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In this work, a series of Cr3+-doped A2NaYF6 (denoted as ANYF:Cr; A = K, Rb, and Cs) fluoroyttrate double-perovskites with broad blue excitation and near-infrared (NIR) emission bands were prepared using a high-temperature solid-state reaction method. The physicochemical and spectroscopic properties of the as-prepared products, including crystal structure, bandgap, morphology, luminescence behaviour and optical performance, were studied in detail. The results show that the Cr3+ activators undergo a decreasing crystal field in ANYF in the direction from K to Cs, yielding a red shift of the emission peak position from 758 to 786 nm, whilst the full-width-at-half-maximum (FWHM) expands from 98 to 104 nm. By virtue of the broadband NIR emission, clear structural images of the tangerine section, mini LED flashlight and circuit board were obtained by merging the optimal RNYF:Cr phosphor on a blue InGaN chip, implying its potential use in light-emitting diodes for non-destructive testing. [ABSTRACT FROM AUTHOR]

To develop non-rare-earth or metal-free phosphors for white light-emitting diodes (WLEDs) are very significant and forward-looking. Here, a yellow-green-emitting g-C 3 N 4 derivative (p -Ph-g-C 3 N 4) consisting of 1,4-phenylene-inserted heptazine units was successfully prepared by 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) via thermal polymerization. Its emission is mainly located at 450–700 nm with the maximum wavelength (λ em,max) of 536 nm, its quantum yield (QY) is 15.7% (λ ex = 430 nm) which is much higher than that of bulk g-C 3 N 4 (ca. 5%). Under the excitation of 430 nm blue-emitting GaN-based chips (ca. 4.0 lm·W−1), p -Ph-g-C 3 N 4 together with non-rare-earth red-emitting K 2 SiF 6 :Mn4+ as phosphors, a series of cold, neutral, and warm WLEDs with good performances were fabricated. As for the best one, its color rendering index (CRI) is 84.3, correlate color temperature (CCT) is 5702 K, luminous efficiency (LE) is 5.40 lm·W−1, moreover, its CIE value (0.30, 0.34) is very close to (0.33, 0.33) of pure white light. The research results indicate p -Ph-g-C 3 N 4 can be used as an efficient metal-free quasi-green phosphor for WLEDs. White LEDs were fabricated by a yellow-green-emitting g-C 3 N 4 derivative and red-emitting K 2 SiF 6 :Mn4+ under the excitation of blue-emitting chips. [Display omitted] • A yellow-green-emitting metal-free g-C 3 N 4 derivative. • The derivative consisting of 1,4-phenylene-inserted heptazine units. • Cold/neutral/warm WLEDs all being fabricated. [ABSTRACT FROM AUTHOR]

A series of ternary dinuclear europium(iii) complexes [Eu2(2,7-BTFDBC)3−n(DBM)2n(Phen)2] (n = 0, 1, or 2) were synthesized by using 2,7-bis(4′4′4′-trifluoro-1,3-dioxobutyl)-(9-ethyl-9H-carbazole) (2,7-BTFDBC), dibenzoylmethane (DBM), 1,10-phenanthroline (Phen) and europium(iii) ions. All these complexes display a broad excitation band in the blue region and high intensity emission with high colour purity. The intensity of emission significantly increases with the increase of DBM in [Eu2(2,7-BTFDBC)3−n(DBM)2n(Phen)2] (n = 0, 1, or 2). The theoretical predictions of the molecular geometry and electronic absorption spectrum of [Eu2(2,7-BTFDBC)(DBM)4(Phen)2] confirm that the pendant phenyl domains engage in multiple T-shaped and parallel-displaced π-stacking interactions with the coordination sphere of two europium(iii) centers. Using [Eu2(2,7-BTFDBC)(DBM)4(Phen)2] as a red phosphor, a single red LED has been obtained with a ∼460 nm-emitting GaN chip. [ABSTRACT FROM AUTHOR]

A novel red-emitting cationic iridium(iii) complex, [(Lm)2Ir(La)]PF6, (Lm: 2-(9-(2-ethylhexyl)-9H-carbazol-3-yl)benzo[d]thiazole, La: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized. Its ultraviolet-visible absorption and photoluminescent properties show that the complex can be efficiently excited by a 465 nm-emitting blue GaN chip, its decomposition temperature (Td) is 340 °C, and its relative emission intensity at 100 °C is 88.3% of 25 °C. Perfect red light with a CIE value of (0.65, 0.34) was obtained when it was used as a phosphor at 6.0 wt% blending concentration in epoxy resin in a blue GaN-based LED. A 465 nm-emitting blue GaN-based LED only using yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce) as a phosphor (1.0 wt% in epoxy resin) emitted cold white, and its corresponding color rendering index (CRI) was 74.1, correlated color temperature (CCT) was 6026 K, and luminous efficiency (ηL) was 25.3 lm W−1. It became a neutral white light LED when the iridium(iii) complex was added at 0.5 wt%, the corresponding CRI was 79.5, CCT was 4004 K, and ηL was 32.6 lm W−1. It further became a warm white LED when the complex was blended at 1.0 wt% and 1.5 wt%, the corresponding CRI were 80.0 and 79.6, CCT were 3650 K and 3133 K, ηL were 25.5 lm W−1 and 22.8 lm W−1, and CIE values were (0.40, 0.39) and (0.43, 0.40), respectively. This complex is a promising red phosphor candidate for red LEDs and warm white LEDs. [ABSTRACT FROM AUTHOR]

A sp2-carbon-linked covalent organic framework (COF) containing tetraphenylethene units was successfully synthesized by using 2,2'-(1,4-phenylene)diacetonitrile and 4′,4‴,4‴'',4‴''''-(Ethene-1,1,2,2-tetrayl)tetrakis(([1,1′-biphenyl]-4-carbaldehyde)) as monomers. After being investigated by powder X-Ray diffraction (PXRD), nitrogen adsorption-desorption and theoretical calculations, the dual-pore eclipsed Kagome structure (AA-K) of the COF was confirmed. The COF emitted bright yellow light with a solid-state photoluminesce quantum yield (PLQY) of 39.2%. It exhibited high thermal stability with a thermal decomposition temperature (T d) of ca. 610 °C, and its relative emission intensity at 90 °C was nearly 80.0% of that at 30 °C. The COF was blended in epoxy resin at different concentrations and used as phosphors, excited by GaN-based blue-emitting chips (λ em,max ≈ 455 nm), a series of white light-emitting diodes (WLEDs) with different correlated color temperature (CCT) can be obtained. At 1.5 wt%, a cold WLED was obtained, its CCT was 6125 K, color rendering index (CRI) was 83.4, Commission Internationale de L'Eclairage (CIE) chromaticity coordinate was (0.32, 0.29), luminous efficiency (η L) was 20.31 lm·W−1. At 2.0 wt%, a neutral WLED was obtained, its CCT was 4293 K, CRI was 79.6, chromaticity coordinate was (0.36, 0.34) and η L was 19.71 lm·W−1. At 2.5 wt%, a warm WLED was obtained, its CCT was 3348 K, CRI was 69.4, chromaticity coordinate was (0.42, 0.42) and η L was 18.81 lm·W−1. The results suggested the COF can be used promising metal-free phosphors in WLEDs. [Display omitted] • A sp2-carbon-linked covalent organic framework (COF) containing tetraphenylethene units was synthesized. • The COF emitted bright yellow light with a solid-state photoluminesce quantum yield (PLQY) of 39.2%. • The thermal decomposition temperature (T d) of the COF was as high as 610 °C. • Cold/neutral/warm white LEDs with high performances were prepared by using the COF and blue-emitting chips. [ABSTRACT FROM AUTHOR]

The luminescence enhancement of near-infrared (NIR) emissive material is critical in emerging applications. In this work, we have prepared an NIR-emitting K 2 NaSc 1- x - y Al x F 6 : y Cr3+ (denoted as KNS 1- x - y A x F: y Cr) solid solution phosphor via the introduction of Al3+, enhancing luminescence in a high-temperature solid-state reaction. The resultant solid solution phosphor exhibited a broad NIR emission band with a high internal quantum efficiency (IQE = 81.1 %) and an enhanced photoluminescence thermal stability (93 % at 423 K) under 432 nm excitation. When compared with the Al-free sample, the IQE and thermal stability are increased by 45.9 % and 22.4 %, respectively. The optimal Cr3+ and Al3+ doping content has been determined and a composition-optimized KNS 0.70 A 0.25 F 6 :0.05Cr phosphor is demonstrated by fabricating an NIR pc-LED device as a light source for light-emitting diode applications. • A KNS 1- x - y A x F: y Cr sample with enhanced NIR luminescence was synthesized using a high-temperature solid-state reaction. • The role of Al3+ in improving luminescent properties was confirmed. • Utilization of the solid solution phosphor in light-emitting diode devices was evaluated. [ABSTRACT FROM AUTHOR]

In this work, a novel Mn4+ doped BaTiOF 4 oxyfluoride red-emitting phosphor was fabricated through a two-step wet chemical synthesis on a large scale at an ambient temperature. The crystal structure, morphology, and elemental composition were confirmed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and energy dispersive X-ray fluorescence spectrometer respectively. The luminescence properties were investigated from emission, excitation and ultraviolet–visible diffuse reflectance (DRS). The as-prepared BaTiOF 4 :Mn4+ product is well crystallized into single orthorhombic phase with particulate morphology and presents sharp red emission lines locating around 631 nm under illumination at 470 nm blue light. The single red LED, based on the novel BaTiOF 4 :Mn4+ phosphor exhibits bright red color with CIE chromaticity coordinate values of x = 0.692 and y = 0.308, revealing it may find application in LED backlighting. A novel oxyfluoride of BaTiOF 4 :Mn4+ red-emitting phosphor, in which Mn4+ located in a distorted octahedral coordination environment, shows intense red emission under the blue light illumination, implying its potential application in LED backlighting. Image 1 • A novel oxyfluoride red emitting phosphor of BaTiOF 4 :Mn4+ has been prepared. • The crystal structure and optimal reaction condition for BaTiOF 4 :Mn4+ have been confirmed. • The luminescence properties and optical performance of BaTiOF 4 :Mn4+ red phosphor have been verified. [ABSTRACT FROM AUTHOR]

New red-emitting phosphors KLiSnF 6 : x Mn4+ (KLSFM, x = 4%, 6%, 8%, 10%, and 12%) for LED lighting were synthesized by an ion-exchange method at room temperature. Among these phosphors, the KLSFM (8 mol%) sample exhibits the strongest excitation in the blue region and emission in the red region. The corresponding translucent fluorescent sheet prepared by the pressure method shows similar luminescent properties which are identical to the powders with the strongest absorption at 467 nm and narrow emission around 632 nm. The fluorescent sheet offers high transmittance in UV–Vis region (close to 100% beyond 550 nm) and better thermal stability and color stability. For comparison, the white pc-LEDs based on the KLSFM (8 mol%) phosphor and fluorescent sheet all emit intense white light with an ideal color rendering index (CRI >93) and a good correlated color temperature (CCT <3500 K). However, the white pc-LED based on the fluorescent sheet have more advantage in application for high-power devices. Working at 200 mA, the LED fabricated with the translucent sheet still keeps excellent performance with a high CRI of 90.1 and a low CCT of 3874 K. The working temperature for this device is only 90 °C after working for 40 min, which is lower than that of the device with the KLSFM (8 mol%) powder, furtherly proving that the translucent sheet has excellent heat dispersion. Therefore, the KLSFM (8 mol%) translucent sheet could be used for high-power pc-LEDs as a red component. [ABSTRACT FROM AUTHOR]

A fully π-conjugated triazine-based 2D covalent organic framework was used as metal-free yellow phosphors for white LEDs under the excitation of blue light chips. [Display omitted] • A fully π-conjugated triazine-based 2D COF. • A periodic hexagonal pore structure in an eclipsed (AA) stacking mode. • White LEDs were fabricated by blue light chips and the yellow-emitting COF. • Cold/neutral/warm white LEDs all can be obtained with good performances. Luminescent covalent organic frameworks (COFs) can be used as metal-free phosphors to replace rare earth-based phosphors for LEDs. Here, a fully π-conjugated 2D COF containing triazine units is synthesized via Knoevenagel condensation by using terephthalaldehyde (TPA) and 2,2′,2′'-((1,3,5-triazine-2,4,6-triyl)tris([1′',1′''-biphenyl]-4′,4′'-diyl))triacetonitrile (TTTA) as monomers. This yellow-emitting COF consists of a periodic hexagonal pore structure and is in an eclipsed (AA) stacking mode. Its solid-state photoluminescence quantum yield (PLQY) is 26.0 %, its thermal decomposition temperature (T d) is ca. 495 °C, and its relative emission intensity at 90 ℃ is 80.0 % of that at 30 °C, at 150 ℃ is 58.9 % of that at 30 °C. Together with GaN-based blue-emitting chips (λ em,max ≈ 460 nm, around 25.0 lm·W−1), a series of cold/neutral/warm white LEDs are fabricated by using the COF as yellow phosphors at different concentrations in epoxy resin. At 2.0 wt%, a cold white LED is obtained with the best performances, its correlated color temperature (CCT) is 5743 K, color rendering index (CRI) is 83.1, Commission Internationale de L'Eclairage (CIE) chromaticity coordinate is (0.33, 0.29), luminous efficacy (LE) is 18.18 lm·W−1. [ABSTRACT FROM AUTHOR]

Red-emitting Mn4+-doped fluoride phosphors are recognized as promising materials for high-performance warm white light-emitting diodes (WLEDs). However, the extensive use of toxic hydrofluoric acid in traditional synthesis methods hinders their development and commercialization. Furthermore, the traditional solid-phase method often has cumbersome sintering steps, high temperature, long holding time, and certain safety hazards, so it is very necessary to develop a green synthesis method with simple steps and low energy consumption. In this study, a low-temperature solid-state method is proposed to synthesize Rb A SiF 6 :Mn4+ (A = K, Cs) phosphors by one step. Optimal emission intensities were observed at Mn4+ concentrations of 1.2 % in RbKSiF 6 and 2.1 % in RbCsSiF 6. These phosphors demonstrated high thermal stability. At 423 K, the photoluminescence intensities of RbKSiF 6 :1.2 %Mn4+ and RbCsSiF 6 :2.1 %Mn4+ reached 114 % and 87 % of their respective values at room temperature. Meanwhile, the chromaticity shifts were almost negligible, and high color purity was achieved for both phosphors. The electro-optical performance of WLED devices utilizing these phosphors, in combination with YAG:Ce3+ and GaN chips, showed high color rendering indices (CRI) and low correlated color temperatures (CCT) across varying currents. Specifically, under a driving current of 20 mA, the device incorporating RbKSiF 6 :1.2 %Mn4+ exhibited a CRI of 94 and a CCT of 3732 K, with a luminous efficacy of 61 lm/W. These findings highlight the potential of green-synthesized RASFM phosphors in advancing the application of warm WLEDs. [Display omitted] • A low-temperature solid-state method without HF is used to prepare red phosphors. • Rb A SiF 6 :Mn4+ phosphors shows highly luminescent efficiency and thermal stability. • The LED incorporating RbKSiF 6 : Mn4+ exhibited a CRI of 94 and a CCT of 3732 K. [ABSTRACT FROM AUTHOR]

In this study, an efficient polyfluoride red-emitting phosphor, Cs 3 RbGe 2 F 12 :Mn4+ (denoted as CRGF:Mn), has been synthesized using a simple co-precipitation method. The crystal and electronic structures, spectroscopic properties, and photoluminescence thermal stability of CRGF:Mn have been systematically characterized. The results show that Mn4+ ions experience a strong crystal field and present a series of intense red emission peaks under blue light excitation. Moreover, CRGF:Mn exhibits a high color purity (95.1 %), high internal quantum efficiency (82.4 %), and enhanced photoluminescence thermal stability at 150 °C, with an intensity of 113 % relative to room temperature. A warm white light-emitting diode exhibiting a low correlated color temperature (3572 K), high color rendering index (90.7), and suitable luminous efficiency (132.6 lm/W) was prepared using CRGF:Mn as a red component, demonstrating viable application in solid-state lighting. • Synthesis of CRGF:Mn polyfluoride red phosphor with a high internal quantum efficiency (82.4 %). • CRGF:Mn exhibits outstanding photoluminescence thermal stability (113 % at 150 °C). • The application prospect of CRGF:Mn for indoor lighting have been elaborated. [ABSTRACT FROM AUTHOR]

The far-red light around 730 nm plays an important role during the plant growth. Herein, broadband far-red LiMgAlF 6 :Cr3+ phosphors were successfully prepared via the hydrothermal method. Under 424 nm excitation, LiMgAlF 6 :0.05Cr3+ exhibits an emission band peaking at 734 nm with a full-width at half maximum (FWHM) of 131 nm, due to the emission from two kinds of Cr3+. Moreover, the broad band could match well with the absorption spectrum of the plant's P FR. The phosphor not only owns a high internal quantum efficiency (IQE) of 45.6%, but also a good resistance towards to thermal quenching. Its emission intensity at 150 °C is 93.9% of the initial intensity at room temperature. Finally, the LiMgAlF 6 :Cr3+ powder was combined with a 460 nm blue chip to form one LED device, which was carried out on the growth of the tomato plants. The LED based on LiMgAlF 6 :Cr3+ can promote the growth of tomato plants, indicating the feasibility of phosphors for the plant-growth lighting. [Display omitted] • A far-red LiMgAlF 6 :Cr3+ phosphor exhibits broad emission from double sites of Cr3+. • The phosphor owns a high quantum efficiency and good thermal stability. • The LED based on LiMgAlF 6 :Cr3+ can promote the growth of tomato plants. [ABSTRACT FROM AUTHOR]

Searching for efficient Mn4+ red phosphors for white lighting and display backlighting has drawn great attention. In this work, an efficient Mn4+-doped fluoroscandate, Rb 2 KScF 6 :Mn4+, with short fluorescence lifetime is prepared via a facile co-precipitation method. It was found that the nonequivalent occupation of Mn4+ for Sc3+ leads to the identifications of sharp red emissions, enhanced zero-phonon line, high quantum efficiency and short fluorescence lifetime upon blue light excitation. Thanks to the luminescent properties, good optical parameters of high color rendering index, low correlated color temperature, and acceptable color gamut were achieved by coating the red Rb 2 KScF 6 :Mn4+ phosphor with yellow Y 3 Al 5 O 12 :Ce3+ or green β -SiAlON:Eu2+ phosphor in various white light-emitting diodes, demonstrating its potential role for white light illumination and backlight display applications. • The crystal and electronic structures were analyzed for a novel Rb 2 KScF 6 :Mn4+ phosphor. • The luminescent properties including an enhanced zero-phonon line and a short fluorescence lifetime were confirmed. • The optical behavior of the Rb 2 KScF 6 :Mn4+ phosphor in multiple white light-emitting diodes was elucidated. [ABSTRACT FROM AUTHOR]

One new kind of red-emitting oxyfluoride phosphors Rb 2 WO 2 F 4 doped with different Mn4+ contents were synthesized via a facile co-precipitation method at an ambient condition. Meanwhile, the luminescent behaviors of Mn4+ in Rb 2 WO 2 F 4 were investigated in detail. The sample prepared with the WO 3 /K 2 MnF 6 molar ratio of 40:1 has a broad excitation band around 465 nm and emits a series of sharp-emitting peaks around 631 nm. The crystal-field strength D q as well as Racah parameters B and C were calculated to be 2151, 583 and 3872 cm−1, meaning that Mn4+ in Rb 2 WO 2 F 4 experiences a strong crystal field. The luminescence decay time was also determined to be 2.15 ms. Finally, a warm white LED was obtained using Rb 2 WO 2 F 4 :Mn4+ as red component. It's color rendering index was improved to 81.4 and color temperature was decreased to 3588 K. Image 1 • New red phosphor Rb 2 WO 2 F 4 :Mn4+ was synthesized by facile co-precipitation method. • Rb 2 WO 2 F 4 :Mn4+ yields narrow-band emission around 631 nm. • The optimum concentration of Mn4+ has been confirmed to be about 11 mol%. [ABSTRACT FROM AUTHOR]

A novel red-emitting phosphor K 2 [MoO 2 F 4 ]•H 2 O:Mn4+ prepared by a simple precipitation method emits the intense red light with the high internal quantum efficiency of 86.5% and the high thermal stability of luminescence. A w-LED fabricated with this red phosphor shows intense warm white-light with a high color rendering index of 94, a low correlated color temperature of 3945 K. Therefore, K 2 [MoO 2 F 4 ]•H 2 O:Mn4+ maybe find application on w-LED lighting. • K 2 [MoO 2 F 4 ]•H 2 O:Mn4+ was designed and synthesized by a simple precipitation method. • This phosphor exhibits intense red-emission and high internal quantum efficiency. • This phosphor has the high thermal stability of luminescence. • A w-LED coating this sample has excellent photoelectric performances. A red-emitting phosphor K 2 [MoO 2 F 4 ]•H 2 O:Mn4+ (denoted as KMOF:Mn4+) was designed and synthesized by a simple precipitation method, and its structure and luminescence properties were studied in details. The as-prepared KMOF:Mn4+ phosphors show broad excitation band in the blue-light region. The as-optimized phosphor KMOF:Mn4+ (3.28 mol%) has the strongest red-emission with high internal quantum efficiency of 86.5% among these samples with different contents of Mn4+. Meanwhile, this sample is of the high thermal stability of luminescence. One white light-emitting diode (w-LED) was fabricated by coating KMOF:Mn4+ (3.28 mol%) and Y 3 Al 5 O 12 :Ce3+ on a GaN chip. This w-LED can emit intense warm white-light and show excellent photoelectric performances with a high color rendering index of 94, a low correlated color temperature of 3945 K, and the high luminous efficiency of 150.1 lm/W. Hence, KMOF:Mn4+ (3.28 mol%) could be a promising red phosphor for w-LEDs. [ABSTRACT FROM AUTHOR]