Hydrothermal Synthesis of Well-Defined Red-Emitting Eu-Doped GdPO₄ Nanophosphors and Investigation of Their Morphology and Optical Properties

Rare-earth-doped GdPO₄ nanoparticles have recently attracted much scientific interest due to the simultaneous optical and magnetic properties of these materials and their possible application in bio-imaging. Herein, we report the hydrothermal synthesis of GdPO₄:Eu³⁺ nanoparticles by varying different synthesis parameters: pH, <Gd>:

molar ratio, and Eu³⁺ concentration. It turned out that the Eu³⁺ content in the synthesized nanoparticles had little effect on particle shape and morphology. The synthesis media pH, however, has showed a pronounced impact on particle size and distribution, i.e., the nanoparticle length can be adjusted from hundreds to tens of nanometers by changing the pH from 2 to 11, respectively. Increasing the <Gd>:

molar ratio resulted in a decrease in nanoparticle length and an increase in its width. The temperature-dependent measurements in the 77–500 K range revealed that the GdPO₄:50%Eu³⁺ sample maintains half of its emission intensity, even at room temperature (TQ_1/2 = 291 ± 19 K).