Increase In Luminescence Intensity Research Articles

Multifunctional Gd2O3:Tm3+, Er3+, Nd3+ particles with luminescent and magnetic properties

Development of novel materials with advanced properties is one of the main research directions of chemistry. New substances are not only crucial for many current technological applications but also should satisfy the needs of tomorrow. Industry often requires reliable, economically effective methods that can provide high quality reproducible results. Here we propose an inexpensive synthesis method that is suitable for synthesis of many types of particles. In this work we focused on Gd2O3:Tm3+, Er3+, Nd3+ particles with luminescence and magnetic properties. Based on the analysis of morphology, structural and optical properties of particles prepared by the standard Pechini methods and its variations, we found that the method with K2CO3 as additive yields particles with smaller sizes (down to tens of nm), higher crystallinity, and up to 1.7 times increased luminescence intensity. We also demonstrate that the unique combination of the particles’ characteristics, for example, the intensity ratio of the luminescent bands corresponding to different REI and the mass susceptibility, strongly depends on the composition, synthesis method, and structure. The variety of the combination of the properties makes these particles a promising candidate for safety markers applications.

IR luminescence of plexcitonic structures based on Ag2S/L-Cys quantum dots and Au nanorods.

The luminescence properties of Ag2S quantum dots passivated with L-Cysteine (Ag2S/L-Cys QDs) are studied in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs). The effect of plasmonic Au/CTAB NRs on IR trap state luminescence (750 nm) is considered. It has been found that the direct interaction between the components of the plexcitonic nanostructure leads to a significant luminescence quenching of Ag2S/L-Cys QDs, with the luminescence lifetime being constant. This is the evidence for photoinduced charge transfer. The spatial separation of the components of plexcitonic nanostructures due to the introduction of a polymer - Poly(diallyldimethylammonium chloride) (PolyDADMAC) provides a means to change their mutual arrangement and achieve an increase in the IR trap state luminescence intensity and a decrease in the luminescence lifetime from 7.4 ns to 4.5 ns. With weak plexcitonic coupling in the nanostructures [Ag2S QD/L-Cys]/[PolyDADMAC]/[Au/CTAB NRs], the possibility of increasing the quantum yield of trap state luminescence for Ag2S QDs due to the Purcell effect has been demonstrated.

Influence of Plasmonic Gold Nanoparticles on the Optical Properties of Oxide Glasses Doped with Rare-Earth Ions

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.

The structural and luminescence properties of plexcitonic structures based on Ag2S/l-Cys quantum dots and Au nanorods.

A technique of obtaining plexitonic structures based on Ag2S quantum dots passivated with l-cysteine (Ag2S/l-Cys QDs) in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs) with controlled luminescence properties has been developed. The structural and luminescence properties of Ag2S/l-Cys QDs with Au/CTAB NRs are studied. The effect of plasmonic Au/CTAB NRs on IR trap state luminescence (750 nm) is considered. It has been found that the direct interaction between the components of the plexcitonic nanostructure leads to a significant luminescence quenching of Ag2S/l-Cys QDs, with the luminescence lifetime being constant. This is the evidence for photoinduced charge transfer. The spatial separation of the components of plexcitonic nanostructures due to the introduction of a polymer – poly(diallyldimethylammonium chloride) (polyDADMAC) provides a means to change their mutual arrangement and achieve an increase in the IR trap state luminescence intensity and a decrease in the luminescence lifetime from 7.2 ns to 4.5 ns. With weak plexcitonic coupling in the nanostructures [Ag2S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs], the possibility of increasing the quantum yield of trap state luminescence for Ag2S QDs due to the Purcell effect has been demonstrated. In the case of formation [Ag2S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs] a transformation of shallow trap state structure was established using the thermostimulated luminescence method.

SiO2 Coated Up-Conversion Nanomaterial Doped with Ag Nanoparticles for Micro-CT Imaging.

In this study, a new method for synthesizing Ag-NaYF4:Yb3+/Er3+ @ SiO2 nanocomposites was introduced. Using a hydrothermal method, the synthesized Yb3+- and Er3+-codoped NaYF4 up-conversion luminescent materials and Ag nanoparticles were doped into up-conversion nanomaterials and coated with SiO2 up-conversion nanomaterials. This material is known as Ag-UCNPs@SiO2, it improves both the luminous intensity because of the doped Ag nanoparticles and has low cytotoxicity because of the SiO2 coating. The morphology of UCNPs was observed using scanning electron microscopy (SEM), and the mapping confirmed the successful doping of Ag nanoparticles. Successful coating of SiO2 was confirmed using transmission electron microscopy (TEM). Fluorescence spectra were used to compare changes in luminescence intensity before and after doping Ag nanoparticles. The reason for the increase in luminescence intensity after doping with Ag nanoparticles was simulated using first-principles calculations. The cytotoxicity of Ag-UCNPs@SiO2 was tested via the cell counting kit-8 (CCK-8) method, and its imaging ability was characterized using the micro-CT method.

Negative Thermal Quenching of Photoluminescence from Liquid-Crystalline Molecules in Condensed Phases

The luminescence of materials in condensed phases is affected by not only their molecular structures but also their aggregated structures. In this study, we designed new liquid-crystalline luminescent materials based on biphenylacetylene with a bulky trimethylsilyl terminal group and a flexible alkoxy chain. The luminescence properties of the prepared materials were evaluated, with a particular focus on the effects of phase transitions, which cause changes in the aggregated structures. The length of the flexible chain had no effect on the luminescence in solution. However, in crystals, the luminescence spectral shape depended on the chain length because varying the chain length altered the crystal structure. Interestingly, negative thermal quenching of the luminescence from these materials was observed in condensed phases, with the isotropic phase obtained at high temperatures exhibiting a considerable increase in luminescence intensity. This thermal enhancement of the luminescence suggests that the less- or nonemissive aggregates formed in crystals are dissociated in the isotropic phase. These findings can contribute toward the development of new material design concepts for useful luminescent materials at high temperatures.

Synthesis of rare-earth nanosized phosphors using microwave processing

Nanomaterials find permanently extending applications in various areas of life. In particular, nanosized phosphors can be used as pharmaceutical carriers capable of emitting ultraviolet or visible light that activates a photosensitizer, thus significantly expanding the possibilities of photodynamic therapy in the treatment of oncological, bacterial and viral diseases. The conditions required for the use of nanosized phosphors in medicine include their fine dispersion and effective luminescence in the red region of visible light spectrum upon stimulation by X-ray radiation of the range accepted for medical applications, particularly for diagnostic and therapeutic purposes in many diseases. The aim of this work was to study the effect of microwave treatment of Y2O3:Eu phosphors prepared by hydrothermal synthesis in ethylene glycol at 230 °C for 6 hours, involving the decomposition of mixed acetate. In order to reduce the aggregation and growth of the resulting particles, Aerosil A300 with average particle size 7 nm was added to the reaction mixture in the course of hydrothermal synthesis in the ratio 1:1 relating to the obtained phosphor. The microwave treatment was carried out at 800 °C for 5 minutes. The developed method provided Y2O3:Eu phosphor samples featuring with increased luminescence intensity in the region 610…700 nm compared to similar phosphors earlier prepared using the rapid thermal annealing (RTA) procedure.

From Structure to Luminescent Properties of B2O3-Bi2O3-SrF2 Glass and Glass-Ceramics Doped with Eu3+ Ions.

Glass-ceramics with the composition B2O3-Bi2O3-SrF2 were synthesized by the conventional melt-quenching technique and subsequent crystallization of the parental glasses. The temperature at which the ceramization was carried out was selected based on differential scanning calorimetry (DSC) analysis. The structure of the studied materials and the formation of SrF2 nanocrystals were confirmed by the Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. It was found that the amount of strontium fluoride introduced into the parental borate-bismuth glass has a significant impact on the growth of SrF2 nanocrystals. In particular, the influence of the crystalline SrF2 phase on luminescence intensity and kinetics was studied using Eu2O3-doped samples. An increase in luminescence intensity was observed in the samples in which SrF2 nanocrystals were formed. This is most likely related to the fact that some of the Eu3+ ions were (after annealing of the glass) located in the crystalline structure of strontium fluoride. This was confirmed both by the luminescence lifetime obtained based on the luminescence decay curves and the calculated Judd–Ofelt parameters, Ω2 and Ω4. The results achieved confirm that the glasses and glass-ceramics described in this work could be considered as a new phosphor for light-emitting diodes (LEDs).

Visible upconversion luminescence of doped bulk silicon for a multimodal wafer metrology.

We report the experimental observation of the UV-visible upconverted luminescence of bulk silicon under pulsed infrared excitation. We demonstrate that non-stationary distribution of excited carriers leads to the emission at spectral bands never to our knowledge observed before. We show that the doping type and concentration alter the shape of luminescence spectra. Silicon nanoparticles have a size between quantum-confined and Mie-type limits (10-100 nm) yet show increased luminescence intensity when placed atop a silicon wafer. The findings demonstrate that upconversion luminescence can become a powerful tool for nearest future silicon wafer inspection systems as a multimodal technique of measuring the several parameters of the wafer simultaneously.

Bosonic condensation of exciton-polaritons in an atomically thin crystal.

The emergence of two-dimensional crystals has revolutionized modern solid-state physics. From a fundamental point of view, the enhancement of charge carrier correlations has sparked much research activity in the transport and quantum optics communities. One of the most intriguing effects, in this regard, is the bosonic condensation and spontaneous coherence of many-particle complexes. Here we find compelling evidence of bosonic condensation of exciton-polaritons emerging from an atomically thin crystal of MoSe2 embedded in a dielectric microcavity under optical pumping at cryogenic temperatures. The formation of the condensate manifests itself in a sudden increase of luminescence intensity in a threshold-like manner, and a notable spin-polarizability in an externally applied magnetic field. Spatial coherence is mapped out via highly resolved real-space interferometry, revealing a spatially extended condensate. Our device represents a decisive step towards the implementation of coherent light-sources based on atomically thin crystals, as well as non-linear, valleytronic coherent devices.

One-Stage Formation of Two-Dimensional Photonic Crystal and Spatially Ordered Arrays of Self-Assembled Ge(Si) Nanoislandson Pit-Patterned Silicon-On-Insulator Substrate.

A new approach to improve the light-emitting efficiency of Ge(Si) quantum dots (QDs) by the formation of an ordered array of QDs on a pit-patterned silicon-on-insulator (SOI) substrate is presented. This approach makes it possible to use the same pre-patterned substrate both for the growth of spatially ordered QDs and for the formation of photonic crystal (PhC) in which QDs are embedded. The periodic array of deep pits on the SOI substrate simultaneously serves as a template for spatially ordering of QDs and the basis for two-dimensional PhCs. As a result of theoretical and experimental studies, the main regularities of the QD nucleation on the pre-patterned surface with deep pits were revealed. The parameters of the pit-patterned substrate (the period of the location of the pits, the pit shape, and depth) providing a significant increase of the QD luminescence intensity due to the effective interaction of QD emission with the PhC modes are found.

Down-Conversion Polymer Composite Coatings with Multipeak Absorption and Emission

Spectral adjustment is an effective method to increase light conversion efficiency of solar cells and to promote the growth of plants. Down-converter (DC) materials are considered to be one of the most effective methods of spectral modification. The focus of this work was to expand the spectral response range of down-conversion layers to achieve multipeak absorption and emission. Sr2CaMoO6:Sm,Na and YVO4:Bi,Eu, which have different excitation peaks in the UV-blue region and varied emission peaks in visible light regions, were prepared in this work. Sr2CaMoO6:Sm,Na can effectively produce red light at 648 nm upon excitation at 408 nm, while YVO4:Bi,Eu can produce red light at 618 nm upon excitation at 365 nm. Polymeric luminescent coatings with one single kind of phosphor were prepared separately before the two phosphors were mixed together in uniform polymer coatings. The two phosphors were also assembled in bilayer coatings with different concentrations. The results showed that high transmittances over 90% were achieved for the two composite coatings with the thickness of 20 and 30 μm. The increase in particle loadings from 1‰ to 4‰ slightly decreased coating transmittance but increased luminescence intensity. The increase in the ratio of Sr2CaMoO6:Sm,Na and YVO4:Bi,Eu from 5/1 to 10/1 resulted in high transmittance of the DC coatings, independent of total filler loadings (3‰ and 4‰) and coating thickness. The relative intensities of emission peaks can be adjusted conveniently by changing filler ratios. In addition, the transmittance and luminescent intensities of the coatings where the two phosphors were assembled in two layers were close to the uniform coatings, suggesting the negligible effect of UV light irradiation order. This work proved that the prepared coatings presented multipeak absorption and emission upon UV light excitation. These coatings can be expected to be applied in fields such as solar cells and agriculture greenhouses.

Tunable Optical Properties of Thin Films Controlled by the Interface Twist Angle.

Control of materials properties has been the driving force of modern technologies. So far, materials properties have been modulated by their composition, structure, and size. Here, by using cathodoluminescence in a scanning transmission electron microscope, we show that the optical properties of stacked, >100 nm thick hexagonal boron nitride (hBN) films can be continuously tuned by their relative twist angles. Due to the formation of a moiré superlattice between the two interface layers of the twisted films, a new moiré sub-band gap is formed with continuously decreasing magnitude as a function of the twist angle, resulting in tunable luminescence wavelength and intensity increase of >40×. Our results demonstrate that moiré phenomena extend beyond monolayer-based systems and can be preserved in a technologically relevant, bulklike material at room temperature, dominating optical properties of hBN films for applications in medicine, environmental, or information technologies.

Optical thermometry based on the thermal coupling of low-lying levels of Sm3+ in highly stable NaGdF4 glass ceramics

• β-NaGdF 4 :Sm 3+ glass ceramics with high silica content are fabricated. • Emission intensity of Sm 3+ is enhanced 4.5 times after crystallization. • Two processes based on a novel strategy are applied to temperature sensing. • The sensitivities are 1393/T 2 and 2823/T 2 for process A and B, respectively. Based on a new scheme of ground state thermal coupling, high sensitive temperature sensing has been realized in the Sm 3+ doped hexagonal NaGdF 4 glass with high thermal stability. Two processes were used to create a temperature sensor with a wide temperature operating range and high relative sensitivity. Under resonance excitation, Sm 3+ was directly populated to 4 G 5/2 from thermally activated 6 H 7/2 (process A) and 6 H 9/2 (process B) rather than ground state 6 H 5/2 . The increase in the anti-Stokes luminescence intensity from 4 G 5/2 with temperature was proposed to determine temperature. Relative sensitivity is 139,300/T 2 (%/K) at 303.6–570 K for process A and 282,300/T 2 (%/K) at 390–773 K for process B. The proposed approach not only effectively eliminates the heating effect caused by a laser and background Stokes-type scattering noise but also provides high quantum efficiency because of the one-photon excitation process. Combine the advantages of high thermal stability of glass and low phonon energy of fluoride, NaGdF 4 :Sm 3+ glass ceramics have considerable potential applications in fiber optic temperature sensing with a wide temperature range and high sensitivity.

Self-assembly-induced luminescence of Eu3+-complexes and application in bioimaging.

Design and engineering of highly efficient emitting materials with assembly-induced luminescence, such as room-temperature phosphorescence (RTP) and aggregation-induced emission (AIE), have stimulated extensive efforts. Here, we propose a new strategy to obtain size-controlled Eu3+-complex nanoparticles (Eu-NPs) with self-assembly-induced luminescence (SAIL) characteristics without encapsulation or hybridization. Compared with previous RTP or AIE materials, the SAIL phenomena of increased luminescence intensity and lifetime in aqueous solution for the proposed Eu-NPs are due to the combined effect of self-assembly in confining the molecular motion and shielding the water quenching. As proof of concept, we also show that this system can be further applied in bioimaging, temperature measurement and HClO sensing. The SAIL activity of the rare-earth (RE) system proposed here offers a further step forward on the roadmap for the development of RE light conversion systems and their integration in bioimaging and therapy applications.

Дефекты и некоторые физические свойства номинально чистых и легированных цинком кристаллов ниобата лития

The features of defect structure and their influence on the properties of LiNbO3:Zn crystals, doped in a wide concentration range, including two concentration thresholds (at ~ 3.0 and ~ 6.8 mol. % ZnO in the melt), were studied by absorption IR spectroscopy in the region of OH--group valence vibrations, photoluminescence in the visible region of the spectrum, and photoinduced light scattering. In LiNbO3:Zn(0.004-2.01 mol. % ZnO) crystals the increase of zinc concentration led to increasing in the OH--group concentration and decreasing the luminescence intensity of luminescence centers associated with NbLi defects. Apparently, the latter was connected with the formation of small energy levels near the bottom of the conduction band as the zinc atoms displaced niobium atoms from the lithium positions in the ideal structure and the NbLi defect concentration decreased, respectively. In highly doped LiNbO3:Zn crystals (4.46-6.5 mol. % ZnO) and in the LiNbO3stoich(6.0 wt. % K2O) crystal there were lower OH--group concentration, the increase of band gap by 0.3-0.4 eV, and the increase of luminescence intensity in the green region of the spectrum due to the formation of new recombination channels compared to weakly doped crystals. In addition, in such crystals, the increase of proton conductivity was observed due to increasing in the concentration of interstitial hydrogen H+ and, as a result, the formation of many small acceptor levels near the valence band.

Luminescence Properties by Li+-ion Modified Na4CaSi3O9: Dy3+ Phosphors

A series of blue-green emitting Na4CaSi3O9: Dy3+, yLi+ (NCSO) phosphors were successfully prepared by high temperature solid state reaction. The phase formation was confirmed by X-ray powder diffraction measurement. The emission spectra of NSCO phosphors were investigated. With the increase of Dy3+ ion concentration, the luminescence intensity increases, the optimal doping concentration of Dy3+ is x=0.04, and then the luminescence intensity decreases due to non-radiative energy transfer. Li+ as a charge compensation agent, influences the luminescence properties of NCSO phosphors. By Li+ doping into lattice and replacing Ca2+ to form negative charge vacancies, which reduce the charge imbalance in the matrix and thus reducing the stress on the matrix lattice, making the lattice more complete and luminous intensity improved. The investigation shows that NCSO:0.04Dy3+, 0.10Li+ phosphor package UV-LED chip could realize white LED.

Dual vis-NIR emissive bimetallic naphthoates of Eu-Yb-Gd: a new approach toward Yb luminescence intensity increase through Eu → Yb energy transfer.

Homo- and heteroligand mono-, bi-, and trimetallic lanthanide naphtoates EuxYbyGd1-x-y(naph)3(Phen)n (n = 0, 1) were obtained and thoroughly investigated. Homoligand naphthoates of the new phase were obtained as anhydrous powders from water. The photophysical properties of the obtained compounds were studied in detail. The first example of Eu-to-Yb energy transfer was found in these systems. Careful selection of the metal ratio allowed a dual vis-NIR emissive complex with a ytterbium quantum yield of 1.5% to be obtained.

Effect of terbium and silver co-doping on the enhancement of photoluminescence in CaSO4 phosphors

Abstract In this work, the photoluminescence properties of CaSO4 crystals co-doped with terbium and silver from silver oxide or silver nanoparticles (NPs) in different concentrations are investigated. Phosphors are obtained by means of a slow evaporation route and calcined at 600 °C for 1 h. X-ray diffraction analysis shows the formation of a single-phase anhydrite structure with orthorhombic symmetry. The photoluminescence properties are investigated using vacuum ultraviolet, ultraviolet and X-ray excitation. All luminescent measurements reveal the characteristic emissions of Tb3+. The analyses using excitation with ultraviolet light show that the Ag NPs are able to generate structural defects more satisfactorily compared to CaSO4:Tb with silver oxide. We also observe that higher concentrations of Ag increase the Tb3+ emission intensity, while higher concentrations of Ag NPs decrease it. The good stability of CaSO4 results in an efficient energy transfer from the host lattice to the activator under X-ray excitation, with the NPs contributing to the increase in luminescent intensity. Investigation of the terbium valence in the CaSO4 host shows a complete reduction of the Tb4+ present in Tb4O7 to Tb3+, as indicated by the X-ray absorption near edge structure. The vacuum ultraviolet excitation spectra reveal three broad bands, attributed to the charge-transfer excitations within SO42− complexes and to the 4f8 → 4f75d1 transitions on Tb3+. Our results also reveal that silver particles are responsible for generating deeper capture centers.

Luminescence intensity of vortex cavitation in a Venturi tube changing with cavitation number

Hydrodynamic cavitation in a Venturi tube produces luminescence, and the luminescence intensity reaches a maximum at a certain cavitation number, which is defined by upstream pressure, downstream pressure, and vapor pressure. The luminescence intensity of hydrodynamic cavitation can be enhanced by optimizing the downstream pressure at a constant upstream pressure condition. However, the reason why the luminescence intensity increases and then decreases with an increase in the downstream pressure remains unclear. In the present study, to clarify the mechanism of the change in the luminescence intensity with cavitation number, the luminescence produced by the hydrodynamic cavitation in a Venturi tube was measured, and the hydrodynamic cavitation was precisely observed using high-speed photography. The sound velocity in the cavitating flow field, which affects the aggressive intensity of the cavitation, was evaluated. The collapse of vortex cavitation was found to be closely related to the luminescence intensity of the hydrodynamic cavitation. A method to estimate the luminescence intensity of the hydrodynamic cavitation considering the sound velocity was developed, and it was demonstrated that the estimated luminescence intensity agrees well with the measured luminescence intensity.