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Sunlight-like full-spectrum phosphor-converted light-emitting diodes (pc-LEDs) require near-infrared (NIR) emission bands to fill the spectrum gap and consequently propel their widespread applications. Although fluoride NIR phosphors have been increasingly investigated, balancing high quantum efficiency (QE), high thermal stability, and wideband NIR emission to obtain excellent overall performance in a single system is still a challenge for Cr3+-doped fluoride NIR phosphor and is significant for direct utilization. Herein, a high-efficiency and thermally stable broadband NIR emission was realized in a novel LiSrGaF6:Cr3+ fluoride phosphor benefitting from a relatively weak crystal field and electron–phonon coupling effect. Upon blue light excitation, the ultra-broad NIR luminescence ranging from 650 to 1150 nm can be achieved with an FWHM of 149 nm peaking at ∼813 nm. Furthermore, this system possesses a high QE of up to 76.88% and its emission intensity at 423 K still maintains 61.62% of its initial intensity at room temperature. An NIR output power of 42.82 mW and photoelectric conversion efficiency of 14.27% of NIR pc-LED devices have also been presented based on this NIR phosphor, demonstrating its possible application in compact nonvisible light sources. In addition, a highly continuous sunlight-like vis-NIR pc-LED was further constructed by employing a blue chip with commercial cyan (BaSi2O2N2:Eu2+), yellow (Y3Al5O12:Ce3+), red (CaAlSiN3:Eu2+), and this LiSrGaF6:Cr3+ NIR phosphor. The as-obtained pc-LED exhibits an ultra-broad spectrum ranging from 400 nm to 1000 nm, exhibiting a higher color reproduction with a color rendering index (CRI) of 95.1 and luminous efficiency (LE) of 50.22 lm W−1. These results indicate that LiSrGaF6:Cr3+ phosphor can be a promising NIR phosphor candidate for high-quality sunlight-like full-spectrum lighting and infrared night vision technology. [ABSTRACT FROM AUTHOR]

The Cr3+-doped near-infrared (NIR) phosphors have been extensively investigated owing to their promising applications in biomedicine, food safety detection, and night vision surveillance. However, achieving broadband (FWHM > 160 nm) NIR emission is still challenging. In this paper, novel Y2Mg2Ga2−xSi2O12:xCr3+ (YMGS:xCr3+, x = 0.005–0.08) phosphors were prepared by a high-temperature solid-state reaction. The crystal structure, photoluminescence properties of the phosphor, and the device performance of a pc-LED were researched in detail. When excited at 440 nm, the YMGS:0.04Cr3+ phosphor exhibited broadband emission in the range of 650–1000 nm, peaking at 790 nm with a full width at half-maximum (FWHM) of up to 180 nm. The wide FWHM of YMGS:Cr3+ is conducive to its extensive application in NIR spectroscopic technology. In addition, the YMGS:0.04Cr3+ phosphor could maintain 70% of the initial emission intensity at 373 K. By combining the commercial blue chip with the YMGS:0.04Cr3+ phosphor, the resulting NIR pc-LED demonstrated a near-infrared output power of 14 mW with a photoelectric conversion efficiency of 5% at a drive current of 100 mA. This work provides a broadband emission NIR phosphor option for NIR pc-LED devices. [ABSTRACT FROM AUTHOR]

For high-efficiency lighting and wide color gamut backlight display, high-quality narrow-band red phosphors for WLEDs are still in high demand. Herein, a novel red-emitting fluoride phosphor Cs2NaGaF6:Mn4+ was successfully synthesized by a simple two-step co-precipitation method and exhibits ultra-intense zero-phonon lines (ZPLs) and long wavelength phonon sidebands under 468 nm blue light irradiation. The ZPL emission peak of Cs2NaGaF6:Mn4+ was located at 627 nm, which is much stronger than its υ6 vibration peak, more matchable with the eye-sensitive region of humans, and beneficial for obtaining higher luminous efficiency of WLEDs. Interestingly, the υ6 vibration peak of this red phosphor is at 636.5 nm, which is larger than that of the common fluoride phosphor A2BF6:Mn4+ (usually at about 630 nm, represented by K2SiF6:Mn4+) at about 6.5 nm. Thanks to the longer wavelength of the υ6 vibration peak, the chromaticity coordinates (0.7026, 0.2910) with a larger x-coordinate value were realized, leading to a potentially wider color gamut of WLEDs. In addition, this phosphor has high thermal stability and its emission intensity at 423 K remains 93.7% of the initial intensity at room temperature. The lumen efficiency of WLED1 packaged with a mixture of Cs2NaGaF6:Mn4+ and YAG:Ce3+ on the InGaN blue chip is 115.7 lm W−1 with the color temperature (Tc) = 3390 K and the colour rendering index (Ra) = 92.5 under 20 mA driving current. The chromaticity coordinates of WLED2 packaged with Cs2NaGaF6:Mn4+ and β-SiAlON:Eu2+ on the InGaN blue chip are (0.3149, 0.3262) and the calculated color gamut is up to 118.4% (NTSC). These results indicate that Cs2NaGaF6:Mn4+ red phosphors have promising applications in the high-quality lighting and display fields. [ABSTRACT FROM AUTHOR]

Phosphor-converted light-emitting diodes (pc-LEDs) have important applications in security surveillance and food testing. However, developing new broadband near-infrared phosphors remains an important issue. Herein, the high-temperature solid-state reaction method was applied to synthesize a new type of Cr3+ doped Mg2Al4Si5O18 broadband NIR phosphor which matches a blue LED chip. It exhibits a broadband near-infrared (NIR) phosphor emission with a focus of 856 nm and a full width at half maximum >200 nm after excitation at 453 nm. The optimum concentration of Cr3+ was established to contain 2 mol%. At 398 K, the luminescence intensity is 45.2% of that at 298 K. The power output of NIR pc-LEDs fabricated by incorporating a 450 nm chip and the Mg2Al4Si5O18:0.02 Cr3+ phosphor is 19.69 mW at 300 mA current. Finally, the developed NIR pc-LED shows significant potential for use in night-vision imaging. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphor-converted light emitting diode (pc-LED) light sources have broad application prospects in environmental science, biomedical and plant growth fields. However, NIR phosphors still suffer from narrowband emission and low thermal stability. Here, we prepared a novel Lu2CaMg2−xSi3O12:xCr3+ (LCMS:xCr3+, x = 0.005–0.06) phosphor with broadband emission by a high-temperature solid state reaction. Under excitation at 450 nm, the emission spectrum of the LCMS:0.05Cr3+ phosphor shows a broadband emission in the range of 650–1000 nm with a large full width at half maximum (FWHM) of 125 nm and an R-line emission of 692 nm. In addition, the LCMS:0.05Cr3+ phosphor has good thermal stability and can maintain 70% emission intensity at 150 °C relative to that at room temperature. The LCMS:0.05Cr3+ phosphor exhibits a high internal quantum efficiency (IQE) of ∼76%. Using this phosphor, a NIR pc-LED with photoelectric efficiencies of 14.8% at 100 mA and 6.0% at 320 mA and NIR output powers of 59.5 mW at 100 mA and 181.0 mW at 320 mA was obtained. The broadband LCMS:0.05Cr3+ phosphor with a NIR emission peaked at 750 nm can serve as a light source for plant cultivation and has superior application prospects in the agriculture field. [ABSTRACT FROM AUTHOR]

An oxyfluoride red phosphor Cs2MoO2F4:Mn4+ was synthesized via a facile co-precipitation route with a certain molecular ratio of CsF and MoO3. X-ray diffraction analysis and its Rietveld refinement reveal that Cs2MoO2F4:Mn4+ crystallized in an orthorhombic structure with the Amam (63) space group. Upon blue light excitation, Cs2MoO2F4:Mn4+ exhibits a series of sharp red emission lines around ∼634 nm and the zero-phonon line (ZPL) is visible at 619 nm. The optimal doping amount of Mn4+ in Cs2MoO2F4 is 1.12%, and the decay curves show a good fit with the single exponential decay model. The fluorescence lifetime of the synthesized phosphors is relatively short and calculated as 3.18 to 2.46 ms, the Mn4+ ions in Cs2MoO2F4 experience a strong crystal field strength with a Dq/B of ∼4.87, and the distinct nephelauxetic ratio β1 is determined to be ∼1.0226. The thermal quenching mechanism of Mn4+ was also studied. Furthermore, by using the as-synthesized Cs2MoO2F4:Mn4+ phosphor as a red component and β-SiALON as a green light component, a WLED was fabricated with a high luminous efficacy of 114.70 lm·W−1 and wide color gamut of 109.1% of the National Television Standard Committee (NTSC) value. Hence, the Cs2MoO2F4:Mn4+ phosphor with a short fluorescence lifetime could potentially be an efficient red compensator for application in rapid-response backlight displays. [ABSTRACT FROM AUTHOR]

A novel Sr2MgB2O6 (SMBO) green-emitting phosphor co-doped with Ce3+–Tb3+ was synthesized at 950 °C via solid-state reactions, and the ultra-narrow-band green emission of Tb3+ was significantly enhanced almost 20 times via energy transfer from Ce3+ to Tb3+. It was found to have a broad excitation band (250 to 400 nm), and the full width at half-maximum (FWHM) of the dominant green emission band around 544 nm was only about 10 nm. The electronic band gap of the SMBO matrix was calculated by density functional theory (DFT) to be 4.60 eV, and this was well verified by the diffuse reflection spectra results. Furthermore, the composition-optimized phosphor SMBO:0.05Ce3+,0.05Tb3+ exhibits excellent thermal quenching resistance (75.3% intensity at 423 K) and relatively high external quantum efficiency (EQE = 48.92%). Finally, two white light-emitting diode (WLED) packages were fabricated via combining a 365 nm n-UV chip, the optimal sample and commercial blue and red phosphors to assess the application potential of the phosphors. The test results indicate that the obtained WLEDs-1 fabricated with K2SiF6:Mn4+ has an outstanding color rendering index (Ra = 85.7) and Commission Internationale de L'Eclairage (CIE) coordinates (0.3242, 0.3334). Meanwhile, the color gamut can reach 87% of the National Television Standards Committee (NTSC) CIE 1931 color gamut. WLEDs-2 fabricated with red emitting CaAlSiN3:Eu2+ produced warm white light with color coordinates of (0.3792, 0.3810), a high color rendering index of 82.3, and a low correlated color temperature of 4065 K. These results reveal the broad prospects of this phosphor for LED-based applications. [ABSTRACT FROM AUTHOR]

The addition of a red-emitting phosphor to YAG:Ce3+-based white light-emitting diodes (WLEDs) greatly facilitates their applications in the field of high-color-rendering-index warm solid-state lighting. It is highly desirable to develop a red phosphor with satisfactory spectral features and low synthesis cost. In this study, a novel non-rare-earth and nonequivalent doping type of Cs2NbOF5:Mn4+ oxyfluoride red-emitting phosphor with high luminous efficiency was obtained via a facile room-temperature co-precipitation method, and its morphology and luminescent properties were investigated in detail. The Cs2NbOF5:Mn4+ phosphor with micro-rod-like morphology exhibited broad band absorption at blue light region (∼474 nm) and narrow bandwidth emissions at red region (∼633 nm). The color purity of the Cs2NbOF5:Mn4+ phosphor was calculated to be about 99%, and the internal quantum yield (QY) under 474 nm excitation was 63.4%. The concentration quenching of Mn4+ in Cs2NbOF5 matrix was mainly due to dipole–dipole interactions, and the activation energy of temperature quenching was calculated to be ∼0.2610 eV. The demonstration of a blue InGaN LED chip in combination with a blend of newly developed Cs2NbOF5:Mn4+ red phosphor and YAG:Ce3+ yellow phosphor greatly decreased the correlated color temperature (CCT) from 6255 to 3517 K while significantly improving the color rendering index (CRI) from 72.5 to 87.5. It deserves to be mentioned that the brand-new matrix to phosphor in the present study can be extended to various niobium/tantalum oxyfluoride series, which is very helpful for developing and designing new red phosphors. [ABSTRACT FROM AUTHOR]