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

Rb-based hexafluoride red-emitting phosphors, Rb 2 SiF 6 :Mn 4+ and Rb 2 TiF 6 :Mn 4+ , 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 Rb 2 SiF 6 and Rb 2 TiF 6 hosts, respectively, in agreement with the XRD results. The phosphors exhibited an intense narrow-band Mn 4+ ( 2 E g → 4 A 2 g ) red emission with internal quantum efficiencies higher than 90% upon blue light excitation. The Franck−Condon analysis of the PLE data yielded the Mn 4+ intra- d -shell transitions to occur at ∼2.47 eV (∼2.34 eV) for the 4 A 2 g → 4 T 2 g transition and at ∼2.86 eV (∼2.83 eV) for the 4 A 2 g → 4 T 1 g transition in the Rb 2 SiF 6 :Mn 4+ (Rb 2 TiF 6 :Mn 4+ ) phosphor. Temperature dependence of the PL spectra from T = 20 to 500 K gave the quenching temperature values ( T q 's) at which the PL intensity has fallen to half its maximum value to be T q ∼ 490 and ∼450 K for Rb 2 SiF 6 :Mn 4+ and Rb 2 TiF 6 :Mn 4+ , respectively, promising for use as high-temperature stable phosphors in solid-state lighting applications.