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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]

The non-equivalent doping of Mn4+ in red-emitting fluoride phosphors effectively shortens the fluorescence lifetime. Herein, we successfully synthesized Rb2NaInF6:Mn4+ phosphors by an ion-exchange method. The compensation mechanism of Mn4+ local symmetry and charge balance in the phosphor were studied in detail by theoretical calculations based on density functional theory. The phosphor Rb2NaInF6:Mn4+ (5.59 mol%) exhibits intense red emission with a short fluorescence lifetime (1.45 ms). Meanwhile, it has excellent colour stability and thermal quenching stability at elevated temperatures. Using Rb2NaInF6:Mn4+, β-SiAlON:Eu2+ and a blue-emitting GaN chip as red, green, and blue components, the white light-emitting diode (w-LED) exhibits a wide colour gamut of 94.1% of the National Television System Committee (NTSC) standard value. So, this work provides valuable information to investigate novel red-emitting fluoride phosphors for LED backlighting. [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]

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 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]

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]

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 novel thiourea loading strategy was proposed to modify KSF phosphor. • The excellent water resistance was obtained after thiourea treatment. • The degradation and restore mechanisms of T-KSF phosphor was revealed. Recently, Mn4+ doped fluoride phosphors have been considered as ideal candidate materials employed in white light-emitting diodes (WLEDs). However, the extremely serious performance deterioration in a wet environment has affected their practical commercial applications. Herein, we developed a novel thiourea loading strategy for greatly improving the moisture resistance of typical K 2 SiF 6 : Mn4+ (KSF) red phosphors through treated by thiourea ethanol solution evaporation. The luminescent properties and moisture resistance have been discussed in detail, and the underlying moisture resistance mechanism was further proposed. The results show that the moisture resistance of KSF phosphor treated by thiourea significantly increased approximately sevenfold than that of untreated counterpart, exhibiting a potential application in the WLEDs backlight with high gamut display. These works brings up a promising alternative strategy for enhancing moisture resistance and provides a deeper understanding on the performance degradation mechanism for a variety of Mn4+ doped fluoride phosphors system. [Display omitted] [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]

• NIR emitting A 2 KAlF 6 :Cr3+ phosphors were prepared by a co-precipitation method. • A 2 KAlF 6 :Cr3+ phosphors exhibit broad NIR emission with high quantum efficiencies. • The phosphors have excellent thermal stability of luminescence. • The full-spectrum WLEDs based on A 2 KAlF 6 :Cr3+have good photoelectric performances. Herein, NIR A 2 KAlF 6 :Cr3+ (A = Rb, Cs) phosphors prepared by a co-precipitation method exhibit broad excitation in the blue region and broad NIR emission with high quantum efficiencies (64% for Rb 2 KAlF 6 :0.025Cr3+, and 60% for Cs 2 KAlF 6 :0.02Cr3+). Furthermore, Rb 2 KAlF 6 :Cr3+ and Cs 2 KAlF 6 :Cr3+ phosphors maintain 95.3% and 90.2% of their room-temperature initial intensity at 150 °C, respectively. The full-spectrum white light-emitting diode (WLED) based on Rb 2 KAlF 6 :Cr3+ exhibits a high color-rendering index (94.8), a high luminous efficiency (99.5 lm/W), and a low correlation color temperature (3666 K). The results reveal that these phosphors can not only apply in full-spectrum illumination but also provide new in-depth insights into the design of NIR phosphors with high efficiency and thermal stability. Near-infrared A 2 KAlF 6 :Cr3+phosphors with high thermal stability and quantum efficiency were designed and prepared for fabricating high-performance full-spectrum white light-emitting diodes. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a single-phase red-emitting phosphor BaGaF 5 :Mn4+ (BGFM) was synthesized by a hydrothermal method, and its crystal structure and luminescence properties were studied in detail. The results show that the excitation spectra of BGFM samples are mainly composed of two bands located at the near-ultraviolet and blue light region, respectively, while the emission spectra show multiple peaks in the red region. Due to the defects generated with the non-equivalent occupation of Ga3+ by Mn4+, the adjacent [MnF 6 ] octahedron is highly distorted, resulting in a strong zero-phonon line (ZPL, 627 nm) in the emission spectrum. Additionally, the materials have shown a high internal quantum efficiency (QE = 63.7%) and good color stability. Finally, a white LED was obtained by mixing BGFM and commercial Y 3 Al 5 O 12 :Ce3+ yellow phosphor on a blue light-emitting diode (LED) chip. [Display omitted] • New red phosphor BaGaF 5 :Mn4+ was synthesized by f a hydrothermal method. • The [MnF 6 ] octahedron is highly distorted, resulting in a strong zero-phonon line. • The lower 2E level energy (15949 cm−1) of Mn4+ was observed in BaGaF 5 :Mn4+. [ABSTRACT FROM AUTHOR]

A red-emitting phosphor with a short fluorescence lifetime plays an important role in LED backlighting. Herein, new red phosphor K 5 In 3 F 14 :Mn4+ (0.59%) with a tetragonal structure was prepared with the non-equivalent doping of Mn4+. The typical luminescent behaviors of Mn4+ can be observed from the phosphors. Different from the fluoride phosphors with the equivalent doping of Mn4+, K 5 In 3 F 14 :Mn4+ (0.59%) has a short decay time (2.74 ms). The white LED fabricated with K 5 In 3 F 14 :Mn4+ (0.59%) and commercial β-SiALON:Eu2+ emits bright white light under a 20 mA current, and its color gamut is up to 103% of the National Television System Committee (NTSC) standard value. So, K 5 In 3 F 14 :Mn4+ (0.59%) is a potential red component for LED backlighting. Red-emitting phosphor K 5 In 3 F 14 :Mn4+ as a new red component has prospective application in the backlighting with a wide color gamut. [Display omitted] • New red phosphor K 5 In 3 F 14 :Mn4+ was prepared with the non-equivalent doping of Mn4+. • The phosphor exhibits narrow-band emission with a short decay time of 2.74 ms. • A white LED with a wide color gamut (103% of NTSC) was obtained with the phosphor. [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]

• Cs 2 KCrF 6 :Mn4+ was designed and prepared at mild conditions. • Cs 2 KCrF 6 :Mn4+ exhibits high blue-light conversion efficiency. • Cs 2 KCrF 6 :Mn4+ has excellently thermal quenching property and color stability. • Cs 2 KCrF 6 :Mn4+ can improve the luminescent performances of w-LED. One red phosphor Cs 2 KCrF 6 :Mn4+ (CKCFM) with the cubic structure was prepared at mild conditions. Mn4+ in CKCFM with the highly symmetrical environment exhibit one broad excitation band peaking at 453 nm and narrow-band emission in the range from 600 to 650 nm. The optimized CKCFM has one highly external quantum yield of 46.7%. At the same time, the sample also has excellent thermal stability and color stability. The emission intensity of CKCFM at 160 °C is still higher than that at 20 °C. At last, one white light-emitting diode (w-LED) was obtained by combining CKCFM and Y 3 Al 5 O 12 :Ce3+with one blue LED chip. It shows excellent performance: color rendering index (Ra) up to 88.3, color temperature (CCT) down to 3986 K, showing that CKCFM can find application in w-LEDs. New red-emitting phosphor Cs 2 KCrF 6 :Mn4+ exhibits high blue-light conversion efficiency and a high thermal-quenching temperature for w-LEDs. [Display omitted] [ABSTRACT FROM AUTHOR]

• Cs 2 KGaF 6 :Mn4+ phosphor with high EQE of 43% was systhesized via co-participated methods. • DFT calculation reveals [MnF 6 ]2- occupied [GaF 6 ]3- and produce a V Cs ′ vacancy to balance the charge mismatch. • Unequivalent doping strategy provides detailed insights into the local structure of Mn4+ substituted in fluorides. • Cs 2 KGaF 6 :Mn4+ phosphor is suitable for wide color gamut displays. [Display omitted] Narrow-band red-emitting phosphors are worth investigating and developing to enhance their luminescence efficiency for white light-emitting diodes (WLEDs) and broaden the color gamut of backlight displays. Herein, a novel red-emitting fluoride phosphor Cs 2 KGaF 6 :Mn4+ (CKGFM) was synthesized, which presents sharp red emission bands, short fluorescence lifetime (τ = 3.81 ms) and high external quantum efficiency (EQE = 43%). To better understand Mn4+ incorporation in CKGFM, density functional theory (DFT) energetic calculations were performed to compare the charge compensation probabilities of an Mn4+ substituted at a Ga3+ or K+ site. The temperature-dependent luminescence trend shows that the CKGFM phosphor has good thermal stability in the temperature range of 15–120 ℃, indicating its potential in backlight LEDs. The as-prepared CKGFM phosphor was used to fabricate one white light-emitting diode (WLED) with β-SiAlON:Eu2+ green phosphor and blue InGaN LED chip, which shows a high luminous efficiency of 106.30 lm∙W−1 and a National Television Standards Committee (NTSC) value of 114.6%. The present study provides detailed insights into the local structure of Mn4+ substituted in fluoride red-emitting phosphors and helps to realize better Mn4+ emission for WLEDs. [ABSTRACT FROM AUTHOR]