Surface engineered environment-stable red-emitting fluorides for white light emitting diodes

Abstract

Poor water stability is the main problem of commercialized Mn 4+ -doped fluorides for white light emitting diode (WLED) application. This work proposes a surface engineering strategy to rebuild a Mn 4+ -free fluoride shell on fluorides to effectively resist the destruction from water molecules. By simple processing using glyoxylic acid (GA) solution, the moisture resistance of the red-emitting fluorides can be significantly improved. The photoluminescence (PL) quantum efficiency (QE) of the surface-engineered K 2 SiF 6 :Mn 4+ (KSFM-GA) still maintain 98.43% after water immersion for 360 h, in sharp contrary to the untreated one (its PLQE decreases to 59.79%). Additionally, PL intensity of the hydrolyzed KSFM can be recovered to 99.1% through the treatment of the reducing GA solution. By using the high-stability KSFM-GA red phosphor, the as-fabricated high-performance warm-WLED device can still maintain 84.6% in luminous efficacy, higher than that (79.6%) with the untreated KSFM, after 500 h of aging in a high temperature (85 °C) and high humidity (85%) environment. • The surface engineering strategy is very simple for processing the commercial fluorides. • The surface reconstructed fluorides well remain the morphology and photoluminescence (PL) properties. • The PL intensity of the surface-engineered fluorides is almost unchanged even after being immersed in water for 360 h. • The reducing glyoxylic acid solution can fully restore the photoluminescence intensity of the hydrated fluorides. • The white-LED device with the surface-engineered fluoride shows improved color stability.