Improved ternary composite ceramic phosphors for warm-white laser lighting

Abstract

The large thermal conductivity of phosphor materials is crucial for laser lighting. Since the laser beam for pumping is focused on a small spot size (usually less than 1 mm²), heat generation is unavoidable at this point. Composite ceramic phosphors for cool-white laser lighting, the correlated color temperature of which is around 5000 K, produced by mixing of yellow photoluminescent light from Y₃A₅O₁₂:Ce (YAG:Ce) with unutilized pumping blue light, were well studied. However, composite ceramic phosphors for warm-white around 3000 K are not as researched; this is because the difficulties in sintering nitride phosphors which are useful as red or orange phosphors. We have proposed improved ternary composite ceramic phosphors for warm-white laser lighting. The ceramic phosphors utilize a red phosphor: ((Ba,Sr)₂Si₅N₈:Eu), a yellow phosphor: (YAG:Ce), and a thermal conducting matrix: (Al₂O₃). There are two types of composite ceramics: Type A with higher emission efficiency, and Type B more effective for warm light. These composite ceramic phosphors have higher saturation input laser power than our previous one, in which Sr₂Si₅N₈ was utilized as a red phosphor. The improved ceramic phosphors (Type A) do not have a saturation peak of at least up to 16 W (power density:20 W/mm²) pumping laser power, but our previous one had a saturation peak at 6 W (power density:7.6 W/mm²). We recently got a good sample, the correlated color temperature of which is 3422 K, output efficiency is 177 lm/W, and general color rendering index (Ra) is 65. The improved ternary composite ceramic phosphors are extremely useful for warm-white laser lighting.