A Novel 3D Architecture of GdPO<sub>4</sub> Nanophosphors: Multicolored and White Light Emission

Homogeneous monoclinic GdPO<sub>4</sub> particles composed of three intersecting lance-shaped crystals forming a penetration twin have been synthesized following a very restrictive, simple, and fast (10 min) method consisting of the hydrothermal reaction of gadolinium acetylacetonate with H<sub>3</sub>PO<sub>4</sub> in a mixture of ethylene glycol and water at 180 °C. Slightly increasing the amount of water in the solvent mixture leads to hexagonal rodlike GdPO<sub>4</sub>·0.5H<sub>2</sub>O nanoparticles, whereas the variation of the Gd source, PO<sub>4</sub> source, aging temperature, and polyol type gave rise to heterogeneous particles. The synthesis procedure is also suitable for the preparation of Eu<sup>3+</sup>-, Tb<sup>3+</sup>-, and Dy<sup>3+</sup>-doped GdPO<sub>4</sub> particles with the same morphology and crystalline structure as the undoped materials. The effect of the doping level on the luminescent properties of the twinlike nanophosphors was evaluated, finding optimum doping levels of 5, 5, and 1% for the Eu<sup>3+</sup>-, Tb<sup>3+</sup>-, and Dy<sup>3+</sup>-doped materials, respectively. The twinlike GdPO<sub>4</sub> nanophosphors were found to be more efficient than the rodlike GdPO<sub>4</sub> ones in terms of emission intensity. Finally, a solid-state single-phase white-light-emitting nanophosphor has been fabricated for the first time in this system by triply doping the GdPO<sub>4</sub> twined particles with appropriate concentrations of Eu<sup>3+</sup>, Tb<sup>3+</sup>, and Dy<sup>3+</sup> and exciting through the Gd–Ln energy-transfer band at 273 nm. In addition to this energy transfer band, other energy charge transfer processes among the three dopants (Eu<sup>3+</sup>, Tb<sup>3+</sup>, and Dy<sup>3+</sup>) have been observed in the triply doped material.