High-efficient, bicolor-emitting GdVO4:Dy3+ phosphor under near ultraviolet excitation
Introduction
During the past several decades, many phosphors doped with rare earth or transition ions have been developed for various applications in the field of cathode ray tubes, plasma display panels, field emission displays, fluorescent lamps, and so on [1], [2], [3]. In recent years, with the development of GaN-based LEDs, it is possible to achieve the solid state illumination by combining the short wavelength GaN-based LEDs with tricolor phosphors. However, the tricolor phosphors for this application are of lack. The present commercialized white LEDs are a combination of blue LEDs with yellow phosphors YAG:Ce3+ [4], which show a low color rendering and are unsatisfied for the high performance illumination. Therefore, exploring high performance phosphors for white LEDs is attractive and interesting challenge to the researchers. We believe that with the development of semiconductor industry, the short wavelength LEDs would be commercialized and their costs will decrease to an acceptable level. The phosphors, which can be effectively excited by near ultraviolet light, would be required.
Generally, the visible emissions from Dy3+ are mainly composed of two bands corresponding to 4F9/2→6H15/2 (blue) and 4F9/2→6H13/2 (yellow) transitions. The 4F9/2→6H13/2transition is very sensitive to the crystal field surrounding the Dy3+ due to its fulfillment of the selective rule for hypersensitive transition, namely, ΔL=2 and ΔJ=2 [5]. Therefore, the Dy3+ doped materials are attractive for practical applications due to the fact that the color coordinates of Dy3+ emissions can be tuned by choosing proper host. However, the emission from Dy3+ is rather weak upon direct excitation with near ultraviolet light, since the f–f absorption transitions are weak while comparing with the 4f–5d or charge transfer transitions. Thus choosing proper sensitizers or sensitizing hosts is an important route to enhance luminescent intensity of Dy3+
Vanadates are excellent hosts for incorporating rare earth due to their good chemical stability, large absorption cross section in near ultraviolet region and effective energy transfer from VO43− groups to RE3+ ions [6], [7], [8], [9], [10]. For example, Eu3+ doped YVO4 phosphor is an excellent luminescent material and has been used in cathode ray tubes for more than 20 years. Quantum yield of Eu3+ doped YVO4 phosphor is as high as 70% [11], [12]. In this study, the GdVO4 is conceived to be incorporated with Dy3+. It is expected that the Dy3+ could be sensitized by VO43− groups while under near ultraviolet excitation, and intense emissions from Dy3+ could be obtained.
Section snippets
Synthesis
Dy3+ doped GdVO4 phosphor was synthesized via a co-precipitation process. The preparative details are described as follows. First, 0.2340 g NH4VO3 was dissolved in 40 mL distilled water and the pH value of solution was adjusted to be about 11 with 2 mol/L NaOH aqueous solution. Then, the solution containing 0.9028 g Gd(NO3)3 and 0.0023 g (0.3 mol%) DyCl3 was poured into the as-prepared NH4VO3 solution under magnetic stirring. The white precipitate was formed at once. After 30 min reaction, the product
Structure, phase and morphology
Fig. 1 shows the XRD patterns of GdVO4:0.3 mol%Dy3+ and GdVO4:5 mol%Dy3+ phosphors as well as JCPDS card No. 86-0996 as a comparison. It can be found that all observed peaks fit in well with the intrinsic diffraction pattern of GdVO4 bulk material [JCPDS card No. 86-0996]. No extra peaks belonging to other phases are observed, indicating that the as-prepared samples are single phase. In addition, GdVO4 belongs to the tetragonal system with space group I41/amd (141). The unit cell parameters for
Conclusions
In summary, bicolor emitting GdVO4:Dy3+ phosphor with high efficiency was prepared via a simple co-precipitation process. This phosphor exhibits high luminescent efficiency under UV excitation. Moreover, the integrated intensity of GdVO4:Dy3+ phosphor is twice times as intense as that of the commercial Y2O2S:Eu3+ phosphor. The optimum doping concentration for obtaining maximal luminescent intensity was confirmed to be 0.3 mol%. The energy transfer mechanism was assigned to the electric
Acknowledgment
This work was partially supported by NSFC, The National High Technology Research and Development Program (“863” Program) of China (2015AA016901), NSFC (National Natural Science Foundation of China, No. 51302182). The Qualified Personnel Foundation of Taiyuan University of Technology (QPFT) (No: tyut-rc201361a), and the Program for the outstanding Innovative Teams of Higher Learning Institutions of Shanxi.
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