Intense Emission Band Research Articles

Tailoring the Luminescent Properties of SrS:Ce3+ by Sr-Deficiency and Na+ Doping.

Ce3+-doped SrS phosphors with a charge-compensating Na+ addition were successfully synthesized via a solid-state reaction method, and the related X-ray diffraction patterns can be indexed to the rock-salt-like crystal structure of the Fm3̅m space group. SrS:(Ce3+)x (0.005 ≤ x ≤ 0.05) and SrS:(Ce3+)0.01,(Na+)y (0.005 ≤ y ≤ 0.030) phosphors were excited by 430 nm UV-Vis light, targeted to the 5d1 → 4f1 transition of Ce3+. The composition-optimized SrS:(Ce3+)0.01, (Na+)0.015 phosphors showed an intense broad emission band at λ = 430-700 nm. The doping of Na+ was probed by solid-state nuclear magnetic resonance. The 430 nm pumped white light-emitting diode structure fabricated with a combination of SrS:(Ce3+)0.01,(Na+)0.015 and Sr2Si5N8:Eu2+ phosphors shows a color-rendering index (Ra) of 89.7. The proposed strategy provides new avenues for the design and realization of novel high color quality solid-state LEDs.

Local structure, spectroscopic properties and intrinsic photoluminescence of the un-doped lead-containing glasses of different composition

The X-ray diffraction, infrared transmission, optical absorption, photoluminescence spectra and decay kinetics of a series of un-doped Pb-containing glasses with compositions of 0.4PbO–0.6GeO2, 0.6PbO–0.4SiO2, 0.7PbO–0.3B2O3, and 0.54PbO–0.34B2O3–0.12GeO2 were studied. Average interatomic distances and coordination numbers for main structural units GeO4, SiO4, BO4, BO3, and PbOn (n = 3 – 6) in all studied glasses were derived from radial distribution functions. The 0.4PbO–0.6GeO2 and 0.54PbO–0.34B2O3–0.12GeO2 glasses upon UV photoexcitation show intense broad emission bands with maxima at 478 and 543 nm, respectively, and weaker broad band with peak about 610 nm. Based on luminescence decay kinetics analysis were proposed fast (band-to-band recombination) and slow (recombination with participation of point defects) mechanisms of intrinsic luminescence in the 0.4PbO–0.6GeO2 and 0.54PbO–0.34B2O3–0.12GeO2 glasses. The 0.6PbO–0.4SiO2 and 0.7PbO–0.3B2O3 glasses under UV – violet photoexcitation reveal only broad emission band with a maximum at 599 and 593 nm, respectively, caused by the band-to-band fast recombination mechanism.

Role of Guest Materials in the Lower Stability of Solution-Coated versus Vacuum-Deposited Phosphorescent OLEDs.

Utilizing different phosphorescent materials as emitter guests, this work investigates the root causes of the lower electroluminescence (EL) stability of solution-coated (SOL) organic light-emitting devices (OLEDs) relative to their vacuum-deposited (VAC) counterparts. The results show that emitter guest molecules aggregate under electrical stress, leading to the emergence of new longer-wavelength bands in the EL spectra of the devices over time. However, the intensity of these aggregation emission bands is much stronger in the case of SOL host:guest systems than that of their VAC counterparts, indicating that guest aggregation occurs much faster in the former. The results reveal that the phenomenon arises from differences in the initial morphologies and are likely associated with the use of solvents in the solution-coating process. Moreover, although excitons can drive this aggregation in the case of SOL emissive layer (EML) devices, the coexistence of excitons and polarons accelerates this phenomenon significantly. The results uncover one of the main causes of the lower stability of OLEDs made by solution coating and reveal the importance of adopting new molecular designs that make them less susceptible to aggregation for the development of SOL OLEDs with high performance.

Ferroelectric and Spectroscopic Properties of Ho3+/Yb3+ Co-Doped Pb(Mg1/3Nb2/3)O3-32PbTiO3 Crystal

In order to design a new multifunctional crystal with excellent ferroelectric and spectroscopic properties, experiments were carried out for Ho3+/Yb3+ co-doped Pb(Mg1/3Nb2/3)O3 -32PbTiO3 ferroelectric crystal using the flux method, the coercive field Ec of which is 11.86 kV/cm. Up-conversion luminescence emission bands, including an intense green emission band at 553 nm, a red band at 663 nm, and a weak infra-red band at 755 nm, are generated at 980 nm excitation. The main spectroscopic parameters, including radiative transition probability A(J′ − J), radiative lifetimes τrad, and branching ratios β, were predicted by applying Judd–Ofelt treatment. The obtained J-O intensity parameters are Ω2 = 0.531 × 10−20 cm2, Ω4 = 1.738 × 10−20 cm2, Ω6 = 0.530 × 10−20 cm2. The radiative lifetime of 5I7 level is 5.45 ms. The fluorescence lifetime of is 5F5 is 92.568 μs. The investigations show that Ho3+/Yb3+ co-doped Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 crystal is a new type of multifunctional crystal integrating ferroelectric and spectroscopic properties, which has a potential application in the developing innovative multifunctional devices and lasers.

Study on luminescence properties of Ce3+ and Eu3+ ions in a nanocrystalline hexagonal Zn4Al22O37 novel system

The present communication is strongly focused on the investigation of synthesis, structural and luminescence properties of cerium (Ce3+ )- and europium (Eu3+ )-activated Zn4 Al22 O37 phosphors. Ce3+ - and Eu3+ -doped Zn4 Al22 O37 novel phosphors were prepared using a solution combustion synthesis route. Structural properties were studied using powder X-ray diffraction and high-resolution transverse electron microscopy. The optical properties were studied using ultraviolet-visible light spectroscopy and Fourier transform infrared spectroscopy; luminescence properties were studied using a photoluminescence (PL) technique. The crystal structure of the prepared Zn4 Al22 O37 host and Ce3+ - and Eu3+ -activated Zn4 Al22 O37 phosphors was investigated and was found to have a hexagonal structure. The measured PL emission spectrum of the Ce3+ -doped Zn4 Al22 O37 phosphor showed an intense and broad emission band centred at 421 nm under a 298 nm excitation wavelength. By contrast, the Eu3+ -doped Zn4 Al22 O37 phosphor exhibited two strong and intense emission bands at approximately 594 nm (orange) and 614 nm (red), which were monitored under 395 nm excitation. The Commission Internationale de l'Eclairage (CIE) colour coordinates of the Ce3+ -doped Zn4 Al22 O37 were investigated and found to be x = 0.1567, y = 0.0637 (blue) at 421 nm and for Eu3+ -doped Zn4 Al22 O37 were x = 0.6018, y = 0.3976 (orange) at 594 nm and x = 0.6779, y = 0.3219 (red) at 614 nm emission. The luminescence behaviour of the synthesized phosphors suggested that these phosphors may be used in lighting applications.

Excitation of L-valine molecules by electrons and photons.

Excitation of L-valine molecules was studied by optical spectroscopy. Optical emission spectra of the L-valine molecule and optical excitation functions of molecular bands and the Hβ spectral line were measured in the gas phase using electron impact. In the spectra of optical emission in the wavelength range of 250–500 nm, intense emission bands were found at energies of incident electrons of 30, 50 and 70 eV. Analysis of structural features of the valine molecule suggested a fragmentation scheme with the formation of excited particles in collisions with electrons. A notable feature of the presented optical excitation functions is a different growth dynamics with an increase in the energy of exciting electrons and the presence of a number of features and kinks, which are especially pronounced for λ = 305 nm and λ = 311 nm. The excitation thresholds were determined from the initial sections of the excitation functions of the most intense spectral lines by the least-squares method. The photoluminescence spectra of L-valine were measured for the first time on a Shimadzu RF-6000 spectrofluorophotometer in the spectral range of 400–800 nm for excitation wavelengths of 250, 275, 333, 351, and 380 nm.Graphical abstract

Changes in the titanium oxide optical properties during crystallization

Crystallization of amorphous titanium oxide films synthesized by magnetron sputtering was carried out at temperatures of 700, 800, and 900oC in an oxygen atmosphere. The refractive index of the films increases during crystallization with a time constant that depends on temperature, which made it possible to determine the activation energy of the crystallization process on the order of 0.6 eV. The growth kinetics model for the titanium oxide nanocrystals, which is used in this work, showed that the indicated activation energy corresponds to the diffusion energy of oxygen vacancies. This process is decisive for the growth of titanium oxide nanocrystals upon annealing in an oxygen atmosphere. The study of photoluminescence has shown that crystallization leads to a change in the ratio of intensities of different emission bands. The bands that are associated with the oxygen vacancy are extinguished. A decrease in the concentration of these vacancies in films leads to an increase in their resistance and stabilization of the films in time. Keywords: titanium oxide films, crystallization, refractive index, photoluminescence.

Effect of laser polarization on molecular emission from femtosecond LIBS

The study indicates that the intensities of molecular emission bands under circular polarization in femtosecond LIBS are higher than those under linear polarization. The change becomes more evident as the laser energy increases.

Thiosemicarbazide functionalized carbon quantum dots as a fluorescent probe for the determination of some oxicams: application to dosage forms and biological fluids.

In this study, highly fluorescent water-soluble nitrogen and sulfur doped carbon quantum dots (N, S-CQDs) were synthesized via a one-step hydrothermal process utilizing citric acid as a carbon source and thiosemicarbazide as a sulfur and nitrogen source. The obtained N, S-CQDs exhibited an intense emission band at 415 nm (λex = 345 nm). In the presence of either piroxicam, tenoxicam or lornoxicam, the emission band at 415 nm was significantly quenched which might be triggered due to destruction of the surface passivation layer of the N, S-CQDs. A linear correlation was found between the reduction in the fluorescence intensity of N, S-CQDs and the concentration of each drug in the ranges of 2.0–25.0 μM, 10.0–100.0 μM and 20.0–200.0 μM with correlation coefficients of more than 0.999 for all drugs. The detection limits were 0.49 μM, 1.58 μM and 4.63 μM for piroxicam, tenoxicam and lornoxicam, respectively. The effect of experimental parameters affecting the performance of the method was investigated and optimized. The developed sensor has the advantages of simplicity, time-saving, convenience and satisfactory selectivity for determination of the studied drugs in dosage forms with high % recoveries (98.86–101.69%). The method was extended for determination of piroxicam in spiked plasma with % recoveries ranging from 97.95–101.36%. The method was validated in accordance with International Council of Harmonization (ICH) standards, and the results obtained were compared statistically to those given by reported methods, indicating no significant differences in the level of accuracy and precision. The mechanism of the quenching process was studied and elucidated. The structure–activity relationship between the three drugs and the quenching efficiency was also studied and discussed.

Design of a β -SiAlON:Eu based phosphor-in-glass film with high saturation threshold for high-luminance laser-driven backlighting

β-Si6−zAlzOzN8−z:Eu2+ (β-SiAlON:Eu) possesses an intense and narrow emission band peaked at ∼530 nm, which makes it a highly suitable green-emitting phosphor for LCD backlight. However, it can hardly be used in high-power laser displays or projectors because of the laser-induced saturation effect. The aim of the present study is to develop a β-SiAlON:Eu based phosphor-in-glass (PiG) film that can withstand high-power density laser irradiation. A facile blade-coating method was employed to fabricate the PiG film. The morphology, quantum efficiency, luminescence spectra, and laser-pumped colorimetric properties of the β-SiAlON:Eu PiG films were investigated. Under excitation of 450 nm, a typical PiG film showed internal quantum efficiency of 58%, which is an acceptable value. The laser-pumped photometric properties of the PiG films were measured in reflection mode. When irradiated with a blue laser, the PiG film attained a high luminous efficacy of 109 lm/W. Furthermore, its saturation threshold reached over 26.4 W/mm2, thus achieving a high lumen density of 1970 lm/mm2 and a high luminous exitance of 1052 lm/mm2. With the above excellent properties, the β-SiAlON:Eu PiG film has great potential for use in high-power and wide-color gamut laser displays or projectors.

Effect of Eu3+ and Tb3+ ions concentration on the mechanical, structural, and photoluminescence properties of phosphate glass fibers

Two series of phosphate glasses belonging to the (65-x) P2O5–35CaO–xRE2O3 system (RE = Eu or Tb; 0 ≤ x ≤ 6 mol%) were prepared by the melt-quenching technique. All compositions were successfully drawn as continuous monofilaments fibers. The effect of Eu3+ and Tb3+ ions concentration on their mechanical, structural, and photoluminescence properties was investigated. The results revealed that the highest tensile strength was 1031 ± 34 MPa for fibers doped with 6 mol% of Eu2O3 and 1014 ± 65 MPa for fibers doped with 6 mol% of Tb2O3. The addition of RE2O3 showed an increase in density and Tg. A structural investigation was carried out using FTIR spectroscopy. The photoluminescence properties in terms of excitation and emission spectra were investigated in detail. The most intense emission band at 611 nm corresponds to the 5D0 → 7F2 transition of Eu3+ ions under 392 nm excitation was observed for fibers doped with 6 mol% of Eu2O3. The most intense emission band at 543 nm corresponds to the 5D4 → 7F5 transition of Tb3+ ions under 374 nm excitation was observed for fibers doped with 6 mol% of Tb2O3. These two compositions exhibited the highest absolute quantum yield, reaching 20.25% and 4.81%, respectively.

Tailored TiO2 nanorod arrays for dye sensitized solar cell applications

A TiO2 layer using titanium (IV) butoxide on fluorine doped tin oxide (FTO) substrate is used as a seed layer for the growth of TiO2 nanorod arrays (TRA). TRAs with length of ∼1 to 2 μm were grown on seed layer (SL) by two step method. In the first step TiO2 SLs were deposited by sol-gel assisted spin coating method and the second step involved the typical hydrothermal technique to grow rutile TRAs. Most of the TRAs grown on FTO substrate without SL were randomly oriented and TRAs with 0.025 M SL was oriented vertically from the substrate. Whereas TRAs grown on 0.05 M SL showed hierarchical nanoflower clusters composed of a bunch of TRAs as petals blooming from the core. The XRD pattern showed all the three TRAs to be crystallized in a tetragonal rutile phase. Photo luminescence spectra revealed that the TRAs on 0.05 M SL have comparatively low intense blue emission band, predicting the suppressed electron-hole recombination rate. The power conversion efficiency of the dye sensitized solar cell (DSSC) with TRAs grown on 0.05 M SL was recorded as 3.18%, which is 3 times greater than that without SL and 1.6 times greater than that with 0.025M SL in our observations.

Bulk growth, structural, optical and mechanical properties of N-phenylanthralinic acid organic scintillation single crystal

Single crystal of organic scintillation material N-Phenylanthralinic acid (NPAA) with the dimension of 10×4x3 mm3 was grown by the temperature-lowering method. X-ray diffraction studies and FT-IR analysis of grown crystal revealed the crystal structure and functional groups present in the crystal. The optical quality of the crystal is ascertained from absorption spectrum and optical bandgap studies. The fluorescence spectra exhibit an intense emission band at 452 nm and fluorescence lifetime is obtained to be very short fluorescence of 1.14 ns for prompt and 18.98 ns for delayed component. TG/ DTA studies reveal the thermal stability and melting point of the crystal. The feasibility of the grown crystal in device application is substantiated from various mechanical parameters such as Vickers hardness, Meyer's index, yield strength and stiffness constant. The chemical etching and surface morphologies of the specimen were examined using an optical microscope.

Frequency upconversion, paramagnetic behavior and biocompatibility of Gd2O3:Er3+/Yb3+ nanorods

A facile base-catalyzed hydrothermal method is used to synthesize a bifunctional luminomagnetic Er3+/Yb3+ doped Gd2O3 nanorods material. The as-synthesized nanorods material is investigated for structural/microstructural, upconversion, and magnetic properties. The intense emission bands at 520 nm, 540 nm, and 654 nm are observed upon excitation with a 980 nm solid state laser. The effect of Yb3+, Er3+ doping concentrations and incident laser power on the upconversion emission properties are also investigated, and the mechanism for the upconversion process is proposed. We further investigated the magnetic properties by room temperature M-H and M-T measurements in the temperature range of 2-300 K by standard ZFC-FC protocols. Cytotoxicity analysis of these bifunctional luminomagnetic nanorods in established cell lines did not show considerable cytotoxicity.

Investigation of the role of chemically active radicals in the antibacterial properties of a low-temperature plasma jet at ambient pressure mixed with argon and air

The work is devoted to the study of a low-temperature plasma jet of atmospheric pressure in a mixture of air with argon, used in plasma medicine. The intensities of the spectral emission bands of OH– (309 nm), N2 (337 nm), and N2 (356 nm) in different parts of the plasma jet were investigated depending on the argon flow rate and the amplitude of voltage pulses at the electrodes of the dielectric barrier discharge. The antibacterial effect of such a plasma jet on the surface of biological tissues has been experimentally investigated. Numerical simulation of ionization processes in the studied plasma source has been performed in the COMSOL Multiphysics software using. The dynamics of the distribution of excited molecules in the plasma torch as well as the kinetic plasma processes inside the plasma torch affecting the spatial distribution of its main characteristics have been analyzed.

Optical band gap modification of Ce/ZnO for visible light photocatalytic H2 production from aqueous methanol solution

Ce (0.5, 1, 2 and 3 mol%) incorporated ZnO crystallites along with bare ZnO were prepared by solution free mechanochemical method and characterized with powder XRD, HR-TEM, SEM, EDX, XPS, UV–visible and Photoluminescence (PL) spectra. The visible light photocatalytic performance of these materials was investigated for H2 evolution with the aqueous 10 vol% methanol solution under one sun conditions using solar simulator. X-ray diffraction data suggests the hexagonal wurtzite structure for Ce incorporated ZnO crystallites and due to incorporation of Ce4+ ion there is expansion in the lattice constants of ZnO, which is attributed to decreases in crystallite size. UV–visible spectra propose the decrease in optical band gap of Ce incorporated ZnO with the increase of Ce content up to 3 mol%. The XPS analysis supports the incorporation of Ce4+ in Ce/ZnO. The PL spectra suggest that, with the insertion of Ce ions into ZnO, intensity of green emission band increases, which reflects the low recombination rate of photogenerated charge carriers which is responsible for higher photocatalytic H2 production. Extent of hydrogen production is affected by calcination temperature of Ce/ZnO. 2 mol% Ce incorporated ZnO calcined at 600 °C produces 43μmolh−1g−1 of hydrogen.

Efficient photocatalytic hydrogen production over Ce/ZnO from aqueous methanol solution

Ce/ZnO crystallites along with bare ZnO were prepared by solution free mechanochemical method and characterized with powder XRD, SEM, EDX, XPS, UV–Visible and Photoluminescence (PL) spectra. The visible light photocatalytic performance of these materials was investigated for H2 evolution with the aqueous 10vol% methanol solution under one sun conditions using solar simulator. X-ray diffraction data suggests the hexagonal wurtzite structure for Ce/ZnO crystallites and the incorporation of Ce4+ ion in ZnO is supported by the shifting of XRD peaks to lower Bragg angles that indicate lattice expansion. With the increase of Ce content in ZnO, the crystallite size of Ce/ZnO decreases and the specific surface area increases. UV–Visible spectra propose the decrease in optical band gap of Ce incorporated ZnO with the increase of Ce content up to 3 mol. %. The XPS analysis supports the incorporation of Ce4+ in Ce/ZnO. The PL spectra propose that, with the insertion of Ce ions into ZnO, intensity of UV emission band decreases that reflects the low recombination rate of photogenerated charge carriers, which is responsible for higher photocatalytic H2 production. The extent of hydrogen production is affected by calcination temperature of Ce/ZnO. 2 mol. % Ce incorporated ZnO calcined at 600 °C produces43 μmolh−1 g−1 of hydrogen.

Photoluminescent Enhancement by Effect of Incorporation Nickel in ZnO Films Grown

Microstructured films of undoped zinc oxide (ZnO) and ZnO doped with nickel (ZnO:Ni) were grown by hot filament chemical vapor deposition (HFCVD) technique on Si (100) substrates at 500 °C. Pellets of ZnO and ZnO:NiO as oxidant agenst were used. A shift to the right around 0.17 degree of the X-Ray Diffraction pattern of the ZnO:Ni film was observed with respect to undoped ZnO films. Morphologically by Scanning Electron Microscopy was noticed a Core-Shell type growth in ZnO undoped and a nanostructured type (Nano-wire) in ZnO doped with Ni. Photoluminescence measurements showed an increase in the intensity of the green emission band of ZnO:Ni. It was attributed to defects of oxygen vacancies (VO), zinc vacancies (VZn), zinc interstitials (Zni), oxygen interstitials (Oi), and oxygen vacancies complex (VO complex) in the structure of the film. The incorporation of Ni atoms in the ZnO structure stresses the crystal lattice, leaving behind a large number of surface defects that increase the emission of PL.

Photoluminescent Enhancement by Effect of Incorporation Nickel in ZnO Films Grown

Microstructured films of undoped zinc oxide (ZnO) and ZnO doped with nickel (ZnO:Ni) were grown by hot filament chemical vapor deposition (HFCVD) technique on Si (100) substrates at 500 °C. Pellets of ZnO and ZnO:NiO as oxidant agenst were used. A shift to the right around 0.17 degree of the X-Ray Diffraction pattern of the ZnO:Ni film was observed with respect to undoped ZnO films. Morphologically by Scanning Electron Microscopy was noticed a Core-Shell type growth in ZnO undoped and a nanostructured type (Nano-wire) in ZnO doped with Ni. Photoluminescence measurements showed an increase in the intensity of the green emission band of ZnO:Ni. It was attributed to defects of oxygen vacancies (VO), zinc vacancies (VZn), zinc interstitials (Zni), oxygen interstitials (Oi), and oxygen vacancies complex (VO complex) in the structure of the film. The incorporation of Ni atoms in the ZnO structure stresses the crystal lattice, leaving behind a large number of surface defects that increase the emission of PL.

GAGG:Cr<sup>3+ </sup>Phosphors for Far-Infrared Light Emitting Diodes

Recently, Far-infrared Light Emitting Diodes have attracted considerable interest in the research field worldwide. Emerging light therapy requires effective red/far-infrared light resources in clinical and plant photomorphogenesis to target or promote the interaction of light with living organisms. Here, Gd3Al4GaO12:Cr3+ (hereinafter referred to as: GAGG:Cr3+) phosphor was synthesized by high-temperature solid-phase method, and the crystal structure, morphology, and luminescence properties of this series of phosphor samples were studied. Through X-ray powder diffraction to obtain pure phase GAGG:Cr3+ series phosphor. Under the excitation of 420nm blue light, a broad band emission from 640 to 850nm is obtained, which is the result of the transition of Cr3+ 4T2→4A2 level. A sharp emission peak at 693nm is the R line belonging to Cr3+ in Gd3Al4GaO12 garnet. R line is assigned to the spin-forbidden 2E→4A2 transitions of Cr3+ ions that occupy the ideal octahedral sites. As the Cr3+ doping concentration increases, the luminous intensity of the sample increases first and then decreases. When the doping concentration of Cr3+ is 0.1mol phosphor,the luminous intensity is strongest at one single broad peak at about 712nm. At 440k, the R sharp line (693nm) and broad band (712nm) emission intensity maintained 78.6% and 71.8% , compared to room temperature intensity, respectively. The change of fluorescence lifetime at different temperatures gives the mechanism of fluorescence change with temperature. The current exploration will pave a promising way to engineer GAGG:Cr3+ activated optoelectronic devices for all kinds of photobiological applications.