Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex

Zhengliang Wang,Guoyun Meng,Huaijun Tang,Qiang Zhou,Zeyu Chen,Kaimin Wang

doi:10.3390/ma10060657

Abstract

A novel orange cationic iridium(III) complex [(TPTA)2Ir(dPPOA)]PF6 (TPTA: 3,4,5-triphenyl-4H-1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)2Ir(dPPOA)]PF6 has high thermal stability with a decomposition temperature (Td) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)2Ir(dPPOA)]PF6 was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I’Eclairage) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency (ηL) was 128.5 lm∙W−1. Such a cold white LED became a neutral white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and ηL was 85.2 lm∙W−1. It further became a warm white LED when [(TPTA)2Ir(dPPOA)]PF6 was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and ηL was 46.1 lm∙W−1. The results show that [(TPTA)2Ir(dPPOA)]PF6 is a promising phosphor candidate for fabricating warm white LEDs.

Highlights

Due to high efficiency, long lifetime, and energy-saving and environmentally-friendly properties, white light-emitting diodes (WLEDs) have attracted significant attention and are used as the new generation solid-state light sources in general illumination, full-color displays, liquid crystal display backlights and so on [1,2,3,4]
Because the main emission of YAG:Ce is in the greenish yellow region, aforementioned commercial WLEDs have low color rendering index (CRI) and high correlated color temperature (CCT)
The blue emission peaks on the left with on the left with the maximum wavelengths around 450 nm were the emission of the blue GaN chips, the maximum wavelengths around 450 nm were the emission of the blue GaN chips, which were not which were not completely absorbed by [(TPTA)2Ir(dPPOA)]PF6 at low blending concentrations

Summary

Introduction

Long lifetime, and energy-saving and environmentally-friendly properties, white light-emitting diodes (WLEDs) have attracted significant attention and are used as the new generation solid-state light sources in general illumination, full-color displays, liquid crystal display backlights and so on [1,2,3,4]. CRI, CCT and efficiency etc.) can be obtained via the second approach, because the red phosphors are mainly excited by the blue GaN chip and the emission of YAG:Ce is seldom affected. As a consecutive and upgraded research by us, in this work, another novel orange cationic iridium(III) complex using dPPOA as auxiliary ligand, but using 3,4,5-triphenyl-4H-1,2,4-triazole (TPTA) instead of CBT as the main ligand was synthesized and used in YAG:Ce-based WLEDs to obtain warm white light. In order to make this new complex effectively excited by the blue light of a GaN chip, adonor–acceptor bipolar unit of triphenylamine–oxadiazole was contained in the auxiliary ligand dPPOA; theoretically, the electron-donating or/and electron-withdrawing functional groups on the main ligand will further. Complex; at the same time, such WLEDs exhibited encouraging light-emitting performances

General Information

Synthesis

Fabrication and Measurements of LEDs

Theabsorption strong absorption band between and

Photoluminescent Properties

Cl2 conjugated

Thermal Stability and Thermal Quenching Properties

Fabrication and Performance of LEDs

Performances

Conclusions