Application of a novel red-emitting cationic iridium(III) coordination polymer in warm white light-emitting diodes

Abstract

A novel red-emitting cationic iridium(III) coordination polymer using 2-(9-(2-ethylhexyl)-9H-carbazol-3-yl)benzo[d]thiazole as main ligands, 4,4′-bipyridine as bridging auxiliary ligands and Clˉ as anions was synthesized. It had high thermal stability with a thermal decomposition temperature (Td) of 345 °C and low thermal quenching with an activation energy (Ea) of 0.2760 eV, with the temperature increasing from 20 °C to 100 °C, its photoluminescent intensity decreased to 76.7%. It can be efficiently excited by blue light of GaN chips, the cold white light of GaN-based LEDs using only Y3Al5O12:Ce3+ (YAG:Ce, 7.0 wt% in silicone) as phosphors can become warmer when it was blended in. When blending concentrations were 0.1 wt% and 0.2 wt%, the cold white light became neutral white light, the correlated color temperature (CCT) decreased from 6157 K to 5240 K, then to 4043 K, the color rendering index (CRI) changed from 72.7 to 81.3, then to 78.6, the luminous efficiency (ηL) changed from 134.1 lm·w−1 to 61.9 lm·w−1, then to 46.3 lm·w−1, the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates changed from (0.32, 0.33) to (0.34, 0.33), then to (0.38, 0.36). At 0.3 wt%, the light became warm white light, the corresponding CCT was 3475 K, CRI was 75.6, ηL was 36.9 lm·w−1, and CIE value was (0.41, 0.40). The results suggest the coordination polymer is a promising red-emitting phosphor candidate for neutral and warm white LEDs, especially for warm white LEDs.