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An optical temperature sensor suitable for label free liquid sensing has been designed and characterized. The sensor combines the photochemical stability of rare earth doped glasses and the high sensitivity of interferometric resonators. It is formed by a planar Fabry-Perot (FP) microcavity filled with the liquid to be monitored. A Ho3+ doped tapered optical fiber has been placed inside the microcavity surrounded by the fluid medium. An external laser is focused on the optical fiber inside the cavity to induce the luminescence of the Ho3+ ions, which couples to the FP optical resonances. The spectral position of the FP resonances is highly sensitive to the refractive index of the cavity medium. A second laser is co-aligned with the first one to locally heat the liquid medium around the optical fiber. An average blue shift of the FP resonances around 32 pm/°C is measured. The limit of detection of the laser induced heating of the liquid medium is about 0.3 °C in the biological temperature range. Alternatively, a hot-plate is used to heat the system. Interestingly, a red shift of the FP modes is observed with 75 pm/°C dependence and 0.12 °C limit of detection features.

An Er3+-doped calcium aluminate glass has been studied in order to establish its suitability as optical temperature sensor based on the fluorescence intensity ratio technique. Temperature-induced changes in the relative intensities of the green emissions associated with the transitions from the 2H11/2 and 4S3/2 thermalized levels to the 4I15/2 ground state under laser excitation at 488 nm has been measured in the range of temperatures from 150 to 762 K. The sensitivity obtained due to temperature changes shows a maximum of 159×10−4 K−1 at 645 K, one of the highest sensitivity values found in Er3+-doped host matrices. Compared to other studies, a different approach has been followed to estimate the calibration the temperature sensor using a low-cost prototype.

Conventional chemical analyses of meat products are time-consuming, expensive and destructive. The advantages of NIR spectroscopy are its speed, portability, suitability for both at-line and on-line analysis, low cost and the possibility of simultaneously measuring many different parameters in a large number of samples. The purpose of this study was to develop and validate calibrations for the prediction of moisture, protein and fat in Iberian pig pork loins using an FT-NIR instrument coupled to a 5-m fibre optic sensor head. The best equations obtained for intact loin in both modes of analysis (full and optimal spectral range) displayed Standard Error of Cross-Validation (RMSECV) of 1.06% and 1.09% and Determination Coefficient of Cross-Validation (RCV2) of 0.69 and 0.77 for fat: RMSECV of 0.87% and 0.77% and RCV2 of 0.67 and 0.73 for moisture; while for protein, the RMSECV values were 0.51% and 0.49% and the RCV2 values were 0.66 and 0.70.

Two different thermal treatments were used to create nanocrystals from a precursor glass. The glass whose composition is Ba 2 TiSi 2 O 8 and doped with 3% of Nd 3+ was prepared using the melt quenching method. A conventional thermal treatment in an electrical furnace was used to obtain transparent glass ceramic samples, which contain Fresnoite nanocrystals with an average size of 35 nm. Moreover, these nanocrystals were obtained in a localized area of the precursor glass by irradiating with a continuous Ar + laser. Evidence of the changes induced by laser irradiation was confirmed by optical spectroscopic, X-ray diffraction, scanning electron and atomic force microscopy.

An appropriated thermal treatment of SrO-BaO-Nb2O 5-B2O5 glass leads to the formation of glass ceramics which are composed of Tm3+-Yb3+ codoped strontium barium niobate (SBN) nanocrystals dispersed throughout an amorphous matrix. The glasses have been fabricated using a melt-quenching method and after a thermal treatment at 620 °C have been obtained the glass ceramic samples. The formation of SBN nanocrystals has been confirmed by the X-ray diffraction patterns. Visible and NIR emission spectra have been reported and confirmed the incorporation of the Tm3+-Yb3+ ions into the SBN nanocrystals. In the glass ceramics samples the decays of Tm3+ levels for the Yb3+-Tm3+ codoped samples are longer than in the Tm3+ single doped samples. This surprising result could be explained in basis to the localisation of the active ions in the SBN nanocrystals. © 2010 Elsevier B.V. All rights reserved.

This paper reports the results obtained in strontium barium niobate (SBN) nanocrystals in glasses doped with 1, 2.5 and 5 mol% of Er3+ ions. The melt-quenching method was applied to fabricate the glasses with composition SrO–BaO–Nb2O5–B2O3 and further thermal treatment was used to obtain glass ceramic samples from the glass precursor. X-ray diffraction patterns confirmed the formation of SBN nanocrystals with an average size of about 50 nm in diameter. Time-resolved fluorescence spectra for the emission of Er3+ ions at 1550 nm have been analyzed in order to confirm the incorporation of the Er3+ ions into the nanocrystals. Green frequency upconversion emission under excitation at 975 nm coming from the ions in the nanocrystals has been obtained. This intense upconversion is about a factor of 500 higher than that obtained from the ions which reside in the glassy phase. Moreover, temporal evolution studies have been carried out with the purpose of determining the involved upconversion mechanism and the importance of these processes as a source of losses for the optical amplification at 1550 nm.

A study of the optical properties of Pr 3+ -Yb 3+ ions in oxyfluoride glass and glass ceramics was carried out. The cross section emissions at 1300 nm corresponding to the 1 G 4 → 3 H 5 transition of Pr 3 ions were obtained. The ceramming process reduced the linewidth of this transition by about 12% and the emission stimulated cross section was increased by a factor of 1.4 compared to the precursor glasses. The mean wavelength is nearly constant (about 1325 nm) above room temperature. After analyzing the luminescence decay curves of Yb 3+ ions, it was found that the majority of the optically active ions in the glass ceramic were located in the fluoride nanocrystals and the rest in the glassy phase. The shortening of distances between the ions turns the energy transfer process into Yb 3+ → Pr 3 . However, emission at 1300 nm Pr 3 was concentration quenched.

Measurements of the optical properties of Er 3+ ions in strontium barium niobate glass and glass ceramics have been carried out. The glasses have been fabricated using a melt-quenching method, and the glass ceramic samples have been obtained from the glass precursor by a thermal treatment. The ceramic samples formed by a glassy phase, and a crystalline phase contains nanocrystals of Sr 1− x Ba x Nb 2 O 6 (SBN) doped with Er 3+ ions with a mean size of ∼50 nm, as confirmed with XRD. Green up-conversion emission has been obtained under excitation at 800 nm, and the temporal evolution of this emission has been reported with the purpose of determining the involved up-conversion mechanism. These optical measures have confirmed that the Er 3+ ions have been incorporated into the SBN matrix, after a thermal treatment, which produced an increment of the up-conversion efficiency.

Red, green, and blue stimulated emissions have been achieved in Ho3+ doped oxyfluoride glass ceramic at room temperature. The material shows three emission bands at the red (650 nm), green (545 nm), and blue (488 nm) regions under infrared excitation at 750 nm. These emission bands are caused by a photon avalanche upconversion process previously reported. A pump and probe experimental setup has been designed to show stimulated emissions at the three bands. The pump power threshold for positive gain in the 490 nm band has been estimated around 2.7 kW/cm2. Higher thresholds are expected for the other bands.

A local nanocrystalline formation in a neodymium doped strontium barium niobate (SBN) glass has been obtained under argon laser irradiation. The intense emission around 880 nm, originated from the F43/2 (F45/2) thermalized level when the glass structure changes to a glass ceramic structure due to the irradiation of the laser beam, has been studied. The intensities and lifetimes change from this level inside and outside the irradiated area made by the laser excitation. They have been analyzed and demonstrated that the desvitrification process has been successfully achieved. These results confirm that nanocrystals of SBN have been created by the laser action confirming that the transition from glass to glass ceramic has been completed. These results are in agreement with the emission properties of nanocrystals of the bulk glass ceramic sample. The present study also suggests that the SBN nanocrystal has a potential application as temperature detector.