Synthesis of Eu-doped SrAl₂O₄ nanophosphors by CO₂ laser vaporization

A new method of synthesizing spherical nanoparticles with photoluminescent spinel structures using a CO₂ laser co-vaporization technique (CoLAVA) is presented. The method applies homogeneous mixtures of oxidic precursors such as Al₂O₃, SrO and Eu₂O ₃ and allows the fabrication of quantities exceeding 10 g h ^-1. During the CoLAVA process, the educt oxides are reacted by a gas phase condensation yielding amorphous spherical particles with diameters ranging from 10 to 100 nm. The as-prepared materials exhibit red emission at 625 nm (1.98 eV) due to the incorporated Eu³⁺. Temperature treatment up to 1200 C under a reducing atmosphere yielded crystalline particles of the same size, which were slightly sintered. These particles consisted of >90 wt.% SrAl₂O₄ with minor fractions of Sr₃Al ₂O₆ and SrCO₃. The amount of the SrAl ₂O₄ spinel increased with increasing temperature, whereas the accompanying phases were decreased. A strong green emission centered at 525 nm (2.36 eV) detected at RT was observed at an onset temperature of 900 C, which is due to the presence of Eu²⁺ in the crystal lattice of SrAl ₂O₄. The red emission was not observed at higher annealing temperatures. The CoLAVA method represents a fast and facile route for the fabrication of nano- to microstructured phosphor materials for a variety of engineering applications.