Papers by Keyword: Luminescence

Abstract: Silica-coating is one of simple methods to colloidally stabilize particles. The present work proposed a method for fabricating silica-coated ruby particles having a particle size of ca. 1 µm (ruby/SiO₂) by a process based on a Stöber method. Two systems were examined, which were the systems using sodium hydroxide (NaOH) and aqueous ammonia (NH₄OH) as base catalysts for a sol-gel reaction. In the NaOH system, not only the ruby/SiO₂ particles with silica shells with a thickness of ca. 61 nm but also core-free SiO₂ particles were produced by adding tetraethyl orthosilicate/ethanol solution and NaOH aqueous solution to ethanol dispersing the ruby particle powder. In the NH₄OH system, it was demonstrated that it was possible to increase the shell thickness to 132 nm by repeating addition of TEOS and NH₄OH to a mixture of ruby particles, water, and ethanol, which meant that it was found to vary the shell thickness. The ruby particles emitted luminescence even after the silica-coating, which found that the silica-coating did not deteriorate luminescence property of ruby particles.

Abstract: This study examined the impact of silica-coating on the luminescence characteristics of indium phosphide (InP) nanoparticles. Silica-coated InP nanoparticles were prepared using three different techniques. The first method utilized tetraethoxysilane (TEOS) as the silica source, resulting in the encapsulation of multiple InP nanoparticles within silica spheres. This approach caused a red-shift in the luminescence peak wavelength of the InP colloidal solution post-TEOS coating, compared to the original InP colloidal solution. Conversely, the second method employed tetramethoxysilane (TMOS), resulting in the formation of irregularly shaped silica-coatings on multiple InP nanoparticles, which reduced the red-shift in the luminescence peak wavelength of the silica-coated InP colloidal solution. The third method involved pre-coating InP nanoparticles with TMOS, followed by thickening the silica shells using TEOS. This technique successfully encapsulated multiple InP nanoparticles within silica spheres, maintaining the luminescence peak wavelength of the InP colloid solution post-coating with TMOS and TEOS nearly identical to that of the original solution. This method merged the advantageous outcomes of the first two methods. Additionally, silica spheres containing InP nanoparticles synthesized using both TMOS and TEOS exhibited the highest luminescence intensity. In summary, this study introduces a novel approach in nanoparticle engineering, enhancing the functional properties of InP nanoparticles and expanding their potential applications in optoelectronic devices.

Abstract: This study synthesized CaAl₂O₄:Eu²⁺ blue phosphors using the sol-gel method. The effects of incorporating citric acid, poly (oxyethylene) (PEG), and HCl in the precursor on the luminescent properties of phosphors were investigated. No significant changes were observed in the photoluminescence (PL) spectra of the phosphors when different precursor solutions were used. However, the use of PEG and citric acid led to a noticeable decrease in the PL intensity. Notably, the use of HCl resulted in an increase in PL. In addition, upon heating the phosphors from room temperature to 110 °C, the PL spectrum remained unchanged, whereas the PL intensity decreased linearly with increasing temperature. This indicated the suitability of CaAl₂O₄:Eu²⁺ for optical temperature-sensing applications.

Abstract: Experiments were carried out in which the luminescence of color centers in lithium fluoride crystals was excited by two different femtosecond lasers with significantly different energies, durations and pulse repetition rates. It was established that in all experiments the main center, the luminescence of which was excited nonlinearly, was the F₃⁺ color center. Unusual experimental data were obtained; a laser with low pulse energy (4 nJ) excited triplet luminescence of these centers (570 nm) but did not excite singlet luminescence (540 nm). Another laser with a higher pulse energy (0.3 mJ), on the other hand, excited singlet luminescence and did not excite triplet luminescence. A proposed diagram of energy levels and quantum transitions is presented, explaining the possible mechanisms of nonlinear excitation of luminescence in these experiments.

Abstract: Metal organic frameworks (MOFs) are three dimensionally arranged compounds of bridged organic ligands coordinately bonded with inorganic cluster. The large surface area with large pore volume of MOFs introduces wide application in catalysis field. With accurate combination of organic and inorganic bridging units we can alter the chemical, thermal stability as well as its porosity. Luminescence is the one of the most important properties exhibited by Metal organic frameworks (MOFs). This luminescent property of MOFs is highly sensitive for guest interaction due to which they are used in the detection of various toxic substances, organic pollutants. Based on their high sensitivity and selectivity they are applied in the field of sensors, different environmental applications, various clean energies, optoelectronic devices, medical and biological applications.

Abstract: Intense efforts are currently in progress to study various sources of basal plane dislocations (BPDs) in SiC epitaxial layers. BPDs can generate Shockley-type stacking faults (SSFs) in SiC epitaxial layers, which have been shown to be associated with the degradation of power devices. This study shows that the star-shaped defect can be a source of several BPDs in the epitaxial layer. We investigate the complex microstructure of the star defect, the generation of BPDs, and expansion of SSFs using various complementary microscopy and optical techniques. We show direct evidence that star-defects can be a nucleation point of single-SSFs that can expand at the core of the defect. Newly found secondary dislocation arrays extending over a few centimeters away are found to be emanating from the primary arms of the star defect. The presence of such dislocation walls and the expansion of single-SSFs will affect the yield of numerous die on a wafer. Further understanding of the formation mechanism of stacking faults generated from star-defects as provided in this study helps understand their effect on SiC-based devices, which is crucial to assess device reliability.

Abstract: The effect of alkali fluoride on the photoluminescence properties of Tb³⁺ doped on the phosphate glass was discovered. However, the composition of the glass samples were 20Li₂O–10AlF₃–69P₂O₅–1Tb₂O₃ (LAPTb) and 20Li₂O–10AlF₃–10NaF–59P₂O₅–1Tb₂O₃ (LANPTb). To study optical properties were examined through their absorption and luminescence spectra. Luminescence spectra were investigated by photoluminescence. Characteristic luminescence bands corresponding to electronic transitions of terbium ions (Tb³⁺) were detected under two direct excitations of Tb³⁺ ions. Upon 377 nm excitation, the glass samples were obtained transition terbium ⁵D₄ → ⁷F₅ at 544 nm showed a green laser. The decay time Tb³⁺ for the ⁵D₄ level has been confirmed and the result was 2.865 ms and 2.982 ms corresponding to LAPTb was LANPTb, respectively. The green laser application has been investigated by a CIE-color-coordinates diagram with a color purity is ~73%.

Abstract: Apatite nanocomposites with graphene (G) or graphene oxide (GO) nanoflakes, as well as with related carbonaceous materials, present promising applications in hard tissue engineering, biomedicine, or drug delivery. Different methodologies have been explored in the last years to prepare apatite-based nanocomposites. Sitting drop vapour diffusion (SDVD) methodology induces the heterogeneous nucleation of biomimetic apatite on the reinforcement material, improving biological properties of the nanocomposites. In this work SDVD was used to prepare G-apatite and GO-apatite nanocomposites. Prior to the SDVD experiments, G flakes were obtained by sonication-assisted liquid-phase exfoliation (LPE) using L-Alanine (L-Aln) as dispersing biomolecule, while a commercial aqueous Graphene Oxide (GO) dispersion was used for the nucleation essays in presence of the same biomolecules. A parallel set of nucleation experiments was performed in presence of Tb³⁺ ions, to endow the nanocomposites of luminescent properties. Characterization by XRD, FTIR, and TEM demonstrated the heterogeneous nucleation of needle-shaped apatite nanocrystals on the surfaces of G and GO flakes. Fluorescence spectroscopy certified the presence of Tb³⁺ ions in the nanocomposites resulting in luminescent materials which can be used in imaging or theragnostic. Finally, in vitro tests with human mesenchymal stem cells revealed excellent cytocompatibility and cell proliferation in presence of the nanocomposites.

Abstract: We report on the thermally-induced precipitation of gold plasmonic nanoparticles in phosphate and silicate glasses, doped with Eu³⁺ and Er³⁺ ions. We studied the structure and optical properties of glasses under the heat treatment below and above glass transition temperature. The heat treatment of the glass at temperatures above transition is shown to facilitate the formation of plasmonic gold nanoparticles and decrease near-infrared luminescence intensity of the ions. The formation of pre-plasmonic gold nanoparticles under the low-temperature heat-treatment leads to the increase of luminescence intensity through the energy transfer process. We showed that nanophase separation in silicate glasses allows precise tuning of localized surface plasmon resonance spectral position of gold nanoparticles and paves the way for the development of new glass-based materials for photonics applications.

Abstract: M₂SiO₄: Tb³⁺, Mn²⁺, Nd³⁺ (M = Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) phosphors suitable for near-ultraviolet-violet radiation excitation were successfully prepared at 1400 °C in N₂ atmosphere by a high-temperature solid-state reaction, and their phase compositions and luminescent performance were also studied by X-ray diffraction (XRD), photoluminescence spectra. Results show that their emission intensity increases in the order of Ca₂SiO₄ > Mg₂SiO₄ > Sr₂SiO₄ > Ba₂SiO₄ matrix phosphor. Ca_1.94SiO₄: 0.02Tb^{3 +}, 0.02Mn²⁺, 0.02Nd²⁺ phosphor exhibits the best luminescence performance.