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In this study, Cr3+‐doped and Mn4+‐Cr3+ co‐doped double perovskite fluoride phosphors K2LiGaF6 are prepared using a simple hydrothermal method. High‐efficiency near‐infrared (NIR) emission near 762 nm is obtained under blue‐light excitation, and the co‐doping effect of Mn4+ on the NIR luminescence properties of Cr3+ is studied. Compared with the Cr3+ single‐doped phosphor, Mn4+, and Cr3+ co‐doped K2LiGaF6 exhibit a sharp increase of 129% in NIR emission, an enhancement in the internal quantum efficiency from 82.5% to 90.0%, and an enhancement in the thermal stability at 425 K from 85.0% to 90.7%. The encapsulated NIR phosphor‐converted light‐emitting diode device at 300 mA exhibits a photoelectric conversion efficiency of 15.3%. These values exceed most previously reported results. This study provides a new approach for enhancing the luminescence properties of Cr3+‐doped fluoride NIR phosphors. [ABSTRACT FROM AUTHOR]

• A brand-new blue-emitting phosphor NaSrScSi 2 O 7 :Eu2+ was prepared. • NaSrScSi 2 O 7 :0.03Eu2+phosphor possesses a high absorption efficiency of 84.35%. • The blue phosphor allows the WLED-2 spectrum to cover more short-wavelength region. A high absorption efficiency blue-emitting phosphor NaSrScSi 2 O 7 :Eu2+ for near-UV-pumped white light-emitting diodes [Display omitted] The Eu2+ ion is extensively used as an activator due to its wide excitation band and high efficiency emission spectrum. However, most Eu2+-activated blue-emitting phosphors have low absorption efficiency in the near-ultraviolet (n-UV) region or lack the short-wavelength blue light emission (<450 nm), resulting in UV light leakage or poor color rendering. Herein, we have successfully prepared a brand-new blue phosphor NaSrScSi 2 O 7 : Eu2+ by solid-state reaction method. The Rietveld refinement of the powder diffraction data, luminescent properties, decay lifetime, quantum efficiencyand thermal quenching have been investigated in detail. Under 345 nm excitation, the NaSrScSi 2 O 7 : 0.03Eu2+phosphor manifests an asymmetric emission spectrum centered at 427 nm, and notably, shows a high absorption efficiency of 84.35%. Finally, we encapsulated two white light-emitting diodes (WLEDs) devices using as-prepared blue-emitting phosphor and three commercial phosphors. At 80 mA drive current, both packaged devices demonstrate warm white light. Meanwhile, the WLED-2 with NaSrScSi 2 O 7 : 0.03Eu2+ blue-emitting phosphor has a lower correlated color temperature of 3726 K, its spectrum complements more short-wavelength spectrum, and the special color rendering index R 6 and R 7 increased from 95.2, 94.5 to 98.3, 96.5, respectively, compared with WLED-1 without present phosphor. These results demonstrate that NaSrScSi 2 O 7 : Eu2+ blue-emitting phosphor is a prospective novel luminescent material for WLEDs. [ABSTRACT FROM AUTHOR]

Supplement illumination is indispensable in the indoor plant cultivation domain. In this research work, double perovskite Ca 2 LuNbO 6 :Mn4+ phosphors were produced. A strategy of enhancing luminescence performance by utilizing A-site cationic fluoride as a flux was proposed. The structure and morphology of Ca 2 LuNbO 6 :Mn4+ phosphor was characterized. Under the excitation of 360 nm, the emission spectra of Ca 2 LuNbO 6 :Mn4+ phosphor cover from 600 nm to 750 nm peaking at 683 nm. It benefits the red section of chlorophyll absorption band and possesses the wavelengths of 680 nm and 700 nm demanded by photosystem I (PS I) and photosystem II (PS II) to realize Emerson enhancement effect. After adding CaF 2 as flux, the emission intensity increases by 2.5 times. Due to its compatibility with the A-site cation of host, CaF 2 agent not only lower the sintering temperature but also increase the crystallite size, which result in the enhancement of luminescence. The D q /B and optical band gap of Ca 2 LuNbO 6 host is 2.32 and 3.79 eV, respectively, which show that Mn4+ ions locate in the [NbO 6 ] octahedra of strong crystal field and host has the suitable optical band gap for Mn4+ ions. With the help of CaF 2 , the thermal stability, activation energy Δ E a , internal quantum efficiency of Ca 2 LuNbO 6 :Mn4+ phosphors are promoted at 373 K from 64.8% to 70.7% of that at 273 K, from 0.33 to 0.36 eV, and from 9.1% to 23.5%. The luminescence lifetime of Ca 2 LuNbO 6 :Mn4+ is the order of a fraction of a millisecond. Finally, the as-prepared Ca 2 LuNb 0.996 O 6 :0.004Mn4+ phosphor was successfully fabricated through a 365 nm near ultraviolet (NUV) chip, which has the peak wavelengths of 683 nm and possesses 680 nm and 700 nm demanded by PS I and PS II. It is implied that Ca 2 LuNbO 6 :Mn4+ phosphor-converted light emitting diode has prospective market in the domain of supplement illumination of plant cultivation. [ABSTRACT FROM AUTHOR]