BiPO4: a better host for doping lanthanide ions.

In the present manuscript it is demonstrated that BiPO(4) is a better alternative to lanthanide phosphate host for making lanthanide ion-based luminescent materials. Hexagonal and monoclinic forms of BiPO(4) phase were prepared based on the reaction of Bi(3+) and PO(4)(3-) ions in ethylene glycol medium at 100 and 185 °C, respectively. From the differential thermal analysis (DTA) studies it is confirmed that the difference in the nucleation mechanism rather than the phase transition is responsible for the monoclinic phase formation at low temperatures (125 °C). Monoclinic BiPO(4) is quite stable and forms random solid solutions with lanthanide phosphates having both monoclinic (monazite) and tetragonal (xenotime) structures, as confirmed by XRD, FTIR and (31)P solid state nuclear magnetic resonance studies. On excitation corresponding to the (1)S(0)→(3)P(1) transition of Bi(3+) in BiPO(4):Ln samples, energy transfer from host to lanthanide ions takes place. The studies are quite relevant as there is a growing interest all over the world in replacing lanthanide based host used for different applications with easily available, easily purifiable and cheap main group elements (like Sb, Bi etc.) based hosts.

Investigations of Ce3+ co-doped SbPO4:Tb3+ nano-ribbons and nanoparticles by vibrational and photoluminescence spectroscopy.

Nano-ribbons and very small nanoparticles (size 2-5 nm) of SbPO4 doped with lanthanide ions (Ce3+ and Tb3+) are prepared at a relatively low temperature of 120 degrees C based on a solution method. Detailed vibrational and luminescence studies on these samples establish that these lanthanide ions are incorporated at Sb3+ site of the SbPO4 lattice. The excitation spectrum corresponding to the Tb3+ emission and the excited state lifetime of the 5D4 level of Tb3+ ions in the sample confirm the energy transfer from Ce3+ to Tb3+ ions in the SbPO4 host. The extent of energy transfer from Ce3+ to Tb3+ in these samples is found to be around 60%. Dispersion of these nanomaterials in silica matrix effectively shields the lanthanide ions at the surface of the nano-ribbons/nanoparticles from the stabilizing ligands resulting in the reduction in the vibronic quenching of the excited state. Our results show significant reduction in the surface contribution in the decay curve corresponding to the 5D4 level of the Tb3+ ions after incorporating the nano-ribbons/nanoparticles in silica. These nanomaterials incorporated in silica matrix can have potential applications in bio-assays and bio-imaging.

Lanthanide-ion-assisted structural collapse of layered GaOOH lattice.

GaOOH nanorods were prepared by hydrolysis of Ga(NO(3))(3)·xH(2)O by urea at ~100 °C in the presence of different amounts of lanthanide ions like Eu(3+), Tb(3+), and Dy(3+). On the basis of X-ray diffraction and vibrational studies, it is confirmed that layered structure of GaOOH collapses even when very small amounts of lanthanide ions (1 atom % and more) are present in the reaction medium during the synthesis of GaOOH nanorods. The incorporation of lanthanide ions at the interlayer spacing of the GaOOH lattice, followed by its reaction with OH groups that connect the layers containing edge-shared GaO(6) in GaOOH, is the reason for the collapse of the layered structure and associated amorphization. This leads to the formation of finely mixed hydroxides of lanthanide and gallium ions. These results are further confirmed by steady-state luminescence and excited-state lifetime measurements carried out on the samples. The morphology of the nanorods is maintained upon heat treatment at high temperatures like 500 and 900 °C, and during this process, the finely mixed lanthanide and gallium hydroxides facilitate diffusion of lanthanide ions into the Ga(2)O(3) lattice, as revealed by the existence of strong energy transfer with an efficiency of more than 90% between the host and lanthanide ions.

Luminescence studies on SbPO4:Ln3+ (Ln = Eu, Ce, Tb) nanoparticles and nanoribbons.

Nanoparticles and nanoribbons of SbPO4 and lanthanide ions (Eu3+, Ce3+ and Tb3+) doped SbPO4 were prepared at a low temperature of 120 degrees C by co-precipitation method in solvents like ethylene glycol and glycerol. By varying the relative ratios of the two solvents, average crystallite size of SbPO4 has been varied over a range of 12 to 46 nm. Based on steady state luminescence studies, existence of energy transfer between host SbPO4 and lanthanide ions has been confirmed. Co-doping SbPO4:Tb3+ nanoparticles/nanoribbons with Ce3+, resulted in improved luminescence due to energy transfer from Ce3+ to Tb3+ ions. Further, these nanomaterials can be incorporated in sol-gel derived silica glass without any deterioration of their luminescence properties. Present study offers a viable method for preparing composite luminescent materials based on nanoparticles/ nanoribbons and glasses.