Tunable luminescence properties and efficient energy transfer in Eu,Mn co-doped Ba2MgP4O13

A series of Ba₂Mg_1−xMn_xP₄O₁₃ (x = 0-1.0) and Ba_1.94Eu_0.06Mg_1−xMn_xP₄O₁₃ (x = 0-0.15) phosphors were prepared by conventional solid-state reaction. X-ray powder diffraction (XRD), the photoluminescence spectra, and the decay curves are investigated. XRD analysis shows that the maximum tolerable substitution of Mn²⁺ for Mg is about 50 mol% in Ba₂MgP₄O₁₃. Mn²⁺-singly doped Ba₂MgP₄O₁₃ shows weak red-luminescence peaked at about 615 nm. The Eu²⁺/Mn²⁺ co-doped phosphor emits two distinctive luminescence bands: a blue one centered at 430 nm originating from Eu²⁺ and a broad red-emitting one peaked at 615 nm from Mn²⁺ ions. The luminescence of Mn²⁺ ions can be greatly enhanced with the co-doping of Eu²⁺ in Ba₂MgP₄O₁₃. The efficient energy transfer from Eu²⁺ to Mn²⁺ is verified by the excitation and emission spectra together with the luminescence decay curves. The emission colors could be tuned from the blue to the red-purple and eventually to the deep red. The resonance-type energy transfer via a dipole-quadrupole interaction mechanism is supported by the decay lifetime data. The energy transfer efficiency and the critical distance are calculated and discussed. The temperature dependent luminescence spectra of the Eu²⁺/Mn²⁺ co-doped phosphor show a good thermal stability on quenching effect.     

Color-tunable properties based on complex anion substitution in Eu2+ doped Ca8Sc2(PO4)6-y(SiO4)1+y phosphor

We synthesized and investigated the effect of Eu²⁺ ions doping in a novel phosphor-silicate Ca₈Sc₂(PO₄)₆(SiO₄) phosphor. The structure and photoluminescence properties were determined by X-ray powder diffraction Rietveld refinement, diffuse reflection spectra, emission-excitation spectra, decay curves and temperature dependence spectra. The phosphors showed an asymmetric broad-band blue emission (Eu²⁺) with peak at 470?nm. Furthermore, we presented the Ca_7.96Sc₂(PO₄)_6-y(SiO₄)_1+y:0.04Eu²⁺ phosphors by co-substituting [Eu²⁺-Si⁴⁺] for [Ca²⁺-P⁵⁺], and different behaviors of luminescence evolution in response to structural variation were verified among the series of phosphors. The results were attributed to the presence of multi Ca²⁺ sites, resulting in the mixing of blue and green emissions for Eu²⁺ ions. The complex anion substitution of [PO₄]^3- by [SiO₄]^4- induced an increased crystal field splitting of the Eu²⁺ ions, which caused a decrease in emission energy from the 5d excited state to the 4f ground state and a resultant red-shift from 470?nm to 520?nm. All the properties indicated that the Ca₈Sc₂(PO₄)₆(SiO₄):Eu²⁺ phosphors have potential application for color-tunable WLEDs.     

Efficient and tunable Mn2+ sensitized luminescence via energy transfer of a novel red phosphor Ca19Mn2(PO4)14: Eu2+ for white LED

The exploration of efficient and high-purity red phosphors is an urgent need in LED development. Due to the compact and compositional-tunable structure of whitlockite compound, manganese-based Ca₁₉Mn₂(PO₄)₁₄ is chosen as phosphor host for Eu²⁺ sensitization. Rietveld refinement, steady-state spectra, decay lifetime analysis and temperature-dependent emission spectra were investigated and clearly discussed. Under 360 nm excitation, Ca₁₉Mn₂(PO₄)₁₄: Eu²⁺ shows a strong Mn²⁺ sensitized emission at 655 nm with FWHM of 82 nm, benefiting from the short-distance-induced high-efficient Eu² -Mn²⁺ energy transfer. Emission engineering of Ca₁₉Mn₂(PO₄)₁₄: Eu²⁺ is achieved by Sr²⁺ co-doping, leading to both tunable peak wavelength (ranging from 650 to 610 nm) and improved intensity (130% of original value). Moreover, Ca₁₉Mn₂(PO₄)₁₄: Eu²⁺ exhibits a promising thermal stability where only 40% of emission intensity is lost at 200 °C. Finally, we explored the working performance of the fabricated RGB phosphor-converted white LED. The present work indicates that Ca₁₉Mn₂(PO₄)₁₄: Eu²⁺ phosphor is of great potential as a promising and efficient red phosphor in phosphor-converted white LED.     

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

A series of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ samples match well with the standard Ca₅(PO₄)₃F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca₅(PO₄)₃F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions respectively. Eu³⁺ co‐doped Ca₅(PO₄)₃F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor.     

The doping concentration dependent tunable yellow luminescence of Sr5(PO4)2(SiO4):Eu

Color tunable yellow-emitting phosphors of Sr_5−5xEu_5x(PO₄)₂SiO₄ (x = 0.05-0.15) were prepared by conventional solid-state reaction method. The X-ray powder diffraction patterns, the photoluminescence excitation and emission spectra were measured. The main excitation bands of the phosphors locate at a broad band extending from 300 to 500 nm, which can match the emission of ultraviolet- and blue-emitting diode chips. The tunable luminescence color was realized by the changing Eu²⁺ doping in Sr₅(PO₄)₂SiO₄. The structure and luminescence properties were investigated. Sr_5−5x(PO₄)₂SiO₄:Eu_5x displays two typical luminescence centers, which originate from two different Sr²⁺ (Eu²⁺) sites in the host. The site-occupation, the luminescence intensity and energy transfer between the Eu²⁺ ions occupying two different crystallographic Sr²⁺ sites were discussed on the base of the luminescence spectra and crystal structure. This is helpful to improve this phosphor for a potential application as a white light emitting diode phosphor.     

Solvothermal synthesis of red and green emitting Ca1.65Sr0.35SiO4:Eu and Ca1.65Sr0.35SiO4:Eu phosphors for solid-state lighting applications

A novel and facile synthetic approach has been trialed, and attempted with success in the preparation of two phosphors namely, a red emitting CaSrSiO₄:Eu³⁺ and a green emitting CaSrSiO₄:Eu²⁺. These phosphors were successfully synthesized using a simple co-precipitating solvo-thermal strategy wherein tetraethyl orthosilicate (TEOS) as silica source and the acetate precursors of strontium (Sr²⁺), calcium (Ca²⁺) and europium (Eu³⁺) are utilized. The material so obtained is subjected to an extensive photoluminescence behavior study. The concentration of the dopant (Eu³⁺and Eu²⁺) plays a significant role in the determination of photoluminescence behavior and hence a systematic and in-depth experimental studies were done and the results are synchronized. On interpretation of the output, it came to light that an intense emission signals sparked in the red region (590 and 615 nm) in the case of phosphor doped with Eu³⁺, which is excited under near ultra violet (395 nm) and blue (466 nm) region. In case of the CaSrSiO₄ sample doped with Eu²⁺_, an intense broad green signal (~510 nm) is obtained under the excitation range of 350–430 nm. The results obtained are quite encouraging and made a strong confirmation as, the solvo-thermally synthesized CaSrSiO₄, which is activated by the dopants namely Eu³⁺ and Eu²⁺ possesses an immense potential and it is exactly tapped by the adopted methodology. Despite its strong impact, it will also assure a strong revolution in the fabrication and thus the commercialization of white LEDs as both the red and green emitting phosphor.     

Tunable Color of Eu2+/Mn2+ Coactivated Na5Ca2Al(PO4)4 via Energy Transfer

Eu²⁺ and Eu²⁺/Mn²⁺‐activated Na₅Ca₂Al(PO₄)₄ phosphors have been synthesized by the combustion method. X‐ray powder diffraction profiles, luminescence spectra, chromaticity variation, and energy transfer of Na₅Ca₂Al(PO₄)₄:Eu²⁺, Mn²⁺ were investigated as a function of the Eu²⁺ and Mn²⁺ concentrations in Na₅Ca₂Al(PO₄)₄. The Na₅Ca₂Al(PO₄)₄:Eu²⁺,Mn²⁺ phosphors can be effectively excited at wavelength ranging from 300 to 430 nm, which matches well with that for near‐ultraviolet (UV) light‐emitting diode (LED) chips. Under excitation at 354 nm, Na₅Ca₂Al(PO₄)₄:Eu²⁺,Mn²⁺ not only exhibits blue‐green emission band attributed to 4f⁶5d¹→4f⁷ of Eu²⁺ but also gives an orange emission band attributed to ⁴T₁→⁶A₁ of Mn²⁺. The emission color of the phosphor can be systematically tuned from blue‐green through white and eventually to orange by adjusting the relative content of Eu²⁺ and Mn²⁺ through the principle of energy transfer. The results indicated that Na₅Ca₂Al(PO₄)₄:Eu²⁺, Mn²⁺ may serve as a potential color‐tunable phosphor for near UV white‐light LED.     

Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

Synthesis and photoluminescence properties of Eu doped Sr9Sc(PO4)7 phosphors for white light-emitting diodes

A series of Eu²⁺-activated Sr₉Sc(PO₄)₇ yellowish-green emitting phosphors were synthesized by conventional solid-state reaction. The photoluminescence (PL) properties and concentration quenching mechanism of the as-prepared phosphors were investigated. The emission spectrum exhibits a broad and asymmetric band peaking at 510 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The excitation spectrum exhibits a broad band extending from 250 to 450 nm, which matches well with the emission of near ultraviolet (n-UV) chips (350–430 nm). Non-radiative transitions between Eu²⁺ ions in the Sr₉Sc(PO₄)₇ host have been demonstrated to be attributable to dipole–dipole interactions, and the critical distance was calculated to be 23.1 Å. These results indicate that Sr₉Sc(PO₄)₇:Eu²⁺ phosphor could serve as a promising candidate for application in n-UV white-light LEDs.     

A reddish orange stoichiometric phosphor LiEu(PO3)4 for white light-emitting diodes

Stoichiometric phosphors LiGd_1−xEu_x(PO₃)₄(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via traditional solid state reactions. The X-ray powder diffraction measurements show that all prepared samples are isostructural with LiNd(PO₃)₄. Eu³⁺ doped phosphors can emit intense reddish orange light under the excitation of near ultraviolet light from 370 to 410 nm. The strongest two at 591 and 613 nm can be attributed to the transitions from excited state ⁵D₀ to ground states ⁷F₁ and ⁷F₂, respectively. The typical chromaticity coordinates (x=0.620, y=0.368) of Eu³⁺ doped phosphors are in red area. The recorded absorbance spectra indicate that there is effective absorbance in the near UV region for all Eu³⁺ doped samples. Present research indicates that LiGd_1–xEu_x(PO₃)₄ is a promising phosphor for white light-emitting diodes.     

Synthesis and photoluminescence properties of MgAl(PO4)O:Eu red phosphor for white LEDs

Eu³⁺-activated MgAl(PO₄)O:phosphor has been synthesized by a high temperature solid state reaction and efficient red emission under near-ultraviolet excitation is observed. The emission spectrum shows a dominant peak at 594 nm due to the ⁵D₀→⁷F₁ transition of Eu³⁺. The excitation spectrum is coupled well with the emission of UV LED (350–410 nm). The effect of Eu³⁺ concentration on the luminescent properties of MgAl(PO₄)O:Eu³⁺ and the mechanism of concentration quenching of Eu³⁺ are studied. The results show that MgAl(PO₄)O:Eu³⁺ is a promising red-emitting phosphor for white LEDs.     

Luminescence properties of Eu2+ and Mn2+ doped Sr1.7Mg0.3SiO4 phosphors

Eu²⁺, Mn²⁺ doped Sr_1.7Mg_0.3SiO₄ phosphors were prepared by high temperature solid-state reaction method. Their luminescence properties were studied. The emission spectra of Eu²⁺ singly doped Sr_1.7Mg_0.3SiO₄ consist of a blue band (455 nm) and a green band (550 nm). The relative intensities of two emissions varied with Eu²⁺ concentration. Eu²⁺ and Mn²⁺ co-doped Sr_1.7Mg_0.3SiO₄ phosphors emit three color lights and present whitish color. The blue (455 nm) and green (550 nm) emissions are attributed to the transitions of Eu²⁺, while the red (670 nm) emission is originated from the transition of Mn²⁺ ion. The results indicate the energy transfer from Eu²⁺ to Mn²⁺. The mechanism of the energy transfer is resonance-type energy transfer due to the spectral overlap between the emission of Eu²⁺and the absorption of Mn²⁺.     

Phase Transformation in Ca3(PO4)2:Eu2+ via the Controlled Quenching and Increased Eu2+ Content: Identification of New Cyan‐Emitting α‐Ca3(PO4)2:Eu2+ Phosphor

A case of phosphor is reported where the cooling rate parameter significantly influences the luminescence property. By quenching the sample after the high‐temperature solid‐state reaction at 1250°C, we successfully prepared the Eu²⁺‐doped α form Ca₃(PO₄)₂ (α‐TCP:Eu²⁺) as a new kind of bright cyan‐emitting phosphor. The unusual emission color variation (from cyan to blue) depends on the cooling rate after sintering and Eu²⁺ doping level as it was observed in the TCP‐based phosphors. By the Rietveld analysis, it is revealed that the cyan‐ and blue‐emitting phosphors are two different TCP forms crystallizing in the monoclinic (space group P2₁/a, α‐TCP) and the rhombohedral structure (space group R3c, β‐TCP), respectively. Upon 365 nm UV light excitation, α‐TCP:Eu²⁺ exhibits an asymmetric broad‐band cyan emission peaking at 480 nm, while β‐TCP:Eu²⁺ displays a relatively narrow‐band blue emission peaking at 416 nm. The Eu²⁺‐doping in Ca₃(PO₄)₂ shifts the upper temperature limit of the stable structural range of β form from 1125°C to ≥1250°C. Moreover, the crystal structures of α/β‐TCP:Eu²⁺ were compared in the aspects of compactness and cation site sets. The emission thermal stability of α/β‐TCP:Eu²⁺ was comparatively characterized and the difference was related to the specific host structural features.     

Fluorescence improvement of Ba1.3Ca0.7SiO4:Eu,Mn phosphors via Dy addition and their color-tunable properties

A series of novel single-phase white phosphors Ba_1.3Ca_0.69−x−ySiO₄:0.01Eu²⁺,xMn²⁺, yDy³⁺ were synthesized by the solid-state method. The excitation spectra of these phosphors exhibit a broad band in the range of 260–410 nm, which can meet the application requirements for near-UV LED chips (excited at 350–410 nm). The emission spectra consist of two broad bands positioned around 455 nm and 596 nm, which are assigned to 5d→4f transition of Eu²⁺, and ⁴T₁→⁶A₁ transition of Mn²⁺, respectively. The luminescence intensity of phosphors enhances obviously by doping Dy³⁺ ions, and the intensity of two bands reaches an optimum when Dy³⁺ amounts to 2 mol%. In addition, thermoluminescence investigation of phosphor was conducted, getting two shallow trap defects with activation energy of 0.43 eV and 0.45 eV, which demonstrates the energy transfer mechanism of Dy–Eu through the process of hole and electron traps. By precisely tuning the Mn²⁺ content, an optimized white light with color rendering index (CRI) of R_a=84.3%, correlated color temperature (CCT) of T_c=8416 K and CIE chromaticity coordinates of (0.2941, 0.2937) is generated. The phosphor could be a potential white phosphors for near-UV light emitting diodes.     

Preparation and Luminescence Properties of Blue‐emitting Phosphor Ba2Ca(PO4)2:Eu2+

Using the conventional high temperature solid‐state reaction method Ba₂Ca(PO₄)₂:Eu²⁺ phosphors were prepared. The phase structure, photoluminescence (PL) properties, and the PL thermal stability of the samples were investigated, respectively. Under the excitation at 365 nm, the phosphor exhibited an asymmetric broad‐band blue emission with peak at 454 nm, which is ascribed to the 4f–5d transition of Eu²⁺. It was further proved that the dipole–dipole interactions results in the concentration quenching of Eu²⁺ in Ba₂Ca_1?x (PO₄)₂:xEu²⁺ phosphors. When the temperature turned up to 150°C, the emission intensity of Ba₂Ca_0.99(PO₄)₂:0.01Eu²⁺ phosphor was 59.07% of the initial value at room temperature. The activation energy ΔE was calculated to be 0.30 eV, which proved the good thermal stability of the sample. All the properties indicated that the blue‐emitting Ba₂Ca(PO₄)₂:Eu²⁺ phosphor has potential application in white LEDs.     

White‐Emitting Tuning and Energy Transfer in Eu2+/Mn2+‐Substituted Apatite‐Type Fluorophosphate Phosphors

Herein, a series of Eu²⁺&Mn²⁺substituted fluorophosphates Ca₆Gd₂Na₂(PO₄)₆F₂ phosphor with apatite structure have been synthesized and investigated by the powder X‐ray diffraction, photoluminescence spectra, fluorescence decay curves, thermal quenching, and chromaticity properties. Particularly, both Eu²⁺ and Mn²⁺ emissions at the two different lattice sites 4f and 6h in Ca₆Gd₂Na₂(PO₄)₆F₂ matrix have been identified and discussed. The dual energy transfer of Eu²⁺→Mn²⁺ and Gd³⁺→Mn²⁺ in Ca₆Gd₂Na₂(PO₄)₆F₂:Eu²⁺,Mn²⁺ samples have been validated and confirmed by the photoluminescence spectra. The dependence of color‐tunable on the activator concentration of Mn²⁺ was investigated to realize white light emission. By varying the doping concentration of the Mn²⁺ ion, a series of tunable colors including pure white light and candle light are obtained under the excitation of 350 nm. Moreover, the fluorescence decay curves have been fitted and analyzed using the Inokuti–Hirayama theoretical model to estimate the Eu–Mn interaction mechanism. We also investigated temperature‐dependent photoluminescence quenching characteristics according to the Arrhenius equation. Preliminary studies on the properties of the phosphor indicated that the obtained phosphors might have potential application as a single‐component white‐emitting phosphor for UV‐based white LEDs.     

Synthesis and photoluminescence properties of novel Ca2LaSbO6:Mn4+ double perovskite phosphor for plant growth LEDs

A novel Mn⁴⁺ activated Ca₂LaSbO₆ (CLS) far-red phosphor was synthesized by high temperature solid state reaction. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence spectra, ultraviolet-visible spectra, luminescence decay times, emission-temperature relationship and internal quantum efficiency (IQE). It is found that CLS:Mn⁴⁺ phosphor has a strong broad excitation band in the range of 200–550?nm. The samples can be excited by ultraviolet and blue light. There is a wide emission band centered at 685?nm between 600?nm and 760?nm. The optimum doping concentration of Mn⁴⁺ is approximately 0.5?mol%. In addition, all the CIE chromaticity coordinates of CLS:0.005Mn⁴⁺ located at far-red region. The concentration quenching mechanism is the dipole-dipole interaction of Mn⁴⁺ activator. Importantly, the CLS:0.005 Mn⁴⁺ sample has an IQE of up to 52.2%. Finally, a 365?nm ultraviolet light emitting diode (LED) chip combined with 0.5?mol% Mn⁴⁺ far-red phosphor was used to fabricate the LED device. All the results indicated that CLS:Mn⁴⁺ phosphors have potential applications in indoor plant cultivation.     

A single‐phase full‐color emitting phosphor Na3Sc2(PO4)3:Eu2+/Tb3+/Mn2+ with near‐zero thermal quenching and high quantum yield for near‐UV converted warm w‐LEDs

A single‐phase full‐color emitting phosphor Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ has been synthesized by high‐temperature solid‐state method. The crystal structure is measured by X‐ray diffraction. The emission can be tuned from blue to green/red/white through reasonable adjustment of doping ratio among Eu²⁺/Tb³⁺/Mn²⁺ ions. The photoluminescence, energy‐transfer efficiency and concentration quenching mechanisms in Eu²⁺‐Tb³⁺/Eu²⁺‐Mn²⁺ co‐doped samples were studied in detail. All as‐obtained samples show high quantum yield and robust resistance to thermal quenching at evaluated temperature from 30 to 200°C. Notably, the wide‐gamut emission covering the full visible range of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ gives an outstanding thermal quenching behavior near‐zero thermal quenching at 150°C/less than 20% emission intensity loss at 200°C, and high quantum yield‐66.0% at 150°C/56.9% at 200°C. Moreover, the chromaticity coordinates of Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ keep stable through the whole evaluated temperature range. Finally, near‐UV w‐LED devices were fabricated, the white LED device (CCT = 4740.4 K, Ra = 80.9) indicates that Na₃Sc₂(PO₄)₃:Eu²⁺/Tb³⁺/Mn²⁺ may be a promising candidate for phosphor‐converted near‐UV w‐LEDs.     

Crystal structure and luminescence properties of a single‐component white‐light‐emitting phosphor Ca8ZnLa(PO4)7:Eu2+,Mn2+

A series of novel green emission Whitlockite‐type Ca₈ZnLa(PO₄)₇:Eu²⁺ and color tunable Ca₈ZnLa(PO₄)₇:Eu²⁺,Mn²⁺ phosphors were prepared by the solid‐state reaction method in a reducing atmosphere. Its crystal structure and phase composition were identified by high‐resolution transmission electron microscopy, selected area electronic diffraction, X‐ray photoelectron spectroscopy, and X‐ray powder diffraction Rietveld refinement, and it was found to be trigonal, belonging to R‐3c(161) space group. The luminescence properties of Eu²⁺ singly doped and Eu²⁺/Mn²⁺ codoped Ca₈ZnLa(PO₄)₇ phosphors were revealed in detail. Ca₈ZnLa(PO₄)₇:Eu²⁺ is excitable over a broad range from 200 to 450 nm with a prominent green emitting. With varied Eu²⁺/Mn²⁺ ratios, fine‐tune emission under 365 nm excitation can be achieved from green (0.221, 0.468) to magenta (0.391, 0.276), especially the warm white light (0.392, 0.352), and CCT 3500 K can be obtained by the process of energy transfer between Eu²⁺ and Mn²⁺. The ET mechanism in this system is managed via the dipole‐dipole interaction with the maximum energy‐transfer efficiency 82.8% based on the decay lifetime data. These results suggest that as‐prepared phosphors can serve as promising candidates of UV‐pumped w‐LEDs.     

Microwave-induced small size effect of (Ba,Sr)3MgSi2O8:0.06Eu, 0.1Mn phosphor for 660 nm-featured bio-lighting

The 660 nm-featured (Ba, Sr) ₃MgSi₂O₈:0.06Eu^{2 +}, 0.1Mn²⁺(AMS-EM) phosphor in violet for red/blue bio-lighting LEDs was prepared by 2.45 GHz microwave (MW) high temperature firing procedure. The phase-pure host phase, (Ba, Sr) ₃MgSi₂O₈, was formed to be responsible for simultaneous red band emission from Mn ion and blue band emission from Eu ion, while the formation of an impurity phase of Sr₂SiO₄ responsible for 505 nm-peaked green band emission for Eu ion was effectively suppressed owing to MW fast-heating procedure. Small sized and agglomeration-free phosphor particles were either observed, which was probably resulted from suppressing the grain growth in as-formed host particles, compared with conventional high-temp solid state (SS) reaction firing procedure. These results indicate that high-temp MW firing procedure is suitable for preparing this simultaneously red- and blue-emitting AMS-EM phosphor in the application of bio-lighting for plant cultivation.