An efficient and stable narrow band Mn4+-activated fluorotitanate red phosphor Rb2TiF6:Mn4+ for warm white LED applications

Abstract

A Rb-based fluorotitanate stable narrow band red-emitting phosphor Rb₂TiF₆:Mn⁴⁺ with an internal quantum efficiency of 91% was synthesized through an efficient and mild coprecipitation method. Herein, by simultaneously using H₂TiF₆ as a Ti source to replace TiO₂ and using H₂O as a substitute for solvent HF, the total consumption of toxic HF can be effectively reduced in the synthesis processes. Further optimization of phosphors can be achieved by investigating the impact of doping concentration, amount of solvent added and reaction stirring time on the luminescence properties of the phosphors. The crystal structures, morphologies, luminescence performance, thermal stability, moisture resistance, and device performance of the as-synthesized phosphors were systematically investigated. The obtained Rb₂TiF₆:Mn⁴⁺ presents more exceptional luminescence properties, thermal stability and longevity under LED working conditions compared to Rb₂ZrF₆:Mn⁴⁺, and worthy of note, its unmodified moisture resistance is obviously superior to that of other Rb-based fluoride red phosphors. By using Rb₂TiF₆:Mn⁴⁺ as a red-light component, a high-quality LED device with desirable performance (Ra = 89, CCT = 3730 K and LE = 158.8 lm W⁻¹) can be obtained, and the variable drive current and temperature tests revealed that the resultant device exhibits excellent performance, which further demonstrates that Rb₂TiF₆:Mn⁴⁺ has efficient and stable light-emitting properties and can be used to fabricate high power WLEDs with preferable heat resistance.