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.

Frontiers of Deep-Red Emission of Mn4+ Ions with Ruddlesden-Popper Perovskites

It is well-known that the chemical composition of the host material significantly affects the spectroscopic performance of transition metal ions. However, it is worth noting that also the structure and symmetry of crystallographic sites play significant roles in transition metal ion luminescence. In this study, we demonstrate three perovskite structures of strontium titanate forming so-called Ruddlesden-Popper phases doped with Mn4+ ions. The observed reduction in the average Ti4+-O2- distance in the series SrTiO3-Sr2TiO4-Sr3Ti2O7 allowed for a record-breaking shift in the spectral position of Mn4+ emission band with a maximum of around 734 nm and led to an improvement of the already impressive thermometric performance of SrTiO3:Mn4+ in ratiometric and lifetime-based approaches. This research encourages a further search for structures that, with the help of the developed correlations between structural and optical properties, could lead to the discovery of phosphors beyond the limits established so far.

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.

K2SnOF4 and K2WO3F2 – different but similar

K2SnOF4 and K2WO3F2 were synthesized via a high-pressure/high-temperature route. Single-crystal analysis showed that both substances crystallize in the orthorhombic crystal system with space group Pnma and are isostructural to each other. The main motifs of the structures are octahedral [SnO2F4]4− and [WO4F2]4− entities for K2SnOF4 and K2WO3F2, respectively. Within the structures, these units are connected to quasi-isolated infinite chains. The substances were further characterized via powder X-ray diffraction, EDX and FT-IR spectroscopy. Doping of K2SnOF4 with Mn4+ yielded a red phosphor material which was analyzed by luminescence spectroscopy. The emission maximum is located at λ max = 631 nm.

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.

Novel Mn4+ doped red phosphors composed of MgAl2O4 and CaAl12O19 phases for light-emitting diodes

The EL spectra and photographs of the as-obtained plant growth LED and white LED by using CMA:Mn⁴⁺ red phosphors.