Marko G. Nikolić

Temperature dependence of emission and lifetime in Eu 3+ - and Dy 3+ -doped GdVO 4

Eu(3+)- and Dy(3+)-doped GdVO(4) samples synthesized by a high-temperature solid-state method are investigated by fluorescence spectroscopy at 298-750 K. They demonstrate potential for development as thermographic phosphors because the experimental and theoretical temperature dependence of the intensity ratio of the two lines agrees well. Experimental lifetime measurements recorded at 10-750 K were fitted using three theoretical models: multiphonon relaxation, temperature quenching through the charge transfer (CT) region, and our modified CT model (TDCT), which considers the temperature dependence of CT energy. The TDCT model yields the best results with good agreement between experimental and fitted lifetime data.

Low-cost, portable photoacoustic setup for solid samples

We have developed a low-cost, portable photoacoustic instrument. The device consists of a detection unit comprising a photoacoustic cell with an embedded laser diode or a light-emitting diode, a photodiode, an electret microphone (60 ? 40 ? 40 mm3), and a signal processing and power supply unit in a box containing batteries and electronics (160 ? 140 ? 60 mm3). A PC or portable computer is required to operate the device and for data processing. The weight of the instrument without the computer is 1.70 kg. The computer, or more precisely, its sound card is the essential part of the apparatus because it generates the signal for the laser diode or light-emitting diode modulation and processes signals from the microphone and photodiode. The computer sound card is used as a dual-phase lock-in amplifier. The software used for the control of the setup was also developed in course of this work. The photoacoustic instrument presented here allows measurements and quantitative analysis of numerous solid-state samples. It is simple in design and use, having a reasonable weight and portability.

Temperature luminescence properties of Eu3+-doped Gd2O3 phosphors

Rare earth (RE) oxides are important hosts for the luminescence of RE activators with numerous practical applications in light-emitting devices. In this work, we investigated the possibility for Gd2O3:Eu3+ usage in phosphor thermometry by observing the temperature changes of trivalent europium ion transitions from the 5D0 and 5D1 energy levels to the ground-state levels. A set of three samples of Eu3+-doped Gd2O3 (1, 5 and 10 at.% Eu3+) was produced via combustion synthesis. The sample crystalline structure is confirmed by XRD measurements. The intensity ratio of the two emission lines was studied as a function of temperature in the temperature range 300–800 K, and lifetime was measured in the interval 10–800 K. All three Gd2O3:Eu3+ samples proved to have good potential for the development of thermographic phosphors.

Thermographic properties of Sm3+-doped GdVO4 phosphor

Rare-earth orthovanadates are important hosts for the luminescence of rare earth activators with considerable practical applications in the artificial production of light. In this paper we investigated the possibility for GdVO4:Sm3+ usage in phosphor thermometry by observing the temperature changes of trivalent samarium transitions from 4F3/2 and 4G5/2 energy levels to the ground state. A set of three samples of Sm3+-doped GdVO4 (0.5, 1 and 2 mol.% Sm3+ with respect to Gd3+ ions) was produced via solid state synthesis. The sample crystalline structure is confirmed from x-ray diffraction (XRD) measurements. Photoluminescence measurements were recorded in the temperature range 293–823 K and the fluorescence intensity ratio of the paired emissions bands was studied as a function of temperature. All three GdVO4:Sm3+ samples proved to have good potential for the development of thermographic phosphors, whereas the maximum sensitivity of approximately 4.5×10-4 K−1 was found for the sample with 2 mol.% Sm3+ in the temperature region around 750 K.

Luminescence thermometry via the two-dopant intensity ratio of Y2O3:Er3+, Eu3+

In this work we investigated the photoluminescence properties of Y2O3:Er3+, Eu3+ as a function of temperature and the possibility to use this material as a temperature sensor. Photoluminescence emission measurements with 532 nm laser excitation were recorded in the temperature range from 303 up to 573 K. The measured intensity ratio of erbium 4S3/2 → 4I15/2 and europium 5D0 → 7F2 emission lines was used for determination of the temperature calibration curve. These emission lines are intense, narrow and well defined. The distance between the lines, being 47 nm, can be easily measured even with a low-resolution spectrometer. The calculated relative sensitivity of the temperature sensor was 1.4% K−1 at 303 K, in the physiological temperature range, meaning that it could be successfully applied in biological studies.

Processing and characterization of up-converting Er3+ doped (Lu0.5Y0.5)2O3 nanophosphor

Abstract In this paper we demonstrate visible up-conversion emission of Er3+ doped (Lu0.5Y0.5)2O3 nanophosphor and discuss possible mechanisms for pumping the upper energy levels of Er3+ ions. Polymer complex solution synthesis yields well crystalline, pure-phase cubic nanopowder with particle size in the 20–50 nm range. Red, green and blue up-conversion emission is measured under near-infrared excitation (1 540 nm), over the temperature range 10–300 K. The red/green intensity ratio indicates that the mechanism responsible for populating red up-conversion is temperature dependent. Decay times are found to be around 0.25 ms for red and green, and around 70 μs for blue emission.

Holographic Measurement of a Tooth Model and Dental Composite Contraction

We have developed a real-time holographic technique to observe deformation induced by dental composite contraction. The standard split beam method was used, in conjunction with in situ holographic plate processing. Experiments were performed on a mechanical model of a human tooth with cavity. A silicone mold was used to manufacture a number of identical casts, using photoactivated composite. A LED lamp was used to induce photo-polymerization reaction in a composite. We have shown that the proposed method is ideal to analyze various polymerization strategies, with the purpose of recommending one which minimizes the polymerization contraction.

Proposal of railway axle counter architecture

Railway axle counters are used to control occupancy of railway sections. Their typical application is occupancy control of level crossing or open railroad sections within the automatic block system. This paper presents possible architecture of railway axle counter using microcontrollers that fulfill SIL 3 safety level defined by IEC 61508 Standard.

Up-conversion luminescence of Tm3+ sensitized by Yb3+ ions in GdVO4

The aim of this work is to study up-conversion (UPC) luminescence in a series of Tm3+/Yb3+-co-doped GdVO4 samples synthesized by the solid-state method. The concentrations of Yb3+ ions were 3, 6 and 9 mol.%, while the concentration of Tm3+ ions was fixed (3 mol.%). X-ray diffraction patterns for all the synthesized samples confirmed successful formation of a pure GdVO4 phase. Quantitative energy-dispersion x-ray analysis confirmed successful doping of Tm3+ and Yb3+ ions into the GdVO4 matrix. Scanning electron microscope images show that the samples are composed of deformed (irregular) spherical particles with an average diameter size in the range of 1.4 − 8.4 μm. Up-converted emission spectra were recorded at room temperature under 980 nm excitation. It was found that all our samples exhibit UPC emission in three different spectral regions: strong emissions are observed at 475 and 800 nm corresponding to the 1G4 → 3H6 and 3H4 → 3H6 transitions, respectively, while emission in the red region at about 650 nm is very weak and is due to the 1G4 → 3F4 transition. It was concluded that conversion of near-infrared radiation into blue emission proved to be very effective in all the synthesized systems. It was found that emission decay curves for all samples exhibit single exponential behavior.

Low-temperature effects on up-conversion emission of Er3+/Yb3+-co-doped Y2O3

Over the past few years, rare-earth-ion-doped materials have attracted a great deal of interest due to their potential application as optical temperature sensors. The luminescence properties of these materials are sensitive and change with temperature. Here, we have investigated the properties of yttrium oxide powder co-doped with Yb3+ and Er3+, synthesized through the spray pyrolysis method at 900??C and additionally thermally treated at 1100??C for 24?h. The structural and morphological characterizations are carried out through x-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). The obtained particles are spherical in shape and have cubic bixbyite structure with the space group Ia-3. Photoluminescent measurements (PL) are recorded in the temperature range from 10 to 300?K using 978?nm radiation. Emission spectra are assigned to the following trivalent erbium f?f electronic transitions: 2H9/2???4I15/2 (blue: 407?420?nm), (2H11/2, 4S3/2)???4I15/2 (green: 510?590?nm) and 4F9/2???4I15/2 (red: 640?720?nm). The fluorescent intensity ratios of the blue, green and red areas under emission bands show significant temperature sensitivity, with the largest value of 2.3?K?1.