Highly Luminescent Quantum Dots in Remote‐Type Liquid‐Phase Color Converters for White Light‐Emitting Diodes

Abstract

QDs. [14][15][16][17] However, they have less than optimal optical properties due to nonradiative recombination by defects. [12,18] As a result, despite the safety issues, Cdbased QDs are still attracting much attention and are seen as promising candidate materials for versatile applications in nonbiological environments owing to their outstanding performance with respect to tunable luminescence across the ultraviolet-visible-near-infrared (UV-vis-NIR) region, broad absorption bands with narrow emission bands, high quantum yields, [19] chemical stability, and photostability. [20,21] It is important to note that QDs have been passivated with higher bandgap semiconductor layers, such as ZnS and CdS, to increase the quantum yield. In the core-shell type QDs, the shell provides physical and chemical stabilities, as well as photostability to the core QDs, which is important for minimizing cytotoxicity, and also offers platforms for ligand exchange and further functionalization. [22] White light-emitting diodes (WLEDs) are commonly fabricated by combining inorganic phosphors with a blue or UV LED. [23,24] However, it is not easy to achieve a tailored and fullspectrum white light with currently available phosphors. The light spectra emitted by phosphor-based WLEDs are tuned by adjusting weight ratios of phosphors with different emission wavelengths. QDs behave like phosphors but their emissive colors are controlled by varying the size and composition. QDs have emerged as a good alternative to the phosphors in LEDs. Quantum dots (QDs) can be integrated into a solid-phase color converter (SCC) for white light-emitting diodes (WLEDs). However, the development of QD-based SCCs is prevented by the limitations of the QDs themselves, nonuniform dispersion or aggregation of the QDs, and heat accumulation by low thermal conductivity of the solid matrix. Herein, the development of new high-quality CdZnSeS/ZnS QDs in a one spot synthesis is reported that have high photoluminescence quantum yield (up to 100% for green wavelengths), narrow emission spectra (full width at half maximum< 27.3 nm), and good color tunability in the green region, 496-586 nm. Seven different color QDs are used to fabricate liquid-phase color converters (LCCs) for application in WLEDs with a remote configuration. The best LCC-based WLEDs show not only intense bright day white light (correlated color temperature = 6029 K) with a maximum luminous efficacy of 222.7 lm W −1 , but also excellent color quality (color rendering index = 95.1, as well as R9 = 94.4, and R13 = 97.1), which is very important in medical diagnostic lighting, dressing and display room lighting, painting and accent lighting. These results indicate remarkable progress both in the synthesis of high-quality QDs and in the development of WLEDs for high-performance commercial lighting devices.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admt.201800235.Semiconductor nanocrystals, namely quantum dots (QDs) have created many innova...

Broad-Band and Stable Phosphor-in-Glass Enabling Ultrahigh Color Rendering for All-Inorganic High-Power WLEDs

“…The R a and R 13 of all PiG-based WLEDs are higher than 91 and 94, respectively, while only PiG2-, PiG3-, and PiG4-based WLEDs exhibit high R 9 (>90). At the film thickness of 150 μm, the PiG4-based WLED has a CRI higher than 95 ( R a = 95.4, R 9 = 95.1, and R 13 = 97.3), an LE of 65 lm/W, and a CCT of 5260 K. However, high CRI is not a perfect color index that can ensure saturated, true, and natural colors of an object . The new color metric of IESTM-30-2015 was adopted to evaluate the color quality of WLEDs. , This color metric consists of the fidelity index ( R f ), gamut index ( R g ), and standardized color icons.…”

Morphology-Dependent Ambient-Condition Growth of Perovskite Nanocrystals for Enhanced Stability in Photoconversion Device

“…Time-resolved PL (TRPL) decays were measured to examine the dynamics of the photophysical properties of the as-prepared CPNCs, as displayed in Figure d. The TRPL decay of the nanoplatelets was faster than that of the nanocubes, with average lifetimes calculated as approximately 10 and 28 ns, respectively. − The absolute PL quantum yields (QYs) of the nanoplatelets and nanocubes were 47 and 80%, respectively. Quantitative X-ray photoelectron spectroscopy (XPS) analysis revealed that the incomplete surface composition of the CPNCs may be a key factor to account for their surface defects or trap states (Figure S3).…”

Electrical monitoring of photoisomerization of block copolymers intercalated into graphene sheets

“…Coulomb-blockade phenomena in nanostructures have also attracted much attention in condensed matter physics. Prototypical examples include a quantum dot separated from source/ drain leads by tunnel junctions in a transistor configuration, where electrons or holes can be injected individually into the quantum dot by varying the gate voltage [10][11][12][13][14][15] . The unique transport behavior in the Coulomb-blockade regime may lead to single-spin quantum bits or coherent many-body interactions between the confined spin and the Fermi reservoir, depending on the tunnel coupling strength.…”