N. F. Santos

Prospects on laser processed wide band gap oxides optical materials

Wide band gap oxide media including 4fn or 3dn ions attracts a considerable attention in the context of photonics and bio-photonics applications due to the electromagnetic widespread spectral range covered by the intraionic radiative relaxation of the charged lanthanide and transition metal ions. Converting ultraviolet commercial light into visible luminescence continues to raise interest for the solid state light market, justifying the demand for new and efficient phosphors with wide spectrum coverage and improved thermal quenching behavior. New materials and methods have been thoroughly investigated for the desired purposes. In this work, we report on laser processing for the growth of oxides media such as ZrO2, ZnO among other oxide hosts. The transparent crystalline materials in-situ doped with different amounts of lanthanide or transition metal ions are explored in order to enhance the room temperature ions luminescence by pumping the samples with ultraviolet photons. Spectroscopic studies of the undoped and doped oxide hosts were performed using Raman spectroscopy, photoluminescence (PL) and photoluminescence excitation (PLE).

Spectroscopic analysis of the NIR emission in Tm implanted AlxGa1-xN layers

AlxGa1-xN samples, with different AlN molar fractions, xu2009=u20090, 0.15, 0.77, and 1, grown by halide vapor phase epitaxy were implanted with Tm ions. Photoluminescence (PL) measurements revealed that after thermal annealing all the samples exhibit intraionic Tm3+ luminescence. In samples with xu2009>u20090, the low temperature emission is dominated by the lines that appear in the near infrared (NIR) spectral region, corresponding to the overlapped 1G4 → 3H5 and 3H4 → 3H6 multiplet transitions. A detailed spectroscopic analysis of NIR emission of the thulium implanted and annealed AlxGa1-xN layers is presented by using temperature dependent steady-state PL, room temperature PL excitation, and time resolved PL. The results indicate that the excitonic features sensitive to the alloy disorder are involved in the excitation population processes of the Tm3+ luminescence and the highest thermal stability for the NIR emission occurs for the AlN:Tm sample.

Defect luminescence in oxides nanocrystals grown by laser assisted techniques

Wide band gap oxides, such as ZnO, SnO2 and ZrO2, 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, SnO2 and yttria stabilized ZrO2 (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.

ZnGa2O4:Mn2+ phosphors grown by Laser Floating Zone

Cubic zinc gallate (c-ZnGa2O4) has attracted the attention of the scientific community due to its potential phosphor applications [1-6], namely in field emission displays (FEDs) and other electroluminescent devices. Among other advantages, this oxide matrix shows superior thermal and chemical stability when compared to ZnS based phosphors [1]. Most of the above mentioned works comprise nanostructures, thin films or pressed pellets while scarce information is found on bulk cZnGa2O4 material. In particular, no records were found regarding c-ZnGa2O4 crystal growth by the laser floating zone (LFZ) technique. In this work, crystalline fibres of manganese doped (0.01 mol %) zinc gallate were produced via LFZ in order to investigate its applicability in efficient phosphors. The transition metal ions are suitable activators and show some advantages over the widely used rare earths, namely at environmental and economic levels.