High Color Rendering Index Ra Research Articles

Effect of ion occupancy and Li+ ion doping on luminescence characteristics of CaLaGaO4:Bi3+ blue phosphor

In recent years, the application of Bi3+ ions doped luminescent materials in the field of optoelectronics has attracted wide attention. In this paper, CaLaGaO4:xBi3+(x = 0.005, 0.0075, 0.01, 0.0125, 0.015, 0.02, 0.025mol) blue phosphors were synthesized by high temperature solid phase method. The theoretical and experimental bandgap values after Bi3+ ions doping is reduced, indicate that electrons can be transferred from valence band to conduction band better after Bi3+ ions doping, which increases the carrier concentration and improves the luminous efficiency. In addition, due to the doping of Li+ ions under 365 nm excitation, the emission intensity is increased by 2.5 times, shows high brightness blue light, with excellent thermal stability (423K/303K = 83 %), quantum efficiency is 56 %, and CaLaGaO4:0.01Bi3+, 0.008Li+ phosphor was mixed with (Ba,Sr)2SiO4:Eu2+ commercial green phosphor and (Ca,Sr)AlSiN3:Eu2+ red phosphor in a certain proportion. The WLED combined with 365 nm chip has a high color rendering index Ra = 90.2. Relevant color temperature CCT = 5502K.

Tunable luminescence and energy transfer in Tb3+,Eu3+ co-doped Gd2Zr2O7 phosphors with high thermal stability for WLEDs

Red phosphors with good thermal stability, high color temperature and color purity are critical in high power warm white LED devices. Herein, a series of single and co-doped Tb3+,Eu3+ polychromatic phosphors with pyrochlore structure based on Gd2Zr2O7 have been prepared for the first time by a conventional solid phase reaction method. Compared to single doped Eu3+ phosphors, Tb3+,Eu3+ co-doped phosphors possess following advantages: improved UV absorption, increased photoluminescence intensity, extended luminescence range and improved thermal stability. At room temperature, the Gd2Zr2O7:Tb3+,Eu3+ phosphors exhibited a gradual shift from yellow-green emission at 544 nm to orange-red emission at 613 nm with increasing doping of Eu3+ ions. Energy transfer efficiency has been evaluated to be 71% by analyzing the fluorescence lifetime of Tb3+ ions. The concentration quenching mechanism under different conditions was analyzed in detail and it was concluded that the quenching of Tb3+ is caused by dipole-dipole interaction. In addition, the activation energy (ΔEa) of the Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphor was calculated to be as high as 0.2674 eV compared to other Tb3+, Eu3+ co-doped phosphors, demonstrating its high thermal stability. WLEDs devices based on Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphors have been prepared, which have low correlated color temperature (CCT) (5283 K), high color rendering index Ra = 85.5 K) and CIE coordinates chromaticity coordinate (0.3371,0.3333). All of the results show that Gd2Zr2O7:Tb3+,Eu3+ phosphors provide a new avenue to develop high quality red emission and high thermal stability phosphors for WLEDs.

A novel blue emitting phosphor LaScO3:Bi3+ for white LEDs: high quantum efficiency, high color purity and excellent thermal stability

Series of blue phosphors La1-xBixScO3 (x = 0–0.6) (LSO) were synthesized by the high temperature solid state method. Under the 365 nm near ultraviolet (NUV) irradiation, when the value of x is increased, the phosphor can emit blue from deep to shallow. The LSO phosphor presents an internal quantum efficiency of up to 98%, high color purity of 92.26% as well as excellent thermal stability. When x ≥ 0.2, Bi3+-doped phosphors have diverse FWHM ranging from 153 nm to 43 nm. Especially, when x = 0.5, the material shows an abnormal thermal quenching, and emission intensity at 573K can reach 128.3% of that at room temperature. The white light emitting diode (LED) was fabricated by combining the NUV LED chip (370 nm) with a mixture of LSO:0.007Bi3+ along with green Y3(Al,Ga)5O12:Ce3+ and red CaSiAlN3: Eu2+ phosphors, which show a high color rendering index Ra = 90.2, a low correlated color temperature CCT = 3999 K. The results demonstrate that LSO phosphor has potential application in the field of white LEDs.

Near-UV excited green-emission enhancement by efficient energy transfer in Na1.8Mg0.9Si1.1O4:Ce3+,Tb3+ phosphor for solid-state lighting applications

Luminescence properties of phosphor play a key role in the performance of white light-emitting-diodes (LEDs). The Tb3+ emission under near-UV excitation is usually very weak due to f-f spin-forbidden transitions. In this paper, we report that Tb3+ emission under near-UV excitation enhances up successfully in Ce3+,Tb3+ co-doped Na1.8Mg0.9Si1.1O4 (NMSO) phosphor, as a result of efficient energy transfer from Ce3+ to Tb3+. The newly-prepared NMSO:Ce3+,Tb3+ exhibits a strong green-emission line at λmax = 545 nm under 340 nm excitation, and the quantum efficiency is 0.82. The maximum energy transfer efficiency is up to 92.3%. The good thermal quenching resistance, high color-rendering index Ra (91.5) and low CCT (4752 K) of the packaged white LED demonstrate that energy transfer of rare earth phosphors is an effective strategy to target tailored optical performance. NMSO:Ce3+,Tb3+ phosphor has potential applications in near-UV chip excited white LEDs as a green-emitting component.

High Color‐Rendering Index and Stable White Light‐Emitting Diodes Based on Highly Luminescent Quantum Dots

AbstractSolid‐phase color converter‐based quantum dots (QDs) white light‐emitting diodes (WLEDs) have become promising next‐generation solid‐state light sources. However, the development of these WLEDs’ production still suffers from constraints involving insufficient color‐rendering index (CRI), low color stability, and short operation lifetimes. Here, thick‐shell Cd0.05Zn0.95S/CdSe/CdxZn1–xS spherical quantum wells are developed with good color tunability from green to red regions and high photoluminescence quantum yield (up to 88% for green wavelengths). QDs with five emission colors are used to fabricate a series of WLEDs, which possess a good correlated color temperature tunability from warm (3210 K) to cool (22 000K) white light, and a high CRI Ra (>90). Specifically, the neutral white light device with Commission Internationale de l´Eclairage (CIE, International Commission on illumination) of (0.36, 0.36) and the standard white light device with CIE of (0.33, 0.33) achieve a CRI Ra up to 95.8 and 95.11, respectively, they also exhibit long operating life and great color stability. These results indicate that the improvement of the performance and stability of the WLED based on thick‐shell spherical quantum wells is remarkable progress in the commercialization of QD‐based solid‐state lighting.

Site occupancy preference of Bi3+ and Bi3+-Eu3+ codoped yttrium galliate phosphors for white LEDs.

A variety of Bi3+-activated and Bi3+-Eu3+ codoped Y3GaO6 phosphor samples were obtained by solid-state reaction. The phase purity and crystal structure of the specimens were characterized via powder X-ray diffraction (XRD) analysis and Rietveld refinement. For the single Bi3+-doped Y3GaO6 phosphor, two different PL peaks at 410 and 595 nm were obtained, resulting from the two different Bi3+ sites occupied. The site occupation is driven by Bi3+ ion concentration. There is an energy transfer from the Bi3+ to Eu3+ ions in the YGO:Bi3+,Eu3+ phosphors. Besides, the energy transfer mechanism, efficiencies, quantum efficiency and thermal stability have been discussed in detail, demonstrating that the sample possesses high quantum efficiency and good thermal stability. The high color-rendering index Ra (92.9, and 81.6) and low CCT (3286 K, and 3904 K) of the white light-emitting diodes (WLEDs) clearly indicate that these samples are promising candidates for WLEDs.

Site-Selective Occupancy of Eu2+ Toward Blue-Light-Excited Red Emission in a Rb3 YSi2 O7 :Eu Phosphor.

Establishing an effective design principle in solid-state materials for a blue-light-excited Eu2+ -doped red-emitting oxide-based phosphors remains one of the significant challenges for white light-emitting diodes (WLEDs). Selective occupation of Eu2+ in inorganic polyhedra with small coordination numbers results in broad-band red emission as a result of enhanced crystal-field splitting of 5d levels. Rb3 YSi2 O7 :Eu exhibits a broad emission band at λmax =622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu2+ ions preferably occupy RbO6 and YO6 polyhedra and show the characteristic red emission band of Eu2+ . The excellent thermal quenching resistance, high color-rendering index Ra (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare-earth phosphors is an effective strategy to target tailored optical performance.

Preferential Neighboring Substitution-Triggered Full Visible Spectrum Emission in Single-Phased Ca10.5- xMg x(PO4)7:Eu2+ Phosphors for High Color-Rendering White LEDs.

Manipulating the distribution of rare-earth activators in multiple cation lattices can achieve versatile color output for single-phased phosphor-converted white light-emitting diodes (LEDs). However, successful cases are barely reported, owing to the uncertain distribution of rare-earth activators and the special combination of three primary colors for white LEDs. Herein, we took whitlockite β-Ca3(PO4)2 as a multiple cation lattice host to manipulate the redistribution of Eu2+ activators, and the surprising Mg2+-guided redistribution of Eu2+ activators among different Ca sites is reported for the first time to regulate the photoluminescence (PL) behavior in series Ca10.5- xMg x(PO4)7:Eu2+ phosphors. The preferential neighboring substitution of smaller Mg2+ cations in Ca(5) and Ca(4) sites triggers a discontinuous evolution of local structure along c axis and induces covalent variable Ca(1), Ca(2), and Ca(3) cation sites for the accommodation of Eu2+ activators. The unique optical feature enables the single-phased Ca9.75Mg0.75(PO4)7:Eu2+ phosphor-converted white LED to exhibit quite high color-rendering index Ra (85) and R9 (91) values. The preferential neighboring-cation substitution reported here can not only manipulate the migration of Eu2+ activators among different cation sites for tunable PL properties, but also carve out a new way for next-generation high-quality solid-state lighting.