A novel PiGF@coated sapphire color converter with dual optical functions for high-brightness laser-driven projection display

The growing demand for color conversion materials in laser projection displays has positioned phosphor-in-glass films (PiGF) as a promising solution. Single-side sapphire-based anti-reflection (AR) and high-reflection (HR) coatings were fabricated via electron beam evaporation on sapphire substrate backsides, involving alternate deposition of Ta 2 O 5 and SiO 2 thin films with varying thicknesses. These coatings significantly enhanced the optical performance of PiGF, improving its suitability for transmissive PiGF devices. The design enhances blue light in the 440–470 nm range, increasing transmittance from 85.5 % to 93.7 %. Visible light (500–700 nm) generated under blue excitation is reflected toward forward emission, boosting sapphire reflectance from 14.2 % to 94.3 %. As a result, excellent optical performance is achieved. In practical tests, the coated sapphire achieves 2770.6 lm at 12.9 W mm −2 and a luminous efficiency (LE) of 213.7 lm·W −1 , representing the 28.6 % improvement over the uncoated β-Sialon:Eu 2+ (β-Sialon) PiGF. This represents the best optical performance of β-Sialon PiGF to date. Building on this, the composite CaAlSiN 3 :Eu 2+ (CASN:Eu) with a color temperature of 6248 K has been developed, paving the way for the commercialization of PiGF composite materials in laser lighting and display applications.