Zirconia is a relatively new material with many promising practical applications in medical imaging, biolabeling, sensors, and other fields. In this study we have investigated lanthanide and niobium doped zirconia by luminescence and XRD methods. It was proven that charge compensation in different zirconia phases determines the incorporation of intrinsic defects and activators. Thus, the structure of zirconia does not affect the Er luminescence directly; however, it strongly affects the defect distribution around lanthanide ions and the way in which activator ions are incorporated in the lattice. Our results demonstrate the correlation between the crystalline phase of zirconia and charge compensation, as well as the contribution of different nanocrystal grain sizes. In addition, our experimental results verify the theoretical studies of metastable (tetragonal, cubic) phase stabilization determined using only oxygen vacancies. Moreover, it was found that adding niobium drastically increases activator luminescence intensity, which makes Ln3+ doped zirconia even more attractive for various practical applications. Although this study was based on the luminescence of the Er ion, the phase stabilization, charge compensation, and luminescence properties described in our results are expected to be similar for other lanthanide elements. Our results suggest that the luminescence intensity of other oxide matrices where lanthanides incorporate in place of tetravalent cations could be increased by addition of Nb ions.
Temperature dependence of the afterglow of persistent luminescence material SrAl 2 O 4 :Eu,Dy is a major problem for outdoor low temperature applications. Therefore this publication deals with tailoring the material for better outdoor use by exploring the second mechanism, that is involved in the afterglowcharge tunnelling from the trapping center to the luminescence center. Structure, morphology, emission and thermally stimulated luminescence properties have been measured for SrAl 2 O 4 :Eu,Dy samples with different added boron percentage. The results indicate a change in morphology of the samples with increasing boron concentration, as well as a change in afterglow times. The low temperature luminescence intensity and afterglow time dependence of boron addition turns out to be different from the room temperature luminescence intensity and afterglow time dependence from boron concentration. Boron addition in necessary amount plays a key role to creating trapping centers in the material that are located spatially close to the luminescence center thus making the material afterglow possible even in low temperatures.
Ln 3 ion luminescence intensity in HfO 2 is increased for up to 15 times (in a sample containing 5 mol%Eu). The effect is described as niobium acting as a charge compensator and neutralizing the charge resulting from + Ln 3 ion insertion in + Hf 4 site and hence reducing the number of defects present. This is the second system where such an effect was observed, so it is expected that other metal oxides would show the same effect. The optical properties of HfO 2 :
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