Published papers

© The Royal Society of Chemistry 2019. CsPbBr3 quantum dots were packed in a cell and irradiated at 468 nm. The sample color changed to black, attributed to the formation of surface defects by photoinduced desorption of surface ligands. The color and photoluminescence properties completely recovered during subsequent dark storage. This can be explained by readsorption of the surface ligands.

© The Author(s) 2019. Published by ECS.. Fluorescent Cd-free quantum dots (QDs) such as InP/ZnS and CuInS2/ZnS have attracted attention for use as color converters for blue light emitting diodes. To protect QDs from oxygen, which degrades them by photo-oxidation during excitation, we fabricated a transparent monolithic silica composite containing the QDs using an aqueous solution of tetramethylammonium silicate (TMAS) as a silica source. The TMAS solution readily dispersed the negatively charged QDs prepared by ligand exchange of 1-dodecanethiol for 3-mercatopropionic acid (MPA). A highly transparent monolithic TMAS-derived silica composite containing the MPA-capped QDs was obtained from the QD dispersion through a sol-gel process. Improved photostability of QDs was explained by the TMAS-derived silica acting as a gas barrier to protect the embedded QDs from photo-oxidation by oxygen in air.

Copyright © 2020 American Chemical Society. CuInS2 (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 &tild;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.

This journal is © The Royal Society of Chemistry. The fluorescence solvatochromism of p-phenylenediamine-derived carbon dots (CDs) was modulated through surface modification with decanoic acid or perfluorodecanoic acid. This is attributed to the adjustment of the dipole interaction between solvent molecules and the CD surface in terms of steric hindrance of a surface modifier and polarization of the modified CD surface.

© The Royal Society of Chemistry 2018. In this work, green-emitting InP/ZnS quantum dots (QDs) modified with 1-dodecanethiol were embedded into silica by two methods to improve their photostability while maintaining a high photoluminescence quantum yield (PLQY) and a color coordinate. A monolithic QD-silica composite prepared by a non-aqueous route with tetraethyl orthosilicate and lactic acid featured low transparency, a loss of the color purity of green, and a PLQY of 1.6%, which was considerably lower than that of the original QDs (67%). The decrease of the PLQY was attributed to QD aggregation in the sol-gel process and degradation of the QDs by the acid. The alternative method involved stirring a toluene dispersion of the QDs with tetramethyl orthosilicate (TMOS) for 20 h or 7 days. The PLQY of the TMOS-modified InP/ZnS QDs (20 h) was 62%, which was only slightly lower than that of the original QDs. The PLQY decreased to 52% when the duration of aging was prolonged to 7 days. This decrease was attributed to desorption of surface modifiers from the QD surface and oxidative degradation by oxygen dissolved in toluene. Herein, the color coordinate was maintained stably. Photostability was evaluated by continuous irradiation of the samples by a blue light emitting diode. The decrease of photoluminescence (PL) intensity was suppressed by the silica encapsulation. In particular, the PL intensity of the TMOS-modified InP/ZnS QD sample (7 d) maintained 99% of its initial intensity. Silica encapsulation of InP/ZnS QDs prevented contact of the QDs with oxygen in the air, resulting in improved photostability.

© 2019 American Chemical Society. 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 Ï€-πstacking interactions and inhibition of the nonradiative relaxation process through the vibration of OH groups, respectively.