A novel fluorescent material K3NbOF6: Mn4+ for light-emitting diode devices

A series of K3Nb1-xOF6:xMn4+ fluorescent materials were prepared by the cation exchange method. Phase structure, morphology, emission, excitation spectrum and LED packaging of fluorescent materials were tested. The fluorescent material particles are micron-sized (5 μm-20 μm) and have a micro-rod morphology. It has two absorption bands, with the blue light region (∼468 nm) being stronger than the ultraviolet region (∼370 nm). Under the excitation of 468 nm, it shows good narrowband emission in the red light region, mainly with anti-stokes v6 (∼627 nm), which is caused by the double barrier of the 2Eg→4A2g transition broken by the coupling effect of electron and phonon. The optimum doping concentration was 9.1 %, and as the concentration increased again, the dipole-dipole interaction between Mn4+ resulted in concentration quenching. When the fluorescent material operates at high temperature (150 ℃), the emission intensity drops to 50.2 % of which at room temperature. At high temperature, the electrons absorb a large amount of heat energy, and the non-radiation transition to 4A2g energy level causes the thermal quenching effect. In addition, the sample also showed good water stability, after 1 h of hydrolysis, the luminescence intensity decreased to 85.6 % of the initial value. The use of LED packaging with fluorescent materials and InGaN-YAG:Ce3+ can effectively reduce the color temperature of LED from 6856 K to 3745 K, and enhance the Color index from 61.5 % to 76.8 %. Which has great potential for development in the fields of plant growth and backlight display technology.

Novel green/red oxyfluoride phosphors with excellent optical properties for near-UV excited white light emitting diode

Novel eye-sensitive Ba3Nb2O2F12(H2O)2:Tb3+ green and Ba3Nb2O2F12(H2O)2:Mn4+ red oxyfluoride phosphors with extremely strong absorption in the UV region were designed and synthesized by simple co-precipitation strategy. Particularly, Tb3+ ions were doped in this matrix for the first time, which greatly improves their absorption efficiency in the near ultraviolet region (367 nm) and emits sharp green light (544 nm). In addition, the Ba3Nb2O2F12(H2O)2:Mn4+ red phosphors have strong zero phonon line (ZPL) emission at 625 nm, which is conducive to improving the sensitivity of human eye and color purity. Meanwhile, the optical properties of the red phosphor are significantly enhanced via doping K+ cations as charge compensators. Crystal field environment and nephelauxetic effect of the as-prepared phosphors before and after K+ cation doping were systematically analyzed. Moreover, these synthesized red/green phosphors have good thermal stability and moisture resistance. Remarkably, the as-prepared Ba3Nb2O2F12(H2O)2:5%Mn4+ or K0.9Ba2.1Nb2O2F12(H2O)2:5%Mn4+ red phosphors can be directly mixed with the as-synthesized Ba3Nb2O2F12(H2O)2:13%Tb3+ green phosphor coating on 365 nm near-ultraviolet LED chip to package WLED devices with excellent electroluminescence performance. These findings are conducive to opening an avenue for screening the unique structure of optical materials.

A highly efficient Mn4+ activated Nb-based oxyfluoride red fluorescent material with excellent water stability: preparation and performance analysis

In this study, an efficient non-rare earth Mn4+-doped K3(NbOF5)(HF2) red fluorescent material was synthesized by using the coprecipitation method. Replacing KF with K2CO3 effectively solved the problem that KF was difficult to stir due to its strong water absorption. The sample was composed of rods. The excitation spectra consisted of two strong excitation peaks at 366 nm and 468 nm. The emission spectra consisted of a series of narrow-band emissions between 580 nm and 680 nm. Besides, the luminescence quantum efficiency (QE) reached 84.3% under the excitation of 468 nm. The fluorescent lifetime of K3(NbOF5)(HF2):Mn4+ was less than 4 ms, which can achieve fast response display in backlight display applications. The WLED was fabricated with K3(NbOF5)(HF2):Mn4+ and commercial YAG:Ce3+ and the commercial InGaN blue chip. At a 30 mA drive current, the WLED device exhibited excellent luminescence properties. The correlated color temperature (CCT) was 3853 K, the Ra was 90.1 and the luminous efficiency was 310.432 lm W-1. Therefore, K3(NbOF5)(HF2):Mn4+ has very broad prospects in WLED lighting and backlight display applications.

Moisture-resistant Nb-based fluoride K2NbF7:Mn4+ and oxyfluoride phosphor K3(NbOF5)(HF2):Mn4+: synthesis, improved luminescence performance and application in warm white LEDs

Herein, high-efficiency Nb-based oxyfluoride K₃(NbOF₅)(HF₂):Mn⁴⁺ and fluoride K₂NbF₇:Mn⁴⁺ phosphors were successfully synthesized using different amounts of HF acid solutions by a simple co-precipitation method. XRD, SEM and EDS were used to characterize the crystal structure, morphology and elemental composition of the phosphors. The emission spectra, excitation spectra and luminescence decay curves were used to study the luminescence characteristics of the samples. The thermal stability of the phosphors was tested and the mechanism of temperature quenching was discussed. Meanwhile, the moisture resistance and application of the phosphors were investigated in detail. The results show that the K₃(NbOF₅)(HF₂):Mn⁴⁺ phosphor has stronger luminous intensity, lower color temperature, and better moisture resistance compared with the K₂NbF₇:Mn⁴⁺ phosphor. The correlated color temperature (CCT) and color rendering index (CRI) of warm white LEDs can be significantly improved by using the K₃(NbOF₅)(HF₂):Mn⁴⁺ (CCT = 3430 K, CRI = 87.3) phosphor as a red light component. So the K₃(NbOF₅)(HF₂):Mn⁴⁺ phosphor has broader application prospect in the field of warm white LEDs.

Design of Novel Highly Efficient Yellow-Orange Color-Tunable Luminescence in Rb2Sr1-yCayP2O7:xEu2+ Solid Solutions for White Light-Emitting Diodes

Traditional white light-emitting diodes (WLEDs) are limited by the energy loss due to reabsorption. Integrating binary complementary color phosphors with near-ultraviolet (n-UV) LED chips can be a good solution, and the core of it is to develop yellow-emitting phosphors. In this work, we have designed Rb₂Sr_1-yCa_yP₂O₇:xEu²⁺ solid solutions with yellow-orange color-tunable luminescence. The crystal structure, luminescence properties, and potential applications for WLEDs were explored systematically. Under n-UV light excitation, the phosphors efficiently emit broadband yellow-orange emission. The reasons and mechanisms of the variation of the PL/PLE spectra have been investigated. The optimal Rb₂SrP₂O₇:0.5% Eu²⁺ sample exhibits a high quantum efficiency of 72.96% with a good color purity of 87.1%. Upon combination of the BAM:Eu²⁺ and Rb₂SrP₂O₇:0.5% Eu²⁺ phosphors with a 380 nm n-UV chip, a WLED device is fabricated and can emit white light with good performance.

A novel Mn4+ doped oxyfluoride red phosphor for rapid-response backlights display

An oxyfluoride red phosphor Cs₂MoO₂F₄:Mn⁴⁺ was synthesized via a facile co-precipitation route with a certain molecular ratio of CsF and MoO₃. X-ray diffraction analysis and its Rietveld refinement reveal that Cs₂MoO₂F₄:Mn⁴⁺ crystallized in an orthorhombic structure with the Amam (63) space group. Upon blue light excitation, Cs₂MoO₂F₄:Mn⁴⁺ exhibits a series of sharp red emission lines around ∼634 nm and the zero-phonon line (ZPL) is visible at 619 nm. The optimal doping amount of Mn⁴⁺ in Cs₂MoO₂F₄ is 1.12%, and the decay curves show a good fit with the single exponential decay model. The fluorescence lifetime of the synthesized phosphors is relatively short and calculated as 3.18 to 2.46 ms, the Mn⁴⁺ ions in Cs₂MoO₂F₄ experience a strong crystal field strength with a Dq/B of ∼4.87, and the distinct nephelauxetic ratio β₁ is determined to be ∼1.0226. The thermal quenching mechanism of Mn⁴⁺ was also studied. Furthermore, by using the as-synthesized Cs₂MoO₂F₄:Mn⁴⁺ phosphor as a red component and β-SiALON as a green light component, a WLED was fabricated with a high luminous efficacy of 114.70 lm·W^-1 and wide color gamut of 109.1% of the National Television Standard Committee (NTSC) value. Hence, the Cs₂MoO₂F₄:Mn⁴⁺ phosphor with a short fluorescence lifetime could potentially be an efficient red compensator for application in rapid-response backlight displays.

Full-visible-spectrum lighting realized by a novel Eu2+-doped cyan-emitting borosilicate phosphor

A novel cyan-emitting Ba₃Ca₄(BO₃)₃(SiO₄)Cl:Eu²⁺ inorganic material was developed and its potential application in full-visible-spectrum lighting was explored.

Mn4+ nonequivalent-doped Al3+-based cryolite high-performance warm WLED red phosphors

Mn⁴⁺ nonequivalent-doped Al³⁺-based cryolite red phosphors with controlled morphology and optimized luminescence properties for high-performance warm WLEDs.