Influence of Synthesis Conditions on the Monoclinic Structure Formation of Gd0.85−yLayPO4:15%Eu and Luminescent Properties

In this study, nanoparticles with a monoclinic crystal structure of Gd0.85−yLayPO4:15%Eu were synthesized through a hydrothermal method. Initial investigations focused on the influence of the precursor on the resulting structure of LaPO4:1%Eu, with variations in synthesis temperature. Various syntheses were conducted using ammonium dihydrogen phosphate (NH4H2PO4) and diammonium hydrogen phosphate ((NH4)2HPO4) as PO43− ion precursors, and the synthesis temperature ranged from room temperature to 200 °C. Based on the synthesis and analysis outcomes, diammonium hydrogen phosphate was selected as the precursor for PO43− ions. Subsequent hydrothermal synthesis was performed at 180 °C to produce nanoparticles with a monoclinic crystal structure. After evaluating the synthesis and analysis results, the decision was made to increase the Eu3+ content from 1% to 15% by replacing La or Gd when a single-phase La0.75Gd0.24PO4:1%Eu with a monoclinic crystal structure was achieved. These structural modifications were carried out in order to stabilize the anhydrous monoclinic structure and improve the luminescence properties of the phosphate. The synthesized samples were characterized using X-ray diffraction and scanning electron microscopy. Luminescence properties were meticulously measured and discussed. The emission intensity of monoclinic structure La0.75Gd0.1PO4:15%Eu was found to be almost twice as high as compared with La0.61Gd0.24PO4:15%Eu. Additionally, magnetization dependence on the applied magnetic field strength was measured, revealing paramagnetic properties in the investigated samples.