YVO4掺杂Eu纳米晶体荧光粉的熔融盐合成以及发光性质

JOURNAL OF RARE EARTHS, Vol. 30, No. 3, Mar. 2012, P. 202

Molten salt synthesis and luminescent properties of YVO4:Eu nanocrystalline phosphors

WANG Fang ( )1, LIU Chenglu ( )1, ZHOU Zhiqiang ( )1, JIA Peiyun ( )1, LIN Jun ( )2

(1. School of Sciences, Northeast Forestry University, Harbin 150040, China; 2. State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China) Received 20 July 2011; revised 21 August 2011

Abstract: YVO4:Eu nanocrystalline phosphors were successfully prepared at 400 ºC in equal moles of NaNO3 and KNO3 molten salts. NaOH concentration and annealing temperature played important roles in phase purity and crystallinity of the nanocrystallines, and the optimum NaOH concentration and annealing temperature were 6:40 and 400 ºC, respectively. The nanocrystallines were well crystallized with a cubic morphology in an average grain size of 18 nm. Upon excitation of the vanadate groups at 314 nm, YVO4:Eu nanocrystallines exhibited the characteristic emission of Eu3+, which indicated that there was an energy transfer from vanadate groups to Eu3+. Moreover, the influence of superficial effect, especially the dangling bonds on the structure and luminescent properties of the nanocrystallines was discussed in detail. Keywords:nanocrystalline; phosphor; luminescence; molten salt; YVO4; rare earths

As an excellent luminescent material, YVO4:Eu has been used as a red phosphor of cathode ray tube television since it was discovered in 1964[1]. Recently, YVO4:Eu nanophos-phors have attracted great attention again due to their poten-tial application in biological fluorescence labeling and gas sensing[2,3]. A good many strategies based on wet chemistry method have been used to synthesize YVO4:Eu nanophos-phors[4–9]. However, in these methods, organic dispersing agents were utilized to prevent the agglomeration of the nanophosphors. The organic compounds adsorbed, chemically or physically, on the surface of the nanophosphors prevent the research of interfacial effect on the luminescence properties and some potential applications of the nanophosphors.

Molten salts have been widely used in heat transfer me-dium, non-ferrous metal synthesis, fuel cell and molten salt reactor. Free from organic dispersing agents, molten salts were developed to prepare nanocrystallines owing to their cost-effectiveness and environmental friendliness. Liu and his co-workers prepared a series of single-crystalline com-plex oxide nanocrystallines of various structural and mor-phology in molten NaOH, KOH or their mixtures[10]. In this paper, we developed a single-step molten salt method to synthesize YVO4:Eu nanocrystallines in equal moles of NaNO3 and KNO3 molten salts, by which single-phase, well crystallized YVO4:Eu nanocrystallines were successfully prepared.

1.1 Synthesis of YVO4:Eu nanocrystallines

NaNO3, KNO3, NH4VO3, NaOH (analytical reagent, Aladdin Reagent (China) Co., Ltd.), Y2O3 and Eu2O3 (99.99%, Shanghai Yuelong New Materials Co., Ltd.) were used as the starting materials. In a typical synthesis of Y0.95Eu0.05VO4 nanocrystallines, 107.3 mg Y2O3 and 8.8 mg Eu2O3 were dissolved in dilute HNO3 solution under stirring, the pH of the solution was adjusted to between 5.0 and 6.0 with NaOH dilute solution, then the solution was dried on water bath at 80 ºC for 6 h to obtain Y(NO3)3 and Eu(NO3)3 mixtures. As-prepared mixtures were added with 117.0 mg NH4VO3, 240.0 mg NaOH, 1699.8 mg NaNO3 and 2022.0 mg KNO3, and fully ground in an agate mortar with suitable amount of ethanol. Subsequently, the powders were trans-ferred into a corundum crucible, heated from room tempera-ture to 400 ºC, kept for 12 h and cooled down to room tem-perature naturally. Finally, the samples were fully washed with deionized water until the nitrate group could not be de-tected and dried in a vacuum drying oven at 150 ºC for 2 h for subsequent characterization. For convenience, the NaOH concentration is defined as the molar ratio of NaOH to the sum of NaNO3 and KNO3 for synthesis of 1 mmol YVO4:Eu nanocrystallines. In the above case, the NaOH concentration was 6:40.

1.2 Characterization

X-ray diffraction (XRD) measurements were performed on a Rigaku-Dmax 2500 diffractometer using Cu K radia-tion ( =0.15405 nm). The morphology and grain size of the

1 Experimental

Foundation item: Project supported by National Basic Research Program of China (2007CB935502, 2010CB327704), National Natural Science Foundation of

China (NSFC 50872131, 60977013, 20921002)Corresponding author: JIA Peiyun (E-mail: jiapeiyun@http://doc.guandang.net; Tel.: +86-451-51688228) DOI: 10.1016/S1002-0721(12)60023-4

WANG Fang et al.,Molten salt synthesis and luminescent properties of YVO4:Eu nanocrystalline phosphors203

samples were inspected on a JEOL 2010 transmission elec-tron microscope (TEM) operating at 200 kV. The excitation and emission spectra were taken on a Hitachi F-7000 spec-trofluorimeter equipped with a 150 W xenon lamp as the ex-citation source. All the measurements were performed at room temperature.

2Results and discussion

2.1 XRD analysis

Fig. 1 displays the XRD patterns of Y0.95Eu0.05VO4 pre-pared at different NaOH concentrations and temperatures in equal moles of NaNO3 and KNO3 molten salts. Fig. 1(1) to Fig. 1(5) provide the patterns of Y0.95Eu0.05VO4 prepared at 250 ºC and NaOH concentration from 0:40 to 8:40. It can be found from these patterns that the optimum NaOH concen-tration for preparing Y0.95Eu0.05VO4 at 250 ºC is 6:40. This optimum NaOH concentration is maybe determined by the chemical properties of the reaction precursors. As we know, a high NaOH concentration can effectively transfer NH4VO3 into NaVO4 which is, of course, in favor of the formation of YV …… 此处隐藏：12803字，全部文档内容请下载后查看。喜欢就下载吧 ……