José Carlos Mesquita Carvalho

Influence of titanium and lutetium on the persistent luminescence of ZrO 2

Non-doped as well as titanium and lutetium doped zirconia (ZrO2) materials were synthesized via the sol-gel method and structurally characterized with X-ray powder diffraction. The addition of Ti in the zirconia lattice does not change the crystalline structure whilst the Lu doping introduces a small fraction of the tetragonal phase. The UV excitation results in a bright white-blue luminescence at ca. 500 nm for all the materials which emission could be assigned to the Ti3+eg → t2g transition. The persistent luminescence originates from the same Ti3+ center. The thermoluminescence data shows a well-defined though rather similar defect structures for all the zirconia materials. The kinetics of persistent luminescence was probed with the isothermal decay curve analyses which indicated significant retrapping. The short duration of persistent luminescence was attributed to the quasi-continuum distribution of the traps and to the possibility of shallow traps even below the room temperature.

Spectroscopic properties and quantum cutting in Tb3+-Yb3+ co-doped ZrO2 nanocrystals

Ultraviolet-visible to near-infrared quantum cutting (QC) materials are a promising tool to enhance the efficiency of conventional crystalline silicon solar cells. The spectroscopic properties of Tb3+–Yb3+ co-doped ZrO2 nanocrystals are presented, and the QC mechanisms in these nanocrystals are investigated. The materials were fabricated using the sol gel method and characterized using X-ray powder diffraction, X-ray absorption near edge structure, and luminescence spectroscopy. The incorporation of Yb3+ ions into the host induced a crystalline phase change of ZrO2 from monoclinic to tetragonal to cubic symmetry and influenced the Tb valence state. The Tb3+ visible emission, excitation intensity (monitored by the Tb3+:5D4 emission), decay time of the Tb3+:5D4 emitter level, and down-conversion (DC) emission intensity increased with Yb3+ concentration. Furthermore, a sublinear dependence of the DC intensity on the excitation power at the Tb3+:5D4 level indicated the coexistence of two different QC mechanis...

Evaluation of iris color stability in ocular prosthesis

UNLABELLED Accurate iris reproduction in the fabrication of ocular prosthesis in order to match the remaining eye is a key factor to mask the loss and achieve an esthetic outcome for anophthalmic patients. This study evaluated the stability of acrylic paints used for replicating iris color in ocular prostheses by the analysis of two factors: the temperature of the acrylic resin polymerization cycle during prosthesis fabrication and the incidence of sun light, which is the main photodegrading agent undermining the longevity of ocular prostheses. An accelerated aging assay was used for both analyses. Specimens simulating the prosthetic iris in the colors blue, yellow, black, brown and green were fabricated, and were submitted to a colorimetric reading before and after undergoing the thermal conditions of acrylic resin polymerization. Next, the specimens were submitted to an artificial accelerated aging assay with ultraviolet radiation A and weekly colorimetric readings during a 3-week period. The color change (Delta E*) values for the four specimens painted with the same color paint were averaged and the resulting values were considered for statistical analysis. Levines test and Students t-test were used to analyze the influence of the temperature of the polymerization cycle during prosthesis fabrication on the color stability of each acrylic resin paint. Friedmans test for three dependent samples was used for analysis of color photodegradation as function of time. Significance level was set at 0.05 for all analyses. It was observed that, after the action of the temperature of the polymerization cycle, alteration above clinically acceptable level of Delta E*> 3.3 was observed only for the yellow color. After the accelerated aging assay, there were statistically significant differences (p<0.05) as a function of time in the green, brown, black and blue colors. Changes were clinically acceptable for the brown and black colors; slightly above the clinically acceptable limit for the green color; and significantly high and impracticable from a clinical standpoint for the blue color. There was no statistically significant differences (p>0.05) for the yellow color, which presented color change only a little above the clinically acceptable limit. IN CONCLUSION 1. Only the yellow color presented alterations above the clinically acceptable levels after the polymerization cycle; 2. After accelerated aging, there was no changes in the yellow color above the clinically acceptable levels; 3. For the green color, degradation was significant and slightly above the clinically acceptable levels; 4. The black, brown and blue colors presented significant alterations as function of time; the alterations of the brown and black colors were within acceptable clinical levels, while the blue color presented a more accentuated degradation over time.

Persistent luminescence of cadmium silicates

The effect of the band gap on the persistent luminescence of cadmium meta- and orthosilicates was studied with VUV–UV–vis photoluminescence and x-ray absorption spectroscopies (XANES and EXAFS). The narrower band gap of Cd2SiO4 is favourable for persistent luminescence from Pr3+ but not from Tb3+ due to the trivalent rare-earth energy level positions in the band gap.