Synthesis and luminescence properties of water dispersibleEu3+-doped boehmite nanoparticles

Abstract

Nanocrystallized boehmite γ-AlOOH·nH2O had been synthesized by spray-drying (SD) of a solution of aluminium tri-sec-butoxidepeptized by nitric acid. The sub-micronic spherical particles obtained had an averagediameter of 500 nm and were built of 100 nm or less platelet-like sub-particles.The average crystallite size calculated from XRD was 1.6 nm following the axis (i.e. one unit cell) and 3–4 nm perpendicular to . As a result of the nanometric sizes of crystallites, there wasa large surface free for water adsorption and it was found to ben = 1.18 ± 0.24H2O per AlOOH. The SD spheres spontaneously dispersed in water at room temperatureand formed stable—over months—suspensions with nanometre-size particles(25–85 nm). Luminescent europium-doped nanocrystallized boehmites AlOOH:Eu(Al0.98Eu0.02OOH·nH2O) were synthesized the same way by SD and demonstrated the same crystallizationproperties and morphologies as the undoped powders. It is inferred from theEu3+ luminescence spectroscopy that partly hydrated europium species areimmobilized on the boehmite nanocrystals where they are directly bonded toα(OH) groups of the AlOOH surface. The europium coordination is schematically written[Eu3+(OH)α(H2O)7−α/2 ]. The europium-doped boehmite from SD spontaneously dispersedin water: the luminescence spectroscopy proves that most of theEu3+ ions were detached from the NPs during water dispersion. The AlOOH:Eu nanoparticleswere modified by the amine acid asparagine (ASN). The modification aimed to render theNPs compatible for further bio-functionalization. After surface modification, the NPseasily dispersed in water; the luminescence spectra after dispersion prove that theEu3+ ions were held at the boehmite surface.