No abstract

No abstract

Highly green emissive solid‐state carbon dots (CDs) with photoluminescence quantum efficiency of 58% are prepared through a rapid microwave assisted heating method. Due to the spatial confinement from the biuret crystal matrix, aggregation among CDs is effectively suppressed, thus allowing the CDs to give efficient emission in the solid‐state. The CDs show excitation independent emission and mono‐exponential decay characteristics with a nearly constant lifetime of ≈13 ns upon varying the detected emissions, indicating the presence of a single type of emissive state in the CDs. Due to their high quantum efficiency and short lifetime, the obtained CDs are applied as the color conversion layer of a near‐ultraviolet micro light‐emitting diode (µLED) chip (405 nm) for visible light communication, achieving a modulation bandwidth of 165 MHz, which is much higher than the bandwidth of the conventional combination of Ce3+‐doped yttrium aluminum garnet phosphor with GaN LED. Moreover, the green emitting solid‐state CDs are applied to fabricate a prototype white LED device, which exhibits good lighting suitability with a color rendering index of 90.6 and a Commission Internationale de L'Eclairage chromaticity coordinates of (0.327, 0.332).

Cu +-activated aluminosilicate oxyfluoride glasses were successfully synthesized by melt-quenching method in air by adding Al powder as a reducing agent. Their luminescent properties were studied systematically via optical absorption, excitation, and emission spectra. Upon UV irradiation, a blue-emitting band of Cu + was observed in glass with relatively low optical basicity. By increasing the optical basicity of glass, obvious redshifts of excitation (290 → 313 nm) and emission (435 →470 nm) peaks were obtained. Through enhancing Cu + content, the excitation and emission bands presented further redshifts, which shifted from 313 to 338 nm and 470 to 560 nm, respectively. It is proposed that the absorption band and emitting color of Cu +-doped glass can be tuned by changing the optical basicity of glass and Cu + concentration. The highest quantum yield can reach 62.5%. More importantly, an investigation of the thermal stability showed that over 85% of the room temperature luminescent intensity is preserved at 200 • C. These results imply that Cu +-activated aluminosilicate oxyfluoride glasses may be utilized for UV-converted W-LEDs.