Analysis of electrical and fluorescent characteristics of lanthanium ortoniobate (LaNbO₄) ceramic matrix co-doped with rare earth ions praseodymium and ytterbium

In this work, new materials based on Pr³⁺ – Yb³⁺ co-doped LaNbO₄ phosphors were prepared. The synthesis was performed by using the solid state reaction method where the dopant ions were inserted into the La³⁺ sites. The systems were analyzed through X-ray diffraction, fluorescence upconversion and electrical measurements in the radiofrequency (RF) region. According to the X-ray diffraction no secondary phase has been detected in the doped samples, and that the lattice parameters followed the Vegard's law. Impedance spectroscopy showed that the Pr/Yb doping caused significant changes in the dielectric properties of the LNO. This can be ascribed to the generation of defects in the crystalline structure of the materials which compensate the positive charge coming from the entry of Pr³⁺/ Pr⁴⁺ and Yb³⁺ ions. In fluorescence, the Pr-Yb doped materials exhibited emissions in the visible (RGB) and infrared regions referring to the electronic transitions between the 4f orbitals of the Pr³⁺ ion. The CIE color coordinates of the samples shift from the green region to the blue region with increasing the Yb³⁺ concentration due to the great increase of the tristimulus Z. It was also evaluated the behavior of the chromatic coordinates with the pumping power. Systems LPY2% and LPY8% did not show significant variations in the CIE characterizing these materials as non-tunable phosphors for use in optical devices in the security area. (author)