Considering a strict global environmental regulation, fluorescent quantum dots (QDs) as key visible emitters in the next-generation display field should be compositionally non-Cd. When compared to green and red emitters obtainable from size-controlled InP QDs, development of non-Cd blue QDs remains stagnant. Herein, we explore the synthesis of non-Cd, ZnSe-based QDs with binary and ternary compositions toward blue photoluminescence (PL). First, the size increment of binary ZnSe QDs is attempted by a multiply repeated growth until blue PL is attained. Although this approach offers a relevant blue color, excessively large-sized ZnSe QDs inevitably entail a low PL quantum yield. As an alternative strategy to the above size enlargement, the alloying of high-band gap ZnSe with lower-band gap ZnTe in QD synthesis is carried out. These alloyed ternary ZnSeTe QDs after ZnS shelling exhibit a systematically tunable PL of 422–500 nm as a function of Te/Se ratio. Analogous to the state-of-the-art heterostructure of InP QDs with a double-shelling scheme, an inner shell of ZnSe is newly inserted with different thicknesses prior to an outer shell of ZnS, where the effects of the thickness of ZnSe inner shell on PL properties are examined. Double-shelled ZnSeTe/ZnSe/ZnS QDs with an optimal thickness of the ZnSe inner shell are then employed for all-solution-processed fabrication of a blue QD light-emitting diode (QLED). The present blue QLED as the first ZnSeTe QD-based device yields a peak luminance of 1195 cd/m2, a current efficiency of 2.4 cd/A, and an external quantum efficiency of 4.2%, corresponding to the record values reported from non-Cd blue devices.

We explore both the synthesis of Cd-free blue quantum dots (QDs) with high-quality photoluminescence (PL) characteristics and the fabrication of high-efficiency QD light-emitting diodes (QLEDs). True blue (445 nm)-emissive, multishelled ZnSeTe QDs with a high PL quantum yield of 84% and a sharp bandwidth of 27 nm are prepared. To obtain a better electron transport layer (ETL) material, the surface of ZnMgO nanoparticles (NPs) is modified by additional Mg reaction, leading to the possible formation of a Mg­(OH)2 layer on the surface-modified ZnMgO (m-ZnMgO) NPs. The presence of a Mg­(OH)2 overlayer, the origin of the desirably reduced electron mobility, is supposedly responsible for the improved charge balance of the QD emissive layer (EML). The Mg­(OH)2 layer is further found to alleviate the emission quenching of the QD EML. Via combination of blue ZnSeTe QDs and m-ZnMgO NP ETL, highly bright, efficient blue QLEDs with the record luminance of 2904 cd/m2 and an external quantum efficiency of 9.5% are demonstrated.

Indium phosphide (InP) has been regarded as the most promising composition of visible quantum dot (QD) emitters for the application to next-generation display devices primarily because of its environmental benignity. Bright, sharp emissivity of InP QDs should be pursued for the realization of high-efficiency, wide-color gamut display devices. Photoluminescence (PL) performance of InP QDs has been greatly improved based on synthetic advances enabling the securement of core size homogeneity and the formation of exquisite core/shell heterostructure. Until now, high-quality fluorescent InP QDs have been attainable exclusively through the use of a hazardous phosphorus (P) precursor of tris(trimethylsilyl)phosphine ((TMS) 3 P) against green chemistry. In this work, we report a synthetic breakthrough of green InP QDs toward narrow, bright emissivity by using a much cheaper, safer P alternative of tris(dimethylamino)phosphine ((DMA) 3 P). For this, QD synthesis proceeds via a so-called two-step approach, where as-grown InP cores are subjected to a stepwise size fractionation process and then placed in the consecutive double shelling of a composition-gradient ZnSe x S 1−x inner and a ZnS outer shell. The chemical composition (x) of the ZnSe x S 1−x inner shell in the range of 0.09−0.36 is varied to explore its effects on PL quantum yield (QY), size, and blue excitation light absorptivity. Because of the effective core size fractionation and elaborately designed heterostructure, the resulting InP/ZnSe x S 1−x /ZnS QDs exhibit exceptional green (527 nm) PL features of a sharp line width of 37 nm and a high PL QY of 87%, which have not been achievable to date from non-(TMS) 3 P-based QDs, when an optimal inner shell composition is applied.

On the basis of bluish-emitting double-shelled quantum dots (QDs) of Zn–Cu–Ga–S (ZCGS)/ZnS/ZnS, Mn doping into ZCGS host with different Mn/Cu concentrations is implemented via surface adsorption and lattice diffusion. The resulting double-shelled Mn-doped ZCGS (ZCGS/Mn) QDs exhibit a distinct Mn2+ 4T1–6A1 emission as a consequence of effective lattice incorporation simultaneously with host intragap states-involving emissions of free-to-bound and donor–acceptor pair recombinations. The relative contribution of Mn emission to the overall photoluminescence (PL) is consistently proportional to its concentration, resulting in tunable PL from bluish, white, to reddish white. Regardless of Mn doping and its concentration, all QDs possess high PL quantum yield levels of 74–79%. Those undoped and doped QDs are then employed as an emitting layer (EML) of all-solution-processed QD-light-emitting diodes (QLEDs) with hybrid charge transport layers and their electroluminescence (EL) is compared. Compared to undoped QDs, doped analogues give rise to a huge spectral disparity of EL versus PL, specifically showing a near-complete quenching of Mn2+ EL. This unexpected observation is rationalized primarily by considering unbalanced carrier injection to QD EML on the basis of energetic alignment of the present QLED and rapid trapping of holes injected at intragap states of QDs.

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In contrast to a substantial progress of heavy metal-free green and red emitters exclusively from indium phosphide (InP) quantum dots (QDs), the development of non-Cd blue QDs remains nearly unexplored. The synthesis of blue InP QDs with a bright, deep-blue emissivity is not likely viable, which is primarily associated with their intrinsic size limitation. To surmount this challenge, herein, the first synthesis of blue-emissive ternary InGaP QDs through In3+-to-Ga3+ cation-exchange strategy is implemented. Pregrown InP QDs turn out to be efficiently Ga-alloyed at a relatively low temperature of 280 °C in the presence of Ga iodide (GaI3), and the degree of Ga alloying is also found to be systematically adjustable by varying GaI3 amounts. Such cation-exchanged InGaP cores are surface-passivated sequentially with ZnSeS inner and ZnS outer shells. As the amount of GaI3 added for cation exchange increases, the resulting double-shelled InGaP/ZnSeS/ZnS QDs produce consistent blue shifts in photoluminescence (PL) from 475 to 465 nm, while maintaining high PL quantum yield in the range of 80–82%. Among a series of QD samples, above 465 nm emitting InGaP/ZnSeS/ZnS QDs are further employed as an emitting layer of an all-solution-processed electroluminescent device. This unprecedented InGaP QD-based blue device generates maximum values of 1038 cd/m2 in luminance and 2.5% in external quantum efficiency.

Last decade witnessed great advancement in the photoluminescent (PL) quality of visible III–V InP quantum dots (QDs) toward bright, sharp emissivity. Now, InP QDs hold an unrivaled position in the field of next-generation display devices. In an effort to offer non-Cd green QDs as potential alternatives to InP counterparts, in this work, the first viable synthesis of II–VI ternary ZnSeTe QDs is explored. After successful growth of ZnSeTe alloy cores enabled by a balanced precursor reactivity of anions (i.e., Se and Te), sequential triple shells of ZnSe/ZnSeS/ZnS with stepwise type-I energetic potentials are formed. The resulting heterostructured ZnSeTe/ZnSe/ZnSeS/ZnS QDs produce tunable PL wavelengths of 495–532 nm along with high PL quantum yields (QY) of 68–83%, depending on a Te/Se feed molar ratio used for core synthesis. To further evaluate performance of the present ZnSeTe QDs as electroluminescent (EL) emitters, the first fabrication of a solution-processed, multilayered green QD-light-emitting diode (QLED) by adopting Te/Se = 0.28-based triple-shelled QDs with a PL peak of 520 nm and QY of 80% is demonstrated. This device produces promising EL outcomes up to 18 420 cd/m2 in luminance and 7.6% in external quantum efficiency, outperforming most of green InP QLEDs reported to date.

band gap (E g ) of 1.35 eV (at 300 K) and excitonic Bohr radius of 9.6 nm can afford most part of visible colors by means of size-mediated quantum confinement effects. Typical InP core sizes for green and red color are 2.2 ± 0.2 and 3.6 ± 0.2 nm, respectively, although the final PL wavelength becomes sensitively dependent on core/shell heterostructural details. Meanwhile, synthesis of highquality blue-emitting InP QDs is relatively challenging, being associated with their tiny core sizes well below 2 nm, usually resulting in only quasi-blue color (>475 nm in PL peak) beyond deep-blue territory (450−465 nm). [4,5] Therefore, InP QDs are regarded as the strongest candidates for green and red color, while blue emitters can be pursued from either ternary InGaP [6] or non-InP ZnSeTe QDs. [7][8][9] Earlier synthesis of InP QDs was implemented with a primitive heterostructure mostly based on single ZnS shell. Despite a great deal of effort toward bright, sharp emissivity, the resulting single-shelled InP/ ZnS QDs yielded only moderate PL outcomes (e.g., <80% in PLQY, >45 nm in FWHM). [10][11][12] Such limited PL performances are unambiguously ascribable to the substantial interfacial strain developed from a large InP−ZnS lattice mismatch (7.7%), which in turn not only prevents the formation of misfit defectfree, perfect heteroepitaxial interface but limits the shell growth to an extended thickness. Thus, notable improvements in PL could be achieved by inserting a larger-lattice constant inner shell (relative to ZnS) prior to ZnS outer shelling, enabling the effective alleviation of the interfacial strain. The common inner shell compositions are GaP, [13,14] alloyed or compositiongradient ZnSeS, [15][16][17][18][19] and ZnSe, [20][21][22][23][24] all of which are intermediate in lattice constant between InP and ZnS, while providing a stepwise type-I electronic band alignment in overall doubleshelled heterostructure. When GaP interlayer was generated via either cation exchange or direct overgrowth, the resulting InP/GaP/ZnS QDs exhibited 40−85% in PLQY and 41−64 nm in FWHM, highly depending on the emission color. [13,14] In such InP/GaP/ZnS heterostructure, the thickness of GaP inner shell was far below 0.5 nm. A difficulty of thicker GaP growth on InP core likely stems from a still large inequality in lattice constant (6.8%), which is only slightly better than that of