Abstract
The polyol-based co-precipitation process was employed for synthesis of GdF3:Pr (core) and GdF3:Pr@LaF3 (core-shell) microspheres (MSs). Subsequently, an amorphous silica layer was deposited surrounding the core-shell MSs, which was verified from high-resolution transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and FTIR results. The absorption spectral results revealed the high solubility with good colloidal stability in aqueous solvents. The detailed structural and morphological analysis, as well as crystallinity of the samples, was investigated through X-ray diffraction, TEM and band gap energy results. The experimentally calculated band gap energy was found to decrease after gradually coating insulating layers of LaF3 and amorphous silica over the surface, because of an effective increase in particle size. The Pr3+-doped GdF3 shows sharp 4f15d1→4f2 emission bands (260-480 nm) as well as typical 4f2→ 4f2 emission lines (460-800 nm) of Pr3+ under 4f2 →4f15d1 excitation. After surface coating, comparative photoluminescence properties of the MSs were investigated by excitation and emission spectra. The origin of the different types of emission transitions were analyzed in details.
Highlights
GdF3 nanoparticles (NPs) as an important member of the lanthanide fluoride compounds (LnF3) that possess very low phonon frequencies of crystal lattices and high radiative transition rate are regarded as a kind of excellent host materials for upconversion as well as down conversion photoluminescence[1,2,3,4]
Our results clearly show that the silica surface modified core-shell-SiO2 MSs exhibit good water dispersibility and colloidal stability in aqueous solvents
Our group has shown strong evidence for the formation of core-shell lanthanide MSs using the fore mentioned synthesis procedure[19,24], and we conclude the same is true for this core-shell structure
Summary
GdF3 nanoparticles (NPs) as an important member of the lanthanide fluoride compounds (LnF3) that possess very low phonon frequencies of crystal lattices and high radiative transition rate are regarded as a kind of excellent host materials for upconversion as well as down conversion photoluminescence[1,2,3,4]. GdF3 can act as a highly efficient host lattice that achieves multicolor luminescence by varying the dopants since the gadolinium ion (Gd3+) is a good intermediate that migrates and transfers energy[5,6,7]. Gadolinium fluoride is known as a multifunctional agent because it has lower vibrational energies than oxides, and the quenching of the excited state of the Ln actions is minimized, resulting in a higher quantum efficiency of the luminescence[7,8,9]. Zhang and co-workers have synthesized raisin-like GdF3 nanocrystals by microwave method[5,11]. Chen and co-workers prepared GdF3 NPs through a one-step solvothermal route by employing poly(acrylic acid) as a capping agent[8]. Yin et al have obtained GdF3 NPs with polyvinyl pyrrolidone as a surfactant and found that the doping of Li+ could enhance the red emission from GdF3:Yb3+, Er3+ 6
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