A yellow-green-emitting graphitic-C3N4 derivative consisting of 1,4-phenylene-inserted heptazine units: Preparation and application as a metal-free phosphor for white LEDs

Abstract

To develop non-rare-earth or metal-free phosphors for white light-emitting diodes (WLEDs) are very significant and forward-looking. Here, a yellow-green-emitting g-C3N4 derivative (p-Ph-g-C3N4) consisting of 1,4-phenylene-inserted heptazine units was successfully prepared by 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) via thermal polymerization. Its emission is mainly located at 450–700 nm with the maximum wavelength (λem,max) of 536 nm, its quantum yield (QY) is 15.7% (λex = 430 nm) which is much higher than that of bulk g-C3N4 (ca. 5%). Under the excitation of 430 nm blue-emitting GaN-based chips (ca. 4.0 lm·W−1), p-Ph-g-C3N4 together with non-rare-earth red-emitting K2SiF6:Mn4+ as phosphors, a series of cold, neutral, and warm WLEDs with good performances were fabricated. As for the best one, its color rendering index (CRI) is 84.3, correlate color temperature (CCT) is 5702 K, luminous efficiency (LE) is 5.40 lm·W−1, moreover, its CIE value (0.30, 0.34) is very close to (0.33, 0.33) of pure white light. The research results indicate p-Ph-g-C3N4 can be used as an efficient metal-free quasi-green phosphor for WLEDs.