Structural and luminescent properties of nanostructured KGdF4:Eu3+ synthesised by coprecipitation method

The single-phase low-temperature cubic form of KGdF4, with the average crystallites size of 19 nm precipitates from a solution. The cubic phase is stable up to approximately 460 degreesC. At higher temperatures the cubic KGdF4 transforms, first to the orthorhombic and then to the trigonal phase, however, the transformation is not complete and the cubic form is still present. The highest concentrations of orthorhombic and trigonal phases were observed at temperatures of 540 and 720 degreesC, respectively. The single-phase high-temperature cubic form of KGdF4 was obtained when the as-received sample was heated at 790 degreesC. In contrast to a coprecipitation (CP) method, the single-phase orthorhombic modification of KGdF4 was obtained by a solid state (SS) reaction conducted at 650 degreesC. In excitation spectra recorded for CP samples the characteristic Eu3+-O2- CT bands expected at similar to260 nm are not present, which indicates that oxygen impurities are practically absent. However, both IR spectra and the D-5(1,2,3)/D-5(0) emission branching ratio points to the presence of OH- groups incorporated into a fluoride lattice and a heat treatment at temperature of at least 650 degreesC is indispensable to get rid of them. Emission spectra for samples with different processing conditions were recorded and are discussed. (C) 2004 Elsevier B.V. All rights reserved.