Editors' Choice—Rb₂SiF₆:Mn⁴⁺and Rb₂TiF₆:Mn⁴⁺Red-Emitting Phosphors

Rb-based hexafluoride red-emitting phosphors, Rb2SiF6:Mn4+ and Rb2TiF6:Mn4+, were synthesized by the coprecipitation method. Optical microscopy observation, X-ray diffraction (XRD) measurement, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and luminescence decay characteristics measurements were used to study the structural and optical properties of the phosphors. The photographs of the bulk samples showed clear crystallographic habits originating from the cubic and trigonal symmetries of the Rb2SiF6 and Rb2TiF6 hosts, respectively, in agreement with the XRD results. The phosphors exhibited an intense narrow-band Mn4+ (2Eg → 4A2g) red emission with internal quantum efficiencies higher than 90% upon blue light excitation. The Franck−Condon analysis of the PLE data yielded the Mn4+ intra-d-shell transitions to occur at ∼2.47 eV (∼2.34 eV) for the 4A2g → 4T2g transition and at ∼2.86 eV (∼2.83 eV) for the 4A2g → 4T1g transition in the Rb2SiF6:Mn4+ (Rb2TiF6:Mn4+) phosphor. Temperature dependence of the PL spectra from T = 20 to 500 K gave the quenching temperature values (Tq's) at which the PL intensity has fallen to half its maximum value to be Tq ∼ 490 and ∼450 K for Rb2SiF6:Mn4+ and Rb2TiF6:Mn4+, respectively, promising for use as high-temperature stable phosphors in solid-state lighting applications.