Fluorescent carbon dots (CDs) are of interest as a promising alternative to quantum dots, partly because they do not include heavy metals. However, most CDs exhibit blue or green emission, while red-emitting CDs are required for a variety of applications. In the present work, CDs were synthesized by refluxing three phenylenediamine (PD) isomers with amino groups at different positions (o-PD, m-PD, and p-PD) in diphenyl ether at 250 °C for 4 h. Upon dispersing the resulting CDs in eight solvents with different polarities, emission colors ranging from green to red were observed. Among these CDs, p-PD-derived CDs exhibited both the longest emission wavelength range, from 538 to 635 nm, and the highest absolute red photoluminescence quantum yield (PLQY) of 15%. Herein the results are discussed based on a comparison of the polymerization processes of o-PD, m-PD, and p-PD. This work demonstrated that the optimum reaction time was 2 h, which yields a p-PD-derived CD dispersion in methanol with red emission and an absolute PLQY as high as 18%. Additionally, the use of 1-decanol and deuterated methanol in place of methanol improved the maximum absolute PLQY to 25% and 36%, respectively. These improved values are attributed to reduced concentration quenching by suppression of π−π stacking interactions and inhibition of the nonradiative relaxation process through the vibration of OH groups, respectively.

YVO 4 :Bi 3+ ,Eu 3+ nanophosphor converts near ultraviolet light to red light and shows lower scattering loss for visible light and longterm photostability. Therefore, the authors produce urethane resin films containing YVO 4 :Bi 3+ ,Eu 3+ nanophosphors on soda-lime glass substrates as spectral shifters to understand the effects of doping of Bi 3+ and Eu 3+ into YVO 4 and the Bi 3+ concentration on photoelectric conversion efficiencies of a monocrystalline silicon photovoltaic module. Under ultraviolet and near infrared light radiation, the YVO 4 :Bi 3+ ,Eu 3+ films enhance the photoelectric conversion efficiency of the module through spectral down-shifting as compared to the bare glass substrate and the YVO 4 film. In contrast, the YVO 4 :Bi 3+ ,Eu 3+ films are not effective for improving the photoelectric conversion efficiency under the simulated solar light radiation. These results are discussed from the aspects of the optical transparency and the photoluminescence properties.

Surface modification of p-phenylenediamine-derived carbon dots with decanoic acid and perfluorodecanoic acid successfully modulated fluorescence solvatochromism.

All-inorganic cesium lead halide perovskite CsPbX 3 (X = Cl, Br, I) nanocrystals have emerged as promising luminescent quantum dots. In this review, we summarize recent work on their synthesis, luminescent properties, and stabilities. Through controlling the composition of the alloyed halides and quantum size effects, the band gaps and emission wavelengths of CsPbX 3 nanocrystals are readily tunable over the entire visible range. Their sharp emission line-widths extend the color gamut of liquid crystal displays. They also exhibit high photoluminescence (PL) quantum yields and fast PL lifetimes. CsPbX 3 nanocrystals with both cubic and plate shapes have been successfully synthesized through several liquid-phase methods, such as hot-injection, room-temperature, and amine-free methods. The sizes and shapes of CsPbX 3 nanocrystals can be controlled via the reaction temperature and the length of the n-alkyl carboxylic acids and n-alkylamines used in their synthesis. Several attempts have been made to improve their stabilities during storage, at high temperature, and under light irradiation, for example by incorporation of CsPbX 3 nanocrystals into silica or polymer matrixes. In the liquid crystal display (LCD) industry, much research currently focuses on achieving the Rec. 2020 color gamut, which is the color standard for ultra-high-definition television broadcasting.1 An LCD backlight is composed of blue LEDs together with phosphors converting blue light to green and red. Extending the color gamut requires sharper emission spectra from the phosphors and finer tuning of their emission wavelengths. K 2 SiF 6 :Mn 4+ has attracted attention because of its sharp red-emission spectrum.2 In contrast, conventional green phosphors doped with rare earths suffer from low color purity. In recent years, LCD backlights based on quantum dots (QDs) with high color purity have been developed. QDs also possess color-tunable properties, because the bandgaps that determine their luminescent colors can be controlled through quantum size effects. Core/shell-type CdSe/ZnS QDs are widely used, but the high toxicity of cadmium and selenium is a major drawback. Alternatively, InP/ZnS QDs have been adopted in LCD backlights, but this solution suffers from the scarcity of indium and the sensitivity of InP to ambient O 2 and H 2 O. Very recently, CsPbX 3 (X = Cl, Br, I) nanocrystals have emerged as promising QDs.3 CsPbX 3 has crystal structure of cubic perovskite, as shown in Figure 1a. CsPbX 3 QDs are novel materials with many attractive photoluminescence (PL) properties, such as high quantum yields (QYs), narrow PL peaks, and emission colors that are controllable by halide anion exchange and quantum size effects. These properties make them potentially applicable in not only wide-colorgamut displays 3,4 (Figure 2), but also photovoltaic devices, 5 lasers, 6 photodetectors, 7 and bioimaging. 8 In this review, we introduce recent work on their synthesis, luminescent properties, and stabilities. Properties of Perovskite CsPbX 3 NanocrystalsHybrid...

CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have attracted much attention as promising materials for next-generation optoelectronic applications. However, improvement of their low stabilities against heating and humidity is needed for practical use. In this work, we focused on perfluorodecanoic acid (PFDA) as a surface ligand and investigated the thermal and chemical stabilities of the photoluminescence (PL) properties of CsPbBr3 NCs. Oleic acid (OA) adsorbed on the NCs was exchanged for decanoic acid (DA) and PFDA. OA-modified and DA-modified NCs exhibited drastic fluorescence quenching to 12.9 and 21.1% of their initial PL intensities, respectively, after heating at 100 °C for 4 h. In contrast, the PFDA-modified NCs maintained 92.1% of their PL intensity after the same heating. Furthermore, the polar solvent resistance was also improved by PFDA modification. These improvements can be attributed to the strong adsorptivity and high chemical stability of the PFDA ligand.

CuInS 2 (CIS) quantum dots (QDs) were investigated as a luminescent downshifting (LDS) material that converts near-ultraviolet (UV) light to visible light and were applied to a single crystalline silicon (c-Si) solar module that has no spectral sensitivity in the near-UV region. The bandgap of the CIS/ZnS core/shell QDs was successfully adjusted to ∼3 eV, which was adequate for the LDS layer in solar devices, by changing the molar ratio of Cu/In. CIS/ZnS/ZnS core/shell/shell QDs with 59.9% absolute photoluminescence (PL) quantum yield were prepared by the hot-injection method and embedded in ethylene−vinyl acetate copolymer (EVA) resin to fabricate QD@EVA films as the LDS layer. The PL intensity of the QD@EVA films under near-UV excitation monotonically increased with increasing QD concentration. The films were attached to a commercial single c-Si solar module. The advantages and drawbacks of the films were discussed based on the results of incident photon-to-electron conversion efficiency and current−voltage curve measurements.

Fluorescent carbon dots (CDs) represent a promising eco-friendly next-generation phosphor. However, most CDs exhibit broad photoluminescence (PL) spectra [full width at half-maximum (fwhm) over 60 nm]; few works on CDs with sharp PL spectra (fwhm less than 40 nm) have been reported. In addition, their syntheses and color tuning require harsh conditions of high temperatures, long reaction times, and high pressures with catalysts. Here, we successfully prepared narrow-bandwidth emissive CDs (fwhm of 27−40 nm) from phloroglucinol in a glycol solvent of 1,2-pentanediol at temperatures as low as 180 °C for a reaction duration of as short as 6 h under ambient conditions without any catalysts via an open reaction system in which dehydration and condensation reactions among phloroglucinol molecules were enhanced. We shifted the emission peak from 463 to 511 nm by selecting seven kinds of solvents with different polarities, that is, emission colors could be tuned from blue to green by taking advantage of fluorescence solvatochromism. The CD-dispersed polymer films showed a similar solvatochromic behavior and sharp PL spectra, verifying the feasibility of applying the CDs to displays with a wide color gamut.

Self-readsorption of surface ligands completely restores the photoluminescence of CsPbBr3 quantum dots damaged by excitation light.