Cerium Phosphate Nanotubes: Synthesis, Valence State, and Optical Properties

Abstract

Metal phosphates are widely utilized in nonlinear optical materials, phosphors, sensors, heat-resistant, and biocompatible materials. A particular emphasis has been placed on the study of rare-earth or rare-earth-doped phosphate materials for applications in photonic devices. [1] This interest is primarily attributed to the position of the 4f electrons, which are well shielded from the effects of the neighboring ions. Such shielding leads to discrete and well-defined energy level schemes, as well as to rather weak coupling between the electronic and vibrational wave functions. The specific luminescence with a characteristic long lifetime originates from the f-f emissions. However, at present, the progress with regard to new luminescent materials is chiefly focussed on short emission wavelengths, which are useful for imaging, lithography, and optical data recording.[2] The rare-earth ions Ce 3+ and Sm 2+ exhibit a 5d-4f emission with a larger absorption in the UV region and a shorter luminescence lifetime due to allowed electric dipole transitions; thus, they display excellent properties for applications in these fields. [3] On the other hand, although the doping of transparent Ce 4+ ions in luminescence materials has been prohibited due to the competitive absorption in UV region, some Ce 3+ /Ce 4+ hybrid systems in glass hosts exhibit a strong blue emission, which possibly results from electron transfer from a donor level to the neighboring Ce 4+ ions, consequently forming excited states of Ce 3+ ions. [4] Taking into account the strong UV absorption of Ce 4+ ions, such hybrid structures are good candidates for materials that display blue emission with high absorption and fast emissive rates. [5] One-dimensional nanomaterials, that is, nanotubes made of, for example, C, BN, WS 2 , VO x , TiO 2 , and InP [6] have been synthesized and display novel properties that are frequently different from those of the bulk forms. However, the synthesis and emission behaviour of nanotube-like hybrid materials containing Ce 4+ /Ce 3+ ions has received much less attention. Herein, we report on a reproducible and controllable route for the production of cerium phosphate nanotubes, the first rare-earth phosphate nanotubes. Tetravalent cerium phosphate (CeP, Ce(HPO 4 ) 2 ·n H 2 O) nanotubes were first synthesized after improving the traditional synthetic route toward a CeP fiber.[7] Subsequent annealing of the assynthesized nanotubes led to a mixture of valence states, and the desired Ce 3+ /Ce 4+ hybrid phosphate nanotubes were obtained for the first time. The nanotubes display novel optical properties; that is, the Ce 4+ ions effectively absorb the UV light, whereas the Ce 3+ ions exhibit strong emission in the blue region of a photoluminescence spectrum.It has been reported that a high PO 4 /Ce ratio (20:1-120:1) in the initial solution and a high reaction temperature (up to 95 8C) are needed to form a CeP fiber. [7,8] In this study, we have increased the PO 4 /Ce ratio to 300:1 and increased the reaction temperature to above ...

Phosphoric acid adsorbed on silica-ceria matrix obtained by sol-gel method: studies of local structure, texture and acid property

“…37,38 These Brønsted acid sites are due to the H 2 PO 4 -species bonded to the matrix surface by Ce-O-P linkages. The result agrees with the conclusion from X-ray photoelectron spectroscopy, where the spectra of phosphorus presented only one photoemission peak due to the dihydrogen phosphate species on the surface of the mixed oxides.…”

“…3 A recent interesting process described in the literature consists of a reproducible and controllable route to produce cerium phosphate nanotubes. 4 Cerium phosphate can have many applications as ceramic material, 5 as a glass presenting optical 6 and luminescent 7 properties, as ion exchanger 8 and catalyst. 9 It can also be prepared as phosphate particles dispersed in hybrid organic-inorganic matrices, aiming at their use in filtering process.…”

Synthesis and properties of PbGeO3 nanostructures

“…These are largely due to the shielding of the 4f electrons in the rare earth ions that lead to weak coupling between the electronic and vibrational wave functions as well as to long-lived luminescence originating from f-f transitions [1][2][3]. Germanates, as an important group of inorganic compounds, are very few in nature.…”

Facile synthesis and characterization of hierarchical CuO nanoarchitectures by a simple solution route

“…The hierarchical architectures, which are composed of the low-dimensional nanostructured units including two-dimensional (2D) quantum wells, one-dimensional (1D) nanowires/tubes/rods, zero-dimensional (0D) quantum dots, have been extensively investigated for their novel collective properties and potential applications in the fields of nanodevice [3][4][5]. Recent researches on various kinds of compound materials, such as transition metal oxide [6], sulfide [7], and other nanostructures [8], have rapidly expanded into controlled hierarchical morphologies.…”