Compared to the conventional opaque persistent luminescence (PersL) materials, transparent PersL glass and glass ceramic are highly desired for night-vision illumination and indication applications. Herein, we report a new transparent oxyfluoride glass and glass ceramic with multi-color persistent luminescence lasting for ∼1 h visible by the naked eye. By adjusting the crystallization duration, controlled growth of 5–20 nm α-Zn2SiO4 nanocrystals in a glass matrix is achieved. Evidently, the coordination environment of Mn2+ evolves from octahedra in the glass host to tetrahedra in the α-Zn2SiO4 nanophase, resulting in the PersL color changing from red to yellow, and then to green, as the crystallization of Mn2+:α-Zn2SiO4 proceeds. The trap statuses in the glass and glass ceramic are studied in detail aided by EPR and TL measurements, demonstrating that the trapped holes with a trap depth distribution of 0.099–0.789 eV for the glass, and 0.094–0.631 eV for the glass ceramic, determine the PersL behaviors. It is noteworthy that this is the first report that oxyfluoride glass and glass ceramic serve as efficient PersL hosts.

The development of a single-ion activated single-phased white-light phosphor is of great importance in the field of near ultraviolet based w-LED lighting. In this work, a Ba2Y3(SiO4)3F:Eu fluoride apatite, which shows a broad emission band covering the entire visible region with tunable color rendition, was successfully synthesized via a high-temperature solid-state route. The microstructure and composition of the phosphor were carefully examined with the aid of XRD Rietveld refinement, HRTEM and SEM analyses, as well as XPS measurement. Spectroscopic studies revealed the site occupancy conditions of Eu2+, i.e., the Eu2+(I) band centering at 470 nm originates from the [BaO9] 4f site, while the Eu2+(II) one peaking at 600 nm comes from the [BaO6F] 6h site. Interestingly, the obtained white light can be readily tuned from cool to warm just by varying the Eu doping content. The brightest luminescence was achieved when the Eu concentration reached 1 mol%, beyond which the d–d interaction-based energy transfer between Eu2+ ions would result in concentration quenching. The underlying mechanism of the incomplete conversion from Eu3+ to Eu2+ under a reducing atmosphere was explored, which was believed to be caused by the rigid framework of the crystal structure. After coupling Ba2Y3(SiO4)3F:Eu with a commercial 3W 370 nm UV chip, the constructed w-LED yielded warm white light with a CIE coordinate of (0.402, 0.371), CCT of 3530 K, and CRI of 83.5, upon being driven by a 350 mA forward-biased current.

Owing to the magnetic dipole nature, the zero phonon line (ZPL) of Mn4+:2E → 4A2 transition is weak unless Mn4+ is situated at a site deviating from the centrosymmetric nature. Herein, we report a brand-new oxyfluoride, Na2WO2F4:Mn4+(NWOF:Mn4+), which shows unprecedented intense red ZPL at ∼620 nm along with relatively weak vibronic transitions under blue light excitation. This peculiar spectral feature is demonstrated to be originated from the highly distorted octahedral coordination environment in the C2v group symmetry surrounding Mn4+. High-resolution spectroscopic studies at 10 K disclose the fine structured electronic/vibronic transitions of Mn4+:2E, 2T1 → 4A2 and the weak electron–phonon interaction (Huang–Rhys factor S < 1) on the Mn4+ emissive state. Benefiting from the intense ZPL, an ultra-high color rendering index with Ra = 92.7 and R9 = 90.0 is achieved in the w-LED using YAG:Ce3+and NWOF:Mn4+ as color converters, and a wide color gamut of 107.1% NTSC in the w-LED using CsPbBr3 quantum dots and NWOF:Mn4+ is obtained. Herein, we first demonstrate that Mn4+-activated oxyfluorides have great potential in w-LED lighting and display applications. Our study can also enlighten researchers to design highly distorted octahedral sites for Mn4+ doping to achieve an ultra-intense ZPL.

Owing to its low cost and admirable luminescent characteristics for use in warm white-light-emitting diode (w-LED) applications, the non-rare-earth Mn4+-activated red phosphor has emerged as a potent competitor of commercial Eu2+-doped nitrides in recent years. In this work, the novel red-emitting phosphor BaMgAl10–2xO17:xMn4+,xMg2+ is successfully synthesized, which exhibits bright and narrow-band luminescence peaking at 660 nm with a full width at half-maximum of merely ∼30 nm upon blue light excitation. The unique structural feature of BMA, i.e., alternating arrangements of Mn4+-doped MgAl10O16/undoped BaO layers in the z direction and Mn4+-doped [AlO6]/undoped [AlO4] groups in the x–y plane, favors efficient Mn4+ luminescence by reducing nonradiative energy loss channels. Unlike previously reported hosts, BMA accommodates Mg2+ in the lattice without destabilizing the crystal structure. Remarkably, partitioning Mg2+ in the host not only greatly enhances Mn4+ luminescence by 1.84-fold but also retards the concentration quenching effect induced by Mn4+ dipole–dipole interactions owing to the reduced number of Mn4+–Mn4+–O2– pairs. Spectroscopy demonstrates that the luminescence of optimized BMA:0.02Mn4+,0.02Mg2+ exhibits a high color purity of 98.3%, good color stability against heat, and excellent resistance to thermal impact. When incorporating BMA:0.02Mn4+,0.02Mg2+ and YAG:Ce3+ phosphors into an oxide glass matrix at various ratios and then coupling the phosphor-in-glass color converters using a blue chip, the chromaticity parameters of the fabricated w-LED are well-tuned, with the correlated color temperature decreasing from 6608 to 3622 K and the color rendering index increasing from 68.4 to 86.0, meeting the requirements for in-door lighting use.

Red-emitting Mn4+ activated oxide phosphors with a cheap price and excellent physical/chemical stability have become a hot research topic for their potential applications in white LEDs (w-LEDs). Herein, we report a novel double-perovskite Gd2ZnTiO6:Mn4+ (GZT:Mn4+) red phosphor. The material microstructures were characterized with the aid of XRD Rietveld refinement and HRTEM observations. The luminescence properties and dynamics of Mn4+ in GZT were studied in detail using low/room temperature steady/transient spectroscopic techniques. The crystal field strength and nephelauxetic effect influencing the Mn4+ emission energy were also analyzed. It is revealed that the special crystal structure of GZT featuring alternately slant-wise arranged [TiO6]/[ZnO6] octahedrons with the [–Mn4+–O2−–Zn2+–] bond angle deviating from 180° is beneficial to achieving efficient Mn4+: 2Eg → 4A2 transition in the deep-red region. After mixing the red-emitting GZT:Mn4+ with the commercial blue and green phosphors in various ratios, and then coupling the mixture with a 365 nm UV chip to build a w-LED, the white light was found to evolve from cool to warm with a tunable correlated color temperature (CCT) from 6977 K to 4742 K, a color rendering index (CRI) up to 82.9, and an improved R9 value to 43, which validates that GZT:Mn4+ is a promising red color converter for UV-based w-LEDs.

Phosphor-in-glass (PiG) color converter, being regarded as a good encapsulant material for long-lifetime high-powered white light-emitting-diode (LED), has developed rapidly in the recent years. However, it still remains a challenge to achieve fine chromaticity tuning of PiG for high-quality indoor lighting. Herein, a transparent garnet-based PiG was successfully prepared by introducing the Y3Mg2AlSi2O12:Ce3+ orange phosphor and the Y3Al4.6Ga0.4O12:Ce3+ green phosphor into TeO2-based glass matrix. The microstructure and luminescent properties of the PiG were investigated in detail. After optimizing the weight ratio of green phosphor to orange phosphor as well as the PiG thickness, facile chromaticity tuning to follow along Planckian locus in the thus-fabricated LED is achieved; correspondingly the correlated color temperature is adjusted from cool white to warm white. Hopefully, the developed garnet-based PiG is applicable in the long-lifetime color-tunable w-LEDs.

The commercially dominant phosphor-converted illumination white light-emitting-diodes (w-LEDs) generally suffer from red deficiency and the poor thermal stability of the organic encapsulants, resulting in cool white light, luminous degradation and chromatic aberration for the embedded YAG:Ce3+ phosphors after long-term working. Aiming to solve these problems, herein, a chromaticity-tunable robust phosphor-in-glass (PiG) inorganic color converter was successfully fabricated by co-sintering YAG:Ce3+,Mn2+,Si4+ phosphor particles and the innovatively-designed TeO2–B2O3–ZnO–Na2O–Al2O3 low-melting precursor glass. At first, the spectrally-modified YAG:Ce3+,Mn2+,Si4+ phosphor was prepared by doping Mn2+ as the red emitter and doping Si4+ as the charge compensator through a solid-state reaction route. Then, the YAG:Ce3+,Mn2+,Si4+ powder was incorporated into a specifically prepared precursor glass to form the PiG composite at 550 °C. Owing to the density and the refractive index matches for the phosphor particles and the glass matrix, the particle dispersion in PiG is quite homogeneous and the adverse light-scattering is depressed. The high-power warm w-LED was constructed by coupling a PiG plate with an InGaN blue chip. Remarkably, the chromaticity coordinate of such a w-LED can be well tuned to follow along the Planckian locus with the correlated color temperature evolving from cool white (5541 K) to warm white (3050 K) and a color rendering index around 70, under a driving current of 350 mA. Moreover, the PiG-based warm w-LED presents much superior thermal stability to the traditional phosphor-in-silicone (PiS)-based one. This work highlights the practical applications of the PiG luminescent material in the long-lifetime high-power warm w-LEDs.

Currently, the development of efficient red-emitting persistent phosphor is still an ongoing challenge. Herein, a novel red-emitting LPL phosphor Ca3Ti2O7:Pr3+ is successfully prepared by a high-temperature solid-state method. XRD Rietveld refinement analyses demonstrate the high phase purity of the sample which crystallizes in an orthorhombic Ccm21 space group with lattice parameters of a = 5.7702(5) Å, b = 19.4829(7) Å, and c = 5.1214(2) Å. Electronic structure of the host matrix is analyzed by the first-principle calculation using CASTEP code. The calculation results show that Ca3Ti2O7 has a direct band gap with CB and VB mainly composed of the Ti-3d and O-2p states, respectively. On the basis of the DR spectrum, the band gap is determined to be 3.6 eV. It is demonstrated that the 612 nm red-emitting persistent luminescence of Ca3Ti2O7:Pr3+ can be either activated by Ti4+–O2– → Ti3+–O– host absorption and Pr3+–O–Ti4+ → Pr4+–O–Ti3+ IVCT in the UV region, or Pr3+:3H4 → 3PJ transition in the blue region. The red afterglow can last for ∼5 min observed by the naked eyes in the dark after ceasing the irradiation source. On the basis of the TL analyses, the trap is found exponentially distributed in the host with the depth of 0.69–0.92 eV. Finally, a possible LPL mechanism for Ca3Ti2O7:Pr3+ is proposed.

New non-rare-earth-based oxide red phosphor discovery is of great interest in the field of energy-efficient LED lighting. In this work, a novel blue-light activated CaMg2Al16O27:Mn4+ (CMA:Mn4+) phosphor, showing strong red emission peaked at ∼655 nm under 468 nm excitation, is prepared by a solid-state reaction route. The microstructure and luminescent performance of this red-emitting phosphor are investigated in detail with the aids of X-ray diffraction refinement, diffuse reflection spectra, steady-state photoluminescence spectra and temperature-dependent PL/decay measurements. The crystal field strength (Dq) and the Racah parameters (B and C) are carefully calculated to evaluate the nephelauxetic effect of Mn4+ suffering from the CMA host. After incorporating CMA:Mn4+ and YAG:Ce3+ phosphor microcrystals into the glass host via a “phosphor-in-glass (PiG)” approach, warm white-light is achieved in the assembled high-powered w-LED device, thanks to the improved correlated color temperature and color rendering index.Keywords: aluminates; luminescent property; Mn4+; phosphor in glass; red phosphors

Compared to the conventional opaque persistent luminescence (PersL) materials, transparent PersL glass and glass ceramic are highly desired for night-vision illumination and indication applications. Herein, we report a new transparent oxyfluoride glass and glass ceramic with multi-color persistent luminescence lasting for ∼1 h visible by the naked eye. By adjusting the crystallization duration, controlled growth of 5–20 nm α-Zn2SiO4 nanocrystals in a glass matrix is achieved. Evidently, the coordination environment of Mn2+ evolves from octahedra in the glass host to tetrahedra in the α-Zn2SiO4 nanophase, resulting in the PersL color changing from red to yellow, and then to green, as the crystallization of Mn2+:α-Zn2SiO4 proceeds. The trap statuses in the glass and glass ceramic are studied in detail aided by EPR and TL measurements, demonstrating that the trapped holes with a trap depth distribution of 0.099–0.789 eV for the glass, and 0.094–0.631 eV for the glass ceramic, determine the PersL behaviors. It is noteworthy that this is the first report that oxyfluoride glass and glass ceramic serve as efficient PersL hosts.

The development of a single-ion activated single-phased white-light phosphor is of great importance in the field of near ultraviolet based w-LED lighting. In this work, a Ba2Y3(SiO4)3F:Eu fluoride apatite, which shows a broad emission band covering the entire visible region with tunable color rendition, was successfully synthesized via a high-temperature solid-state route. The microstructure and composition of the phosphor were carefully examined with the aid of XRD Rietveld refinement, HRTEM and SEM analyses, as well as XPS measurement. Spectroscopic studies revealed the site occupancy conditions of Eu2+, i.e., the Eu2+(I) band centering at 470 nm originates from the [BaO9] 4f site, while the Eu2+(II) one peaking at 600 nm comes from the [BaO6F] 6h site. Interestingly, the obtained white light can be readily tuned from cool to warm just by varying the Eu doping content. The brightest luminescence was achieved when the Eu concentration reached 1 mol%, beyond which the d–d interaction-based energy transfer between Eu2+ ions would result in concentration quenching. The underlying mechanism of the incomplete conversion from Eu3+ to Eu2+ under a reducing atmosphere was explored, which was believed to be caused by the rigid framework of the crystal structure. After coupling Ba2Y3(SiO4)3F:Eu with a commercial 3W 370 nm UV chip, the constructed w-LED yielded warm white light with a CIE coordinate of (0.402, 0.371), CCT of 3530 K, and CRI of 83.5, upon being driven by a 350 mA forward-biased current.

Red-emitting Mn4+ activated oxide phosphors with a cheap price and excellent physical/chemical stability have become a hot research topic for their potential applications in white LEDs (w-LEDs). Herein, we report a novel double-perovskite Gd2ZnTiO6:Mn4+ (GZT:Mn4+) red phosphor. The material microstructures were characterized with the aid of XRD Rietveld refinement and HRTEM observations. The luminescence properties and dynamics of Mn4+ in GZT were studied in detail using low/room temperature steady/transient spectroscopic techniques. The crystal field strength and nephelauxetic effect influencing the Mn4+ emission energy were also analyzed. It is revealed that the special crystal structure of GZT featuring alternately slant-wise arranged [TiO6]/[ZnO6] octahedrons with the [–Mn4+–O2−–Zn2+–] bond angle deviating from 180° is beneficial to achieving efficient Mn4+: 2Eg → 4A2 transition in the deep-red region. After mixing the red-emitting GZT:Mn4+ with the commercial blue and green phosphors in various ratios, and then coupling the mixture with a 365 nm UV chip to build a w-LED, the white light was found to evolve from cool to warm with a tunable correlated color temperature (CCT) from 6977 K to 4742 K, a color rendering index (CRI) up to 82.9, and an improved R9 value to 43, which validates that GZT:Mn4+ is a promising red color converter for UV-based w-LEDs.

The commercially dominant phosphor-converted illumination white light-emitting-diodes (w-LEDs) generally suffer from red deficiency and the poor thermal stability of the organic encapsulants, resulting in cool white light, luminous degradation and chromatic aberration for the embedded YAG:Ce3+ phosphors after long-term working. Aiming to solve these problems, herein, a chromaticity-tunable robust phosphor-in-glass (PiG) inorganic color converter was successfully fabricated by co-sintering YAG:Ce3+,Mn2+,Si4+ phosphor particles and the innovatively-designed TeO2–B2O3–ZnO–Na2O–Al2O3 low-melting precursor glass. At first, the spectrally-modified YAG:Ce3+,Mn2+,Si4+ phosphor was prepared by doping Mn2+ as the red emitter and doping Si4+ as the charge compensator through a solid-state reaction route. Then, the YAG:Ce3+,Mn2+,Si4+ powder was incorporated into a specifically prepared precursor glass to form the PiG composite at 550 °C. Owing to the density and the refractive index matches for the phosphor particles and the glass matrix, the particle dispersion in PiG is quite homogeneous and the adverse light-scattering is depressed. The high-power warm w-LED was constructed by coupling a PiG plate with an InGaN blue chip. Remarkably, the chromaticity coordinate of such a w-LED can be well tuned to follow along the Planckian locus with the correlated color temperature evolving from cool white (5541 K) to warm white (3050 K) and a color rendering index around 70, under a driving current of 350 mA. Moreover, the PiG-based warm w-LED presents much superior thermal stability to the traditional phosphor-in-silicone (PiS)-based one. This work highlights the practical applications of the PiG luminescent material in the long-lifetime high-power warm w-LEDs.