Solid-phase color converter-based quantum dots (QDs) white light-emitting diodes (WLEDs) have become promising next-generation solid-state light sources. However, the development of these WLEDs’ production still suffers from constraints involving insufficient color-rendering index (CRI), low color stability, and short operation lifetimes. Here, thick-shell Cd 0.05 Zn 0.95 S/CdSe/Cd x Zn 1– x S spherical quantum wells are developed with good color tunability from green to red regions and high photoluminescence quantum yield (up to 88% for green wavelengths). QDs with five emission colors are used to fabricate a series of WLEDs, which possess a good correlated color temperature tunability from warm (3210 K) to cool (22 000K) white light, and a high CRI Ra (>90). Specifically, the neutral white light device with Commission Internationale de l´Eclairage (CIE, International Commission on illumination) of (0.36, 0.36) and the standard white light device with CIE of (0.33, 0.33) achieve a CRI Ra up to 95.8 and 95.11, respectively, they also exhibit long operating life and great color stability. These results indicate that the improvement of the performance and stability of the WLED based on thick-shell spherical quantum wells is remarkable progress in the commercialization of QD-based solid-state lighting.
High quality blue emitting quantum dots (QDs) are regarded as promising nanomaterials for lasers, photovoltaic cells and displays. However, few reports realize high photoluminescence quantum yield (PL QY), narrow emission band width and pure blue emitting (450∼460 nm) simultaneously. Herein we propose a facile one-step synthesis of thick shell blue emitting CdZnS/ZnS QDs. ZnS shell was overcoated on the prepared cores by directly introducing zinc oleate/S TBP solution (zinc oleate powder and S dissolved in TBP) into mixture without any purification steps and the thickness of ZnS shell was controlled by adjusting the adding amount of zinc oleate/S TBP solution. The optimal QDs with ten monolayers of ZnS shell exhibit pure blue light (∼455 nm) with narrow line width (full width half maximum, FWHM 17.2 nm) and high photoluminescent quantum yield (QY) (92%). Due to the thick ZnS shell, nonradiative recombination of the QD solids is suppressed efficiently.
Environmentally friendly zinc selenide (ZnSe) based core/shell quantum dots (QDs) are promising emitting materials for special light sources and displays. However, ZnSe-based core/shell QDs with violet-blue emission that simultaneously possess thick shells and narrow emission linewidths are still challenging thus far. We herein use a gradient ZnSe x S 1-x /ZnS shell strategy to target this goal. The ZnSe x S 1-x mid shell helps the lattice strain relaxation during the growth, whereas the wide bandgap ZnS outer shell benefits the optical properties by passivating the emitting cores and improving the quantum confinement effect. These ZnSe core QDs show a unity zinc blende structure and high crystallinity . The optimized ZnSe/ZnSe x S 1-x /ZnS QDs exhibit tunable emission wavelengths (415–445 nm), narrow photoluminescence linewidths (10.2–14.2 nm), thick shells (>3.9 nm), and high photoluminescence quantum yields (>50%). We postulate that these excellent features are due to the use of alloyed ZnSe x S 1-x layer at the core/shell interfaces. This study provides a feasible idea for the development of blue ZnSe-based QDs with perfect emitting properties.
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