Photoluminescence Emission Measurements Research Articles

Tetracycline Removal through the Synergy of Catalysis and Photocatalysis by Novel NaYF4:Yb,Tm@TiO2-Acetylacetone Hybrid Core-Shell Structures.

Novel hybrid core-shell structures, in which up-converting (UC) NaYF4:Yb,Tm core converts near-infrared (NIR) to visible (Vis) light via multiphoton up-conversion processes, while anatase TiO2-acetylacetonate (TiO2-Acac) shell ensures absorption of the Vis light through direct injection of excited electrons from the highest-occupied-molecular-orbital (HOMO) of Acac into the TiO2 conduction band (CB), were successfully synthesized by a two-step wet chemical route. Synthesized NaYF4:Yb,Tm@TiO2-Acac powders were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, diffuse-reflectance spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence emission measurement. Tetracycline, as a model drug, was used to investigate the photocatalytic efficiencies of the core-shell structures under irradiation of reduced power Vis and NIR spectra. It was shown that the removal of tetracycline is accompanied by the formation of intermediates, which formed immediately after bringing the drug into contact with the novel hybrid core-shell structures. As a result, ~80% of tetracycline is removed from the solution after 6 h.

Graphene-based strontium niobate-zinc oxide heterojunction photocatalyst for effective reduction of hexavalent chromium

A hydrothermal technique was employed to synthesize a Sr2Nb2O7-rGO-ZnO (SNRZ) ternary nanocatalyst, in which ZnO and Sr2Nb2O7 were deposited on reduced graphene oxide (rGO) sheets. The surface morphologies, optical properties, and chemical states, of the photocatalysts were characterized to understand their properties. The SNRZ ternary photocatalyst was superior over the reduction of Cr (VI) to harmless Cr (III) compared to the efficiencies obtained using bare, binary, and composite catalysts. The effects of various parameters, including the solution pH and weight ratio, on the photocatalytic reduction of Cr (VI) were investigated. The highest photocatalytic reduction performance (97.6%) was achieved at pH 4 and a reaction time of 70 min. Photoluminescence emission measurements were used to confirm efficient charge migration and separation across the SNRZ, which improved the reduction of Cr (VI). A feasible reduction mechanism for the SNRZ photocatalyst is proposed. This study presents an effective, inexpensive, non-toxic, and stable catalyst, for the reduction of Cr (VI) to Cr (III) using SNRZ ternary nanocatalysts.

Nanodiamond-promoted white light emission in Eu, Dy, and Cu-containing phosphate glass: quantitative analysis and colorimetric study.

A thorough analysis of glass containing Eu2 O3 and Dy2 O3 , or Eu2 O3 , Dy2 O3 , and CuO melted together with nanodiamond powder was pursued based on measurements of optical absorption, photoluminescence (PL) emission and excitation spectra, and colorimetry. Nanodiamond facilitated the stabilization of Cu+ and Eu2+ ions with blue-emitting characteristics that, along with yellow-emitting Dy3+ and red-emitting Eu3+ led to the white light-emitting glass. Novel intensity notations implemented in intensity-based spectral ratios, and difference intensity correlation analysis were proposed for the assessment of PL properties. The chromaticity and correlated colour temperature of the emission were ultimately investigated as a two-parametric problem based on: (1) the different ionic components; and (2) the various excitation wavelengths employed. The optical analysis approach adds to the characterization methods to further fundamental understanding and provide helpful analytical tools for designing materials for tunable white light-emitting devices.

(Invited) Deep Level Defects in AlN Studied By UV-Visible Spectroscopy

Ultraviolet-visible (UV-Vis) spectroscopy was used to measure the optical absorption and emission from high-quality, 2-inch AlN substrates grown by physical vapor transport (PVT). Spatially uniform UV absorption coefficients below 20 cm-1 at 4.68 eV (265 nm) were demonstrated. The complementary spectroscopic data were used to elucidate the mechanism of UV absorption reduction in AlN containing high levels of the carbon impurity and co-doped with Si. Formation of a carbon-silicon defect complex, which shifted the absorption deeper in the UV, was demonstrated by photoluminescence (PL) emission and PL excitation (PLE) measurements. Additional deep levels in AlN related to cation vacancy complexes with oxygen were identified and discussed.

Ion irradiation-induced effects on optical and structural properties of Ge nanoparticles synthesized by laser ablation

We present here the effects of swift heavy ion irradiation on the optical and structural properties of Germanium (Ge) nanoparticles (NPs) synthesized by using laser ablation of bulk Ge wafer in liquids. The Ge NPs have been irradiated with 120 MeV Ag ions of various fluences ranging from 5 × 1012 to 1 × 1014 ions/cm2. The effect of ion irradiation on optical and structural properties of the Ge NPs has been studied with transmission electron microscopy (TEM), Raman scattering, and photoluminescence (PL) emission measurements. We have observed a decrease in the average size of the Ge NPs upon increasing the fluence of irradiation, amorphization at high fluence, and smaller NPs started to grow in the vicinity of larger sized NPs under ion irradiation. Therefore, the proper selection of fluence can be tuned to modify the existing NPs and synthesize new NPs. The NPs became amorphous at the higher fluence with the core remaining crystalline while the shell transformed into an amorphous phase. From Raman scattering results, the shift observed in peak position and the increase in the broadening in the Ge phonon vibrational peak indicates a reduction in NPs size. The PL emission is also blue-shifted upon increasing the irradiation fluence.

Broadening the excitation spectrum of BaMgAl10O17:Cr3+ using Eu2+ as a codopant

BAM:Eu is a very well known, commercial phosphor that is used for tricolor fluorescent lamps and plasma display panels. In recent years, Cr3+ doped BAM had been suggested as a phosphor for LED lamps for plant growth. However, excitation spectrum of Cr3+ is narrow. To overcome this problem, we have attempted co-doping by Eu2+. Eu2+ → Cr3+ energy transfer was observed in BaMgAl10O17:Eu2+,Cr3+ phosphor. The energy transfer was established by photoluminescence emission, excitation and lifetime measurements. Efficiency of the energy transfer is 40.2%. By virtue of this energy transfer, the excitation spectrum corresponding to Cr3+ emission covers a broad spectral region 340–430 nm. These phosphors were prepared by facile combustion synthesis which is a fast method. It is suggested that this phosphor will be useful for preparing LED lamps based on near ultraviolet, violet and blue chips.

Physical Investigations of Titanium Dioxide Nanorods Film Prepared by Hydrothermal Technique

In this work, well-oriented and homogeneous titanium dioxide (TiO2) nanorods (NRs) was synthesized by hydrothermal method. In this method, vertically aligned arrays of TiO2 were built on the conductive Fluorine–Tin–Oxide (FTO) glass substrate. Nanoparticles (NRs) of TiO2 showed a tetragonal shape with a square top face, according to the image of the field emission scanning electron microscope (FE-SEM). The TiO2 NRs are polycrystalline, having two phases: rutile and anatase, according to X-ray diffraction (XRD) analysis. The optical properties of a TiO2 nanorods arrays were examined, including transmittance, absorption coefficient, and energy bandgap. An optical energy band gap of 3.18 eV was obtained. According to the photoluminescence emission measurement, the energy bandgap was 3.3 eV. For further study of the optical properties of the TiO2 Nanorods films, reflectance spectrum was used as a function of wavelength to estimate the value of the energy bandgap and its value was 3.45 eV. By comparing the values ​​obtained from the three methods, it is found that they are closely alike, which confirms the formation of the TiO2 nanostructure.

Multiparametric luminescence thermometry from Dy3+, Cr3+ double activated YAG

The multiparametric luminescence thermometry with Dy3+, Cr3+ double activated yttrium aluminium garnet – YAG is demonstrated. Phospors were synthesized via Pechini method and their structure is confirmed by X-ray diffraction analysis. Mean crystallite size of powders was calculated to be ~22 nm. Morphology was investigated using scanning electron microscopy showing combination of dense, different size chunks constituted of spherical particles bellow 50 nm in size. Photoluminescence emission spectra of the Dy3+, Cr3+ double activated YAG consist of blue and yellow Dy3+ emissions and the broad, deep red Cr3+ emission. The decrease in the Dy3+ emission intensity with the increase in the Cr3+ content indicates the efficient energy transfer from Dy3+ to Cr3+ of ~90%. Temperature-dependant photoluminescence emission measurements are performed under 484 nm and 582 nm excitation in the steady-state domain and in the 175 K–650 K temperature range. The noted alterations of luminescence with temperature present an excellent base for studying the multiparametric temperature readouts. The luminescence intensity ratio, the most frequently exploited luminescent thermometry temperature readout method, was tested using: i) the combination of Dy3+ and Cr3+ emissions, ii) using the double excitation approach, and iii) using Cr3+ emission only, with relative sensitivities of 0.64 %K−1 at 175 K, 0.96 %K−1 at 200 K and 2.2 %K−1 at 200 K, respectively.

Structural and spectroscopic characteristics of Eu3+ embedded titanium lead phosphate glasses for red luminescence

A series of Eu3+ incorporated titanium lead phosphate glasses with the chemical compositions of 1 mol% Eu2O3+ xTiO2+(50–x)PbO+49P2O5 (where x = 1, 3 and 5) have been prepared by the melt quenching procedure. Structural investigations have been performed through XRD and FTIR spectra. Optical properties are investigated by absorption, excitation, photoluminescence emission, decay lifetime and CIE chromaticity measurements. Using absorption transition from 7F0 and 7F1 levels, the nephelauxetic ratio (β) and bonding parameter (δ) are estimated to determine the type of bonding between Eu3+ ions and the surrounding ligands. The absorption as well as the excitation spectra show that the band at 393 nm corresponding to 7F0 → 5L6 transition is very strong. Upon excitation at 393 nm, Eu3+ embedded titanium lead phosphate glasses exhibit maximum emission intensity for 5D0 → 7F2 transition at 611 nm which emits red color. Using Judd-Ofelt (JO) theory, the JO parameters Ω2, Ω4 and Ω6 have been estimated from the absorption and these parameters follow the trend of Ω2>Ω4>Ω6 for all glasses. These JO parameters are used to predict the branching ratio (βR), radiative transition probability (AR), stimulated emission cross-section (σPE) and radiative lifetime (τR). The larger value of spontaneous emission cross-section, suggests that the present glass samples are encouraging materials for Eu3+ embedded optical amplifiers and laser materials. Using the decay profile which shows single exponential, the luminescence decay lifetime of Eu3+ ions for the 5D0 metastable state is evaluated. The fluorescence quantum efficiencies have been evaluated which indicate that the values may be enhanced with the increase of titanium dioxide (TiO2) in the glass matrix. The color purity (CP) of the red emission and correlated color temperature (CCT) of these samples are calculated using the CIE (Commission Internationale de l’Eclairage) chromaticity diagram. Our investigation reveals that the present glasses may be utilized as red luminescent materials and red laser source for 5D0 → 7F2 emission at 611 nm.

Titanate Tubular Loaded Diatom Fabricated by a Facial Hydrothermal Method for Photocatalytic Enhancement under Visible Light Irradiation

In this study, homogeneous titanate tubular (TNT) and diatom/TNT composites (D/TNT) were prepared by a facile hydrothermal method. The crystalline structure and morphology of the synthesised samples were studied by X-ray diffractometry (XRD), Raman spectroscopy, Transmission Electron Microscopy (TEM). Furthermore, the photocatalytic activity for degradation of methylene blue (MB) was investigated under sunlight irradiation. The results showed that the MB degradation by D/TNT was higher than bare TNT. Optical properties of the synthesized materials with enhanced photocatalytic activity could be explained through both UV-vis diffuse absorption and photoluminescence emission measurement. These results indicated that there was bandgap narrowing and longer carrier lifetime in the composite sample.

Structural, mechanical, thermal and optical properties of NaCl:Ce3+ single crystals grown in large size by the Czochralski method

NaCl:XCe3+ crystals (with X = 0.0 (pure NaCl), 0.001, 0.003, 0.005, 0.006, 0.008 and 0.01) have been grown in large size by using the resistance heating Czochralski method and characterized structurally, mechanically, thermally and optically by carrying out X-ray diffraction (XRD), micro-hardness, thermal stress, optical absorption, photoluminescence (PL) emission, photoluminescence excitation (PLE), thermo-luminescence (TL) and decay time measurements. XRD analysis indicates compression of the NaCl host lattice due to incorporation of Ce3+ ions. Hardness analysis has confirmed that Ce3+ doping improves the hardness of NaCl crystal in proportion with the Ce3+ concentration. Thermal stress analysis indicates that the grown crystals are of high quality. Optical absorption spectra obtained for the Ce3+ doped crystals have illustrated the presence of four peaks at 203, 215, 223, 303 and 414 nm. The Ce3+ doping has been found to influence the excitation and emission peaks due to Ce3+ (4f↔5d) transitions. The TL glow curves obtained show one sharp peak located at about 145 °C; the peak at 120 °C becomes prominent on bleaching with F-light after irradiation. The luminescence decay time has been found to gradually decrease with the increase in Ce3+ concentration. The PL and TL performances have been found to be maximum for the NaCl:0.008Ce3+ crystal. The present study indicates that the NaCl:Ce3+ crystals grown can be considered as promising materials for their use in dosimetry and scintillation applications.

Fabrication and scintillation characterizations of high concentration Ce[formula omitted] doped BaF2 transparent ceramic

In this study, high concentration (5 mol%) of cerium doped barium fluoride transparent ceramic was fabricated by hot pressing method t a temperature of 1200 °C under 30 MPa. XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), PLE (Photoluminescence Emission) measurements was used to investigate the phase composition, microstructure as well as photoluminescence properties of Ce3+: BaF2. XEL (X-ray Excited Luminescence) and pulse height spectrum were used to investigate the scintillation properties of this ceramic. The phase composition and microstructure analyses showed that the Ce3+: BaF2precursor nanoparticles prepared by the co-precipitation method were uniform and have a average size of 25 nm. The highest transmittance of the ceramic was 77% at the wavelength of 2300 nm. The PL (photoluminescence) spectrum showed that the 5d–4f transition of Ce3+: BaF2 transparent ceramic is located at 340 nm. X-ray excited luminescence exhibited only one violet peak at 392 nm. Scintillation decay time measurements showed only a slow component of 437 ns under 662 keV gamma excitation.

Controlling Microarray Feature Spreading and Response Stability on Porous Silicon Platforms by Using Alkene-Terminal Ionic Liquids and UV Hydrosilylation.

In an attempt to develop reversible sensors based on ionic liquid/porous silicon (IL/pSi) platforms, we introduce an approach using task-specific, alkene-terminal ILs (AT-ILs) for direct grafting to the hydrogen-passivated as prepared-pSi (ap-pSi) surface via UV-hydrosilylation to address previous shortcomings associated with IL pattern impermanence (i.e., spread). By employing photoluminescence emission (PLE) and Fourier-transform infrared (FT-IR) imaging measurements, we demonstrate that the covalent grafting of AT-ILs onto the ap-pSi surface via photochemical hydrosilylation not only mitigates such feature spreading but also greatly improves PLE pattern stability. Significantly, we have discovered that, upon hydrosilylation, the resulting contact pin printed IL features remain stable to repeated challenges by toluene vapors, demonstrating the utility of AT-IL hydrosilylation for producing high-fidelity microarray features on pSi toward robust optical sensory microarrays.

The effect of Gd3+ doping on luminescence properties of (Gd, Ce): SrF2 nanopowders and transparent ceramics

The effect of doping of Gd3+ ions into Ce: SrF2 on luminescence properties was investigated in (Gd, Ce): SrF2 nanoparticle powders synthesized via the co-precipitation method, which contained fixed amount of Ce3+ ions and variable amounts of Gd3+ ions. (Gd, Ce): SrF2 nanoparticle powders showed UV range emissions under λex = 273 nm and λex = 298 nm excitation. Photoluminescence emission, excitation, and lifetime measurements revealed the existence of Ce3+ → Gd3+ radiative energy transfer and provided evidence to the prevailing effect of Ce3+ in excitation and emission in the (Gd, Ce) co-doped system due to the existence of fully allowed 4f-5d transitions. The presence of Gd3+ was shown to affect the crystal field and symmetry around Ce3+ ions and enhances the absorption efficiency by two-fold. Furthermore, (Gd, Ce): SrF2 transparent ceramics with 13.2% of in-line optical transmittance in the UV spectral range was obtained via the vacuum hot-pressing method. The increase in the UV luminescence emission intensity of Ce3+ in presence of Gd3+, as well as the ability to process (Gd, Ce): SrF2 as transparent ceramics, are what make (Gd, Ce): SrF2 a promising material for optical applications in the UV region.

Effect of Eu3+ ion concentration on the structural and photoluminescence properties of Ba1.3Ca0.7SiO4 ceramic-based red phosphors for solid-state lighting applications

In this study, Ba1.3Ca0.7SiO4: Eu3+ red-orange phosphors were synthesized by the solution combustion method. The effect of varying Eu3+ molar percentages on the material properties including its intrinsic quantum efficiency (IQE) was investigated. XRD results showed synthesized phosphor is hexagonal T-phase Ba1.3Ca0.7SiO4 and the average crystallite size calculated using the Scherer’s formula was estimated to be ∼33 nm. SEM result showed the synthesized Ba1.3Ca0.7SiO4: Eu3+ phosphor had granular shaped and slightly agglomerated particles. The EDS shows that prepared samples contain Ba, Ca, Eu, Si, and O as expected. UV–vis measurement confirms the percent reflectance in the UV- region to be dependents on Eu3+ ions and the estimated bandgap vary between 3.80 and 4.23 eV. Photoluminescence emission measurements of all prepared samples at room temperature appeared to be entirely from inter configurational Eu3+ emission and depend both on the site symmetry as well as ion concentration. Hence, the peak centred at 592 nm is due to transition 5D0 →7F1, while the peak centred at 615 nm is due to transition 5D0 →7F2. The quadrupole-quadrupole multipolar interaction was found to be exclusively responsible for luminescence quenching. The Judd-Ofelt intensity parameters (Ω2, Ω4), asymmetry ratio (R0), and average decay lifetime of the nanocrystals showed dependence on concentration. High IQE values were obtained at low Eu3+ ion concentrations but the efficiency decreased with increasing ion concentration. The CIE color coordination confirmed that the emitted color fall in the strong orange-red region of the emission spectrum.

Electrochemical deposition of p-type β-Ni(OH)2 nanosheets onto CdS nanorod array photoanode for enhanced photoelectrochemical water splitting

In this study, a novel three-dimensional (3D) CdS@Ni(OH)2 nanorod array (NRA) photoanode with a type-II band alignment and a p-n junction has been designed and constructed via a simple electrochemical deposition of hierarchical β-Ni(OH)2 nanosheets onto the surfaces of the CdS NRAs. The 3D CdS@Ni(OH)2 NRA photoanode fabricated under the optimal deposition current exhibits remarkably improved photoelectrochemical water splitting performance, and obtains a photocurrent density of up to 1.1 mA/cm2, 5-fold that of the pure CdS NRA photoanode. Most importantly, the solar-to-hydrogen conversion efficiency of the 3D CdS@Ni(OH)2 NRA photoanode is 3.3-fold higher than that of the pure CdS NRA photoanode at 0.67 V vs. RHE. The electrochemical and photoluminescence emission measurements confirm that the enhanced PEC water splitting capability of the prepared 3D CdS@Ni(OH)2 NRA photoanode is attributed to the efficient charge separation, which is achieved by the synergistic action of the type-II energy alignment and the p-n junction.

Synthesis and luminescence properties of novel NaSCN: xCe3+ phosphor

ABSTRACTThe blue-emitting novel phosphor NaSCN: xCe3+(x = 0.005,0.01,0.02) is reported here for the first time. The synthesis method is simple, time saving, and cost effective. X-ray power diffraction (XRD) analysis confirmed the formation of said phosphor, and SEM images were recorded for the surface morphology. Photoluminescence emission (PL) and excitation (PLE) measurements were also recorded. Variations in emission intensity with the Ce3+concentration were observed and recorded leading to determination of the critical concentration. The concentration quenching observed in this phosphor is due to mainly electric multipole interaction. The CIE1931 color co-ordinates and the critical distance were determined.

Luminescence of Ce-doped aluminophosphate glasses

The effects of BaO network modifier on the structure, optical properties and luminescence of Ce-doped aluminophosphate glasses were investigated. Glasses were prepared by the melt quenching method in air with different chemical compositions: 50 or 60 mol% P2O5 + 5, 15 or 25 mol% SiO2 + 4–19 mol% BaO + 15 mol% Al2O3 + 1–6 mol% Ce2O3 such the total summed up to 100 mol%. Density was determined to be within 2.7–3.0 g/cm3, while the index of refraction was estimated using the Gladstone-Dale relation using the experimentally-obtained density values to be around 1.48. For each glass series, Raman spectra varied according to the BaO and/or Ce2O3 content. For 1 mol% Ce-doped glasses, the ultraviolet (UV) transparency cutoff was within 317–328 nm, with the cutoff wavelength increasing to 367–373 nm for 6 mol% doped glasses. Scintillation was characterized by radioluminescence (RL) measurements under X-ray excitation, and luminescence by photoluminescence emission (PL), excitation, and fluorescence lifetime measurements. PL and RL results showed a broad band centered around 3.3–3.6 eV with a fluorescence lifetime of about 30 ns. The highest RL output was observed from the 60P2O5·14BaO·5SiO2·15Al2O3·6Ce2O3 glass.

Ultrahighly-efficient and pure deep-blue thermally activated delayed fluorescence organic light-emitting devices based on dimethylacridine/thioxanthene-S,S-dioxide

A novel deep-blue emissive dopant material, 2,7-bis(9,9-dimethylacridine-10(9H)-yl)-9,9-diphenyl-9H-thioxanthene 10-,10-dioxide (DMA-ThX), is synthesized for use in highly-efficient thermally activated delayed fluorescence organic light-emitting devices (TADF OLEDs). The molecular design of DMA-ThX retains the overlap between the lowest singlet excited state (S1) and the lowest triplet excited state (T1) because of its twisted molecular structure. From photoluminescence emission measurements at low temperature, the difference between the S1 and the T1 energy levels of DMA-ThX is found to be 0.07 eV. Furthermore, the external quantum efficiency of the deep-blue-emitting TADF OLEDs with DMA-ThX-doped bis[2-(diphenylphosphino)phenyl] ether oxide is 18.4%, which is significant, and the Commission Internationale de l'Eclairage coordinates are (0.14, 0.14), indicative of very pure deep-blue emission.

Interconnected ZnO branches as an effective electron transfer layer in perovskite solar cells

In this paper, ZnO nanobranches are successfully synthesised by a simple solution-based process and served as electron transport layer in perovskite solar cells (PSC). The structure and chemical composition of the synthesized ZnO branches and nanowires were characterised by using a scanning electron microscopy equipped with an energy dispersive spectroscopy. Also the X-ray diffraction measurements and photoluminescence emission measurements were performed to gain understanding of the crystal phase and quality of the samples. The proposed ZnO nanobranches outperforms conventional vertically aligned ZnO nanowire by almost 85% due to the enhanced charge collection and reduction in structural defects from the second annealing process.