Large micro-sized K2TiF6:Mn4+ red phosphors synthesised by a simple reduction reaction for high colour-rendering white light-emitting diodes

Abstract

A simple chemical method for synthesising large micro-sized K₂TiF₆:Mn⁴⁺ phosphors (50–100 μm) is presented, based on a direct reduction reaction with K₂TiF₆ particles immersed in KMnO₄/HF solution. The Mn⁴⁺ concentration in K₂TiF₆ primarily increases as the initial KMnO₄ concentration is increased, subject to the diffusion of Mn⁴⁺ ions. However, the relative emission intensity of our synthesised K₂TiF₆:Mn⁴⁺ is first enhanced and then declines with increasing KMnO₄ concentration, with an optimum KMnO₄ concentration of 0.016 g ml⁻¹, which most likely depends on the concentration quenching effect. The synthesised K₂TiF₆:Mn⁴⁺ (0.35–4.4 at%) phosphors show good thermal stability and can be adopted to fabricate high CRI (R_a > 85) white LEDs for indoor lighting.