Abstract
SrLa4-x-ySi3O13: xTb3+, yEu3+ phosphor was prepared by high temperature solid-state method. The luminescent centers of Eu3+ and Tb3+ occupying La3+ lattice sites in hosts were confirmed by Rietevld refinement method. The phenomenon of self-cross-relaxation energy transfer is observed between Tb3+ ions from 5D4-7FJ to 7F6-5D4 transition. Additionally, the direction of energy transfer (ET) was observed from Tb3+ to Eu3+ ions, and ET efficiency became more efficient as the concentration of activator increases. The type of ET between Tb3+ and Eu3+ ions was demonstrated to be the dipole-dipole mechanism. The multi-color lights were realized covering the green to red visible region by the route of energy transfer. Furthermore, the decrease of Eu3+ emission intensity resulting from thermal quenching can be effectively compensated by Tb3+→Eu3+ ET. The excellent luminescent properties and thermal stability show this phosphor to be a promising candidate for white LEDs.
Highlights
INTRODUCTIONCommercial white LED is usually made by yellow phosphor Y3Al5O12:Ce3+ (YAG: Ce3+) and blue LED chip
At present, commercial white LED is usually made by yellow phosphor Y3Al5O12:Ce3+ (YAG: Ce3+) and blue LED chip
All X-ray diffraction (XRD) profiles of as-above samples were indexed by CaLa4Si3O13(PDF#71-1368), without any impurity phase
Summary
Commercial white LED is usually made by yellow phosphor Y3Al5O12:Ce3+ (YAG: Ce3+) and blue LED chip. The luminescent properties of Eu3+ ions strongly depend on the lattice location of the Eu3+ dopant Such as, Yamada et al had synthesized CaLa4Si3O13: Eu3+ red phosphor with a high efficiency which was more than that of Y2O2S:Eu3+ red phosphor.[15]. Oxyapatite-related silicate compounds were considered to be an kind of effective host of the rare-earth activator as a new series of rare silicate phosphors with the bone structure of AB9(SiO4)6O2 and A2B8(SiO4)6O2 (A=alkali metal, B=rare earth).[16] There are two important lattice sites in these oxyapatite hosts, that is, nine coordinated 4f site with C3 point symmetry and seven coordinated 6h sites with C5 point symmetry, which are suitable for adjusting various rare earth (RE) and transition metal ions.[17,18,19] Previously, the crystal structure and optical properties of Eu3+ doped CaLa4(SiO4)3O2 have been reported. For clearly analyzing ET processes and direction in the Tb3+-Eu3+ double-doped phosphors, their photoluminescence excitation/emission spectra, PL decay behaviors were tested and their energy transfer efficiencies were calculated
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