Sr3Bi(PO4)3:Eu2+, Mn2+: Single-phase and color-tunable phosphors for white-light LEDs
Introduction
In recent years, luminescent materials were used in various fields, such as telephone screens, fluorescent lamps and white-light emitting diodes (WLEDs) [1], [2]. As a result, lots of luminescent materials were synthesized by different methods, e.g., CaSiO3:(Pb, Mn) [3], Y3Al5O12:Ce3+ [4], LaPO4:Eu3+ [5], (Y, Eu)2O3 [6], Yb/Ho doped M2O2S (M = Y, Gd, La) [7], CaWO4 and CaWO4:Eu3+ [8], (Ca, Mg, Sr)9Y(PO4)7:(Eu2+, Mn2+) [9], Ba3Lu(PO4)3:(Eu2+, Mn2+) [10], SrAl2O4:(Eu2+, Dy3+) [11], and so on. WLEDs have been drawn an increasing attention recently because of their potential application in backlight for liquid crystal displays and solid-state lighting. And warm WLEDs with low correlated color temperatures (CCTs) are favored for solid-state lighting applications in room lighting. WLEDs involve an electroluminescence process, which is a non-thermal generation of light resulting from the application of a voltage to a substrate [12]. Comparing with the traditional incandescent or fluorescent lamps, WLED-based lighting can provide significant power saving, longer lifetime, higher luminous efficiency and brightness, and environmental friendliness [13], [14].
White light emission can be obtained by co-doping ion pairs base on the energy transfer mechanism (e.g., Ce3+ → Tb3+, Eu2+ → Mn2+) [9], [15]. Energy transfer is a process that a certain excitation center transfers all or part of the excitation energy to another luminescent center. Energy transfer can only occur when the energy differences between the ground and excited states (sensitizer and activator) are equal (resonance condition), and a suitable interaction between both systems exists. Generally, the donor ion is defined as the “sensitizer’’ and the acceptor ion is called the ‘‘activator’’. It is well known that the transition metal Mn2+ ions can give a broad emission band from green to red, depending on the crystal field of the host materials [16]. And the disadvantage of Mn2+ ion is that the d–d transition is forbidden and difficult to be pumped. However, Eu2+ ion has been proven to be an efficient sensitizer for Mn2+ ion. Moreover, white light can be realized from the Eu2+ and Mn2+ co-doped single-phased phosphors by adjusting the ratio of the Eu2+ and Mn2+ [17].
Recently, phosphate phosphors have been emerged as a popular family of luminescent materials and show great potentials for WLEDs, because the tetrahedral rigid three-dimensional matrix of phosphate compound is thought to be ideal for charge stabilization [18]. Herein, we report on the synthesis of Sr3Bi(PO4)3:Eu2+, Sr3Bi(PO4)3:Mn2+, and Sr3Bi(PO4)3:Eu2+, Mn2+ phosphors by solid state reaction. The luminescent properties of synthesized samples were investigated carefully.
Section snippets
Experiment
Sr3Bi(PO4)3:0.01Eu2+, Sr3Bi(PO4)3:0.06Mn2+, and Sr3Bi(PO4)3:0.01Eu2+, xMn2+ (x = 0, 0.02, 0.04, 0.06, and 0.08) phosphors were synthesized by solid state reaction. SrCO3, NH4H2PO4, Eu2O3, and MnO were chosen as raw materials. All starting materials were of analytical reagent and used directly without any further purification. The dopant concentration of Eu2+ ions is 1% mol. The dopant concentration of Mn2+ ions is in the range of 0–8 mol%. The typical process is as follows. Firstly, the
Result and discussion
Sr3Bi(PO4)3 materials have the structural type of eulytine, which consists of a three-dimensional packing of (PO4)3− tetrahedron and (BiO6)9− octahedron [19]. The octahedra form a three-dimensional network by sharing edges among themselves. But the (PO4)3− tetrahedron is completely independent and share four of their O atoms with different neighboring (BiO6)9− octahedra. Sr3Bi(PO4)3 has a cubic crystal structure with a space group of I43d (No. 220) and lattice parameter values of a = b = c = 10.199 Å
Conclusion
Sr3Bi(PO4)3:Eu2+, Sr3Bi(PO4)3:Mn2+, and Sr3Bi(PO4)3:Eu2+, Mn2+ phosphors were synthesized by solid state reaction. The structure and luminescence characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometer. En2+ and Mn2+ ions can well dope in Sr3Bi(PO4)3 host material. Sr3Bi(PO4)3:Eu2+ and Sr3Bi(PO4)3:Mn2+ samples show characteristic emission bands of Eu2+ and Mn2+ ions, respectively. The emission color could be tuned through tuning the co-doping
Acknowledgements
This work is supported financially by the Major Project of Hebei North University (No. ZD201303) and Zhangjiakou Science and Technology Bureau (Nos. 13110038I-11 and 1101019B), and the Science and Technology Department of Heibei Province Project (No. 13210336).
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