Optical Materials: X最新文献

We report the optically stimulated luminescence (OSL) of natural alexandrite (BeAl₂O₄:Cr³⁺) from Brazil. Luminescence was stimulated using 470 nm blue, 525 nm green and 850 nm infrared light. The dose-response of the OSL is linear in all cases, a desirable feature of dosimetry applications. The influence of preheating on OSL suggests that electron traps associated with the thermoluminescence of alexandrite contribute to the OSL. Mechanisms responsible for luminescence in alexandrite have been briefly considered.

The influence of the synthesis method on both microstructure and morphological and electronic properties of CH₃NH₃PbI₃ (MAPbI₃) films prepared by different methods were investigated experimentally by Urbach energy and scanning electron microscopy (SEM) measurements, as well as computationally by Density Functional Theory (DFT) calculations.

This study was performed with samples prepared by three different methods including one step anti-solvent assisted spin coating and two-steps new approach that use a route in which in a first step a layer of the inorganic precursor (PbI₂) is deposited by conventional thermal evaporation and then in a second step the MAPbI₃ compound is formed through a reaction of the PbI₂ layer deposited in the first stage and a layer of the organic precursor methylammonium iodide (MAI) deposited by close spaced sublimation (CSS) and also by dipping in a MAI solution.

Improvement of luminescent thermometers requires not only the search for high-sensitivity thermometric outputs, but also availability of multiple thermometric parameters affording a combined and reliable response. We hereby detail for the first time the luminescence of Eu³⁺ in manganese tungstate (Eu³⁺:MnWO₄) solids obtained by coprecipitation under ultraviolet excitation and how this material provided an optical thermometric response from 77 K to 373 K via excitation and emission spectra. Processing of up to five thermometric parameters, namely bandwidths, band positions, band shifts and luminescence intensity ratios, resulted in relative thermal sensitivities as high as 1.56% K⁻¹ and temperature uncertainties between 0.01 and 2 K depending on the choice of the spectral parameter. In addition, we demonstrate that Eu³⁺:MnWO₄ also act as a qualitative colorimetric thermosensor because of progressive change of emission color to greenish-yellow to bluish-green upon heating under UV excitation. Therefore, our results show that the combination of broadband tungstate emissions with the 4f-4f narrow emissions of Eu³⁺ is an effective approach to achieve a multiparametric luminescent thermal response via emission, excitation and visual observation, which makes Eu³⁺:MnWO₄ a promising candidate for advanced thermometry applications.

The study is dedicated to investigation of the structural, luminescent and photoconversion properties of epitaxial converters based on the single crystalline films of Ce³⁺ doped Ca₃Sc₂Si₃O₁₂ (CSSG:Ce) garnet. These SCFs with different thicknesses were grown using the liquid phase epitaxy method onto: (i) undoped Gd₃Ga_2.5Al_2.5O₁₂ (GAGG (2.5)) substrates; (ii) Ce³⁺ doped Gd₃Ga_2.5Al_2.5O₁₂ (GAGG:Ce (2.5) and Gd₃Ga₃Al₂O₁₂ (GAGG:Ce (3) substrates. For the first time, we have examined the phosphor conversion properties of the mentioned film and film-crystal converters under the excitation of a blue LED. We have established a trend line in the color coordinate diagram by systematically varying the film thickness in the 2–30 μm, 17–22 μm and 7–22 μm ranges for CSSG:Ce film/GAGG (2.5) crystal, CSSG:Ce film/GAGG:Ce (2.5) crystal and CSSG:Ce film/GAGG:Ce (3) crystal composite converters, respectively.

In the present paper, we study the optical, electrical, and sensing properties of titanium dioxide (TiO₂) film deposited on glass plates using a vacuum coating technique (High Hind Vacuum). The optical properties were studied using UV–visible and the result found that the band gap of fabricated thin film is 3.3 eV. The structural properties of the deposited film have been explored by XRD. XRD measurement revealed that the crystallite size is 25.7 nm and it showed that the deposited film is anatase phase and nanometric range. The experimental work was done for the study of LPG sensing properties at 300 K in the laboratory. Results found that the TiO₂ film fast response/recovery time (91 s/180 s) and a maximum response of 29 % toward LPG.

A semi-empirical method is introduced to estimate the emission energy of the Mn⁴⁺ ion in fluorides and oxides without using spectroscopic data as inputs. The method is based on the calculation of the nephelauxetic function he at the octahedral crystal sites occupied by the Mn⁴⁺ cations in the considered host lattices. Only structural data are required for this calculation. The model reproduces the experimental emission energy of Mn⁴⁺ in 51 tested fluorides and 101 tested oxides within ±300 cm⁻¹ in 98% of the fluorides and within ±500 cm⁻¹ in 85% of the oxides. The accuracy is lowered as the he value, i. e. the covalency of the Mn–O bonding, is raised.

Cerium doped (Lu,Y)₂SiO₅ (or LYSO) single crystals have been studied by means of luminescence excitation spectroscopy in the temperature range from 7 up to 300 K. Vacuum ultraviolet excitations in 4.5–8 eV energy range from synchrotron radiation of 1.5 GeV storage ring of MAX IV synchrotron facility. It is shown that both type of Ce³⁺ emission centers (seven and six coordinated centers) are excited under any excitation energy used. It was concluded that the same energy transfer processes from host lattice to impurity ions are involved independently on coordination of Ce³⁺. It is also demonstrated that excitonic mechanism of energy transfer is dominant under chosen excitation and intrinsic and bound excitons are included in excitation of Ce³⁺ luminescence in LYSO.

Academic studies of imperfections in insulating crystals and glasses initially assumed the sites were simple and isolated. In part this was the result of the original simplistic characterisation and modelling. Unfortunately many textbooks, teaching and publications engrained this viewpoint. More detailed techniques invariably showed those ideas to be incorrect, with numerous examples of extremely long range interactions, multi-sites packages, and even phase separations or nanoparticle inclusions. Despite these examples, current defect models still often focus on extremely localised sites. This seems particularly inappropriate, as in many modern applications the materials are heavily doped, and in a powder format. It therefore seems essential to include, or reintroduce, analysis techniques which can reveal both the long range effects, and the variations that exist as a function of powder size and method of production. Where such data exist, they reveal considerable complexity. This overview thus comments on past and future analysis techniques with the sensitivity to enhance detailed models. Site models require, and will benefit from, a wider acceptance of medium and long range interactions. Realistically, many sites exist simultaneously, so models will never be perfect, but improved characterisation can assist not only the science, but also commercial developments. Inevitably there are self citations as we have actively exploited a range of techniques that can reveal evidence of long range defect production and sensitivity to extended lattice perturbations.

Doxorubicin (DOX) interaction with 2D boron nitride (BN) nanoparticles was studied experimentally and theoretically. The BN nanoparticles, namely nanoflakes, were obtained by direct liquid-phase exfoliation via preliminary stratification in a planetary ball mill from massive hexagonal BN. 2D BN nanoparticles and DOX/BN composites were characterized using visible steady-state, time-resolved fluorescence, FTIR and Raman spectroscopy, Coherent Anti-Stokes Raman Scattering (CARS) microscopy and density functional theory (DFT). The BN nanoflakes from 2 to 3 layers up to hundred nm in lateral direction possessed crystalline properties that formed the DOX/BN composites with fluorescence in the range of 520–750 nm that can be used in DOX detecting. The calculations revealed a notable electron transfer between the BN monolayer and the DOX molecule, which, however, is partly offset by the redistribution of charge within the monolayer. The energy of interaction of the BN with DOX was estimated as 1.96 eV, indicating that the DOX/BN composite formation is an exothermic process. The Fluorescence quenching of DOX/BN occurs with increased BN nanoparticle concentration. The optimal concentration for composite formation was chosen. In CARS imaging of the Lewis lung carcinoma cells after treatment with DOX/BN, brightly luminous points are observed inside the cells, indicating the accumulation of DOX/BN composites that can be used in bioimaging and theranostics.

The integration of highly transparent and highly conductive layers plays a crucial role in the advancement of various next-generation optoelectronic technologies. Here, we demonstrate a comparison of optical, electrical and wettability properties of Aluminum-doped Zinc Oxide (AZO) deposited by Atomic Layer Deposition Technique (ALD) with commercially available Fluorine-doped Tin Oxide (FTO) and Indium-doped Tin Oxide (ITO) Transparent Conductive Oxide (TCO) layers. Their impact on the electro-optical modulation behavior when applied in Liquid Crystal (LC) device assemblies are compared and discussed. The AZO layers performance prove that are fully competitive to the commercial FTO and ITO layers and verify the high demand for the next generation indium tin oxide (ITO)-free technology.