Green and Orange Emissive Carbon Dots with High Quantum Yields Dispersed in Matrices for Phosphor-Based White LEDs

Abstract

Carbon dots (CDs) have aroused more interest in the LED phosphor. High quantum yields and suppressing solid-state luminescence quenching are the key factors for CDs to prepare highquality phosphors. In this work, orange and green emissive CDs (O-CDs and G-CDs) with very high absolute quantum yields (abs. QYs: 85.19% at natural pH and 96.12% at pH 9.0 for G-CDs; 34.89% in aqueous solution and 77.54% in ethanol for O-CDs) were achieved. Then, sodium silicate and PVA were selected as matrices to suppress their aggregation-induced quenching effect. Phosphor powder was prepared by microwave-assisted pyrolysis of sodium silicate and films by self-assembling of PVA in the presence of the CDs. The phosphor powder simultaneously containing G-CDs and O-CDs (G-O-CDsphosphor) presents bright yellow fluorescence but owns a relatively low abs. QY. However, O-CDs/PVA and G-CDs/PVA phosphor films possess very high abs. QYs of 51.51% and 72.81%, respectively. LEDs constructed by coating G-O-CDs-phosphor on a blue chip exhibited a cool white color and a color rendering index (CRI) of 78. Interestingly, high-quality warm white LEDs owning a superior CRI of 93 were achieved by the O-CDs/PVA and G-CDs/PVA films. By comparison, PVA is more suitable to maintain the high performance of G-CDs and O-CDs for high-quality phosphors.

Green Preparation of Fluorescent Nitrogen-Doped Carbon Quantum Dots for Sensitive Detection of Oxytetracycline in Environmental Samples

“…For F-7000 fluorescence spectrometric measurements (Hitachi High Technologies, Tokyo, Japan), excitation and emission slits were set at 5 nm, and the excitation light-source wavelengths were set at 320 nm (ON-CQDs) and 280 nm (WN-CQDs). The fluorescence quantum yield of N-CQDs was determined by absolute method (also known as absolute quantum yield) [53][54][55]. Time-resolved fluorescence decay curve measurements were also performed on the FLS980 series of fluorescence spectrometers (Edinburgh Instruments, Livingston, UK).…”

One-Step Green Solvothermal Synthesis of Full-Color Carbon Quantum Dots Based on a Doping Strategy

“…Interestingly, the mixed solution of CQDs before separation exhibited red emission under 395 nm UV lamp excitation, although the yields of g-CQDs and yg-CQDs were higher than that of or-CQDs. As shown in Scheme and Figure S8a, the PL excitation spectra of long wavelengths CQDs and the PL spectra of shorter wavelengths overlap greatly, so we reasonably deduce that this phenomenon is the result of energy transfer between CQDs . For example, the emission peak of b-CQDs matches well with the excitation peak of yg-CQDs.…”

“…As shown in Scheme 2 and Figure S8a, the PL excitation spectra of long wavelengths CQDs and the PL spectra of shorter wavelengths overlap greatly, so we reasonably deduce that this phenomenon is the result of energy transfer between CQDs. 54 For example, the emission peak of b-CQDs matches well with the excitation peak of yg-CQDs. Under the premise that the total volume of the solution and the concentration of b-CQDs remain unchanged, more yg-CQDs are dissolved, and weaker b-CQD emission will be observed.…”

Defect modulation and luminescence improvement of Mn4+-activated La(Mg, Nb)O3 phosphor with improved stability for plant cultivation

“…Light emitting diodes (LEDs) are regarded as the most suitable candidate for next-generation lighting sources and have been applied in many areas due to their enormous advantages, such as high efficiency, energy saving, environmental friendliness, and long working lifetime. [1][2][3][4][5][6] In particular, LEDs have been applied in the agricultural industry as the light source for indoor plant cultivation, so that the plants can be controlled in a specific environment, such as under a constant temperature and specific growth environment. [7][8][9] Indoor plant cultivation can protect the plants from bad weather and allow the vegetables to continuously grow without being affected by external factors, which is a good solution to the lack of food in the world.…”