Layer-stacking structure enabling K2TiF6:Mn4+ platelet crystals for inorganic high-power WLEDs packaging

Abstract

Conventional high power white LEDs (WLEDs) rely on coating micrometer-sized phosphor powder blends onto LED chips array using organic resins, which suffer from thermal simulation and yellowing of resin. Bulk phosphor crystals with platelet morphology, geometrically compatible with chip surfaces, offer an ideal solution to eliminate organic encapsulants. Redemitting fluoride ceramic plates have been prepared but no platelet crystal form has been reported. Herein, the hexagonal K₂TiF₆:Mn⁴⁺ was specifically selected for its pronounced layered stacking of [TiF₆]^2- octahedral sheets perpendicular to the caxis, favoring the growth of platelet crystals. Red-emitting platelets up to 5 mm were successfully grown via a coolinginduced crystallization method, and the effects of precursor saturation, cooling protocols, and Mn⁴⁺ doping level on crystal quality and photoluminescence were systematically investigated. The optimized crystals exhibit internal and external quantum efficiencies of 90.6% and 70.2%, respectively, along with markedly enhanced moisture resistance compared to powder counterparts. Combined with Y₃Al₅O₁₂:Ce³⁺-corundum ceramic plates, these crystals enable a pseudo all-inorganic packaging architecture that eliminates organic binders. The resulting WLEDs achieve a color-rendering index (R_a) of 84.8, an R₉ value of 42, a correlated color temperature of 3183 K, and a luminous efficacy of 79.3 lm W^-1. This work establishes a controllable platelet crystal-growth strategy toward orgnic binder-free phosphor-converted WLEDs.