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Using a green and convenient method to prepare fluoride red phosphor is an important challenge for industrialization applications. In this work, K2SiF6:Mn4+ red phosphor was successfully prepared through a brief one-step co-precipitation method without HF. A simplified and non-toxic ion exchange strategy for the formation of narrow-band red-emitting K2SiF6:Mn4+ phosphors was developed using different solvent (HAc, H3PO4, HNO3, HCl, H2O). The photoluminescence intensity of the prepared K2SiF6:Mn4+ red phosphor was the highest when the pH of the reaction solution was 1.0. Furthermore, using K2SiF6:Mn4+ as red component, the warm white light LED (light-emitting diode) with low correlated color temperature (CCT = 4095 K), high color rendering index (CRI, Ra = 87) was achieved, which proved that the phosphor synthesized by this method had great application potential. The preparation method provided in this article is safer and more environmentally friendly, and has important commercial and social value. [ABSTRACT FROM AUTHOR]

Mn4+-activated perovskite-structured ANaWO2F4 (A = Li, Na, K) red phosphors were successfully prepared by a facile co-precipitation method. By changing the A-site ions, the tolerance factor (t) of host material ANaWO2F4 became adjustable. Red emissions in LiNaWO2F4:Mn4+, Na2WO2F4:Mn4+ and KNaWO2F4:Mn4+ were found to be gradually increased. The relationship between the structure and their photoluminescence properties was discussed. The results suggested that a t-dependent photoluminescence behavior may exist in perovskite-structured phosphors. As the tolerance factor increases, the emission intensity of ANaWO2F4 (A = Li, Na, K) red phosphors increases. This work also provides a reference for the exploration and optimization of Mn4+-activated perovskite-structured red phosphors. [ABSTRACT FROM AUTHOR]

A 657 nm red emission from a novel rare earth free oxide-based CaO–0.5Al2O3–0.5Nb2O5:xMn4+ (0.001 ≤ x ≤ 0.008) phosphors with high water-resistance property were prepared by solid-state reaction method. The composition and structure of the as-prepared phosphors was studied. Under relative ultraviolet (331/365 nm) and blue (465 nm) light excitation, the as-prepared phosphor presents a 657 nm red emission that assigned to the 2Eg → 4A2g transition of Mn4+ ions. The red light source in CaO–0.5Al2O3–0.5Nb2O5:Mn4+ system was discussed, and the water resistance property of the phosphor was also investigated. The as-prepared phosphor presents more proper red emission position than those of similar oxide-based Mn4+-activated phosphors and shows excellent water-resistance property compared with commercial used K2SiF6:Mn4+ phosphor. With the further optimization of its photo-luminescent properties, the as-prepared CaO–0.5Al2O3–0.5Nb2O5:Mn4+ phosphors may find its potential application in the field of white LEDs. [ABSTRACT FROM AUTHOR]

In this work, a novel red-emitting oxyfluoride phosphor Na2NbOF5:Mn4+ with an ultra-intense zero-phonon line (ZPL) was successfully synthesized by hydrothermal method. The phase composition and luminescent properties of Na2NbOF5:Mn4+ were studied in detail. The photoluminescence excitation spectrum contains two intense excitation bands centered at 369 and 470 nm, which match well with commercial UV and blue light-emitting diode (LED) chips. When excited by 470 nm blue light, Na2NbOF5:Mn4+ exhibits red light emission dominated by ZPL. Notably, the color purity of the Na2NbOF5:Mn4+ red phosphor can reach 99.9%. Meanwhile, the Na2NbOF5:Mn4+ phosphor has a shorter fluorescence decay time than commercial K2SiF6:Mn4+, which is conducive to fast switching of images in display applications. Profiting from the intense ZPL, white light-emitting diode (WLED) with high color rendering index of Ra = 86.2 and low correlated color temperature of Tc = 3133 K is realized using yellow YAG:Ce3+ and red Na2NbOF5:Mn4+ phosphor. The WLED fabricated using CsPbBr3 quantum dots (QDs) and red Na2NbOF5:Mn4+ phosphor shows a wide color gamut of 127.56% NTSC (National Television Standard Committee). The results show that red-emitting Na2NbOF5:Mn4+ phosphor has potential application prospects in WLED lighting and display backlight. [ABSTRACT FROM AUTHOR]

In this paper, a novel violet excited reddish-orange emitting Sr 3 Ga 2 Sn 1 · 5 Si 2 · 5 O 14 :Sm3+ (SGSSO:Sm3+) phosphor with high thermal stability was designed and synthesized by the high temperature solid state reaction method for the first time. The photoluminescence (PL) properties of the SGSSO:Sm3+ phosphors were investigated systematically. Under 402 nm violet light excitation, SGSSO:Sm3+ phosphor shows reddish-orange emission at 598 nm that is attributed to the 4G 5/2 → 6H 7/2 transition of the Sm3+ ions. Importantly, the PL intensity of SGSSO:Sm3+ at 423 K can maintain 87% of the initial value at room temperature. The high thermal stability of Sm3+ in SGSSO was speculated to be attributed to the energy transfer mechanism of trap formed by the hetero-valent substitution of Sm3+ at Sr2+ sites. Finally, a WLED has been fabricated by combing the violet LED chip with the as-prepared reddish-orange emitting phosphor, commercial blue BaMgAl 10 O 17 :Eu2+ (BAM:Eu2+) and green (Ba,Sr) 2 SiO 4 :Eu2+ ((Ba,Sr)S:Eu2+) phosphors. The results indicated that the as-prepared SGSSO:Sm3+ phosphor can be a potential candidate of the reddish-orange component for violet chip pumped white-light-emitting-diodes. • A novel Sr 3 Ga 2 Sn 1 · 5 Si 2 · 5 O 14 :Sm3+ reddish-orange phosphor was synthesized for the first time. • Sr 3 Ga 2 Sn 1 · 5 Si 2 · 5 O 14 :Sm3+ phosphor can be excited by 402 nm violet light and exhibited a dominant reddish-orange emission. • Sr 3 Ga 2 Sn 1 · 5 Si 2 · 5 O 14 :Sm3+ phosphor demonstrated a high thermal stability. [ABSTRACT FROM AUTHOR]

Abstract: A series of red-emitting Eu3+-doped K2LaNb5O15 niobate phosphors with tetragonal tungsten bronze-type structure were synthesized by the solid state reaction method. The structure of new tungsten bronze-type K2EuNb5O15 was identified by Rietveld refinements to crystallize in the tetragonal space group P4bm, which is isostructural to K2LaNb5O15. The relative intensity of the emission from both 5D0→7F2 and 5D0→7F1 increases with increasing Eu3+ ion concentration. The quenching mechanism of the K2La1−x Nb5O15:xEu system was investigated in detail. The relationship between Photoluminescence properties and the TTB-type structure was discussed. The quantum efficiency of K2EuNb5O15 excited under near-UV light (399nm) is 132% of that of commercial Y2O3:Eu3+ (394nm). The results demonstrated K2EuNb5O15 phosphor as a potential candidate for white light emitting diode pumped by near-UV or blue chip. [Copyright &y& Elsevier]

The discovery of pure-red emitting phosphor is great meaningful for the achievement of high color rendering index white light emitting diodes, but still a challenge due to the strict crystal field limitations. In this work, we demonstrate the preparation of a 630 nm pure-red emitting Ca 3 Si 2 O 7 :Eu2+ phosphor for the first time through a CO reduction strategy. The changes in crystal field strength caused by different methods for the preparation of Ca 3 Si 2 O 7 :Eu2+ are investigated and discussed based on the understanding of the thermodynamic theory and structure resolution. Finally, a white light-emitting diode with a high color rendering index (Ra = 98) is accomplished by combining the as-prepared Ca 3 Si 2 O 7 :Eu2+ pure-red emitting phosphor with a 375 nm chip and the commercial used blue and green phosphors. The results also demonstrate the generalizability of the weak reduction strategy for the exploration of "redder" Eu2+ doped phosphors. Pure-red emitting Ca 3 Si 2 O 7 :Eu2+ phosphor was developed by solid state reaction under CO reduction based on the understanding of the thermodynamic theory. Benefiting by the weaker reduction minimizes the impact on the initial crystal field, Eu2+ ions thus presenting an unprecedented 630 nm emission in the as prepared stronger crystal field silicate matrix. [Display omitted] • Pure-red phosphor Ca 3 Si 2 O 7 :Eu2+ was prepared by solid state reaction under CO reduction atmosphere. • The reducing activity of CO is weaker than that of H 2 at 1250 °C according to the thermodynamic theory. • Weak reduction minimizes the impact on the initial crystal field. [ABSTRACT FROM AUTHOR]

Abstract: A series of red-emitting Eu3+-doped phosphors SrLa2Mg2W2O12 were successfully prepared by the solid state reaction and their luminescence properties were investigated in detail. Under 464nm light excitation, the emission intensity at 613nm increased with the Eu3+ ion concentration rising, and the quenching effect did not appear until the Eu3+ ion concentration reached 25%, and the critical distance was calculated to be 7.74Å. The emission intensity of Sr(La0.75Eu0.25)2Mg2W2O12 is approximately three times higher than that of the commercial red phosphor Y2O3:Eu3+ under the blue light, meanwhile, the quantum efficiency of Sr(La0.75Eu0.25)2Mg2W2O12 is about two times higher than that of Y2O3:Eu3+. The Commission Internationale de l′Eclairage chromaticity coordinate of Sr(La0.75Eu0.25)2Mg2W2O12 is (x=0.660, y=0.340), which is closed to the standard of NTSC (x=0.670, y=0.330). The results indicate that Sr(La1−x Eu x )2Mg2W2O12 could be a potential red phosphor in fabrication of blue chips WLEDs. [Copyright &y& Elsevier]

A series of high quantum yield Li 2 Ge 4 O 9 :Mn4+ phosphors are prepared by solid-state reaction method, and their structure has been determined by X-ray powder diffraction with Rietveld refinement. The excitation spectra of Li 2 Ge 4 O 9 :Mn4+ exhibits two excitation bands at 300–400 nm and 400–500 nm corresponding to 4A 2 →4T 1 and 4A 2 →4T 2 transition of Mn4+ ions respectively, and emission spectra from 625 to 750 nm with the strongest emission peak at 671 nm owing to the 4E→4A 2 transition of Mn4+ ions. The optimal Mn4+ doping concentrations of Li 2 Ge 4 O 9 host are determined to be 0.3 mol% and the optimum synthesis temperature is found 800 °C. The Li 2 Ge 4 O 9 :Mn4+ phosphor demonstrated high quantum yield. The as-prepared phosphor shows excellent water-resistance and thermal stability property compared with commercial used K 2 SiF 6 :Mn4+ phosphor. Finally, a white LED with improved Ra (from 72.5 to 82) and reduced Tc (from 6530 K to 6107 K) was fabricated by using a 450 nm blue chip with Y 3 Al 5 O 12 :Ce3+ and the as-prepared Li 2 Ge 4 O 9 :0.003Mn4+ phosphor. • Li 2 Ge 4 O 9 :Mn4+ phosphor was synthesized by flux method. • Li 2 Ge 4 O 9 :Mn4+ presented red light emission under UV light excitation. • Li 2 Ge 4 O 9 :Mn4+ have high quantum yield and good moisture resistance. [ABSTRACT FROM AUTHOR]

Site preferences of Eu2+ ions on the Ba2+ sites and the Ca2+ sites were discovered in the mixed cation borosilicate Ba 2 CaB 2 Si 4 O 14 (BCBSO). Eu2+ ions are more likely to locate on the Ba2+ sites over the Ca2+ sites according to the Density Functional Theory (DFT) calculation and the photoluminescence spectrum analysis. The emission band centered at 408 ​nm was confirmed to be generated from the Eu2+ ions located on the Ba2+ sites, while the emission band centered at 548 ​nm was considered to be generated from the Eu2+ ions on the Ca2+ sites. Dual sites occupation results in a collective emission band covering 380 ​nm–780 ​nm in BCBSO:Eu phosphors. By further doping with Sr2+ ions, crystal environment of the luminescence centers could be well modulated, resulting in the tunable emission from yellow to white under UV excitation. The photoluminescence quantum yield was significantly improved from 17.9% to 36.8%. Finally, a series of white LEDs with tunable CCT (from 5132 ​K to 3402 ​K) and high Ra (reach up to 89.6) were obtained using the Ba 2(1- y /3) Ca (1- y /3) Sr y B 2 Si 4 O 14 :0.03Eu single-phase white light emission phosphors. A single-phase white light emission Ba 2(1- y /3) Ca (1- y /3) Sr y B 2 Si 4 O 14 :Eu2+ phosphor with superior advantage in color tunability was designed via tendentious multiple sites occupation strategy. [Display omitted] • Synthesis of Ba 2(1- y /3) Ca (1- y /3) Sr y B 2 Si 4 O 14 :Eu2+ phosphors. • Sites preference of Eu2+ on the sites of Ba2+ and Ca2+. • Cationic substitution to modulate the surrounding lattice environment of Eu2+. • Generation of warm white light by single-phase phosphors. [ABSTRACT FROM AUTHOR]

Sr 4 Nb 2 O 9 :Eu3+ phosphors were prepared by flux method. SrF 2 was found to be the appropriate flux and its effect on the crystal structure and optical properties were investigated. The structure of Sr 4 Nb 2 O 9 :Eu3+ has been determined by X-ray powder diffraction with Rietveld refinement. The optimal Eu3+ doping concentrations and the SrF 2 usage in Sr 4 Nb 2 O 9 were determined to be 0.13 mol and 5 wt% respectively. The spectra analysis indicated that the phosphors could be excited by near UV light of 394 nm and blue light of 465 nm, and yield an intense red light with a maximum at 614 nm. The as prepared phosphor shows its advantages in quantum yield and thermal stability when compared with that of CaMoO 4 :Eu3+, Y 3 Al 5 O 12 :Ce3+, CaAlSiN 3 :Eu2+ phosphors. Finally, a white LED with improved R a (from 75.6 to 82.5) was fabricated by using a 450 nm blue chip with Y 3 Al 5 O 12 :Ce3+ and the as-prepared Sr 4 Nb 2 O 9 :0.13Eu3+, 0.05SrF 2 phosphor. • Sr 4 Nb 2 O 9 :Eu3+ phosphor was synthesized by flux method. • Sr 4 Nb 2 O 9 :Eu3+ presented red light emission under UV light excitation. • Sr 4 Nb 2 O 9 :Eu3+ have high PL intensity and internal quantum efficiency. [ABSTRACT FROM AUTHOR]