Defect luminescence in oxide nanocrystals grown by laser assisted techniques

摘要

Wide band gap oxides, such as ZnO, SnO_2 and ZrO_2, are functional materials with a wide range of applications in several important technological areas such as those including lighting, transparent electronics, sensors, catalysis and biolabeling. Recently, doping and co-doping of oxides with lanthanides have attracted a strong interest for lighting purposes, especially among them nanophosphors for bioassays. Tailoring the crystalline materials physical properties for such applications often requires a well-controlled incorporation of dopants in the material lattice and a comprehensive understanding of their role in the oxides matrices. These undoped or intentionally doped oxides have band gap energies exceeding 3.3 eV at room temperature and are known to exhibit optically active centers that span from the ultraviolet to the near infrared region. Typically, by using photon energy excitation above the materials band gap, high quality undoped materials display narrow emission lines near the band edge due to free and bound-exciton recombination, as well as shallow donor-acceptor recombination pairs. Additionally, broad emission bands are often observed in these wide band gap hosts, hampering some of the desired physical properties for further applications. Recognizing and understanding the role of the dopant-related defects when deliberately introduced in the oxide hosts, as well as their influence on the samples luminescence properties, constitutes a matter of exploitation by the scientific community worldwide. In this work, we investigate the luminescence properties of undoped and lanthanide doped oxide materials grown by laser assisted techniques. Laser assisted flow deposition (LAFD) and pulse laser ablation in liquids (PLAL) were used for the growth of ZnO, SnO_2 and yttria stabilized ZrO_2 (YSZ) micro and nanocrystals with different morphologies, respectively. Regarding the YSZ host, trivalent lanthanide ions were optically activated by in-situ doping and co-doping. The influence of the defect energy states on the optical properties of the different undoped and doped metal oxide hosts is investigated under ultraviolet and infrared excitation by means of photoluminescence and photoluminescence excitation.