Papers by Keyword: Luminescence

Abstract: This paper is related to the problem of enhancing the optical and functional performance of luminescent gas sensors via its excitation by photonic nanojets. The novel sensor structure consisting of the array of alumina microparticles covered by optical sensitive layer was designed. The parameters of the photonic nanojets generated in both transmission and reflection modes has been numerically end experimentally studied. It was shown that PNJ in reflection mode demonstrates an unexpectedly high enhancement of photoluminescence. It was obtained that the excitation of the sensitive layer by photonic nanojets extends the limit of gaseous ammonia detection up to 0.1 ppm for reflection mode and up to 0.02 ppm for transmission mode.

Abstract: The luminescence properties Dy³⁺, Eu³⁺ and Sm³⁺ doped magnesium sodium borate glasses were investigated. The glasses samples containing the composition 30MgO-70Na2B4O7.10H2O-xRE₂O₃ (where RE = Dy³⁺, Eu³⁺, and Sm³⁺, x = 0.1, 0.5, and 1.0 mol %) are prepared by the conventional melt quenching technique. The optical properties have been evaluated using Ultraviolet-Visible Spectroscopy and Photoluminescence Spectroscopy. The X-ray Diffraction pattern was studied to confirm the amorphous nature of the prepared glass. The absorption spectra yield the most intense absorption bands and transition energy levels for Dy³⁺, Eu³⁺, and Sm³⁺ located at 347 nm (⁶H_15/2 → ⁶P_7/2), 393 nm (⁷F₀ → ⁵L₆), and 403 nm (⁶H_5/2 →⁶P_5/2) respectively. The emission spectra demonstrate the highest emission intensity centered at 463 nm (⁴F_9/2 → ⁶F_11/2 + ⁶H_9/2), 612 nm (⁵D₀ → ⁷F_J), and 599 nm (⁴G_5/2 → ⁶H_7/2) for Dy³⁺, Eu³⁺, and Sm³⁺ respectively. Dy³⁺ emits combination of blue, yellow, and red light, Eu³⁺ emits red light and Sm³⁺ emits orange to red light. The higher the content of Dy³⁺, Eu³⁺, and Sm³⁺, the higher the spectral or peak intensity for both absorption and emission. The findings could be useful for development of laser, light emitting diode (LED), and color displays applications. KEY WORDS: Luminescence, Borax glass, Magnesium, Dysprosium, Europium, Samarium.

Abstract: Er³⁺ doped potassium sodium niobate (KNN: Er) ultrafine powders have been prepared by pulsed laser ablation in water. X-ray diffraction (XRD) pattern of the sample demonstrated that the as-synthesized powders were crystalized in orthorhombic phase. Scanning electron microscopy (SEM) and transmittance electron microscopy (TEM) images exhibited that the morphology of ultrafine powders are cube-like. Under the excitation of 980 nm laser, the sample exhibits green emission, which is originated from the transition of thermal coupled energy levels (²H_11/2, ⁴S_3/2) to ground state level ⁴I_15/2. Temperature dependent up-conversion emission intensity associated with thermal quenching of total green emission band and the fluorescence intensity ratio (FIR) between two sub-emission bands related to population of thermal coupled energy levels are investigated for temperature sensing in the temperature range of 300 K to 480 K. The temperature sensing performances related to different technique were discussed. A maximum relative sensitivity reaches 1.01% K^-1 at 464 K for emission intensity thermometry and that is 0.84% K^-1 at 374 K for FIR thermometry technique. All these results show that KNN: Er ultrafine phosphors prepared via pulsed laser ablation in water have prospect for non-contact temperature sensing.

Abstract: This paper reports a tunable luminescence of europium (Eu ³⁺) doped zirconia (ZrO₂) nanoparticles as a function of hydrothermal temperature, europium concentrations, time and pH value. The nano-sized Eu doped ZrO₂ (Eu:ZrO₂) particle was synthesized by hydrothermal method at the temperature of 200 °C and time up to 48 h. The nano-sized Eu:ZrO₂ particles have a diameter of about 10 nm. The luminescent properties of nano-sized Eu:ZrO₂ particle was enhanced in the sample when high temperature, high Eu ³⁺ concentration and prolonging hydrothermal time were used at pH 7. These results suggest the use of Eu:ZrO₂ nanoparticles followed by thermal annealing in tuning the luminescence of Eu:ZrO₂ nanoparticles which have potential applications as phosphors in solid state lighting.

Abstract: In the present work, we studied the structural and optical properties of zinc-titania tellurite glass (75-x)TeO₂-20ZnO-5TiO₂-xEr₂O₃ doped with erbium ion Er³⁺ (where mol % : x= 0 (host), 0.5, 1, 1.5). The reported glasses were synthesized using tradition melt quench method. The X-ray diffraction and thermal profile were utilized to study the amorphous nature of the mentioned glass. Optical absorption UV-Visible-NIR spectra were measured for optical energy gap and Er³⁺ absorption bands analysis. Both visible and near infrared luminescence were performed at room temperature using 980 nm laser diode excitation where the optical transition mechanism of the Er³⁺ in the glass is finally proposed. Broad luminescence in the present glass suggests its potential for broadband optical application.

Abstract: Metal nanoparticles have attracted more and more attention in the last years due to their unique chemical and physical properties which are very different from the metal bulk material. In particular, when the size of nanoparticles decreases below two nm, nanoparticles can be described as nanoclusters (NCs), and they present peculiar optical properties. The excited electrons in addition to specific absorption bands show also a bright luminescence related to the quantum size effect which produce discrete energy levels. Optical properties (absorption and fluorescence) of these NCs are widely used in many different applications in science and engineering, such as chemical sensors, fluorescent probes for bio imaging or in environmental issues. In the present study, we report on the synthesis of silver nanoclusters (AgNCs) in aqueous phase using silver nitrate as precursor salt and L-Glutathione (GSH) as stabilizer. AgNCs were characterized using absorption and fluorescence spectroscopy, and transmission electron microscopy (TEM). The strong absorption and luminescence shown by these NCs are very promising for a possible exploitation both as label for bioimaging and for optical sensors for heavy metal ions.

Abstract: The Dy³⁺-doped glasses of the M₂O₃:CaO:SiO₂:B₂O₃ (M₂O₃ = Y₂O₃ and La₂O₃) materials have been successfully fabricated with the 0.5 % mol of the Dy₂O₃ concentration, and thoroughly investigated based on the physical, optical, photo- and radioluminescence properties. The developed glass materials were prepared from the compositions of 25M₂O₃:10CaO:10SiO₂:(55-x)B₂O₃:0.5Dy₂O₃ by the conventional melt-quenching technique at 1,400°C. The clear sample of the doped La₂O₃ glass demonstrated higher density and the molar volume than those of the doped Y₂O₃ glass. From the spectrophotometry, the absorption peaks of the Dy³⁺ ions were clearly observed in both glasses. The photoluminescence (PL) spectra of the developed glasses indicated two-colors with two strongest peaks at 577 nm (⁴F_9/2®⁶H_13/2) and 482 nm (⁴F_9/2®⁶H_15/2). In addition, the emission spectra from the radioluminescence (RL) were identical to those from the PL measurements. From the results of the PL and RL measurements, the Y₂O₃ glass had higher emission in the intensity than the La₂O₃ glass. The X-ray absorption near edge spectroscopy (XANES) with the synchrotron radiation was carried out in fluorescent-yield mode to determine the average oxidation number of the Dy ions dispersed in the glass matrices. The DyL₃-edge XANES spectra of both developed glasses were nearly identical with the sharp white line at 7795.5 eV and the edge energy of 7793 eV. Compared to the XANES spectrum of the pure Dy₂O₃ standard, both glasses showed the difference smaller than 0.5 eV, and therefore confirmed the oxidation number of the Dy ions of 3+.

Abstract: New approaches to enhance properties of silicon based quantum dot heterostructures for optical device application were developed. That is strain driven heteroepitaxy, small-sized quantum dots, elemental compositions of the heterointerface, virtual substrate, plasmonic effects, and the quantum dot charging occupation with holes in epitaxially grown Ge quantum dots (QDs) on Si (100). Experiments have shown extraordinary optical properties of Ge/Si QDs heterostructures and mid-infrared quantum dot photodetectors performance.

Abstract: A novel blue-emitting phosphor, Li₃Gd₃Te₂O₁₂:Tm³⁺ for white light-emitting diodes (W-LEDs) was prepared by solid-state synthesis and its structure and luminescence properties were investigated. This phosphor shows a satisfactory blue performance (peak at 458 nm) due to the ¹D₂ → ³F₄ transition of Tm³⁺ excited by 361 nm light. Investigation of Tm³⁺ content dependent emission spectra indicates that x = 0.03 is the optimum doping content of Tm³⁺ ions in the Li₃Gd₃Te₂O₁₂ host. The critical distance and the concentration quenching mechanism were also investigated. In particular, the color purity of as-prepared sample is close to that of the commercial blue phosphor BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺). The present work suggests that the Li₃Gd₃Te₂O₁₂:Tm³⁺ phosphor is a potential blue-emitting candidate for the application in the near-UV WLEDs.

Abstract: The aim of this paper is to study the photoluminescence spectra and photoluminescence excitation spectra in LiF-O, LiF-WO₃ and LiF-TiO₂ crystals at 20-300 K. It is shown that the luminescence centers in LiF-WO₃ and LiF-TiO₂ crystals are oxygen ions O^2- disturbed by defects. Two absorption bands within 6-4.5 eV and two luminescence bands with maxima at 3.1 eV and 2.64 eV correspond to these centers. The absorption and emission spectra of the oxygen center (3.1 eV luminescence band) are close to those for the (O^2-- V_a) center.