Disappearance and Recovery of Luminescence in Bi³⁺, Eu³⁺ Codoped YPO₄ Nanoparticles Due to the Presence of Water Molecules Up to 800 °C

Abstract

YPO(4) nanoparticles codoped with Eu(3+) (5 at. %) and Bi(3+) (2-10 at. %) have been synthesized by a simple coprecipitation method using a polyethylene glycol-glycerol mixture, which acts as capping agent. It has been found that the incorporation of Bi(3+) ions into the YPO(4):Eu(3+) lattice induces a phase transformation from tetragonal to hexagonal, and also a significant decrease in Eu(3+) luminescence intensity was observed. This is related to the association of the water molecules in the hexagonal phase of YPO(4) in which the nonradiative process from the surrounding water molecules around Eu(3+) is dominating over the radiative process. On annealing above 800 °C, luminescence intensity recovers due to significant removal of water. 900 °C annealed Bi(3+) codoped YPO(4):Eu(3+) shows enhanced luminescence (2-3 times) as compared to that of YPO(4):Eu(3+). When sample was prepared in D(2)O (instead of H(2)O), 4-fold enhancement in luminescence was observed, suggesting the extent of reduction of multiphonon relaxation in D(2)O. This study illustrates the stability of water molecules even at a very high temperature up to 800 °C in Eu(3+) and Bi(3+) codoped YPO(4) nanoparticles.

Photochemical studies of monodispersed YPO 4 :Eu microspheres: The role of surface modification on structural and luminescence properties

“…It implies that perfect crystallinity and crystal structure of the luminescent materials play a critical role in photoluminescence efficiency. These luminescence properties of Eu ion doped YPO 4 1D nanostructures are in good agreement with previously published reports [7,9,40].…”

“…Although, XRD pattern of core/shell and core/shell/Si MSs displays all diffraction planes can be readily indexed to pure hexagonal rhabdophane YPO 4 phase (JCPDS No.42-0082), which are in good agreement with the previously reported observations[7,10,21,27,28]. No impurity peak related to amorphous carbonate, oxides or phosphates are detected over the entire range of XRD, confirming the phase purity, successful doping of europium ion into the YPO 4 crystal lattice as well as LaPO 4 layer deposition over the YPO 4 :Eu MSs.…”

“…Among the rareearth phosphate materials, yttrium phosphate has been used as a host material for many rare-earth activators because of its chemical stability and physical robustness [7][8][9][10].…”

“…These surfaces attached either chemically bonded or physically adsorbed high vibrational energy molecules have abilities to quench the luminescence intensity at a large extent. Additionally, these surface attached impurities (traps centers) may act as nonradiative recombination centers, which are responsible for the reduction of the luminescence intensity of the luminescent materials[7]. In order to improve the luminescence efficiencies and reduce the quenching of the core nanoparticle, an undoped crystalline LaPO 4 layer is grown over the luminescent seed core MSs.…”

Neutron diffraction reveals the existence of confined water in triangular and hexagonal channels of modified YPO4 at elevated temperatures

“…, enhances luminescence intensity and scintillation efficiency which makes it practically suitable candidate in scintillators industry 6,[22][23][24][25] .Further, dopedYPO4remains in the tetragonal phase. However, on increasing the concentration of Eu In X-ray diffraction, scattering is due to interaction of X-rays with the electronic charge cloud of atoms, whereas in neutron diffraction, scattering is due to interaction of neutron with nuclei of atoms.…”