Effect of crystallite size on structural and luminescent properties of nanostructured Eu3+:KGdF4 synthesised by co-precipitation method

The Eu3+:KGdF4 powders with average crystallite size of 20 and 25 nm have been obtained from solution by co-precipitation method. Morphology of the as-received powders was examined by XRD and TEM methods. Behaviour of these two powdered batches, characterised by different size of nanocrystallites, versus thermal treatment has been studied by X-ray powder diffraction, thermogravimetric, infrared spectroscopy and emission spectroscopy methods. The phase transitions between low-temperature cubic, orthorhombic, trigonal and high-temperature cubic modifications of KGdF4 were detected for both samples heated in 300-790 °C temperature range. Abundance of the particular polymorphic form observed at given temperature differs considerably for samples of different initial crystallite size. Besides, significant differences in number of lattice defects, water contents and emission properties were observed for these two samples. The properties of material precipitated from solution are also compared with structural and optical properties of the Eu3+:KGdF4 fluoride synthesised by a solid-state reaction.