at 1/1.…”