Maximum Emission Intensity Research Articles

Local Bi–O bonds correlated with infrared emission properties in triply doped Gd2.95Yb0.02Bi0.02Er0.01Ga5O12 via temperature-dependent Raman spectra and x-ray absorption fine structure analysis

A correlation function between the Raman intensities and the nearest-neighbor mean-square relative displacement (MSRD) of local Bi–O bonds is successfully established based on x-ray absorption fine structure (XAFS) and temperature-dependent Raman spectra in the temperature range 77–300 K in amorphous and crystalline Gd2.95Yb0.02Bi0.02Er0.01Ga5O12. The structural symmetries of Gd2.95Yb0.02Bi0.02Er0.01Ga5O12 are described by using of local Bi–O bonds. More importantly, Gd2.95Yb0.02Bi0.02Er0.01Ga5O12 is found to show excellent infrared (IR) emission properties due to changes in Bi–O bonds, and the IR emission intensities are found to depend on , by using temperature-dependent photoluminescence spectroscopy. The maximum emission intensity at 1533 nm is obtained when at the lowest symmetry. This work shows that temperature-dependent Raman intensities can be used effectively to analyze the local covalent bonds around absorbing atoms as well as to study the emission properties of this visible-light-activated IR luminophor.

Intense 2.0 µm emission from Ho3+/Yb3+ co-doped Na5Lu9F32 single crystal excited by 980 nm

This paper reported on optical spectra of Na5Lu9F32 single crystals co-doped with ~ 0.91 mol% Ho3+ and various Yb3+ concentrations by using an improved Bridgman method. The emission spectra and fluorescence decay curves were measured to investigate the luminescent properties of the Ho3+/Yb3+ co-doped Na5Lu9F32 and the energy transfer process from Yb3+ to Ho3+ ion. Compared with the Ho3+ singly doped Na5Lu9F32 crystal, the Ho3+/Yb3+ co-doped crystal had an obviously enhanced emission at 2.0 µm via the 980 nm laser diode excitation because of the efficient energy transfer from Yb3+ to Ho3+ ion. The maximum emission intensity at 2.0 µm was obtained at about 6.99 mol% Yb3+ concentration when the concentration of Ho3+ ions is fixed at ~ 0.91 mol% in the current research. The maximum emission cross section of the above sample at 2.0 µm was calculated to be 1.23 × 10−20 cm2 according to the measured emission spectrum. The energy transfer efficiency from Yb3+:2F5/2 to Ho3+:5I6 for the crystal was estimated up to 90.8% indicating that Yb3+ ions can efficiently sensitize the Ho3+ ions.

Co-Precipitation Synthesis and Photoluminescence Properties of Sc<sub>0.88</sub>Lu<sub>0.05</sub>(V<sub>1-x</sub>P<sub>x</sub>)O<sub>4</sub>:Eu<sup>3+</sup><sub>0.07</sub> Red Phosphor for White Light Emitting Diodes

Sc0.88Lu0.05(V1-xPx)O4:Eu3+0.07(0≤x≤0.5) phosphors were synthesized by co-precipitation method. The structure, morphology and luminescence spectra of samples were investigated by XRD, SEM and fluorescence spectrophotometer, respectively. The samples doped with Eu3+, Lu3+and PO43-can maintain the body-centered tetragonal structure of ScVO4and the morphology essentially remains unchanged with slight agglomeration. The excitation spectrum intensity of Sc0.88Lu0.05(V1-xPx)O4:Eu3+0.07increase within the near UV excitation (360-410nm). The optimum doping concentration of PO43-is 0.2(x value), and the maximum emission intensity of Sc0.88Lu0.05(V0.8P0.2)O4:Eu3+0.07is about 35 % higher than the Sc0.88Lu0.05VO4:Eu3+0.07under 365 nm excitation. Decay curve of5D0state for as-prepared samples fits the single order exponential behavior, the lifetime of5D0increase first and then decrease with the increase of PO43-doping concentration. The internal quantum efficiency is up to 66.73% under 365nm excitation, When the temperature rises to 200°C, the emission intensity maintains 79.3% of that in the room temperature. Sc0.88Lu0.05(V0.8P0.2)O4:Eu3+0.07phosphor shows high internal quantum efficiency and thermal stability, which is suitable for the UV-pumped white LED as red phosphor.

Mechanistic insights into the urea-induced denaturation of kinase domain of human integrin linked kinase

Integrin-linked kinase (ILK), a ubiquitously expressed intracellular Ser/Thr protein kinase, plays a major role in the oncogenesis and tumour progression. The conformational stability and unfolding of kinase domain of ILK (ILK193–446) was examined in the presence of increasing concentrations of urea. The stability parameters of the urea-induced denaturation were measured by monitoring changes in [θ]222 (mean residue ellipticity at 222nm), difference absorption coefficient at 292nm (Δε292) and intrinsic fluorescence emission intensity at pH7.5 and 25±0.1°C. The urea-induced denaturation was found to be reversible. The protein unfolding transition occurred in the urea concentration range 3.0–7.0M. A coincidence of normalized denaturation curves of optical properties ([θ]222, Δε292 and λmax, the wavelength of maximum emission intensity) suggested that urea-induced denaturation of kinase domain of ILK is a two-state process. We further performed molecular dynamics simulation for 100ns to see the effect of urea on structural stability of kinase domain of ILK at atomic level. Structural changes with increasing concentrations of urea were analysed, and we observed a significant increase in the root mean square deviation, root mean square fluctuations, solvent accessible surface area and radius of gyration. A correlation was observed between in vitro and in silico studies.

Synthesis, characterization and aggregation-induced emission of alternating copolymers containing cyclophanes and tetraphenylethenes

The alternating copolymers containing tetraphenylethenes bonded to pseudo-para or pseudo-meta [2.2]paracyclophanes were synthesized by palladium catalyzed Suzuki-Miyaura cross-coupling reaction. Relatively high molecular weights of polymers were obtained by the reaction of their corresponding comonomers using Pd(OAc)2 as a catalyst with S-Phos as a ligand and K3PO4 as a base under a high base to monomer ratio. The maximum emission intensity of polymer in THF increases gradually as the addition of water fraction increases. The polymers exhibited aggregation-induced emission in aggregated state. In particular, the photoluminescence quantum yield of those tetraphenylethenes bonded to pseudo-meta [2.2]paracyclophanes is up to 0.334 when the water fraction reaches to 90%. The polymers used in the detection of 2,6-dinitrotoluene are more sensitive than that of small molecule containing the same conjugated segment of the polymers. They are promising candidates for potential uses in the optoelectronic applications.

Synthesis-temperature effect on the luminescence under light and UV excitation of Eu3+ doped lithium lanthanum borate phosphor

Eu3+ doped lithium lanthanum borate phosphors were prepared by the solid-state reaction with different temperature in the range of 400 – 700°C. Influence of preparing temperature on the phosphor structure and luminescence property were investigated. X-ray diffraction indicates the obvious structure of monoclinic Li3La2(BO3)3 and orthorhombic LaBO3 formed in powder. Li3La2(BO3)3 was constructed better with increasing of the synthesis-temperature between 500 – 700°C. For absorption spectra, phosphor can absorb more photons in visible light and near-infrared region with the synthesis temperature rising. Visible light with 394 nm and ultraviolet with 275 nm were used to monitor the emission spectra and the strongest emission at 613 nm wavelength was founded. Powders prepared at 600 and 700°C performed the maximum intensity of emission when they were excited with mentioned ultraviolet and visible light, respectively. This difference corresponds to the variation of Li3La2(BO3)3 and LaBO3 structure via thermal synthesis. Phosphor in this work is suitable for using in the ultraviolet-light converter, display, light source and performs an interesting potential for neutron-imaging application.

Luminescence study and Judd-Ofelt analysis of Nd3+ doped lithium lanthanum borate glass for green laser device

Lithium lanthanum borated glasses doped with Nd3+ (LiLaBNd) were synthesized to study in luminescence properties and laser potential. Refractive index, density and molar volume of glass increase with increasing of Nd3+ concentration. Glasses absorb photon in visible light and near- infrared region corresponding to energy transition from 4I9/2 ground state of Nd3+. Covalent nature and interaction between Nd3+ and ligand result to small red shift of Nd3+ energy level. The strongest emission with 1059 nm corresponds to 4F3/2→4I11/2 transition of Nd3+ under 808 nm excitation. The optimum concentration of Nd2O3 for this glass is 0.50 mol% which creates the maximum intensity of emission. Luminescence decay curve indicated cross relaxation process between Nd3+with low probability and life time value as 114 microsecond for 0.50 mol% doped glass. Judd-Ofelt analysis was used to evaluate several radiative parameters. Narrow effective bandwidth, high stimulated emission cross section and branching ratio indicated the advantage potential to develop LiLaBNd glass for using as laser medium in green emitting laser device.

Small Thermal Quenching, Narrow Green Emitting γ-AlON: Ce3+, Mn2+ Phosphor: Luminescence and Energy Transfer

A series of γ-AlON: Ce3+, Mn2+ phosphors were prepared via a high-temperature solid-state reaction. The phase formation and morphology, photoluminescence excitation and emission spectra, absorption spectra, lifetime, and thermal stability were investigated in detail. The γ-AlON: Ce3+, Mn2+ phosphor showed two emission bands under 285 nm excitation. The first broad band at 400 nm was attributed to Ce3+ ion emission, and the narrow band found at 517 nm was assigned to the Mn2+ ions. The critical distance of energy transfer from Ce3+ to Mn2+ has been calculated according to the concentration quenching method. The mechanism of energy transfer from Ce3+ to Mn2+ was of the resonance type and occurred via a dipole − dipole interaction. After doping Ce3+ in the γ-AlON matrix, the absorption, internal quantum, and external quantum efficiencies of γ-AlON: Ce3+, Mn2+ can be increased to 68.8%, 60.9%, and 41.9%, respectively. Furthermore, γ-AlON: Ce3+, Mn2+ exhibited superior thermal stability, with the emission intensity measured at 150°C maintaining 99% of the maximum emission intensity.

Luminescent Rhodamine 6G/silica hybrid nanofibers with potential temperature sensing ability

Photoluminescence properties of Rhodamine 6G dye confined in electrospun silica fiber are investigated in this manuscript. Uniaxial tensile test and environmental stability of such hybrid fibers are examined. Homogeneous distribution of Rhodamine 6G in silica fibers is confirmed by fluorescence image. Only J-type dimers are confirmed in our electrospun Rh6G/SiO2 hybrid fibers, and the increase of the Rh6G concentration gives rise to a progressive red shift and a broadening in the maximum emission spectra. The emission intensity of electrospun hybrid fibers can be sensitive to the temperature and the relative maximum emission intensity may decrease gradually in the whole measured temperature range.

Temporal and spatial dynamics of optical emission from laser ablation of the first wall materials of fusion device

Laser-induced breakdown spectroscopy (LIBS) has been developed to in situ diagnose the chemical compositions of the first wall in the EAST tokamak. However, the dynamics of optical emission of the key plasma-facing materials, such as tungsten, molybdenum and graphite have not been investigated in a laser produced plasma (LPP) under vacuum. In this work, the temporal and spatial dynamics of optical emission were investigated using the spectrometer with ICCD. Plasma was produced by an Nd:YAG laser (1064 nm) with pulse duration of 6 ns. The results showed that the typical lifetime of LPP is less than 1.4 μs, and the lifetime of ions is shorter than atoms at ∼10−6 mbar. Temporal features of optical emission showed that the optimized delay times for collecting spectra are from 100 to 400 ns which depended on the corresponding species. For spatial distribution, the maximum LIBS spectral intensity in plasma plume is obtained in the region from 1.5 to 3.0 mm above the sample surface. Moreover, the plasma expansion velocity involving the different species in a multicomponent system was measured for obtaining the proper timing (gate delay time and gate width) of the maximum emission intensity and for understanding the plasma expansion mechanism. The order of expansion velocities for various species is These results could be attributed to the plasma sheath acceleration and mass effect. In addition, an optimum signal-to-background ratio was investigated by varying both delay time and detecting position.

Structural, magnetic, and thermionic emission properties of multi-functional La1-xCaxB6 hexaboride

Herein, we report the synthesis of nanocrystalline La1-xCaxB6 (0 ≤ x ≤ 1) hexaboride powders by solid-state reaction and their subsequent consolidation via spark plasma sintering. The structural, magnetic and thermionic emission properties of La1-xCaxB6 hexaboride are investigated. All of the synthesized nanocrystalline hexaboride powders are single phase with the CsCl-type structure and no ferromagnetic impurity phases have been detected from X-ray diffraction. Magnetic measurements show that weak ferromagnetism at room temperature is found in nanocrystalline La1-xCaxB6 hexaboride powders, and the magnetism was attributed to the presence of the intrinsic defects, based on the data of the HRTEM. Thermionic emission measurements indicate that the maximum emission intensity for bulk La0.4Ca0.6B6 at 1873 K reached 20.02 A/cm2, which is more than three times higher as compared to bulk CaB6 (∼6.04 A/cm2). When the La doping was increased to 40 at%, the work function of CaB6 decreased from 2.95 to 2.76 eV, indicating an improvement in the thermionic emission performance. Therefore, the quasibinary La1-xCaxB6 hexaboride may have an application as a promising cathode.

Energy transfer based emission analysis of Eu3+ doped Gd2O3-CaO-SiO2-B2O3 glasses for laser and X-rays detection material applications

The Eu3+-doped CaO-Gd2O3-SiO2-B2O3 glasses were prepared to study photoluminescence, lasing potential and scintillation properties. Glasses absorb photons in ultraviolet, visible light and near infrared regions and are assigned to the energy transitions of Gd3+ and Eu3+. Ultraviolet with 275nm can generate the strong red emission with 614nm via energy transfer form Gd3+ to Eu3+. X-ray scintillation study exhibits strong emission pattern due to Gd-Eu energy transfer. The optimum concentrations of Eu3+ ion in this glass is 0.30mol% as it results maximum emission intensity. The fluorescence lifetime of the 5D0 level decreases from 1.763 to 1.726ms when concentration increased from 0.05 to 0.40mol%. From Judd-Ofelt analysis, this glass exhibit high potential for using as laser medium for red laser device with high lasing power and energy extraction ratio. Moreover, this glass performs the integral scintillation efficiency as 13% compared with BGO.

Using front-face fluorescence spectroscopy for prediction of retinol loss in milk during thermal processing

The objectives of the present study were to model the kinetics of retinol loss and assess the potential of predicting retinol loss during thermal processing using front-face fluorescence spectroscopy (FFFS). A factorial design with three different temperatures (70, 80 and 90 °C) and five heating times (0, 5, 10, 15 and 30 min) was used in this study. The kinetics of the retinol degradation process fitted well a first-order reaction. Further, several milk native fluorophores were selected as fluorescent markers for development of retinol prediction models such as tryptophan, dityrosine, Maillard intermediate compounds and riboflavin. The maximum emission intensities of the markers were used to evaluate the correlation of retinol concentration with fluorescent markers and to establish the corresponding prediction models of retinol concentration. Retinol concentration was significantly correlated (P < 0.05) with all the fluorescent markers. The optimum prediction model was obtained from 45 samples using three fluorescent predictors, with an R2 of 0.87. The results obtained are encouraging and suggest that FFFS, as a low-cost, rapid, direct and non-destructive technique, has the potential to replace existing conventional analytical techniques practiced for retinol evaluation in heat treated milk and be adopted by dairy industry.

Enhancing Upconversion Luminescence of LiYF4:Yb,Er Nanocrystals by Cd2+ Doping and Core–Shell Structure

In this work, we report a phenomenon that upconversion emission intensity of Er3+ was enhanced by cadmium. Cd2+ was taken with 0, 3, 10, 20, 30, and 40 mol % as a new dopant to codope LiY0.78Yb0.20Er0.02F4, meanwhile the doping effects on the crystal structure, morphology, and upconversion fluorescence emission are investigated by XRD, Rietveld refinement, TEM, and upconversion spectroscopy analysis methods in detail. The green upconversion emission intensity was enhanced, and the maximum emission intensities were enhanced to twice when 10 mol % Cd2+ was codoped into tetragonal LiYF4, while its decay lifetime was reduced. Additionally, we further designed the synthesis of the homogeneous LiYF4:20%Yb,2%Er,10%Cd@LiYF4 of which the emission intensity is 11 times higher than that of the Cd2+-free nanocrystals, meanwhile an intriguing morphology of core–shell nanocrystals was obtained. This investigation may be useful for the design and improvement of upconversion materials for fulfilling the prerequisite of t...

Temperature dependent photoluminescence of Dy3+ doped LiCaBO3 phosphor

A single phase white light emitting Dy3+ doped LiCaBO3 phosphors were prepared by solid-state reaction method at 700 °C. The crystal structure properties were analyzed by utilizing powder X-ray Diffraction and followed by the profile fitting to calculate the lattice parameters. The FESEM, UV–Vis, photoluminescence excitation and emission spectra, decay time and quantum yield measurement were utilized to characterize the samples. The temperature dependent photoluminescence emission and decay times were recorded in the temperature range 100–480 K. The phosphor exhibits two emission bands at 485 nm (blue) and 578 nm (yellow) originating from the f–f transition of Dy3+. The optimized doping concentration for maximum emission intensity was 2 mol%. A near white emission was achieved with color co-ordinate (0.35, 0.39) and CCT value 4955 K. The material had excellent thermal and color stability. The absolute quantum yield is 0.25. So the near white emission, excellent thermal stability and suitable quantum yield of LiCaBO3: Dy3+ can be a promising candidate for near UV–LED pumped white light emitting diode.

Red-Shifted Firefly Luciferase Optimized for Candida albicans In vivo Bioluminescence Imaging.

Candida albicans is a major fungal pathogen causing life-threatening diseases in immuno-compromised patients. The efficacy of current drugs to combat C. albicans infections is limited, as these infections have a 40–60% mortality rate. There is a real need for novel therapeutic approaches, but such advances require a detailed knowledge of C. albicans and its in vivo pathogenesis. Additionally, any novel antifungal drugs against C. albicans infections will need to be tested for their in vivo efficacy over time. Fungal pathogenesis and drug-mediated resolution studies can both be evaluated using non-invasive in vivo imaging technologies. In the work presented here, we used a codon-optimized firefly luciferase reporter system for detecting C. albicans in mice. We adapted the firefly luciferase in order to improve its maximum emission intensity in the red light range (600–700 nm) as well as to improve its thermostability in mice. All non-invasive in vivo imaging of experimental animals was performed with a multimodal imaging system able to detect luminescent reporters and capture both reflectance and X-ray images. The modified firefly luciferase expressed in C. albicans (Mut2) was found to significantly increase the sensitivity of bioluminescence imaging (BLI) in systemic infections as compared to unmodified luciferase (Mut0). The same modified bioluminescence reporter system was used in an oropharyngeal candidiasis model. In both animal models, fungal loads could be correlated to the intensity of emitted light. Antifungal treatment efficacies were also evaluated on the basis of BLI signal intensity. In conclusion, BLI with a red-shifted firefly luciferase was found to be a powerful tool for testing the fate of C. albicans in various mice infection models.

Whitening-dependent changes of fluorescence of extracted human teeth.

To evaluate in vitro the fluorescence properties of extracted human teeth whitened with 40% hydrogen peroxide. A total of 28 extracted human teeth were pumiced for 1 minute using a low-speed dental handpiece and a disposable rubber cup. Pre-whitening fluorescence measurements (T0), maximum excitation (Exmax ), maximum emission (Emmax ), and maximum intensity (Imax 108 ), were performed using a spectrofluorometer. After T0 measurements, the teeth were whitened using the in-office method with 40% hydrogen peroxide, three times for 20 minutes. The fluorescence parameters were measured under the same conditions 7 and 14 days after bleaching (T1 and T2, respectively). Exmax exhibited a broader range 7 days after whitening and decreased after 14 days. The Emmax and Imax 108 displayed a narrower range after whitening. The mean Exmax differed significantly between the time points (F = 20.09. P < .001). The corresponding analysis for the mean Emmax differed significantly between the time points (F = 16.69, P < .001). The same was true for the mean Imax 108 (F = 9.69, P < .001). Within the limitations of this study, whitening provoked statistically significant changes in fluorescence of the intact teeth in vitro. The appearance of human teeth and dental materials and their changes upon aging and exposure to different agents (staining, whitening) is a topic of great relevance to esthetic dentistry. While some appearance parameters, such as color, translucency, and gloss, have been thoroughly studied, fluorescence and its influence on overall tooth appearance is still not well understood, yet it has influenced the development of fluorescence emitting restorative materials.

Zn vacancies creation via (2 × 2) surface reconstruction

Zinc vacancies have been incorporated in ZnO via (2 × 2) surface reconstruction during the epitaxy growth. Evolution of in situ reflection high-energy electron diffraction (RHEED) patterns indicate Zn-polar surface (2 × 2) reconstruction was realized under extreme O-rich conditions. Atom sized triangular pits and islands were presented by the high resolution scanning tunneling microscopy (STM) images, which stand for a single Zn vacancy per (2 × 2) surface unit cell. The neutral acceptor-bound exciton (A0,X), peak located at 3.344 eV, and red luminescence (RL), maximum emission intensity at ~1.76 eV, which related to Zn vacancy, have been studied by variable-temperature/power steady-state photoluminescence (PL) spectroscopy.

Infrared spectroscopic characterization of Na5Lu9F32 single crystals doped with various Er3+ concentrations

This work reports on optical spectra of Na5Lu9F32 single crystals doped with various Er3+ concentrations from 0.5 to 5 mol%. In our improved Bridgman method, the X-ray powder diffractions were investigated and optical parameters were also calculated by the Judd–Ofelt theory. Results showed that Er3+ ions entered the Lu3+ sites successfully without causing any obvious peak changes, and the doping concentration of Er3+ had important influence on the Er3+ local structure in Na5Lu9F32 crystals. The maximum emission intensities of ~1.5 and ~2.7 μm were obtained in present research when the doping concentration of Er3+ were 4 and 5 mol%, respectively, under the excitation of 980 nm LD. In these doping concentration, the maximum emission cross-sections were calculated to be 1.37 × 10−20 cm2 (~1.5 μm) and 2.1 × 10−20 cm2 (~2.7 μm). The gain cross-section at 2.7 μm was also estimated according to the absorption and emission cross section spectra. All these spectroscopic characterizations suggested that this fluoride crystal would possess promising applications in infrared lasers.

Photoluminescence behaviour of cerium activated yttrium aluminium garnet intercalated PMMA composite thin films

In this study, 0.04 mol cerium (Ce) doped yttrium aluminum garnet (Y3Al5O12) nano phosphor particles were synthesized by co-precipitation. It was evaluated that precursor of Ce doped YAG (Ce:YAG) calcined at 1250 °C for 4 h had a mean size of ~80 nm and whereas sample calcined for 12 h had a mean size of ~260 nm. Mean size and morphology of the nanoparticles were characterized by X-ray diffraction and scanning electron microscopy. These Ce:YAG nanoparticles of two different sizes were suspended in PMMA and coated by airbrush method on the glass substrates of different grades of surface roughness. Photoluminescence (PL) behavior of these PMMA-Ce:YAG composite thin films was investigated and maximum emission intensity was observed in the samples having thickness 2.28–3.97 µm and 1.21–2.50 µm for 4 h and 12 h, respectively. It was found that the maximum PL emission intensity was noted at 523 nm for 2.7 µm thick coating having nanoparticles of mean size ~80 nm (calcined for 4 h) with spherical morphology. The surface roughness of coating was found to be 0.217 µm. The adhesion strength of PMMA-Ce:YAG film on glass substrate was investigated by pull off adhesion test technique and its estimated value was 1.13 MPa.