Zero-Dimensional Organic–Inorganic Copper(I) Bromide for White Light-Emitting Diode Applications with an Ultrahigh Color Rendering Index

A novel orange-yellow-emitting polymethyl methacrylate derivative grafted with cationic iridium(III) complex units was synthesized and used as down-conversion luminescent materials in light-emitting diodes (LEDs). The polymer had a thermal decomposition temperature (Td) of 275 °C. With the temperature increasing from 20 to 100 °C, its photoluminescent intensity decreased to 76.8% with thermal quenching activation energy (Ea) of 0.2775 eV. A series of LEDs was fabricated by 460 nm blue GaN chips and the polymer blended in silicone at different concentrations. At 4.0 wt %, a cold white LED was obtained, the correlated color temperature (CCT) was 10,050 K, color rendering index (CRI) was 71.2, luminous efficiency (ηL) was 5.3 lm·w−1, and Commission Internationale de L’Eclairage (CIE) chromaticity coordinates were (0.30, 0.24). At 5.0 wt.%, the LED emitted neutral white light, its CCT was 4938 K, CRI was 75, ηL was 13.8 lm·w−1, and the CIE value was (0.34, 0.27). At 5.5 wt %, 6.0 wt %, 7.0 wt %, and 8.0 wt %, the LEDs all emitted warm white light; their CCTs were 3446, 3093, 2557, and 2337 K, respectively; their CRIs were 73.6, 71.8, 63.8, and 59.0, respectively; their ηL were 18.1, 16.3, 14.8, and 13.7 lm·w−1, respectively; and their CIE values were (0.36, 0.30), (0.40, 0.35), (0.45, 0.38), and (0.50, 0.42), respectively. At 9.0 wt %, the blue light of GaN chip was completely absorbed by the polymer and only the orange-yellow light of the polymer emitted. The results suggested the polymer was a promising orange-yellow-emitting phosphor candidate for white LEDs, especially for warm white LEDs.

This work reports an excellent quantum efficiency and superior color purity CaAl12O19–CaAl4O7–MgAl2O4:Mn4+ (CCM:Mn4+) red-emitting phosphor. This phosphor can be excited by a broad excitation band ranging from 300 to 500 nm, and it generates an intense broadband red emission peaking at 656 nm. The CCM:0.5%Mn4+ phosphor-possessed superior color purity of 100%, a long lifetime of 0.49 ms, and high activation energy of 0.286 eV. Four different prototypes of plant growth light-emitting diodes (LEDs) with high quantum efficiencies of 81.8, 72.1, 67.2, and 61.1% were fabricated by coating the optimized CCM:0.5%Mn4+ phosphors onto UV (365 nm), NUV (395 nm), violet (410), and blue (460 nm) LED chips, respectively. The 81.8% and 72.1% QE values are the highest values reported for the 365 nm UV-pumped and 395 nm NUV-pumped LEDs based on Mn4+-doped oxide phosphors. Furthermore, a white LED with a high color rendering index (CRI) of 90, correlated color temperature (CCT) of 2416 K, and luminous efficacy of radiation (LER) of 216 lm/W was realized using a blue LED chip and a mixture of CCM:0.5%Mn4+ and commercial YAG:Ce3+ phosphors. Our results demonstrate great potential for using CCM:Mn4+ phosphors for plant growth LEDs and white light-emitting diode (WLED) applications.

Luminescent properties of Ca2Mg0.75Al0.5Si1.75O7:Ln (Ln = Ce3+, Dy3+, Eu3+, Sm3+) and their application for UV white light-emitting diodes

Eu3+ doped YVO4 is excellent traditional red phosphor, but shifting its efficient excitation band to a longer wavelength is necessary for application in white light-emitting diodes, and is a big challenge that calls for good solution. Following the observation that cation substitution usually is an effective way to manipulate the band-gap of phosphors, we carried out ab initio calculation for the band-gap of pure and Bi3+ doped LnVO4 (Ln = Y, Lu, and Sc). The results show that the band-gap decreases with the cationic radius from Y3+ to Sc3+, and the doping of Bi3+ further decreases their band-gaps. The experimental results on the Eu3+ doped and Eu3+, Bi3+ co-doped LnVO4 (Ln = Y, Lu, and Sc) phosphors confirm this. In particular, the excitation of Eu3+ and Bi3+ co-doped ScVO4 is shifted to approach 400 nm, which fulfills the excitation requirement of near-ultraviolet-based white light-emitting diodes, and implies that Eu3+ and Bi3+ co-doped ScVO4 should be a promising candidate as red phosphor in white light-emitting diodes.

Recently, the investigation of quantum dots (QDs) as a color converter for white light-emitting diodes (WLEDs) application has attracted a great deal of attention. Because the narrow emission wavelength of QDs can be controlled by their particle sizes and compositions, which is facilitated to improve the color gamut of display as well as color rendering index (CRI) and the correlated color temperature (CCT) of WLEDs. In a typical commercially available LCD display, the color gamut is approximately to 75 % which is defined by the National Television System Committee (NTSC). In order to enhance NTSC, the full width at half-maximum (FWHM) of color converter should be less than 30 nm. Therefore, the QDs are the best choice for display application due to the FWHM of QDs is meet the demand of display application. In this study, the hot injection method with one-pot process is used to synthesis of colloidal ternary ZnCdSe green (G-) and red-emission (R-) QDs with a narrow emission wavelength around 537 and 610 nm. By controlling the complex reagents-stearic acid (SA) and lauric acid (LA), high performance of G- and R-QDs can be prepared. The quantum yields (QYs), particle sizes and FWHM for G- and R-QDs are 70, 30 %, 3.2 ± 0.5, 4.1 ± 0.5 nm and 25, 26 nm, respectively. In order to explore the performance of QDs-based WLEDs, mixing ratios effect between G-QD and R-QD are studied and the WLED is packed as conformal-type. Different ratios of R-QD and G-QD (1:10, 1:20 and 1:30) are mixed and fill up the 3020 SMD blue-InGaN LED, and named as LED-10, LED-20 and LED-30. After that, UV curable gel is deposited on the top of QD layer to form WLED and named as LED-10*, LED-20* and LED-30*. The results show that the Commission International d’Eclairage (CIE) chromaticity coordinates, color rendering index (CRI), luminous efficacy of LED-10*, LED-20* and LED-30* are (0.27, 0.21), 53, 1.9 lm/W, (0.29, 0.30), 72, 3.3 lm/W and (0.25, 0.34), 45, 6.8 lm/W, respectively. We can find that the positions of CIE can be controlled simply by adjusting the ratios of G- and R-QDs. Besides, the LED-10 and LED-20* device shows the high CRI, implying that it has great potential for application on backlight of display technology and solid-state lighting.

We successfully synthesized SrLa2Mg2W2O12:xMn4+ (x = 0.002, 0.004, 0.006, 0.008, 0.010, 0.012, 0.014) phosphors through a high-temperature solid-state reaction. The phase of sample was shown by X-ray powder diffraction (XRD). The morphology of the sample was observed by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), which showed the irregular morphology of SrLa2Mg2W2O12 (SLMW) powders. Additionally, the photoluminescence excitation (PLE), emission (PL) and ultraviolet–visible reflection spectra were also presented. As shown in results, the phosphor could be stimulated by the ultraviolet (UV) and near ultraviolet (NUV) light and then exhibited far-red emission (697 nm). The optimum doping concentration of Mn4+ is 1 mol%. The thermal stability of phosphors has been investigated and discussed (I423K/I298K = 64.6%), and the internal quantum efficiency (IQE) of SLMW:0.01Mn4+ phosphors is as high as 51.2%. Finally, a far-red light-emitting diodes (LEDs) was fabricated by combining a 365 nm near-ultraviolet InGaN chip with SLMW:0.01Mn4+ phosphor. The Color Rendering Index (CRI), correlated color temperature (CCT) and luminescent efficiency (LE) values were 29.5, 1159 K and 5.6 lm/W, respectively. All of these indicated that SLMW:Mn4+ as a far-red phosphor can be applied to LEDs lamp and it has enormous potential applications in white light-emitting diodes (w-LEDs).

Optical processes in semiconductors: by Jacques I. Pankove. 422 pages, 6×9 in. Englewood Cliffs, N.J., Prentice-Hall, 1971

Light-emitting diodes (LEDs) are currently undergoing rapid development as plant growth light sources in a plant factory with artificial lighting (PFAL). However, little is known about the effects of supplementary light and pulsed LEDs on plant growth, bioactive compound productions, and energy efficiency in lettuce. In this study, we aimed to determine the effects of supplementary white LEDs (study I) and pulsed LEDs (study II) on red leaf lettuce (Lactuca sativa L. ‘Sunmang’). In study I, six LED sources were used to determine the effects of supplementary white LEDs (RGB 7:1:1, 7:1:2, RWB 7:1:2, 7:2:1, 8:1:1, 8:2:0 [based on chip number] on lettuce). Fluorescent lamps were used as the control. In study II, pulsed RWB 7:2:1 LED treatments (30, 10, 1 kHz with a 50 or 75% duty ratio) were applied to lettuce. In study I, the application of red and blue fractions improved plant growth characteristics and the accumulation of antioxidant phenolic compounds, respectively. In addition, the application of green light increased plant growth, including the fresh and dry weights of shoots and roots, as well as leaf area. However, the substitution of green LEDs with white LEDs induced approximately 3.4-times higher light and energy use efficiency. In study II, the growth characteristics and photosynthesis of lettuce were affected by various combinations of duty ratio and frequency. In particular, biomass under a 1 kHz 75% duty ratio of pulsed LEDs was not significantly different from that of the control (continuous LEDs). Moreover, no significant difference in leaf photosynthetic rate was observed between any pulsed LED treatment utilizing a 75% duty ratio versus continuous LEDs. However, some pulsed LED treatments may potentially improve light and energy use efficiency compared to continuous LEDs. These results suggest that the fraction of red, blue, and green wavelengths of LEDs is an important factor for plant growth and the biosynthesis of bioactive compounds in lettuce and that supplementary white LEDs (based on a combination of red and blue LEDs) might be more suitable as a commercial lighting source than green LEDs. In addition, the use of suitable pulses of LEDs might save energy while inducing plant growth similar to that under continuous LEDs. Our findings provide important basic information for designing optimal light sources for use in a PFAL.

Single-phase “greener” phosphor with broadband emission made of colloidal quantum dots (QDs) is most desirable for use as color convertors in white light-emitting diodes (WLEDs). Here, we demonstrate a single “cadmium-free” component system consisting of Cu-doped InP core/ZnS barrier/InP quantum well/ZnS shell QDs, which exhibits two emission peaks by controlling the barrier thickness under single-excitation wavelength, one of which being attributed to Cu-doped InP, and the other resulting from InP quantum well. The dual emissive peaks were successfully tuned in a range from visible to near-infrared by simple control of the core size and the well thickness, respectively. Using optimal structures as color converters, we successfully obtained WLED with a color rending index (CRI) up to 91 and CIE color coordinates of (0.338, 0.330) by combination with blue LED chip, indicating this single-phase phosphor with great promise for use in solid-state lighting due to flexibly tunable dual emission peak position in...

Application of chelation effect in improving the triple properties of K2SiF6Mn4+ phosphors through composite modification

Highly efficient Cu-In-Zn-S/ZnS/PVP composites based white light-emitting diodes by surface modulation

Improving the thermal stability of phosphor in a white light-emitting diode (LED) by glass-ceramics: Effect of Al2O3 dopant

Novel Sm3+/Eu3+ co-doped Sr7Sb2O12 red-emitting phosphor for white LED

Lead-free halides, recognized for their nontoxic properties and remarkable stability, have emerged as promising candidates for various optoelectronic applications. In this work, we report the discovery of a novel all-inorganic zinc halide, Rb3ZnCl4I. With the doping of Mn2+ ion, the as-obtained Rb3Zn1-xMnxCl4I single crystals show intense green photoluminescence with a full width at half-maximum (fwhm) of 52 nm and a peak at 525 nm. The sample with x = 0.30 exhibits the maximum photoluminescence quantum yield (PLQY), reaching a value of 44.14%. We further explored their potential applications in white light-emitting diodes (WLEDs) and X-ray detection. The constructed WLED exhibits a color rendering index (CRI) of 84.1 along with a correlated color temperature (CCT) of 6491 K, demonstrating the material's suitability for high-quality solid-state lighting. Notably, Rb3Zn0.70Mn0.30Cl4I exhibits remarkable stability under X-ray irradiation. Upon being continuously exposed to X-ray irradiation for 10 min at a dose rate of 26.5 Gy/min, the radioluminescence intensity retains 90% of its initial value. This work not only introduces a new member to the family of environmentally friendly and stable lead-free halides but also paves the way for further exploration and development of metal halides in various high-tech fields.

The development of high-performance luminescent materials is essential for advancing optoelectronic applications, particularly in the field of solid-state lighting and displays. This study investigates the structural, optical, and thermal properties of the 0D organic-inorganic hybrid metal halides (OIHMHs) (2,6-DTP)2ZnCl4·DMF and its Sb3+-doped derivatives, aiming to enhance the luminescent efficiency and stability for potential applications in white light-emitting diodes (WLEDs). The Sb3+-doped (2,6-DTP)2ZnCl4·DMF samples showed broad emission spectra covering the entire visible region, with distinct peaks at 505 and 647 nm with the photoluminescence quantum yield (PLQY) of 91.9% and high thermal stability. Furthermore, the (2,6-DTP)2ZnCl4·DMF-based WLEDs exhibited stable white light emission with a high color rendering index (CRI) of 91 and a correlated color temperature (CCT) of 5635 K. This research provides valuable insights into the design and optimization of efficient luminescent materials for optoelectronic applications, contributing to the development of next-generation lighting technologies.