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Artificial light fishing technology has been used in marine fisheries for thousands of years. The light source with multi‐color adjustable output is expected to become a new generation of fish‐attracting lamps. Herein, a new method of crystal‐site engineering through reducing atmospheres is proposed for the development of Eu2+ doped single‐phase phosphor with multi‐excitation and multi‐emission properties. Following this approach, the distribution ratio of Eu2+ at Ca2+ and Sr2+ sites in CaSrSiO4 (CSO) can be modulated. Importantly, Eu2+ at both lattice sites exhibit non‐interfering optical properties, CSO:Eu2+ phosphor realizes multi‐color output from green to yellow and then to red when Eu2+ occupies the Sr2+ and Ca2+ sites in a relatively balanced ratio. Benefitting from the tunable color range covering the spectral sensitivity regions of most marine fishes, this phosphor may eventually be applied in futuristic innovative fish‐attracting lamps. [ABSTRACT FROM AUTHOR]

A Sm3+-doped YGa1.5Al1.5(BO3)4 (abbreviated as YGAB) phosphor was synthesized via a solid-state reaction with mechanical activation assistance in a high-energy density stirred bead mill. The samples were characterized by laser particle size analysis, specific surface area analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and fluorescence spectroscopy. In addition, the photoluminescence characteristics, luminescence decay, thermal stability, and LED application of the phosphors were also investigated. The results show that the mechanical activation of mixed raw materials before calcination can reduce the particle size and the activation energy of crystallization, resulting in the formation of the YGAB crystal phase at a lower calcination temperature. The mechanical activation in grinding can accelerate the subsequent solid-phase reaction, make Sm3+ ions more easily diffuse into the YGAB lattice, and improve the crystal structure of the synthesized phosphor, thus enhancing the optical properties of the phosphor. According to the photoluminescence emission (PL) and excitation (PLE) spectra, Sm3+ doped in the YGAB lattice can provide an efficient emission under 405 nm excitation. The optimum doping concentration of Sm3+ ions is 0.03 mol%. The optimum photoluminescence intensity, quantum yield, and fluorescence lifetime of the phosphor synthesized from mixed raw materials ground for 45 min can be obtained. The temperature-dependent PL spectra show that the emission intensity of the YGAB:0.03Sm3+ phosphor at 425 K is 84.7% of its initial intensity at room temperature. It is indicated that the YGAB:0.03Sm3+ phosphor synthesized could be used as one of the promising LED lighting materials. [ABSTRACT FROM AUTHOR]

The minimization of thermal quenching, which leads to luminescence loss at high temperatures, is one of the most important issues for near‐infrared phosphors. In the present work, we investigated the properties of near‐infrared Ca(Sc,Mg)(Al, Si)O6 : Cr3+ phosphors with a pyroxene‐type structure under blue light excitation. The CaScAlSiO6 : Cr3+ end member of Ca(Sc,Mg)(Al,Si)O6 : Cr3+ phosphor led to broadband emission at a full‐width half maximum of 215 nm, whereas the CaMgSi2O6 : Cr3+ end member exhibited high thermal stability at 150 °C, with an intensity of 88.4 % of that at room temperature. The structural analysis and density functional theory calculations revealed the absence of soft conformations and local space confinement contributed to the high structural rigidity and weakened the thermal quenching effect. [ABSTRACT FROM AUTHOR]

We report an organic solvent–assisted (OSA) co-precipitation strategy for the production of Mn4+-activated K2TiF6 phosphor. The phosphor particle size was controlled through the selection of organic solvents with an alcohol functional group and different carbon chain lengths used in the synthesis. The synergistic effect of the organic solvent and hydrofluoric acid results in large smoothed hexagonal-shaped crystal sheets of particles that become larger as the carbon chain length of the organic solvent increases. The photoluminescence (PL) properties of K2TiF6:Mn powders strongly depend on the size and thickness of the particles. The addition of n-butanol during the synthesis increases the emission intensity of K2TiF6:Mn by 208%. The PL quantum efficiency of phosphors prepared using the n-butanol-assisted strategy is much higher (98.2%) than that of conventionally prepared phosphors (89.9%). Our findings demonstrate a way to prepare the K2TiF6:Mn phosphor with targeted morphology and very high quantum efficiency and also provide the route for the optimization of all Mn4+-activated fluoride phosphors used in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

A solvent‐vapor transport route produces centimeter‐sized single‐crystal red phosphors. The epitaxial growth route to yield its core–shell structure at ambient temperature was adopted. These red phosphors could be applied in all‐inorganic WLED devices. Cs2TiF6:Mn4+ (CTFM) single crystal provides enhancement of quantum efficiency, moisture resistance, and thermal stability compared to polycrystalline powders. The internal quantum efficiency can reach as high as 98.7 %. To further improve waterproof stability, the Cs2TiF6 (CTF) shell with tunable thickness has been epitaxially grown on the CTFM single crystal surface and a unique three‐step photoluminescence intensity evolution mechanism has been proposed. By combining as‐prepared CTFM@CTF core–shell structured single crystal, YAG:Ce single crystal and blue‐chip, warm WLEDs with excellent color rendition (Ra=90, R9=94), low correlated color temperature (CCT=3155 K), and high luminous efficacy were fabricated without any organic resins. [ABSTRACT FROM AUTHOR]

The environmentally friendly and low‐priced CaYAlO4:Tb3+ nanophosphors are combined with good optically transparent materials for the application in 3D printing. For ultraviolet (UV) light‐emitting diode excitation, CaYAlO4:Tb0.07Cey and CaYAlO4:Ce0.05Tbx nanophosphors are prepared by a sol–gel route and systematically studied for optimal excitation at 380 nm to give strong green emission to which human and aquatic animals eyes are generally sensitive. This is benefited from the dipole and spin allowed transition of Ce3+ and the 92.5% efficient energy transfer from Ce3+ to Tb3+ in this host. Polydimethylsiloxane, with 92% transmittance in the visible spectral region, is a valid choice to make the shaped artwork by a templating method, combined with the nanoparticles to give a uniform distribution, as determined by X‐ray microcomputed tomography. Polylactic acid is also employed to create a frog artwork by the fused deposition modeling method. The final 3D‐printed colorful artwork is displayed herein together with that produced by the templating method under different light source excitation to suggest a novel expression of aesthetic concepts and a potential application in the future marine environment such as a lamp to attract aquatic animals or a buoy to guide ships. [ABSTRACT FROM AUTHOR]

Crystal phosphors have many unique advantages compared with powdery ones. Herein, room‐temperature‐grown millimeter‐sized single‐crystal phosphors of Cs2XF6:Mn4+ (X = Ge, Si, and Ti) with remarkably higher external quantum efficiency than the corresponding powdery samples are reported. In addition, as compared with the powdery ones, the crystal samples exhibit much better stability toward water under different pH conditions. The red light‐emitting diodes (LEDs) based on Cs2XF6:Mn4+ crystals show significantly improved luminous efficiency than those based on their corresponding powders. An assembled white LED device composed of the two layers of phosphors, i.e., the crystal (such as Cs2GeF6:Mn4+) and commercial Y3Al5O12:Ce3+, on a blue chip exhibits intense warm white light with high luminous efficiency (up to 193 lm W−1), high color rendering indexes (88), and low correlated color temperatures (3107 K). Hence, these crystals with greatly improved efficiency and stability can be potentially applied in high‐quality LED backlighting display and white LED lighting, especially inside the micro‐LED devices. [ABSTRACT FROM AUTHOR]

In this work, a novel fluoroaluminate red phosphor of Cs2NaAl3F12:Mn4+ with excellent color purity was fabricated via the introduction of Mn4+ in the octahedral center. The crystal and electronic structures, luminescence properties and optical performances were characterized and investigated in detail. The evidences showed that Cs2NaAl3F12:Mn4+ well-crystallized into a single phase with particulate morphology, and the non-equivalent occupation in Cs2NaAl3F12 resulted in sharp red emissions with improved color purity upon blue light illumination. For solid-state lighting, the optical parameters consisted of the "blue-yellow-red" contributions significantly improved to a high color-rendering index of 88.7 and a low color temperature of 3856 K, indicating the potential use of Cs2NaAl3F12:Mn4+ for warm white light-emitting diode applications. [ABSTRACT FROM AUTHOR]

Luminescence of monoclinic lithium metatitanate (Li2TiO3) powders activated with different quantities of Mn4+ is studied in detail. Its strong deep‐red emission arising from the Mn4+ 2Eg → 4A2g spin forbidden transition is centered at around 688 nm and is suitable for luminescence thermometry. Structural and electron paramagnetic resonance analyses show that Mn4+ ions are equally distributed in two almost identical Ti4+ sites in which they are octahedrally coordinated by six oxygen ions. Calculations based on the exchange charge model of the crystal field provided values of Racah parameters (B=760 cm−1, C= 2993 cm−1), crystal‐field splitting Dq= 2043 cm−1, and the nephelauxetic parameter β1=0.9775. The maximal quantum efficiency of 24.1% at room temperature is found for 0.126% Mn4+ concentration. Temperature quenching of emission occurs by a cross‐over via 4T2 excited state of the Mn4+ ions with T1/2=262 K and is quite favorable for the application in the lifetime‐based luminescence thermometry since relative changes in emission decay values are exceptionally‐large (around 3.21% at room temperature). We derived theoretical expressions for the temperature dependence of the absolute and relative sensitivities and discuss the influence of host material properties on lifetime sensitivities. [ABSTRACT FROM AUTHOR]

(Ca1−x−yMgxSryCl2/SiO2):Eu2+ phosphors with intense violet-blue emission were synthesized through a high temperature solid-state reaction method. The colour of the emission is tunable from violet-blue to blue as well as to the violet spectral region by adjusting the concentration of Mg2+ or Sr2+, respectively. An abnormal shift in emission wavelength with the ratio of alkaline earth metal ions was observed and explained by combining electronegativity with the crystal field splitting equation. The UV light content in the emission spectra of (Ca0.8Mg0.2Cl2/SiO2):0.003Eu2+ was successfully reduced below 0.1%, thus providing a safer violet-blue light source for phototherapy. Moreover, the measurement results showed an emission band peaked at 440 nm with a full-width at half maximum of 40 nm under 343 nm excitation, which matches with the most effective range for the treatment of hyperbilirubinemia. CIE chromaticity coordinates of (0.156, 0.044) and an internal quantum efficiency of 41.7% were obtained. The temperature-dependent photoluminescence spectra of (Ca0.8Mg0.2Cl2/SiO2):0.003Eu2+ were also presented. These excellent properties reveal that the violet-blue emitting phosphor could be a potential candidate in converting near-UV radiation to violet-blue emission for phototherapy when combined with UV LED chips. [ABSTRACT FROM AUTHOR]

A series of red-emitting phosphors composed of Li2ZrF6:Mn4+ (LZF:Mn) have been synthesized via an ionic-exchange reaction route at room temperature. The microstructure and optical characterizations have been investigated according to the detailed experiments. The morphology of the phosphor LZF:Mn changes with the concentration of HF, the reaction time and temperature. The uniform crystals of LZF:Mn with regular hexagonal tablets have been obtained in 30–40 wt% HF solutions by conducting the reaction at room temperature for about 8 h. The influences of reaction parameters on the morphology and photoluminescence properties of LZF:Mn have been systematically investigated. The luminescence intensity of LZF:Mn has been optimized by controlling the synthesis procedure and parameters. The white light-emitting diode (WLED) fabricated with LZF:Mn and Y3Al5O12:Ce3+ (YAG:Ce) on InGaN LED chip displays a warm white light with correlated color temperature (CCT) at 3789.4 K and color rendering index (CRI) of 91. [ABSTRACT FROM AUTHOR]

Red phosphors composed of Mn4+-activated complex fluorides have attracted considerable attention for applications in warm white light-emitting diodes (WLEDs). In the present study, we report a facile strategy to synthesize a novel red phosphor LiSrGaF6:Mn4+ (LSGF:Mn) at room temperature, and we also discuss its formation mechanism. Mn4+ ions occupy Ga3+ sites located at the centers of distorted [GaF6]3− octahedrons and emit intense red luminescence when excited by UV or blue light. The effects of synthesis conditions such as the type of strontium salts, the concentrations of K2MnF6 and NH3·H2O, and the reaction temperature have been investigated. The luminescence intensity of the phosphor LSGF:Mn has been improved by optimizing the synthetic parameters. The as-prepared phosphor LSGF:Mn exhibits broad and intense absorption in the blue region and bright luminescence in the red region, which indicate that it is promising for applications in warm WLEDs. [ABSTRACT FROM AUTHOR]

The Mn4+ activated fluostannate Na2SnF6 red phosphor was synthesized from starting materials metallic tin shots, NaF, and K2MnF6 in HF solution at room temperature by a two-step method. The formation mechanism responsible for preparing Na2SnF6:Mn4+ ( NSF:Mn) has been investigated. The influences of synthetic parameters: such as concentrations of HF and K2MnF6 in reaction system, reaction time, and temperature on crystallinity, microstructure, and luminescence intensity of NSF:Mn have been investigated based on detailed experimental results. The actual doping concentration of Mn4+ in the NSF:Mn host lattice is less than 0.12 mol%. The most of K2MnF6 is decomposed in HF solution especially in hydrothermal system at elevated temperatures. The color of the as-prepared NSF:Mn samples changes from orange to white when the temperature is higher than 120°C, which indicates the lower concentration of luminescence centers in the crystals. A series of 'warm' white light-emitting diodes with color rendering index ( CRI) higher than 88 and correlated color temperatures between 3146 and 5172 K were obtained by encapsulating the as-prepared red phosphors NSF:Mn with yellow one Y3Al5O12:Ce3+ ( YAG:Ce) on 450 nm blue InGaN chips. The advantage of the synthetic strategy to obtain NSF:Mn can be extended to developing Mn4+-doped red phosphors from low-costing metals at room temperature for large-scale industrial applications. [ABSTRACT FROM AUTHOR]

A series of Ca3Y(GaO)3(BO3)4:Tb3+,Eu3+ phosphors were prepared by a high-temperature solid-state reaction. Their phase structures were confirmed by powder X-ray diffraction and the element distribution was measured using transmission electron microscopy elemental mapping. The photoluminescence emission and excitation spectra and fluorescence lifetime were studied and discussed in detail. The results revealed that Eu3+ ions can be efficiently sensitized by Tb3+ ions under near-UV excitation. In addition, the energy transfer efficiency can be controlled by adjusting the ratio of Eu3+ and Tb3+ to realize colour tunable emission from green to red. For Ca3Y(GaO)3(BO3)4:0.50Tb3+,0.10Eu3+, the emission intensity at 425 K is 78.11% of that at 300 K, being available to near-UV LEDs. [ABSTRACT FROM AUTHOR]

Red phosphor BaSiF6:Mn4+ has been synthesized by a hydrothermal method at 120°C for 24 h, in which either Si or SiO2 is used as silicon source. HF as weak acid performs a complex agent for the formation of anion groups [SiF6]2− and [MnF6]2−. The luminescence properties of undoped BaSiF6 have been firstly observed. The dependence of luminescence intensities of BaSiF6:Mn4+ on the concentrations of HF and KMnO4 in precursory solution has been investigated. The as-prepared BaSiF6:Mn4+ exhibits high chemical stability even in deionized water. [ABSTRACT FROM AUTHOR]

Abstract A red phosphor with a broad excitation band in blue region and sharp emission peaks in red region is needed for compensating the red components of white light-emitting diodes (WLEDs) by converting blue light with a yellow phosphor Y 3 Al 5 O 12 :Ce3+ (YAG:Ce). The red phosphor LiSrAlF 6 :Mn4+ (LSAF:Mn) with morphology of flaky particles about 50 μm in diameter has been synthesized by an ion-exchange reaction route at room-temperature in air. The as-synthesized phosphors were characterized by x-ray powder diffraction (XRD), scanning electron microscope (SEM), and temperature-dependent photoluminescence (PL) spectra. The excitation spectrum of LSAF:Mn shows a broad-band excitation from 400 to 500 nm that is due to the spin-allowed transition of 4A 2g → 4T 2g of Mn4+, indicating a potential application for solid state lighting. The optimal PL intensity of the phosphor LSAF:Mn has been obtained by optimizing the synthetic parameters. Highlights • Synthesis of LiSrAlF 6 :Mn4+ at room temperature and its reaction mechanism. • The phosphor shows good thermal stability and optical properties. • The influence of synthesis conditions on luminescence is studied. [ABSTRACT FROM AUTHOR]

An investigation is reported on the coating of the alkaline earth sulfide based red emitting phosphor Ca0.8Sr0.2S:Eu2+, Tm3+ by a thin layer of SiO2 or TiO2 using the sol–gel process. Their alkoxides were used as precursors and were dissolved in an aqueous ethanol medium. EDX (energy dispersive X-ray), SEM (scanning electron microscopy) and powder XRD (X-ray diffraction) were used to characterize the coating. The properties of coated phosphors were also tested; resistances of coated phosphors to moisture and other atmospheric components have been enhanced to a great degree without more loss of their optical properties. When the ratio of oxide ranges from 2% to 5% in weight, the brightness of phosphor has no remarkable change but the stability has been improved greatly. [Copyright &y& Elsevier]

The exploration of Cr3+-doped near-infrared (NIR) phosphors for light-emitting diodes has attracted widespread attention. In this work, we present a fluoride double perovskite K 2 LiScF 6 :Cr3+ NIR-emitting phosphor through a co-precipitation method. It was found that the Cr3+ activators undergo a weak crystal field and present a NIR emission band peaking at 768 nm under blue light excitation (430 nm). Meanwhile, the K 2 LiScF 6 :Cr3+ exhibits a high activation energy (0.537 eV), a weak electron-phonon coupling (EPC) effect and a remarkable photoluminescence thermal stability at 423 K, with an intensity of 95.1% of that at room temperature. Profiting from the luminescent properties, clear night vision images and human palm vein photographs were realized by coating the K 2 LiScF 6 :Cr3+ phosphor on a blue InGaN chip and using it as a lighting source, suggesting its applicability in light-emitting diodes for NIR spectroscopy applications. • A novel near-infrared phosphor of K 2 LiScF 6 :Cr3+ has been synthesized. • The low thermal quenching behavior of Cr3+ in K 2 LiScF 6 host was verified. • The applications of K 2 LiScF 6 :Cr3+ for night vision and vein imaging were evaluated. [ABSTRACT FROM AUTHOR]

Here we reported a tunable full-color-emitting Ba 3 P 4 O 13 :Eu 2+ phosphor and the phase selection depending on Eu 2+ doping concentration in two different polymorphic forms of Ba 3 P 4 O 13 . With increasing Eu 2+ doping concentration, the crystal-phase of Ba 3 P 4 O 13 :Eu 2+ phosphor transformed from low-temperature form (low-Ba 3 P 4 O 13 phase) to high-temperature form (high-Ba 3 P 4 O 13 phase) when other synthesis conditions remained constant. The emission from Ba 3 P 4 O 13 :Eu 2+ was strongly related to the specific crystal-phase structure of Ba 3 P 4 O 13 host, and the luminescent colors of Ba 3(1- x ) P 4 O 13 :3 x Eu 2+ were tuned successfully from blue to white and eventually to yellow following the crystal-phase transformation triggered by the Eu 2+ doping. The temperature-dependent photoluminescence properties for the selected Ba 3(1- x ) P 4 O 13 :3 x Eu 2+ phosphors were also investigated. The results suggest low-Ba 3 P 4 O 13 : Eu 2+ phosphor has better thermal stability than high-Ba 3 P 4 O 13 : Eu 2+ phosphor. [ABSTRACT FROM AUTHOR]

Bi 3+ and Eu 3+ co-activated Ca 14 Al 10 Zn 6 O 35 (CAZO) phosphors were synthesized by a solid state sintering method. X-ray diffraction (XRD), scan electron microscopy (SEM), photoluminescence (PL) and decay studies were employed to characterize the as-prepared phosphor samples. A dual-emission composed of blue and red luminescence is observed in Bi 3+ and Eu 3+ co-activated CAZO phosphors, which has potential application in artificial lighting to improve the plant growth. The highest intensities of emissions of CAZO:Bi 3+ and CAZO:Bi 3+ ,Eu 3+ are obtained at the concentration of Bi 3+ at 0.5 mol% and 1.0 mol%, respectively. The overall luminescence color can be tunable from blue, purple, to red by changing the molecular ratio of Bi 3+ to Eu 3+ . The mechanism of energy transfer from Bi 3+ to Eu 3+ has been demonstrated by decay times of Bi 3+ emissions which are varied with Eu 3+ content doped in host lattice. The efficiency of energy transfer from Bi 3+ to Eu 3+ increases with the increase of Eu 3+ concentration, which leads to that the internal quantum yields (QY) of both Bi 3+ and Eu 3+ co-activated CAZO are higher than either of Bi 3+ or Eu 3+ singly doped phosphor. [ABSTRACT FROM AUTHOR]

A facile strategy to modify the surface of K 2 SiF 6 :Mn4+ (KSFM) with commercially available hydrophilic hydroquinone (HQ) has been developed and waterproof stability (moisture resistance) of the KSFM has been significantly improved. It has been demonstrated that there are strong interactions between KSFM and HQ on the interface due to the hydrogen bonds of fluorine in KSFM with hydrogen in HQ. The relative luminous intensity of HQ-modified KSFM (denoted as KSFM-HQ) remained 99.7% of its initial value after immersion in water for 336 h, remarkable higher than that of KSFM which remained only 38.0%. It is proposed that the high water resistance of KSFM-HQ is achieved via two possible mechanisms: in situ decomposition of dark brown manganese (owing to the hydrolysis of [MnF 6 ]2−) on the KSFM crystal surface and consequently the formation of a more protective Mn4+-free layer. The process effectively combines the advantages of transparent organic materials (herein HQ) before immersion in water and durable moisture resistance of inorganic materials (herein K 2 SiF 6) on surface after immersion in water. The importance of HQ loading on moisture-sensitive fluoride phosphors has been further confirmed by using HQ-treated K 2 GeF 6 :Mn4+ (KGFM) as an additional example. This strategy provides a one-of-a-kind way to the development of water-resistant Mn4+-doped fluoride phosphors with high luminous stability for potential applications in water-borne fluorescent anti-counterfeiting ink and even warm WLEDs operating in high humidity. [Display omitted] • A novel hydrophilic and transparent organic hydroquinone molecules modified K 2 SiF 6 :Mn4+ red phosphor has been developed. • The hydrophilic modified K 2 SiF 6 :Mn4+ red phosphor and its related LED device show highly improved water/moisture resistance. • A double-protection mechanism combining the advantages of both organic and inorganic coating materials has been proposed. [ABSTRACT FROM AUTHOR]

A novel red-emitting phosphor Ca 8 MgLu(PO 4 ) 7 :Eu 3+ was synthesized by a high-temperature solid-state reaction method. Its crystal structure, photoluminescence emission and excitation spectra, and decay time were investigated in detail. X-ray diffraction (XRD) results indicate that Ca 8 MgLu(PO 4 ) 7 crystallizes in single-phase component with a whitlockite-like structure and the space group R 3 c of β -Ca 3 (PO 4 ) 2 . The emission spectrum shows a dominant peak at 612 nm due to the dipole 5 D 0 → 7 F 2 transition of Eu 3+ , and the luminescence intensity keeps increasing with increasing the content of Eu 3+ to 100%. The excitation spectrum is coupled well with the emission of near ultraviolet (NUV) LED (380–410 nm). The CIE coordinates of Ca 8 MgLu(PO 4 ) 7 :Eu 3+ phosphor is (0.654, 0.346), being close to the standard value of National Television Standard Committee (NTSC) for red phosphor, (0.670, 0.330). The internal quantum efficiency of the phosphor is 69% under the excitation of 394 nm. The results show that Ca 8 MgLu(PO 4 ) 7 :Eu 3+ is a very appropriate red-emitting phosphor with a high ratio of red and orange for NUV-based white LEDs. [ABSTRACT FROM AUTHOR]

Abstract: A series of Ce3+ and Tb3+ doped color-tunable novel phosphors with both phosphate and silicate hosts, Na2Ca4(PO4)2SiO4, were synthesized by a solid-state process for the first time as far as we know. The photoluminescence properties, energy transfer (ET) among rare earth ions and temperature quenching effect were investigated. Dipole–dipole and dipole–quadrupole interactions were proved to be responsible for ET mechanisms of Ce3+–Ce3+ and Ce3+–Tb3+ in Na2Ca4(PO4)2SiO4, respectively. Furthermore, the emitting color of phosphors can be tuned from blue to green by increasing the dopant concentrations of Tb3+ ions. Finally, temperature-quenching measurement revealed that the as-synthesized phosphor had good thermal characteristics, which indicates that the phosphor can be served as a key material for phosphor-converted white LEDs. [Copyright &y& Elsevier]

Abstract: Novel phosphors of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ were synthesized by a solid-state process and characterized with X-ray diffraction, photoluminescence (PL), PL excitation (PLE), and fluorescence decay time. The relationship between the observed Ce3+ emission properties and the crystal structure of Na2Y2B2O7 is built and the result shows that Ce3+ ions occupy two non-equivalent Y3+ sites in the host. The codoping of Tb3+ in Na2Y2B2O7:Ce3+ can tune the emitting colour from blue to green and increase the luminescence quantum efficiency to 75.2% by the energy transfer of Ce3+→Tb3+. The energy transfer processes of Ce3+–Ce3+ and Ce3+–Tb3+ are analysed and determined to be electric dipole–dipole and dipole–quadrupole, respectively. The broad PLE spectra of Na2Y2B2O7:Ce3+ and Na2Y2B2O7:Ce3+,Tb3+ are well matched with the emission from near UV LED chips, which indicates that they are promising blue and green phosphors for phosphor-converted white LEDs. [Copyright &y& Elsevier]

Abstract: Infrared to visible up-conversion emissions in Yb3+–Er3+ co-doped KGd2F7 samples excited at 980 nm are presented in this paper. Green (2H11/2,4S3/2→4I15/2), red (4F9/2→4I15/2) and violet (2H9/2→4I15/2) emissions are observed under low pumping power, and the green emission is dominant. The dependences of these emissions as function of the pumping power intensities and the doped rare-earth ion concentrations are described. The results indicate that the green and red emission of Er3+ ion result from two-photon excitation processes, and the violet emission of Er3+ ion from three-photon processes. The most efficient composition for green emission is 2–4 mol% Er3+ and 10–20 mol% Yb3+ in synthesized samples. The mechanisms for explaining these up-conversion properties have been provided. [Copyright &y& Elsevier]

Hexagonal NaY1−xYbxF4:Ln3+ (x=0.05–1.00, Ln3+=Er3+ or Tm3+) have been prepared through hydrothermal synthesis. Powder X-ray diffraction (XRD) patterns have been presented to characterize the synthesized samples. The concentration of doped rare earth and pumping power on the upconversion emissions have been extensively investigated under 980 nm excitation. NaY1−xYbxF4:Er3+ emit green (2H11/2, 4S3/2→4I15/2), red (4F9/2→4I15/2), weak violet (2H9/2→4I15/2) and weak UV (4G11/2→4I15/2) upconversion emission. NaY1−xYbxF4:Tm3+ exhibit intense blue (1G4→3H6, 1D2→3F4), weak red (1G4→3F4) and UV (1D2→3H6) upconversion emission. A two-photon process account for the green and red emission of an Er3+ ion with the energy transfer from Yb3+ ion. One blue emission (1G4→3H6) of Tm3+ results from a three-photon excitation, and the other (1D2→3F4) from a four-photon process. The measured data about emission intensity suggest that hexagonal NaYF4:Yb3+/Er3+ is a more efficient upconverting phosphor than cubic one. Comparison of the measured properties in our work with values from the reported literature suggests that hydrothermally synthesized NaYF4:Yb3+/Er3+ (or Tm3+) samples emit more pure green or blue emission than solid-state synthesized samples with certain concentration of doping rare earth ions. [Copyright &y& Elsevier]

Mn4+-activated fluorides rank among the most significant red phosphors for white light emitting diodes (LEDs) with enhanced color rendition, while their poor moisture resistance hinders further application. Surface coating with a protective layer is general approach to improving moisture resistance. However, these methods usually suffer from complex post-processing and poor shell stability. Herein, the introduction of passivation ions (Nb5+) may suppress the hydrolysis of [MnF 6 ]2–, which provides a facile approach to obtaining moisture-resistant fluoride phosphors. Compared to K 2 TiF 6 :5.0%Mn4+, the moisture resistance and luminescence intensity of K 2 Ti 0.949 Nb 0.051 F 6.051 :5.0%Mn4+ improved significantly following the addition of Nb5+. In addition, the combination of as-prepared K 2 Ti 0.949 Nb 0.051 F 6.051 :5.0%Mn4+ red phosphor, YAG:Ce yellow phosphor and blue-chip enables the production of warm white LEDs with excellent color rendition (Ra = 90.2), low correlated color temperature (CCT = 3816 K), and high luminous efficacy (132.2 lm/W). • A facile strategy for improving moisture-resistance of fluoride red phosphors without surface modification is proposed. • The water resistance of K 2 TiF 6 :Mn4+ can be significantly improved by Nb5+. • Warm white LEDs with excellent color rendition (Ra = 90.2) and high luminous efficacy (132.2 lm/W) have been fabricated. [ABSTRACT FROM AUTHOR]

• A novel single-component white-light-emitting CYAB phosphor has been synthesized. • Tunable photoluminescence and energy transfer among Ln3+ ions are discussed. • The synthesized phosphors possess significant resistance to the thermal-quenching. • WLED devices were fabricated exhibiting low CCT and high Ra. The white light-emitting diodes, contributing as a light initiator for the succeeding generation, is now becoming a consistently developing and attractive research area. However, the weak thermal stability, high correlated color temperature (CCT), and low color rendering (Ra) restrict its effectiveness for large-scale implementation. In this work, we reported for the first time the incorporation of rare-earth ions Ce3+-Tb3+-Sm3+ into Ca 3 YAl 3 B 4 O 15 (CYAB) in the fabrication of WLEDs, which showed tunable photoluminescence properties to accomplish exceptional thermal stability, single-phase white light emission, and efficient energy transfer among Ce3+, Tb3+, Sm3+ ions, respectively. The crystal structure and the rare earth ion dopants in the cation borate CYAB phosphors were quantitatively evaluated, that highlighting the preferences at 9-fold-coordinated Y sites. The sensitization effects were studied by evaluating the photoluminescence, lifetime curves, and quantum efficiencies, respectively. Besides this, the CY 0.45 AB:0.50Tb3+,0.05Sm3+ and CY 0.65 AB:0.03Ce3+,0.20Tb3+,0.12Sm3+ phosphors possess significant resistance towards thermal quenching phenomena. The white LED either containing CY 0.45 AB:0.50Tb3+,0.05Sm3+ phosphor blended with the commercial blue phosphor or the single-phase WLED only containing CY 0.65 AB:0.03Ce3+,0.20Tb3+,0.12Sm3+ phosphor exhibited warm white emissions either with low CCT ≈ 4543 K or 3913 K and high Ra with 86.0 or 84.4, respectively. These results are superior to the commercial WLED containing Y 3 Al 5 O 12 :Ce3+ phosphor and blue LED chip (CCT ≈ 7746 K, Ra ≈ 75), that furnish either as a good candidate for the fabrication of warm WLED. [ABSTRACT FROM AUTHOR]

Nb5+ is proved to play a major role in improving the moisture-resistant performance of Mn4+ by self-suppressing the hydrolysis of [MnF 6 ]2− groups, which may provide a new approach to substantially improve the waterproof stability of Mn4+-activated (oxy)fluoride red phosphors. • Cs 2 NbOF 5 :Mn4+ shows much better moisture resistance than fluoride red phosphor. • Nb5+ is proved to play a leading role in improving the water-resistant properties. • The water resistance of Mn4+-activated fluorides can be improved by Nb5+. • Warm WLEDs with high luminous efficacy of 174 lm/W have been fabricated. Mn4+-activated fluoride red phosphors, the most important red phosphors for warm white light emitting diodes (LEDs), usually suffer from inherent poor moisture resistance which is a major obstacle to their long-lasting outdoor applications in a high humidity environment. Surface modification of phosphors by coating with either organic or inorganic shells is an effective way to improve waterproof stability. However, the coating procedure usually has a negative impact on the luminous efficacy due to the increased passivation shell thickness. In this work, Mn4+-activated oxyfluoroniobate (Cs 2 NbOF 5), a highly efficient phosphor with internal quantum efficiency of ca. 82%, has been successfully synthesized and it is interesting to note that Cs 2 NbOF 5 :Mn4+ can exhibit remarkably improved waterproof stability even without surface coating compared to well-accepted commercial fluoride red-emitting phosphor, K 2 SiF 6 :Mn4+. The results obtained indicate that Nb5+ ions inside red phosphor play a crucial role in improving the water-resistant performance of Mn4+, which provides a new concept for overcoming the downside of their waterproof in humid conditions and maintaining the luminescence efficiency. In the final phase white LEDs with a high luminous efficacy of 174 lm/W (higher than commercial fluoride red phosphors), low correlated color temperature (3164 K) and high color rendering index (R a = 90 and R 9 = 85) have been fabricated using Cs 2 NbOF 5 :Mn4+. [ABSTRACT FROM AUTHOR]

Polyhedral anions have been used as supporting host structure to improve the luminescent properties of phosphors. However, the underlying mechanism for improving the thermal stability of luminescence by anion modification is rarely studied. In this paper, it was reported for the first time that thermal quenching and luminescent properties of red-emitting phosphors, Na 2- n Y(MoO 4) 1+ n (PO 4) 1- n :Tb3+,Eu3+, can be adjusted by the ratio of acid radicals. Rietveld refinements and Debye temperature calculations show that the subtle replacement of [MoO 4 2– by [PO 4 3– results in the shrinkage of the crystal lattice and an improvement in lattice rigidity of the host, but does not change the crystal type. A detailed explanation of the mechanism for adjustable thermal stability of luminescence is provided via temperature-dependent X-ray diffraction, Raman, formation energy, and work function. The strategy of anion modification reveals an effective method for improving the thermal stability and tuning the luminescent spectra of phosphors, it also sheds light on the development of new phosphors. Furthermore, Na 1.4 Tb 0.5 (MoO 4) 1.6 (PO 4) 0.4 :0.5Eu3+ red-emitting phosphor with an internal quantum efficiency of 66.67% can be efficiently excited with blue light (465 nm) and the integrated intensity at 425 K is 86.4% of that at 300 K. The controllable local structure-dependent luminescence makes this novel red-emitting phosphor attractive for both blue and near-UV chips based WLEDs. The luminescent properties especially the thermal stability of the red-emitting phosphors efficiently excited with blue light (465 nm), Na 2- n Y(MoO 4) 1+ n (PO 4) 1- n :Tb3+,Eu3+, can be controlled by varying the ratio of acid radicals in the host. Image 1 • We reported for the first time that the lattice rigidity and the thermal stability of luminescence of red-emitting phosphors, Na 2- n Y(MoO 4) 1+ n (PO 4) 1- n :Tb3+,Eu3+, can be improved by subtle anion replacement method. • The underlying mechanism of enhancing thermal stability of luminescence was analyzed via temperature-dependent XRD and Raman spectra, formation energy analysis and work function study. • Na 1.4 Tb 0.5 (MoO 4) 1.6 (PO 4) 0.4 :0.5Eu3+ can be efficiently excited with blue light to produce intensely red emission with the intensity at 425 K is as high as 86.4% of that at 300 K. [ABSTRACT FROM AUTHOR]

In this work, we present a novel Mn4+-activated Rb 2 NaAlF 6 red phosphor synthesized through a cation exchange route at room temperature. The structural and optical features were characterized by X-ray diffraction, energy dispersive X-ray spectrometer, scanning electron microscopy, X-ray fluorescence, emission, excitation, and luminescence decay curves. The straightforward evidences have shown that the as-prepared Rb 2 NaAlF 6 :Mn4+ crystallizes into single cubic phase with regular octahedral particulate morphology, and exhibits broad excitation band and sharp emission lines in the red and blue regions. The luminescence properties, thermal stability and optical performance were systematically investigated to recognize the luminescence behavior of Rb 2 NaAlF 6 :Mn4+ and its potential application for white light illumination. The results suggest that the Rb 2 NaAlF 6 :Mn4+ phosphor exhibits excellent thermal stability and is capable of tuning the cold white light to warm in white light-emitting diodes. A novel fluoroaluminate red-emitting phosphor of Rb 2 NaAlF 6 :Mn4+, showing regular octahedral particulate morphology, outstanding thermal stability, intense red emission lines and broad blue excitation band characteristics, was presented in this work. With the introduction of this phosphor, the R a and T c data of commercial WLED can be significantly improved, indicating its potential use for warm white light illumination. Image 1 • The red luminescence from a novel Rb 2 NaAlF 6 :Mn4+ red phosphor was presented. • The crystal structure and luminescence properties have been confirmed. • The concentration quenching mechanism and optical performance have been elucidated. [ABSTRACT FROM AUTHOR]

A WLED device with extremely high color-rendering index up to 91.4 was firstly fabricated by the novel multi-center activated single-component white light-emitting phosphor, Sr 2 LaGaO 5 :Dy3+,Sm3+, with a deep UV-LED chip. • A novel single-component white light-emitting phosphor has been synthesized. • The phosphor co-doped with Dy3+ and Sm3+ is firstly used in deep UV pumped WLEDs. • A deep UV chip pumped WLED with Ra up to 91.4 has been fabricated with the phosphor. • The Ra value is the highest among single-component white phosphor-converted WLEDs. • No energy transfer among host and dopants provides a new route to tune PL properties. Single-component white light-emitting phosphors for phosphors-converted WLEDs are a hot spot of solid-state lighting field. Dy3+ is a promising candidate for white light generation in single-component hosts; however, the inappropriate ratio of yellow light to blue and the lack of red light restrict its applications in full-color display and indoor lighting. Here, a novel multi-center activated single-component white light-emitting phosphor, Sr 2 LaGaO 5 :Dy3+,Sm3+, has been designed and synthesized. It is surprisingly found that there is no evident energy transfer between the host and the dopants even though they satisfy the rule of spectral overlap, which can be explained from the special structure of the phosphor. The co-excitation of the host and the dopants would be a facile strategy to finely tune the luminescent spectra of phosphors. By adjusting the doping concentrations of Dy3+ and Sm3+, we can control the relative intensities of the emissions peaked at 493 nm and 574 nm from Dy3+, 604 nm from Sm3+ and the broadband within the range of 400 – 500 nm from the host. Therefore, the emission color of the co-doped phosphors can be tuned from white light to orangish red region with correlated color temperature decreasing from 5708 K to 1971 K. A WLED device with extremely high color-rendering index (Ra) up to 91.4 was fabricated by coating the synthesized phosphor with a deep UV LED chip. And it is the first time to use a single-component white light-emitting phosphor co-activated with Dy3+ and Sm3+ in deep UV chip excited WLEDs with high Ra. [ABSTRACT FROM AUTHOR]

A novel red-emitting Na 2 Tb 0.5 (MoO 4)(PO 4):0.5Eu3+ phosphor was successfully synthesized via high temperature solid-state reaction method to explore new red emissions with high thermal stability and high colour purity. The results indicate that the alternating tetrahedrons of [PO 4 ]3- and [MoO 4 ]2- formed in the three-dimensional structure play a decisive role in isolating Tb3+ and Eu3+ ions. This structural isolation increases the concentration quenching of Tb3+ and Eu3+ in single-doped phosphors by more than 50%. In co-doped phosphors, the energy transfer from Tb3+ to Eu3+ was verified by the overlap of luminescent spectra and variations in decay curves. The emission colour of Na 2 Y 1- x - y (MoO 4)(PO 4): y Tb3+, x Eu3+ can be tuned from green to red through the energy transfer process by adjusting the ratio of Tb3+/Eu3+. The emission intensity at 150 °C is 84.7% compared to room temperature, as well as the remarkable correlated colour temperature (2425 K) and high colour purity (95.3%) with CIE chromaticity coordinates (0.654, 0.345) make Na 2 Tb 0.5 (MoO 4)(PO 4):0.5Eu3+ as an incredible red-emitting phosphor for both display devices and warm white lighting applications. Image 1 • This phosphor emits high-purity red light (95.3%), it can therefore be used in display devices. • The remarkable CCT (2425 K) also reveals the application value for warm white lighting. • The emission at 425 K is 84.7% of that at room temperature, demonstrating the excellent thermal stability and providing a reliable red light source. • The energy transfer process has been investigated to evaluate the relationship between decay curves and Eu3+ doping amount. [ABSTRACT FROM AUTHOR]

The local crystal structure engineering becomes an important strategy to design new phosphors with enhanced optical and thermal performance of white light-emitting diodes. Herein, a series of Na 3 Sc 2 (PO 4) 3 : Eu2+ and K y Na 2.97-y Sc 2 (PO 4) 3 : 0.03Eu2+ phosphors were synthesized via traditional high temperature solid-state reaction method. X-ray powder diffraction analysis and Rietveld refinement provide insight in the detailed crystal structure. Furthermore, Eu2+ doped Na 3 Sc 2 (PO 4) 3 exhibits bright blue emission in 400–540 nm spectral range with a maximum value at ~ 460 nm under n -UV light excitation. The concentration quenching mechanism of Eu2+ in Na 3 Sc 2 (PO 4) 3 is certified to be a dipole-dipole interaction. Additionally, crystal structure tailoring is a potential strategy to design new phosphors for particular applications. Therefore, the effects of K+ substitution on the structure and photoluminescence of Eu2+ activated Na 3 Sc 2 (PO 4) 3 is presented in detail. Rietveld refinement data revealed that unit cell volume and Na/K–O band length increase when K+ occupy the Na+ sites. This sensitive local structure resulted in a considerable enhancement of the photoluminescence intensity of Eu2+. Incorporation of K+ in the crystal structure is a feasible route to realize fine-tuning of emission color and broaden the color gamut. In the meantime, Na 2.7 K 0.27 Sc 2 (PO 4)3 : 0.03Eu2+ phosphor exhibits excellent thermal stability at high temperature over a significant radiative recombination of energy transfer from traps to Eu2+. These results confirm that Na 2.7 K 0.27 Sc 2 (PO 4)3 : 0.03Eu2+ phosphor might be used as a blue component in n -UV chip activated white light-emitting diodes for the next-generation of indoor solid-state lighting applications. • Partial K+ substitution at Na+ sites leads to more than 4 folds enhancement of Eu2+ emission. • K+ co-doping is a feasible route to realize the fine-tuning of color emission and broaden the color gamut. • Thermal stability of K 0.27 NSP: 0.03Eu2+ tends to be much better than that of NSP: 0.03Eu2+. [ABSTRACT FROM AUTHOR]

The title phosphor is synthesized by a new environmentally friendly hydrothermal method from solutions of SiO2, KHF2, and Mn(HPO4)2 (autoclave, 180 °C, 6 h). [ABSTRACT FROM AUTHOR]

Red phosphors K2XF6:Mn4+ (X: Si, Ti, Ge) are precipitated from a 40% aq. [ABSTRACT FROM AUTHOR]