The electronic and optical properties of a narrow-band red-emitting nanophosphor K2NaGaF6:Mn4+ for warm white light-emitting diodes

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2018-01, Vol.6 (12), p.3016-3025
• Main Authors: Jiang, Chunyan, Brik, Mikhail G, Li, Lihua, Li, Liyi, Peng, Jie, Wu, Jianan, Molokeev, Maxim S, Ka-Leung, Wong, Peng, Mingying
• Format: Article
• Language: English
• Subjects: Charge exchange; Dipole interactions; Dipoles; Emission spectra; Energy levels; Fluorides; Light emitting diodes; Manganese ions; Nanophosphors; Optical properties; Organic light emitting diodes; Quantum efficiency; Quenching; Synthesis; Thermal resistance; White light
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c7tc05098d

Recently, as a key red component in the development of warm white light-emitting diodes (WLEDs), Mn4+-doped fluorides with narrow red emission have sparked rapidly growing interest because they improve color rendition and enhance the visual energy efficiency. Herein, a red nanophosphor, K2NaGaF6:Mn4+, with a diameter of 150–250 nm has been synthesized using a simple co-precipitation method. Rietveld refinement reveals that it crystallizes in the space group Fm3m with the cell parameter a = 8.25320(4) Å. The exchange charge model (ECM) has been used to calculate the energy levels of Mn4+ ions in K2NaGaF6, which match well with the experimental spectra. The as-synthesized phosphor exhibits a narrow red emission at around 630 nm (spin-forbidden 2Eg → 4A2 transition of Mn4+ ions) when excited at 365 nm (4A2g → 4T1g) and 467 nm (4A2g → 4T2g), with a quantum efficiency (QE) of 61% and good resistance to thermal quenching. Based on the structure, the formation mechanism of ZPL has been discussed. In addition, the concentration-dependent decay curves of Mn4+ in K2NaGaF6 were fitted using the Inokuti–Hirayama model, suggesting that the dipole–dipole interactions determine the concentration quenching. Finally, encouraged by the good performance, a warm LED with a CRI of 89.4 and CCT of 3779 K was fabricated by employing the title nanophosphor as the red component. Our findings suggest that K2NaGaF6:Mn4+ can be a viable candidate for the red phosphor used in warm WLEDs.