Application of an orange-yellow emitting cationic iridium(III) complex in GaN-based warm white light-emitting diodes

An orange-yellow emitting cationic iridium(III) complex [(ptpy)(2)Ir(BCP)]PF6 (ptpy: 2-(p-tolyl)pyridine; BCP: bathocuproine) was synthesized. [(ptpy)(2)Ir(BCP)]PF6 exhibited high thermal stability with the thermal decomposition temperature (T-d) of 375 degrees C, with the temperature increasing from 20 to 100 degrees C, the photoluminescent intensity of [(ptpy)(2)Ir(BCP)]PF6 decreased to 79.9%. It can be efficiently excited by blue light (lambda(max) = 457 nm) of GaN chip, and a series of GaN-based light-emitting diodes (LEDs) were fabricated by using it as phosphors blended in silicone at different blending concentrations. At 1.0 wt.%, a cold white LED was obtained, the corresponding color rendering index (CRI) was 77.1, correlated color temperature (CCT) was 6278 K, luminous efficiency (eta(L)) was 68.4 lm W-1, and Commission Internationale de L'Eclairage (CIE) value was (0.32, 0.25). At 2.0 wt.%, a neutral white LED was obtained, the corresponding CRI was 74.2, CCT was 4737 K, eta(L) was 75.4 lm W-1, and CIE value was (0.34, 0.27). At 2.5, 3.0, 4.0 and 5.0 wt.%, four warm white LEDs were obtained, among them, the maximum eta(L) was 85.8 lm W-1 (at 4.0 wt.%), the maximum CRI was 73.7 (at 2.5 wt.%), their CCT changed between 3410 K and 2328 K, the CIE values were (0.37, 0.30), (0.41, 0.34), (0.46, 0.39) and (0.49, 0.41) respectively. The results suggest [(ptpy)(2)Ir(BCP)]PF6 is a promising phosphor candidate for white LEDs, especially for warm white LEDs.