Graphitic-C3N4 modified by 9-phenylcarbazole groups and used as a metal-free phosphor in white light-emitting diodes

Abstract

Graphitic-C₃N₄ (g-C₃N₄) and some of its derivatives can be used as cheap and renewable rare-earth-free phosphors for replacing widely-used rare-earth-based phosphors in LEDs. Here, a 9-phenylcarbazole modified g-C₃N₄ derivative (g–C₃N₄–PhCz) was synthesized via thermal polymerization by using melamine as the main precursor and 6-(4-(9H-carbazol-9-yl)phenyl)-1,3,5-triazine-2,4-diamine as the molecular dopant at the molar ratio of 30:1, 450 °C, for 2 h. Such g–C₃N₄–PhCz emits bright greenish-yellow light with a high quantum yield of 30.1 %, which is much higher than that of bulk g-C₃N₄ (around 5.0 %). Moreover, it shows high thermal stability (thermal decomposition temperature is up to 465 °C) and low thermal quenching property (photoluminescence intensity retains 91.5 % at 110 °C relative to that at 30 °C). Under the excitation of GaN-based blue light chips, a series of high-quality cold/neutral/warm white LEDs were successfully fabricated by using g–C₃N₄–PhCz together with red-emitting K₂SiF₆:Mn⁴⁺ (also rare-earth-free) as phosphors. For example, the Commission Internationale de l'Éclairage (CIE) chromaticity coordinates can reach (0.3320, 0.3330) which is very close to (0.3333, 0.3333) of pure white light. Relative to the luminescent property of g-C₃N₄, that of g–C₃N₄–PhCz has been significantly improved and it is more suitable for white LEDs.