Luminescence properties of Ce-doped ZrO2 phosphors synthesized by combustion method.

Zr1-x Cex O2 with x = 0.005, 0.01, 0.02, and 0.03 samples were synthesized using a combustion technique. The X-ray diffraction results revealed that Ce-doped ZrO2 nanoparticles were in a monoclinic structure up to 1 mol% Ce concentration. The increase in the Ce concentration caused more distortion in the monoclinic structure of zirconia. The samples showed a mixed phase (monoclinic + tetragonal) beyond 1 mol% Ce content. The crystallite size (D) and strain (ε) were calculated from the Williamson-Hall equation. The D decreased from 25 ± 1 to 20 ± 1 nm and ε increased from 0.03 to 0.28% with an increase in Ce concentration. Photoluminescence (PL) spectra of Zr1-x Cex O2 showed emission in the blue region under an excitation wavelength of 290 nm. Zr0.995 Ce0.005 O2 showed the highest PL intensity with an average lifetime of 0.93 µs, and the PL intensity decreased with the increase in the Ce concentration. Thermoluminescence (TL) glow curves of Zr1-x Cex O2 were measured after gamma irradiation (500 Gy) with a heating rate of 5 K s-1 . The TL curve of Zr0.995 Ce0.005 O2 showed two prominent peaks at 412 K (peak 1) and 600 K (peak 2). The first TL glow peak was shifted towards a higher temperature at 440 K above 1 mol% Ce concentration. Repetitive TL measurements on the same aliquot exhibited excellent repeatability. Kinetic parameters associated with the TL peaks were calculated using the curve fitting method. Peak 1 followed non-first-order kinetics. The value of the activation energy of the 440 K peak was found to be 0.95 ± 0.01 eV for Zr0.99 Ce0.01 O2 . These findings showed that Zr1-x Cex O2 might be used in lighting and radiation dosimeter applications.

Synthesis and luminescence studies of Tb-doped MgO-MgAl2O4-Mg2SiO4 ceramic for use in radiation dosimetry.

In the present work, MgO ceramic samples with different terbium concentrations were produced and the Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) properties analyzed and discussed, aiming the use in radiation dosimetry. The samples were produced using MgO, Mg(NO3)2·6H2O, Al2O3, SiO2 and Tb(NO3)3·6H2O precursors in stoichiometric concentrations with five different terbium concentrations between 0.1 and 0.5 mol% and after, heat-treated at high temperature ~1500 °C. X-ray diffraction measurements on samples showed the formation of MgO as principal phase, and others in low concentration due to MgAl2O4, Mg2SiO4 and Tb4O7 phases. The TL glow curve of samples showed an intense and well-defined peak having the maximum at ~210 °C and other less intense at ~350 °C. The sample with 0.1 mol% of terbium concentration presented highest luminescence peak when compared to the other samples. The relationship between 210 °C TL peak intensity and dose was linear to doses between 1 and 20 Gy and the minimum detectable dose obtained by interpolation taking into account three times the standard deviation of the zero dose reading, was ~40 µGy. A fading of ~20% during the first 5 hours after irradiation of 210 °C peak was observed. TL emission spectra showed strong emission lines due to Tb3+ ion. The OSL signal presented a linear behavior to doses between 1 and 10 Gy using 532 nm wavelength stimulation.

Study of paramagnetic and luminescence centers of microcline feldspar.

Microcline feldspar crystal has been analyzed in order to determine the centers suitable for use in ESR and luminescence dating. ESR measurements at RT showed the Fe3+ line, and at 77K the Si-O(-) ..X signal with g=2.0052, 2.0098 and 2.0128. TL glow peak at 157 and 300 degrees C in UV interval were observed and in the VIS range we noted peaks at 150, 280 and 340 degrees C. TL growth curve of the 340 degrees C peak could be fitted by a saturating exponential equation and can be used in TL dating. Emission curves showed band widths 1.95+/-0.09, 2.73+/-0.08 and 4.94+/-0.50 eV. Transitions from 4T1-->6A1)of Fe3+ can be associated with the 1.95 eV band and the transition from 4A1 4E(G)-->6A1(S) with 2.73 eV band.

Spectroscopic properties of lead fluoroborate glasses doped with ytterbium.

A new lead fluoroborate glass (PbO-PbF2-B2O3) doped with ytterbium (Yb:PbFB) is presented. Samples with different concentrations of Yb3+ were produced and had their emission cross-sections, fluorescence lifetimes and minimum pump intensities determined. They have high refractive index of 2.2 and a density of 4.4 g/cm3. For a doping level of 1.153x1020 ions/cm3, the fluorescence lifetime, after excitation at 968 nm, is 0.81 ms, which is comparable to Yb:tellurite laser glass. Also, an emission band at 1022 nm is measured with emission cross-section of approximately 1.07x10-20 cm2 and fluorescence effective linewidth of 60 nm, which is comparable to Yb:phosphate laser glass.

Optical properties of Nd doped Bi2O3-PbO-Ga2O3 glasses.

The optical properties of a new family of neodymium doped BPG (Bi2O3-PbO-Ga2O3 ) glasses are presented. We measured a high refractive index, of 2.5, and a transmission cutoff in the far infrared at 8microm. Three intense emission bands are observed centered at 877nm, 1066nm and 1341nm. The emission cross-section is 10 -20 cm 2 and the total spectral linewidth is 30nm at 1066nm. The Judd-Ofelt parameters are calculated and used to evaluate transition probability, radiative lifetime and branching ratios. The optical properties of these Nd:BPG glasses show promise for their use as a new active laser material.