Room-temperature synthesis and warm-white LED applications of Mn4+ ion doped fluoroaluminate red phosphor Na3AlF6:Mn4+

Abstract

A novel red fluoroaluminate phosphor, cryolite Na₃AlF₆:Mn⁴⁺, has been designed and synthesized via a facile two-step method at room temperature. Under blue light excitation, it exhibits intense sharp line red fluorescence (∼630 nm) with high color purity. The crystal structure, morphology and doping concentration of the samples were characterized in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ICP-AES. The influence of synthesis conditions, raw materials and doping concentration on crystal structure and photoluminescence (or decay behavior) has been investigated carefully. The optimal composition, Na₃AlF₆:1.58%Mn⁴⁺, shows a bright red light and excellent thermal stability (∼99.93% of the emission intensity at 200 °C relative to 23 °C) upon ∼467 nm blue light excitation. A warm high-power white LED with a high color rendering index (Ra = 92.7 and R9 = 94) and low color temperature (CCT = 3903 K) was fabricated based on the blue InGaN chip, commercial yellow phosphor YAG:Ce³⁺ and red phosphor Na₃AlF₆:Mn⁴⁺.