Preparation of (Gd,Y)AlO3:Eu3+ by citric-gel method and their photoluminescence under VUV excitation
Introduction
The tri-color phosphors for Plasma display panels (PDP) applications should have good luminescent characteristics under vacuum ultraviolet (VUV) light. As far as red phosphor is concerned, Y2O3:Eu3+ and (Y,Gd)BO3:Eu3+ are widely used as red component. However, Y2O3:Eu3+ phosphor has low luminescent efficiency; and (Y,Gd)BO3:Eu3+ has poor color purity because it displays an orange-red emission instead of a red one. In order to improve the performances of PDP, it is urgent to improve current used red VUV phosphors or explore novel red phosphors with high luminescent efficiency and color purity [1]. Gadolinium ortho-aluminate is an attractive optical material with good chemical and physical stability, and it crystallized with slightly distorted orthorhombic perovskite structure isomorphous with GdFeO3 [2]. Gd3+ located slightly within the x–y plane in the center (space group is D162h–Pbnm). It could be predicated that Eu3+ replaces Gd3+, whose site symmetry is Cs, to realize Eu3+ pure red emission. In addition, it has been suggested that green and blue emission could be achieved using GdAlO3 host lattice by doping with Tb3+ and Sm3+ to realize tri-color phosphors in the same matrix.
GdAlO3 has been prepared by several techniques, mostly by solid-state reaction, which is always at high temperature (∼1600 °C) [3], [4]. Besides that, it is difficult to control morphology. Sol–gel processing is a relative easy way for making uniform and high quality phosphors because it allows molecular mixing of constituents leading to chemical homogeneity [5]. Among the sol-gel methods, the citric-gel method has been widely used to prepare multi-component oxides because it involves the formation of a mixed-ions citrate that due to the three-ligand nature of the citric acid, resulting a transparent three-dimensional network upon drying gel [6]. In this paper, (Gd,Y)AlO3:Eu3+ phosphors were prepared by citric-gel method, and their luminescent properties under VUV excitation were evaluated.
Section snippets
Experimental
Gd2O3 (99.99%), Eu2O3 (99.99%), Y2O3 (99.99%) and Al(NO3)3·9H2O (A.R.) were used as starting materials. Stoichiometric amounts of starting materials were dissolved in diluted nitric acid (A.R.), and citric acid was added into the above solution as the chelating agent. The resultant mixture was stirred at 80–90 °C for 3–4 h until slight yellow homogenous gels formed by slow evaporation. The gels were dried in oven at 120 °C overnight in air, fully ground and fired at 1000 °C in air for 4 h then
Results and discussion
According to result of XRD, all samples are single phase and appear to be white color in body. For example, Fig. 1 shows the XRD pattern of the GdAlO3 dry gel sintered at 1000 °C for 4 h, which indicates that all the peaks are due to the GdAlO3 phase (JCPDF 46-395) and no second phase is detected. The sintering temperature is about 1600 °C by solid-state reaction (XRD pattern is not given here). The as-prepared GdAlO3 is readily identified as an orthorhombic symmetry with lattice parameters
Conclusions
Single phases of (Gd,Y)AlO3:Eu3+ were successfully obtained at 1000 °C for 4 h by citric-gel method. In VUV region, the two bands with maximum at about 157 and 170 nm were observed and could be attributed to AlO3 group absorption and the CT band of Gd3+–O2−. When Y3+ partially replaces Gd3+ in GdAlO3:Eu3+, the position of band from 125 to 175 nm shifts to higher energy region. Under 147 nm excitation, the PL spectra show the strongest emission at 614 nm corresponding to pure red emission of Eu3+ in
Acknowledgement
This work was supported by Program for New Century Excellent Talents in University (NCET, 04-0978), Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP, 20040730019) and The Key Science Research Project of Ministry of Education of China (105170).
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