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Red-emitting K3HF2WO2F4:Mn4+ for application in warm-white phosphor-converted LEDs – optical properties and magnetic resonance characterization†
Abstract
We report novel efficient Mn4+ phosphors of composition K3HF2MO2F4:Mn4+ (M = Mo, W) containing [HF2]− and octahedral [MO2F4]2– building units. The phosphor exhibits strong absorption at 450 nm and an external quantum yield of 90%. K3HF2WO2F4:0.01Mn4+ provides a sufficiently high quenching temperature T1/2 of about 400 K and is applicable as a converter for (In,Ga)N LEDs. The EPR spectrum is consistent with the presence of a MnF62– species at giso = 1.983. 19F MAS NMR results confirm the 2 : 1 ratio of the metal-bound fluoride species to the hydrogen difluoride group as predicted from the chemical formula. There are two distinct M-bonded species in a 1 : 1 ratio, indicating that the W and Mo octahedra are exclusively of the MO2F42– type, with the two oxygen atoms in cis-position. Their extremely sharp 19F resonances indicate a fast, near-isotropic reorientational process at room temperature that is on the millisecond timescale. For the HF2– group, the 19F and 1H MAS NMR spinning sideband profiles reveal the geometry of a linear centrosymmetric three-spin system with an H–F bond distance of 1.14 Å.
- This article is part of the themed collection: Celebrating Latin American Talent in Chemistry
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