In this work, transition metal ion- doped zinc-based quantum dots (QDs) are synthesized via a greener controllable method to avoid the toxicity of the traditional cadmium-based QDs and broaden the tunable emission. Herein, the tunable emission of Cu-doped ZnInS/ZnS core-shell QDs (Cu:ZnInS/ZnS) can cover from 500 to 620 nm by varying the Cu dopant concentration from 1 to 20% and the maximum quantum yield can reach 49.8%. Based on the single-doped QDs, Cu,Mn co-doped ZnInS/ZnS core-shell QDs (Cu,Mn:ZnInS/ZnS) with a photoluminance (PL) quantum yield of 30.4% are obtained. All the as-synthesized QDs have the zinc blende structure and the average size is about 3.55 nm. Besides, the interaction mechanism between the Cu and Mn dopant luminescence centers is proposed in this work, which is rarely investigated in the previous report. Diffusion priority and energy transfer between these two dopants are supposed to play an important role in the co-doped QDs and Cu ions could affect the splitting of Mn d states. Color coordinates of these doped QDs show the line-tunability from (0.200, 0.397) to (0.408, 0.508) on the Commission Internationale de L'Eclairage (CIE) chromatic diagram, showing a promising potential in high-quality white light output by integration of these QDs with blue chips.
Development of tunable-emission solid fluorescent materials remains a challenge due to tedious synthesis strategies. Polymorphism plays a critical role in tuning solid state photophysical properties of crystalline materials. In this work, tunable emission of organic fluorescent crystals was achieved through polymorphic manipulation. The X-shaped tetrasubstituted molecule 2,5-bis(5-methyl-2-thienyl) terephthalaldehyde was synthesized as a model compound, which is pH insensitive and has large Stokes shifts. It adopts an extended conjugated system and enhanced conformational flexibility and occupies an intercrossed excited state of charge-transfer (CT) and local excitation (LE). Two polymorphs were prepared by controlling the cooling rate. The polymorphism-dependent emission and the interconversion between Form I (530 nm) and Form II (570 nm) provide an opportunity to unveil the inherent mechanism of different emission and the possible relationship between structure, packing, and function. With the incorporation of X-ray photoelectron spectroscopy, solid-state 13C NMR spectra, crystal structure analysis, and computational simulation, the dissimilar molecular structure and packing modes were intuitively and systematically investigated. Noncovalent interaction (NCI), atoms in molecules (AIM) approaches, and Hirshfeld surface analysis were used to further explain the fluorescence tuning from both different molecular packing modes and intermolecular interactions. The results demonstrated that electron delocalization degree and overlap of adjacent aromatic systems were responsible for the dissimilar photophysical properties.
Indium-rich environmentally-friendly quantum dots (QDs) have received widespread attention due to the absence of cadmium. In this paper, AgInS2 (AIS) QDs are synthesized by hot injection method. By adjusting the ratio of indium/silver (In/Ag = 1, 2, 3, 4, 5), the AIS QDs exhibit a blue shift from 868 nm to 603 nm with the indium composition increases. Therein, the AIS QDs with the ratio of In/Ag = 4 show a highest photoluminescent (PL) quantum yields (QYs) up to 57%. AIS QDs are coated with ZnS shell to passivate the surface defects, and the PL QYs of obtained core/shell AIS/ZnS QDs is increased to 72%. By using these AIS/ZnS QDs as light emitters, light emitting diodes are assembled with a stacked multi-layer structure ITO/PEDOT:PSS/Poly-TPD/QDs/ZnO:Mg/Al. The resulted electroluminescent (EL) device exhibits a maximum external quantum efficiency (EQE) of 1.25% and an open circuit voltage of 4.6 V corresponding to a maximum brightness of 1120 cd m−2. Although the performances of the as fabricated AIS/ZnS-based device lag much behind than those of the Cd-based ones, they are expected to be enhanced with much more studies on the synthesis of the QDs and the optimization of device structure.
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