HF‐free molten salt route for synthesis of highly efficient and water‐resistant K₂SiF₆:Mn⁴⁺ for warm white LED

Abstract

Solid-state white-light-emitting diodes (WLEDs) have attracted more and more attention for its long lifetime, high efficiency, low cost, and environment-friendly relative to incandescent and fluorescent of traditional lighting. 1−4 At present, the white light of commercial WLED is mainly obtained through the combination of blue InGaN chip and Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+) yellow phosphor. Due to the deficiency of red emission, the inherent disadvantages of these WLEDs, such as low color rendering index (CRI, Ra<80) and high color temperature (CCT>6000K), limit their application in illuminating system. 5−8 Fortunately, some red-emitting phosphors that can be added directly to commercial WLED to improve the quality of LEDs have been developed. The non-rare-earth ion Mn 4+ has attracted our attention because its emission peak is located in the red region of 620 to 750 nm under blue and ultraviolet light excitation. 9−11 Among the Mn 4+-doped red phosphors, the emission peak of the Mn 4+-doped fluoride is located at 620 to 640 nm due to the weak coordination bond. In recent years, various Mn 4+activated fluoride phosphors such as A 2 XF 6 :Mn 4+ (A = K, Na, Cs, etc X = Si, Ge, Ti, etc) are gradually replacing the Eu 2+-doped nitride as red phosphors for manufacture the WLEDs because of their superior thermal stability, optical properties, and facile synthetic condition. 12−18

Improved Moisture-Resistant and Luminescence Properties of a Red Phosphor Based on Dodec-fluoride K3RbGe2F12:Mn4+ through Surface Modification

“…A slight red shift has been observed in the temperature-dependent emission spectra of KRGF:Mn with the temperature increasing from 298 to 553 K (Figure b) . In addition to the emission position and intensity, the full width at half-maximum (fwhm) is another important parameter of luminescent materials with narrow band emission .…”

“…To demonstrate the commercial value of red phosphor OA-M-KRGF:Mn, a WLED2# device has been fabricated using as-synthesized OA-M-KRGF:Mn, commercial YAG:Ce phosphors, and a blue InGaN chip. The electroluminescence spectra of the two typical WLED1# and WLED2# (Figure a) emit “cold” and “warm” white light, respectively. − As a comparison, the white light generated by the WLED1# shows the CIE chromaticity coordinates ( x = 0.3241, y = 0.3357), CCT (6210 K), and CRI 75, whereas, the color coordinates, CCT, and CRI of the WLED2# are at ( x = 0.4258, y = 0.3980), 3677 K and 92, respectively. The optical properties of the WLEDs and photographs of the as-fabricated LEDs driven at 30 mA currents are shown in Figure S12.…”

“…A slight red shift has been observed in the temperaturedependent emission spectra of KRGF:Mn with the temperature increasing from 298 to 553 K (Figure 9b). 35 In addition to the emission position and intensity, the full width at halfmaximum (fwhm) is another important parameter of luminescent materials with narrow band emission. 13 The increasing temperature causes the fwhm of the emission spectra change from 23.5 to 26.7 nm, which is related to the structure rigidity and symmetry.…”

Recyclability of CsPbBr3 quantum dot glass nanocomposites for their long-standing use in white LEDs

“…The fabricated WLED produces cool white emission with a CCT value of 5920 K and a corresponding LER value of 68.3 lm W À1 at a driving current of 20 mA, demonstrating that it is desirable for most lighting applications. Although the LER values of PQD GNCs lag behind WLEDs based on chemically synthesized perovskite 54 or phosphor materials, 55,56 they have great potential among perovskite QD glass nanocomposites for light-emitting applications. 6,57 The sharp emission peaks result in a relatively low CRI value of 36, which is relatively low compared to the currently available commercial white LEDs.…”

Mn4+-activated oxyfluoride K3TaOF6 red phosphor with intense zero phonon line for warm white light-emitting diodes

“…Thanks to the specic electronic structure of the Mn 4+ (3d 3 electron conguration) ion, obvious broadening of the color gamut of LED-lit LCD backlights has been observed by employing Mn 4+ -activated red phosphors. [12][13][14][15][16][17][18] Theoretically, both Stokes and anti-Stokes photon vibrational sidebands could be easily implemented in the transition of Mn 4+ : 2 E/ 4 A 2 . 16,17 Whereas, only when Mn 4+ ions have distorted coordination geometries can the ZPL transition of Mn 4+ : 2 E/ 4 A 2 occur.…”