| White-light-emitting diode (WLED) is regarded as an eco-friendly light source because of its small size, low energy consumption, high luminous efficiency, long lifetime, and environmentally benign. In recent years, silicate-based luminescent materials have been given considerable attention owing to their favorable luminescence properties and high chemical stability.Generally, luminescence of Eu3+ provides the red component and that of Eu2+, the blue or green. In this paper, materials doped Eu3+, part of Eu3+ is reduced to Eu2+, the luminescence of the phosphor consists of both Eu3+ and Eu2+ that a white light emission is achieved. Luminescence of the Eu3+ ion originates from its 4f6→4f6 transition consisting of sharp lines in the red region. The positions of its emission lines are independent of the host materials; Eu2+ presents broad emission from the parity-allowed transitions 4f65d1-> 4f7, which presents wide-emission range changing in the blue-green-yellow or red band. The emission band position can be tuned by selecting different host materials. Nevertheless,only a few studies have been considered this topic, thus inspiring us to explore the luminescence properties of Eu2+/Eu3+ co-doped single-phase white-light-emitting phosphors.A novel MgSrLa8-x(SiO4)6O2:xEu (MSLSO:xEu) phosphor was synthesized through a high-temperature solid-state reaction. The orthogonal experiment was used to study the synthesis conditions, and the influence factors of primary and secondary were as follows:firing temperature, doping concentrations and hold time. Crystal structures, luminescent properties, fluorescence decay time, and oxygen vacancies were investigated systemically. XRD analysis shows a typical oxyapatite structure with the space group of P63/m. Europium can enter crystal matrices simultaneously in the form of Eu3+ and Eu2+ and occupy nonequivalent crystallographic positions in a lattice, thus forming the various optical centers. Under ultraviolet light excitation, the phosphors simultaneously show the blue-green emission of Eu2+ and the green-yellow-red emission of Eu3+. The optimal doping contents of Eu is 7.5 mol% (x = 0.075). White light can be realized with CIE coordinate of(0.3664, 0.3260) by adjusting the concentration of Eu. The results suggest that the MSLSO:Eu2+/Eu3+ (0.075) phosphor is a promising candidate for white LEDs.The lifetimes of 5D1 and 5D0 levels in the current study are considerably longer than those of the reports from references, and the lifetimes of 5D1 level are longer than those of the 5D0 level. We speculate that the energy transmission from 5D1 to 5D0 is interfered. Under normal circumstances, transfer of energy from the 5D1 level to 5D0 level rapidly occurs in phosphors; therefore, the lifetime of the 5D1 level is relatively short and the lines of the intense 5D1 emission cannot be observed. In this host, the transfer of energy from 5D1 to 5D0 was hindered by oxygen vacancies; thus, the energy cannot be transmitted from 5D1 to 5D0.Therefore, the lines of the intense 5D1 emission can be observed and 5D1 level lifetimes are extremely long. There are three series of sharp oxygen vacancy peaks in the excitation spectra monitored at different wavelengths. As the wavelength of detected signals increases, the luminescence maxima of the peaks are displaced to the long-wave region of the spectrum. |
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