Structural and luminescence properties of barium orthosilicate doped with europium and samarium ions

摘要

The development of white light-emitting diodes (WLEDs) in solid-state application is advanced by studying the properties of barium orthosilicate ceramics doped with europium and samarium. Ceramic materials based on the composition of 60BaO-30SiO2-10Na2O-4Eu2O3-3Sm2O3 samples were successfully prepared via solid-state reaction method sintered at 1200 ºC for 5 hours. The structural and optical properties of the ceramics were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectroscopy. The XRD profiles indicated that the crystalline phase of synthesized samples was dominated by orthorhombic phase of Ba2SiO4 and SiO2 monoclinic. An increment in Ba concentration intensified the crystallinity of the ceramics. The local network structures were represented by FTIR spectrum around 1220 – 1050 cm-1, 930 cm-1, and 1434 cm-1 assigned the presence of Si-O-Si, Si-O-Ba and SiO3 unit, respectively. The results showed that the presence of Ba caused the breaking of network bonds and generated non-bridging oxygen (NBO) of Si-O-(Si, Ba). The optical properties of Ba2SiO4: Eu3+ were analysed by PL Spectroscopy which revealed a spectrum of five emission peaks for Eu3+ centred at 580 nm, 591 nm, 612 nm, 651 nm and 706 nm. Reddish-orange emission was originating from the 5D0?7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ under excitation of 394 nm. The ceramic with 4 mol% Eu3+ dopant exhibited the highest intensity for Ba2SiO4. The co-doping of Sm3+ was found to stimulate the enhancement in luminescence intensity and to sensitize the emission in Ba2SiO4: Eu3+. The results suggested that the luminescence emission of this mechanism relied on the energy transferred from Sm3+ to Eu3+. The optimum doping concentration of Sm3+ ions was determined to be 3 mol%. For Eu3+/Sm3+ co-doped sample, down conversion luminescence spectra excited at 407 nm emitted five emission transitions of 5D0?7FJ (J = 2, 4) and 4G5/2?6HJ/2 (J = 5, 7, 9) respectively. Among them, the 5D0?7F2 of Eu3+ and 4G5/2?6H7/2 of Sm3+ were the strongest transitions, leading to an intense red colour emission.