Synthesis of yellow fluorescent dyes derived from benzoxanthene that can be used in colour converters for remote phosphor LED systems

The current commercially available yellow organic dyes are not stable enough to be used for remote phosphor LED applications. Therefore new yellow benzoxanthene dicarboximide dyes to convert blue light from LED into light of longer wavelengths were synthesized. The spectral properties of the dyes and their stability in PET films were examined. The compounds showed high photoluminescence quantum yield and above all superior photostability under operation conditions (10% reduction in photoluminescence at 450 nm irradiance of 0.016 W/cm² at 60 °C). With extrapolated lifetimes up to 27000 h, a huge improvement in stability was established when compared to the commercially available yellow dyes exhibiting lifetimes lower than 1000 h.