Luminescence and energy transfer of a color tunable phosphor Tb3+, Eu3+ co-doped KCaY(PO4)2
Introduction
Lanthanide (Ln3+) doped luminescent material is a hot topic in material science and has been widely studied in recent years. One of the interesting characteristics of Ln3+ ions are their sharp emissions due to 4f–4f transitions, make them possess advantages like high color purity, large Stokes shift and high luminescence quantum efficiency, which are of great importance for their possible lighting and display application [1]. Most of the recent phosphors are of single-chromatic, and combination of different phosphors is used when a multi-chromatic emission is needed. However, problems like different degradation rates and re-absorption among phosphors are inevitable. Using single-host multicolor phosphor could solve the above-mentioned problems. Besides, the realization of tunable multicolor emission under a single excitation wavelength in phosphors is beneficial for potential application in display device. The multicolor tuning of phosphors can be achieved by co-doping Ln3+ ion into suitable host lattice, such as Tm3+–Dy3+ [2], Tb3+–Eu3+ [3] and Tm3+–Dy3+–Eu3+ [4].
Phosphates are excellent hosts for luminescent materials because of their facile synthesis condition, good chemical stability and low cost. In this study, Tb3+, Eu3+ co-doped KCaY(PO4)2 (KCYP) phosphors were synthesized. Host structure, luminescent spectra, decay time and Tb3+→Eu3+ energy transfer process were analyzed. Under NUV excitation, KCaY(PO4)2:Tb3+, Eu3+ phosphors can generate color-tunable emission from green to red by changing Eu3+/Tb3+ ratio.
Section snippets
Experimental
The KCaY(PO4)2:Tb3+, Eu3+ phosphors of composition KCaY(1−x−y) (PO4)2:xTb3+/yEu3+ (x=0.20 and y=0–0.15) were prepared by a solid-state reaction method. Stoichiometric amounts of the starting materials were mixed homogeneously in the presence of acetone using an agate mortar. The samples were preheated at 900 °C for 2 h (heating rate: 10 °C/min) and then sintered at 1250 °C for 6 h (heating rate: 6 °C/min) in air atmosphere. The X-ray diffraction (XRD) measurements were carried out on a Rigaku
Results and discussion
Fig. 1a shows the XRD patterns of representative Tb3+/Eu3+-doped KCaY(PO4)2 samples. Most of the diffraction peaks can be indexed to the standard card JPCDS 51-1632 (KCaY(PO4)2. The XRD pattern of KCaY(PO4)2:0.20Tb3+, KCaY(PO4)2:0.20Eu3+ and KCaY(PO4)2:0.20Tb3+, 0.07Eu3+ samples displays similar profile with a minute difference in their diffraction peak intensities. This implies that the doping of Tb3+/Eu3+ ions and the synthesis conditions do not cause obvious change in the crystal structure
Conclusion
A series of Tb3+, Eu3+ co-doped KCaY(PO4)2 phosphor was synthesized by solid-state reaction. The results reveal that the doped Tb3+/Eu3+ ions were effectively built into the Y3+ site of the KCaY(PO4)2 host lattice. Excitation and emission spectra confirm that Tb3+ can efficiently sensitize Eu3+ emission under UV excitation and the schematic energy transfer processes are suggested. The emission color of KCaY(PO4)2:Tb3+, Eu3+ phosphor could be continuously changed from green (0.361, 0.540) to red
Acknowledgment
This research was supported by Guangxi Natural Science Foundation (Grant no. 2014GXNSFBA118046), and the Scientific Research Foundation of Guangxi University (Grant No. XBZ120573).
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