Nanocrystalline Eu 3+ Doped M 3 Al 2 O 6 (M : Ba, Ca and Sr) Red Phosphors Prepared by Sucrose-PVA-Metal Ion Complex Rou
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1023-JJ05-08
Nanocrystalline Eu3+ Doped M3Al2O6 (M : Ba, Ca and Sr) Red Phosphors Prepared by Sucrose-PVA-Metal Ion Complex Route Alp Manavbasi, Palkin Zed, and Jeffrey C. LaCombe Chem. & Met. Engineering, University of Nevada, Reno, Reno, NV, 89557
ABSTRACT Nanocrystalline (99.5%) (where M = Ba, Ca, Sr) was added to 5 wt% aqueous PVA and an aqueous solution of sucrose and this mixture was aged at 80 °C for 1h. A molar ratio of sucrose to the metal ions of 4:1 was used for the preparation. Further heating of this aged solution at 250 °C yields a highly viscous liquid and complete evaporation of the solution with accompanying release of fumes of NOx gases. No visible precipitation or turbidity was observed during the heating and viscous polymeric resin formation stages. Complete evaporation yields a black, voluminous, fluffy precursor which was easily ground to fine powders. These precursor powders were then calcined in air at 1100 °C for 2h in air in order to obtain the expected nanocrystalline phosphor materials. All phosphor powders obtained were white color in body. The phase identification was performed by a x-ray powder diffractometer (Phillips PW 2273) using CuKα radiation (40 kV, 30 mA). The average crystallite size was calculated based on the Williamson-Hall technique, using the built-in software (JADE 6.1). The average particle size and distribution were measured using photon correlation spectroscopy on a Microtrac NanotracTM ULTRA instrument. The excitation and emission characteristics of the samples were recorded at room temperature using a Hitachi F-4500 fluorescence spectrophotometer equipped with a 150W Xe-lamp as an excitation source. DISCUSSION The powder XRD patterns for the phosphor particles heat treated at 1100 °C for 2h are shown in Figure 1. All the characteristic peaks of Ca3Al2O6 and Sr3Al2O6 compounds match well with the JCPDS card no. 38-1429, and 24-1187, respectively. In the B3A diffraction pattern, the dominant phase is found to be Ba3Al2O6, although it was not possible to prepare single phase Ba3Al2O6 compound (JCPDS #: 25-0075) even after heat treating at 1200 °C for 12 h. No obvious shifting of the diffraction peaks was observed as Eu3+ doping concentration increased, which suggests that the crystal structure and lattice parameters of host lattices do not significantly change when Eu3+ impurity is introduced into the host matrix. This also indicates that the sucrose-PVA based method efficiently distributes the Eu3+ ions throughout the host lattices without any segregation. The average crystallite size for Ba3Al2O6, Ca3Al2O6, and Sr3Al2O6 was found to be 52, 41 and 46 nm, respectively. Photon correlation spectroscopy analysis revealed that the particle size distribution of the agglomerated nanocrystalline phosphor particles prepared at 1100 ° C (2h) have a range of sizes extending from 400 nm to 3 µm (Figure 2). The average particle size of phosphors was found to be 1.0 µm for Ca3Al2O6, and ~1.5 µm for Ba3Al2O6 and Sr3Al2O6 powders. Figure 3 shows the room temperature photoluminensce
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