M.J.V. Bell

Spectroscopy of Nd3+ and Yb3+ codoped fluoroindogallate glasses

The Nd–Nd and Nd–Yb energy transfer processes are studied in lead fluoroindogallate glasses with the following molar composition: 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XNdF3 (with X=0.1, 0.5, 1, 2, 4, and 5), 30PbF2–20GaF3–15InF3–15ZnF2–(20–X)CaF2–XYbF3 (with X=0.1, 0.5, 1, 2, 3, and 5), and 30PbF2–20GaF3–15InF3–15ZnF2–(19–X)CaF2–XYbF3–1NdF3 (with X=0.1, 0.5, 1, 2, 3, and 5.5). The Dexter, Yokota–Tanimoto, and Holstein formalisms were used to treat the experimental data. The following microparameters of energy transfer were obtained: CDD(Nd–Nd)≈7×10−40, CDA(Nd–Nd)=2.5×10−40, and CDA(Nd–Yb)≈3×10−40 cm6/s. It was also shown that the energy migration between Nd ions depends on the third power of temperature (T3) up to a saturation value of about 80 K. This behavior was attributed to the site to site energy migration. The Yb doped samples presented no nonradiative losses for the Yb3+ emission at 969 nm.

Er3+:Yb3+ codoped lead fluoroindogallate glasses for mid infrared and upconversion applications

In this work, two sets of lead fluoroindogallate glasses were studied with the aim of using them as active media for laser devices at the mid infrared (∼2.8 μm) and visible (∼0.54 μm) regions. The infrared and upconverted emissions of Er3+ in single and Er3+:Yb3+ codoped samples were analyzed, and it was observed that the best set of samples for 2.8 μm emission was the single doped one, and that as the upconversion (anti-Stokes luminescence) increased as a function of Yb3+ concentration, the infrared emission decreased in the same manner. The results suggest that the codoping with Yb3+ favors only the upconversion processes which depopulate the 4I11/2 level, reducing the 2.8 μm emission intensity. On the other hand, the Yb3+ codoping will certainly increase the efficiency of an upconversion based device. Quantum efficiencies of infrared emissions and radiative lifetimes were calculated by using the Judd–Ofelt approximation. Er3+–Er3+ and Er3+–Yb3+ energy transfer efficiencies were calculated using the mea...

Cooperative luminescence in Yb3+-doped phosphate glasses

In this paper we present results on cooperative luminescence performed on Yb3+-doped metaphosphate glasses under 980 nm excitation. We have measured emission spectra and decay lifetimes in the visible and infrared regions as a function of Yb concentration. It was observed that, up to 10% of Yb concentration, cooperative emission increases while lifetime is observed to decrease. Such behaviour is attributed to the Yb interaction with OH− radicals and energy migration among Yb ions.

Thermal lens study of the OH− influence on the fluorescence efficiency of Yb3+-doped phosphate glasses

In this work, the thermal lens (TL) technique is used to determine the fluorescence quantum efficiency (η) of Yb3+-doped phosphate glasses. The role of nonradiative processes such as energy migration among Yb ions and the interaction with OH− radicals are presented and discussed. Two sets of samples with the same Yb concentrations were prepared, one at ambient conditions (set A) and the other in N2 atmosphere (set N). The TL technique was shown to be very sensitive to the amount of OH radicals. Moreover, the η values obtained from the TL method are in good agreement with the calculate ones (based on lifetime measurements). The results indicate that TL can be a valuable technique to evaluate the quantum efficiency and nonradiative rates in ion-doped materials.

Thermo-optical properties of tellurite glasses doped with Eu3+ and Au nanoparticles

This work presents a study of tellurite glasses doped with Eu3+ and Au nanoparticles. Luminescence of Eu3+ ions in the yellow?red region was examined as a function of Au nanoparticles concentration, while the thermal lens technique furnished the thermal diffusivity of the samples. The influence of the nanoparticles concentration on the thermal diffusivity of the glass and the Eu3+ luminescence is discussed.

Energy transfer processes and heat generation in Yb3+-doped phosphate glasses

In this work we present a study of energy transfer processes in Yb3+-doped phosphate glasses with different OH− contents and Yb3+ concentrations. Fluorescence and thermal lens (TL) techniques were used in order to analyze the Yb3+–OH− and Yb3+-other impurity interactions. The role of OH− groups is also presented and discussed. The results show that in the low concentration region up to ∼3×1020Ybions∕cm3, the interaction between Yb3+ and OH radicals is the dominant process reducing the lifetime, increasing the TL dioptric power, and then endangering the performance of the system. For the high Yb3+ concentration limit, the Yb3+-other impurity interaction, which is favored by energy migration, is comparable to the Yb3+–OH− energy transfer, even for high OH− concentration. The nonradiative decay rate due to hydroxyl groups follows Forster-Dexter theory [Ann. Phys. 2, 55 (1948); J. Chem. Phys. 21, 836 (1953)] except at low Yb3+ concentration, being more active at low OH− levels, where quenching rate is probabl...

Optical measurements of Nd3+/Yb3+ codoped fluoroindogallate glasses

We report on the optical properties of Nd 3+ -Yb 3 codoped lead fluoroindogallate melted glasses, with the following molar composition: 30PbF 2 -20GaF 3 -15InF 3 -15ZnF 2 -(20-x)CaF 2 -xNdF 3 and 30PbF 2 -20GaF 3 -15InF 3 -15ZnF 2 -(19-x)CaF 2 -xYbF 3 -1NdF 3 (with x = 0.1, 0.5, 1, 2, 4, 5). Photoluminescence and time resolved photoluminescence measurements were performed to investigate energy transfer processes among Nd 3+ and Yb 3+ ions. The time decay of the 4 F 3/2 Nd 3+ level was monitored as a function of Yb concentration. As a result, it was concluded that the C DA parameter characterizing the cross-relaxation among Nd 3+ ions is C DA(Nd Nd) = 1.3 × 10 -40 cm 6 /s and the energy transfer efficiency from Nd 3+ to Yb 3+ ions is about 85% for the 1 mol% Nd 3+ :5 mol% Yb 3+ sample.

Energy transfer between CdS nanocrystals and neodymium ions embedded in vitreous substrates

Experimental evidence has been observed for energy transfer from CdS nanocrystals, synthesized by the fusion method, to Nd(3+) ions embedded in vitreous substrates. These dot samples doped with neodymium have been investigated by combined optical absorption (OA), photoluminescence (PL), and time-resolved photoluminescence (PLRT) techniques. Radiative and nonradiative energy transfers between CdS dot and Nd(3+) ion levels, to our knowledge not reported before, can be clearly observed in the PL spectra where the emission band valleys correspond exactly to the energy absorption peaks of the doping ion. The PLRT data reinforce these energy transfer mechanisms in which the increasing overlap between the CdS PL band and the OA to the Nd(3+) levels decreases stimulated emissions from the doping ions.

Quantification of whey in fluid milk using confocal Raman microscopy and artificial neural network

In this work, we assessed the use of confocal Raman microscopy and artificial neural network as a practical method to assess and quantify adulteration of fluid milk by addition of whey. Milk samples with added whey (from 0 to 100%) were prepared, simulating different levels of fraudulent adulteration. All analyses were carried out by direct inspection at the light microscope after depositing drops from each sample on a microscope slide and drying them at room temperature. No pre- or posttreatment (e.g., sample preparation or spectral correction) was required in the analyses. Quantitative determination of adulteration was performed through a feed-forward artificial neural network (ANN). Different ANN configurations were evaluated based on their coefficient of determination (R2) and root mean square error values, which were criteria for selecting the best predictor model. In the selected model, we observed that data from both training and validation subsets presented R2>99.99%, indicating that the combination of confocal Raman microscopy and ANN is a rapid, simple, and efficient method to quantify milk adulteration by whey. Because sample preparation and postprocessing of spectra were not required, the method has potential applications in health surveillance and food quality monitoring.

Control of growth and the processes of energy transfer from CdSe quantum dots for Nd3+ ions in a vitreous system: Thermal annealing time

The authors report clear evidence of radiative and nonradiative energy transfer from CdSe quantum dots to Nd3+ ions in a glass system synthesized by melting method. An efficient control of energy transfer can be obtained by controlling the mean radius of the CdSe quantum dots. Increase of about 100% of the near infrared Nd3+ emission (4F3/2 → 4I9/2) was observed as a function of thermal annealing time.