K2NaAlF6:Mn4+ red phosphor: room-temperature synthesis and electronic/vibronic structures. Issue 8 (9th February 2018)

• Record Type: Journal Article
• Authors: Yi, Xiaodong; Li, Renfu; Zhu, Haomiao; Gao, Jun; You, Wenwu; Gong, Zhongliang; Guo, Wang; Chen, Xueyuan
• Is Part Of: Journal of materials chemistry. Volume 6:Issue 8(2018)
• Page Start: 2069
• Page End: 2076
• Publication Date: 2018-02-09
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c7tc05784a
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : K2 NaAlF6 :Mn 4+ red phosphor was synthesized via the co-precipitation approach at room-temperature and its fine electronic/vibronic structures were revealed. Abstract : In this work, we propose a co-precipitation method for the synthesis of K2 NaAlF6 :Mn 4+ red phosphor at room-temperature using methanol as the precipitating agent with a synthetic yield of ∼77%. The prepared sample (Mn ion doping concentration of 2.31 at%) exhibits a broad absorption band peaked at 466 nm and sharp emission lines centered at 631 nm with a high photoluminescence quantum yield up to 85%. The electronic/vibronic structures of the Mn 4+ ions in the K2 NaAlF6 crystal were investigated in detail for the first time by means of low-temperature (3 K) and high-resolution spectroscopy. This revealed that the Mn 4+ ions mainly occupy three distinct crystallographic sites, which differs from the hypothesis that the Mn 4+ ions will substitute the Al 3+ ions in the K2 NaAlF6 crystal, likely due to the charge mismatch between the Mn 4+ and Al 3+ ions. In particular, the unusually high intensity of the zero-phonon line at 622.40 nm implies that the corresponding Mn 4+ ions resided in a non-centrosymmetric local site, which was corroborated by the observed energy level splitting of the 2 E state. By employing the 2.31 at% sample as a red phosphor, we fabricated a warm white light-emitting diode (WLED) with a low correlated colour temperature (3911 K), a high colour rendering index ( R a = 94) and a luminous efficacy of 89 lm W −1 . These findings provide deep insights into the optical properties of Mn 4+ ions in hexafluoroaluminate hosts, and they show the great promise of K2 NaAlF6 :Mn 4+ as a red phosphor for highly efficient warm WLEDs and wide-gamut displays.