Preformed sol-gel synthesis and characterization of lanthanide ion-doped yttria-alumina materials

Abstract

PACS 78.55.Hx, 81.05.Je, 81.20.Fw Powders of yttria-alumina materials YAlO 3 (YAP) and Y 3 Al 5 O 12 (YAG) have been prepared from commercially-available preformed sols, and the products were compared with those from preformed solnitrate, nitrate-citric acid and alkoxide methods. The preformed sol route offers an alternative cheap and rapid method, and different sizes of the nanometre-scale precursors are available. Characterization was carried out by SEM, XRD, TG-DTG-DTA and FTIR-DRIFTS. On doping with Er 3+ , the maximum intensity of green emission was found for a dopant ion concentration of 1.0-1.2 mol%, with cross-relaxation to depopulate 2 H 11/2 / 4 S 3/2 becoming more important at higher dopant ion concentrations. A memory effect of the precursor sol upon the luminescence intensity of the product was able to distinguish precursors from two different suppliers. Demonstrations are given of the use of site-selective luminescence spectra in monitoring the purity of the yttria-alumina products. catalytic applications [22], partly because they are widely available and much cheaper than alkoxides. Preformed sols are stable mixtures of dispersed particles within a given size range, which by contrast to the conventional hydrolysis-polymerization sol-gel reactions of alkoxides, enable the sol and gel processes to be isolated and performed in two steps. This is attractive because it offers potential control over the particle size, crystallinity and microstructure of the product. The preformed sol route has other advantages that different-size precursors are readily available in aqueous solutions, employed herein, or as dispersed powders. The alumina sols consist of porous aggregates of rod-or platelet-boehmite (γ-AlO.OH.nH 2 O) crystallites [22]. It has been envisaged [22] that nanometer-scale mixing of preformed sols of widely-different sizes, such as large alumina and small silica particles, results in isolated large particles dispersed in a sea of smaller particles.The goal of the present study was to utilize preformed sols in the preparation of YAP and YAG. These materials were doped with the lanthanide ion Er 3+ , which has intense, well-characterized emission properties. In addition, several areas were investigated concerning the resulting luminescence properties of the doped YAP and YAG materials: the concentration-intensity dependence of the luminescence, the possible occurrence of precursor memory effects, and the site-selective resolution of product materials. A preliminary report of some areas of the present study was made at the IUPAC International Congress on Analytical Sciences [23].

Effects of local structure of Ce3+ ions on luminescent properties of Y3Al5O12:Ce nanoparticles

“…2(a). The intense and broad envelope of band at ~3421 cm −1 is due to the O-H vibration caused by H 2 O in the sample27. The absorption bands at 1635 and 1458 cm −1 should be ascribed to stretching vibrations of the -COO- groups20.…”

Structural and optical properties of YAG:Ce3+ phosphors by sol–gel combustion method

“…2 shows the FT-IR spectra of the YAG:Ce 3+ precursor and the YAG:Ce 3+ phosphors sintered at different temperatures. The absorption band centered at 3415 cm À1 is due to O-H vibration caused by H 2 O in the samples [13]. Such an absorption band is much broader than the standard FT-IR spectrum of citric acid, and this implies that citric acid in the precursors has been coordinated with metal ions such as Y 3+ , Al 3+ and Ce 3+ .…”

Lanthanide Luminescence in Solids

“…These situations have different repercussions upon the emission spectra, giving broad features for the second and third cases together with quenching of emission for the third. The compound YAG is an example of the first scenario since Y 4 Al 2 O 9 (YAM), YAP, and hexagonal-YAlO 3 (YAH) phases may coexist [77]. A sensitive test for the purity of the product is to use excitation lines which strongly excite one phase, but not another.…”