Aiqin Zhang

Tunable white light emission of Eu,Tb,Zn-containing copolymers by RAFT polymerization

In this work, a novel copolymer PS–Eu–Tb–Zn, which can match a 365 nm UV chip, was synthesized by the RAFT polymerization of Tb(p-BBA)3UA, Eu(TTA)2(Phen)MAA, Zn(BTZ)UA and styrene. TG-DTG and PL analyses indicate that the copolymer PS–Eu–Tb–Zn displays favorable thermal stability and luminescence properties. When excited at 365 nm, the copolymer exhibits emission peaks at 421 nm (blue emission), 488, 543 nm (green emission), 589 and 615 nm (red emission). The white light of the copolymer can be obtained by tuning the ratios of the three complexes and excitation wavelengths. The CIE coordinates (0.352, 0.330) of the copolymer are optimal upon excitation at 365 nm. For the fabricated white LED using a 365 nm UV chip with the copolymer, the CCT is 5684 K, and the CRI is 83.1. All the results indicate that the copolymer can be applied as a phosphor for the fabrication of NUV-based white LEDs.

Synthesis, characteristic and intramolecular energy transfer mechanism of reactive terbium complex in white light emitting diode

Abstract A reactive Tb(III) complex with 2-aminobenzoic acid (2-ABAH) and acrylonitrile (AN) as ligands was synthesized. The structure of the complex was characterized by elemental analysis and Fourier transform infrared spectrometry (FT-IR). The results indicated that the ligands were coordinated with Tb(III) ion. Thermal gravity-derivative thermogravimetric (TG-DTG) analysis indicated that the complex kept stable up to 198 °C. Luminescence properties were investigated by UV-vis absorption spectra and fluorescence spectra. The results suggested that being excited at 361 nm, the complex exhibited characteristic emission of Tb(III) ion, revealing that the complex could be excited by 365 nm ultraviolet chip. The HOMO and LUMO, Δ E (HOMO–LUMO) , molecular frontier orbital, and the singlet state and triplet energy state levels of the ligands were calculated at the B3LYP/6-31+G (d) level. The results indicated that intramolecular energy transfer mechanism followed Dexter exchange energy transfer theory. Both the calculation for excited state of ligand and energy transfer mechanism could provide the theoretical basis for the design of high luminescent materials of rare earth complexes with organic ligands.

Synthesis and luminescent properties of terbium complex containing 4-benzoylbenzoic acid for application in NUV-based LED

Abstract A novel Tb(III) ternary complex Tb(p-BBA) 3 MAA was synthesized with 4-benzoylbenzoic acid (p-BBA) and methacrylic acid (MAA) as ligands. The complex was characterized by IR, UV-visible, thermogravimetric analysis and fluorescence spectroscopy. Monitored at 544 nm, the complex displayed wide and strong excitation band at 300-400 nm, which matched well with the 365 nm-emitting UV chip. The complex exhibited excellent green emission at 544 nm ( 5 D 4 → 7 F 5 transition of Tb 3+ ) under an excitation at 365 nm. Besides, the complex showed high thermal stability. Its intramolecular energy transfer process was further discussed. Furthermore, the complex also had higher fluorescence lifetime (1.38 ms) and higher quantum yield (0.372). Finally, electroluminescent properties indicated that when used to fabricate LED with 365 nm UV chip (power efficiency is 18.6 lm/W), the complex remained its favorable optical performance. These results implied that Tb(p-BBA) 3 MAA could be used as a green phosphor for NUV-based white LED.

Combining emissions of hole- and electron-transporting layers simultaneously for simple blue and white organic light-emitting diodes with superior device performance

An efficient deep-blue fluorescent organic light-emitting diode (OLED), showing an emission peak at 432 nm, a high luminance of 14 140 cd m−2, and an external quantum efficiency (EQE) of 5.07% (which exceeds the theoretical limit), was developed by employing a simple bilayer structure. Such high device performance was achieved by combining emissions of the hole-transporting layer 4P-NPD and the electron-transporting layer Bepp2, simultaneously. Furthermore, based on the blue emission of the above-mentioned 4P-NPD/Bepp2, by handily arranging complementary phosphors doped in both 4P-NPD and Bepp2 sides, a series of simple two-, three-, and four-color hybrid white OLEDs (WOLEDs) without the interlayer between fluorescent and phosphorescent emitting layers were demonstrated. These hybrid WOLEDs realize superior device efficiency, the maximum EQE reaching 18.87%, 15.49%, and 18.44% for optimized two-, three-, and four-color WOLEDs, respectively. Moreover, the four-color hybrid WOLED also exhibits a very high color rendering index (CRI) of 93–94 over a wide luminance range of 83.68–17 050 cd m−2. To our knowledge, this is among the best efficiencies for very high CRI WOLEDs using such simple structures. The realization of high device performance was explored in detail, and was ascribed to the precise management and effective utilization of singlet and triplet excitons via the proposed novel device structure.