Intense Emission Band Research Articles

Characterization of low-temperature-grown ZnO nanoparticles: The effect of temperature on growth

The growth temperature of semiconducting nanoparticles is well known to be an essential factor in determining their structure and quality of characteristics. To create high-quality ZnO nanostructures, it is critical to optimize the growth temperature. The sol-gel approach is used to render ZnO NPs at different growth temperatures in this report. The influence of growth temperature on the material properties of ZnO nanoparticles has been extensively investigated. The scanning electron microscopy (SEM) images show needle-like structures when synthesized at low temperatures (35 and 45 °C) that transformed into spherical particles as the temperature of the growing medium increased to 75 °C. X-ray diffraction (XRD) analysis displays an increase in crystallinity with annealing temperatures. The average crystallite sizes of ZnO nanoparticles rose with increasing growth temperature and varied from 28 to 34 nm. The XRD peaks positions shift slightly towards lower 2θ angles with the growth temperatures brought about by a change in lattice parameters. The Fourier transform infrared spectroscopy (FTIR) study revealed the presence of a Z–O bond at around 680 cm−1. The intensity of the defect level emission (DLE) band decreased, as the growth temperature exceeded 35 °C. The photoluminescence (PL) study further demonstrated that the prepared nanoparticles had a strong emission peak at 546 nm. PL measurements confirm that with increasing growth temperature, the excitonic peak intensity increases, indicating that the quality of ZnO nanoparticles improves. The estimated bandgap changed from 3.31 to 3.24 eV with the growth temperature.

Electron paramagnetic resonance and optical properties of green-emitting Mn(II)-doped hardystonite phosphor prepared by sol-gel method

A series of Mn(II)-doped hardystonite phosphors was obtained by using a sol-gel technique. Structural, morphological, and optical properties of the prepared samples were investigated by X-ray diffraction, Fourier transform infrared, scanning electron microscopy and diffuse reflectance spectrum. The photoluminescence excitation and emission spectra of the prepared phosphors exhibited a strong band at ~ 254 nm and an intensified emission band at ~ 525 nm, respectively. Of all the prepared phosphors, 0.03Mn(II) doped hardystonite phosphor possessed a highly intense emission band, which demonstrated that 0.03 mol was the optimized concentration of Mn(II) ions. All the prepared phosphors emitted a bright green color, as confirmed by the Commission International de I′Eclairage co-ordinates. Electron paramagnetic resonance study suggested the existence of Mn(II) ions at sites with octahedral symmetry (g value ~2) and the dominance of covalent bonding in the prepared phosphors.

Eu3+ heavily doped tellurite glass ceramic as an efficient red phosphor for white LED

To design a phosphor for near ultraviolet (n-UV) based white light emitting diodes (wLED) with low correlated color temperature (CCT) and high CRI, a series of highly Eu3+ activated tellurite samples was prepared. Glass ceramic (GC) containing Eu2Te6O15 microcrystals were obtained as a function of crystallization time from 0 to 4 h at 435 °C. X-ray diffraction (XRD) and cathodoluminescence measurement confirm the existence Eu2Te6O15 microcrystals in translucent glass ceramic, improving the luminescence properties of the samples. Upon 393 nm excitation two intense emission bands centered at 594 nm and 614 nm were observed with an increase of 200% for the crystallized samples at 435 °C for 4 h with respect to as-fabricated glasses. Radiometric properties of heavily (10 mol %) Eu3+ doped samples as a function of crystallization time were investigated and the maximum luminous efficacy (LE) obtained is 12.01 lm/W for a crystallization time of 4 h. A green phosphor (SrBaSiO4:Eu2+) on top of samples was used the construct a white light-emitting diode and the results show that the color coordinate temperature (CCT) can be tuned from 4729 K to 3405 K as crystallization time increase from 0 to 4 h with a diminishing of LE from 34.3 to 19 lm/W. The results show that tellurite glass and GC present enormous potential as phosphor converters in solid state lighting application.

Synthesis, Optical Properties, Preliminary Antimycobacterial Evaluation and Docking Studies of Trifluoroacetylated 3‐Pyrrolyl Boron‐Dipyrromethene

AbstractThe article provides the route to trifluoroacetylated fluorescent boron dipyrromethene dye (2). The compound performs intensive absorption and emission bands in near‐red wavelength region. Photophysical properties of 2 are investigated in different solvents. A notable increase of fluorescence quantum yield after trifluoroacetyl group insertion connected with a change in intramolecular interactions parameters. The role of molecular geometry aspects in observed photophysical properties and molecular fragments rotation energy barriers are explained by quantum‐mechanical calculations. 2 performs considerable antimycobacterial activity. According to molecular docking simulations, 2 is capable of affinity binding in the active sites of mycobacterial MycP1 and MycP3 serine proteases. The geometries of final ligand‐protein complexes show the possibility of protein active site covalent modification at the serine residue of the catalytic triad. At lower concentrations, 2 can act as a fluorescent dye for microscopy analysis and corresponding staining patterns are shown for Mycobacterium smegmatis and Staphylococcus aureus cells.

Quantitative analysis of trace N2, Ar in O2 using glow discharge optical emission spectroscopy.

A trace level of N2 and Ar gases in O2 ambience were quantitatively analyzed for the first time by glow discharge optical emission spectroscopy. Microplasma was generated in a compact gas cell by a metal (Au) electrode pair of 1mm diameter and ∼1mm separation with the driving voltage of ∼0.9kV and the current of ∼5 mA in ∼60 Torr. 358 and 813nm optical emission bands were used for N2 and Ar detection, respectively. A spectroscopy fiber bundle having a circular input cross section of ∼700 µm in diameter and an output of 100 µm in width and 3mm in height was employed to promote the signal collection efficiency while preserving high spectral resolution. As a result, the detection sensitivities <1 ppm (3 - σ) were attained for both N2 and Ar within 10s. The detection accuracy was also promoted by correcting the N2 and Ar band signal intensities using the neighboring O emission band intensities, which led to detection errors <2% (3 - σ) for both N2 and Ar.

Visible and near-infrared emission and energy transition of Er3+-Pr3+-Yb3+ tri-doped lanthanum aluminium silicate glasses

In this study, Er3+-Pr3+-Yb3+ tri-doped lanthanum aluminium silicate glasses of various doping concentrations were successfully prepared using the conventional melting method. The visible and near-infrared emission properties of Er3+-Pr3+-Yb3+ tri-doped lanthanum aluminium silicate glasses under excitations at 455, 520, and 976 nm were investigated. Moreover, the upconversion (UC) emission spectra of glass under excitation by the 980 nm laser were also investigated. The results showed intense emission bands centered at the visible and near-infrared emission ranges. In addition, the energy transition process between Er3+ and Pr3+ was discussed, and the role of Yb3+ in enhancing the absorption and emission of this system was demonstrated.

Optical and luminescence properties of Sm2O3 doped SrO–PbO–ZnO–P2O5–TeO2 glasses for visible laser applications

The spectroscopic and structural characteristics of various concentrations of Sm2O3 doped strontium lead zinc phospho-tellurite glasses with molar composition x% Sm2O3 + 5SrO + (15-x) PbO + 20 ZnO + 50 P2O5 + 10 TeO2 (where x = 0.25, 0.5, 0.75, 1 mol%) have been reported here. The XRD and FTIR measurements are performed to explore the structural characteristics of the glasses. The absorption spectra reveal that the bands at 400 nm and 1220 nm are highly intense in comparison to others. The Judd-Ofelt intensity parameters Ωλ (λ = 2, 4, 6) have been evaluated from the absorption and thereby the radiative and lasing parameters are estimated. The most intense excitation band around 400 nm is opted as the excitation wavelength to study luminescence properties. Luminescence spectra exhibit the most intense emission band at 598 nm pertaining to 4G5/2 → 6H7/2 transition which is responsible for reddish-orange colour origination. We have measured the experimental lifetime of the 4G5/2 excited state by the suitable fittings of the decay curves. Luminescence concentration quenching (x> 0.75%) and the reduction of decay lifetimes have been observed owing to enhancement of non-radiative energy losses through the cross-relaxation channels. The higher values of quantum efficiency and stimulated emission cross-section promote the lasing action of the present glasses. The location of CIE chromaticity coordinates recommends that these glasses could be utilized as reddish-orange color emitting laser materials.

Synthesis and study on structural, morphological, optical properties and photocatalytic activity of CuO:Erx3+ photocatalysts

Copper oxide (CuO) and Erbium-doped Copper oxide (CuO:Erx3+, x = 0.025, 0.05, 0.1) nanoparticles were synthesized via combustion reaction. The samples were employed to degrade methylene blue (MB) dye under visible light illumination. The synthesized nanoparticles' microstructural, morphological, optical, and vibrational properties were investigated. The structure of the nanoparticles was found to be monoclinic. A redshift in the Raman modes was observed with the addition of dopant. FESEM images of CuO and CuO:Er3+0.05 displayed agglomerated nano-spheres to nano-flowers-like morphology. The bandgap calculated from UV-DRS spectra showed a red shift in bandgap values from 1.31 eV to 1.22 eV. Photoluminescence spectra revealed a significant decrease in the band emission intensity with doping. Photocatalytic studies indicated that doping has significantly enhanced the degradation performance of CuO nanoparticles. In particular, the CuO: Er3+0.05 sample eminently exhibited the highest degradation efficiency of 96%. A mechanism for the photocatalytic degradation of MB dye by CuO and CuO:Erx3+nanoparticles has been proposed.

Growth, structure, and polarized spectroscopy of monoclinic Er3+:MgWO4 crystal

We report on the growth, structure, and polarized spectroscopy of a novel promising laser crystal, erbium-doped magnesium monotungstate, Er3+:MgWO4. 1.01 t.% Er3+:MgWO4 was grown by the Top-Seeded Solution Growth method using Na2WO4 as a solvent. The crystal structure was refined by the Rietveld method. Er3+:MgWO4 belongs to the monoclinic class (sp. gr. P2/c, wolframite-type structure, lattice parameters: a = 4.6939(6) Å, b = 5.6747(4) Å, c = 4.9316(6) Å and β = 90.7858(4) Å. The transition intensities for Er3+ ions were determined using the Judd-Ofelt theory accounting for an intermediate configuration interaction (ICI). Er3+ ions in MgWO4 exhibit intense, strongly polarized and broad absorption and emission bands owing to their accommodation in distorted low-symmetry sites (C2). The stimulated-emission cross-section for the 4I13/2 → 4I15/2 transition is 0.31×10−20 cm2 at 1637 nm (light polarization: E || b ). The radiative lifetime of the 4I13/2 state is 4.85 ± 0.05 ms. The multiphonon non-radiative relaxation for Er3+ excited multiplets is quantified. Er3+ ions in MgWO4 feature large Stark splitting of the ground-state, ΔE(4I15/2) = 435 cm-1. Er3+:MgWO4 is attractive for low-threshold lasers at ∼1.64 µm.

Ce concentration dependence on scintillation properties of Ce-doped yttrium pyrosilicate single crystal

Yttrium pyrosilicate (Y2Si2O7) single crystals are successfully grown by the floating-zone method with 0.5–10.0% of Ce-doping concentration. X-ray diffraction patterns indicate a single phase of Y2Si2O7 without the impurity phase. The series photoluminescence (PL) and scintillation properties are systematically explored in this study, including PL emission, PL decay time, X-ray induced scintillation spectra, X-ray induced scintillation decay time, afterglow profile, and pulse height spectra. Ce-doped Y2Si2O7 is presented interesting properties including the intense emission band at 390 nm from Ce3+ 5d-4f transition on both PL emission contour maps as well as X-ray-induced scintillation spectra in all samples. The afterglow level at 20 ms after X-ray irradiation of the Ce-doped YPS is comparable with commercial scintillators such as CdWO4 and Tl-doped CsI. Under 137Cs (662 keV) γ-ray irradiation 137Cs (662 keV), the highest scintillation light yield of Ce-doped Y2Si2O7 is reach up to 17,200 ph/MeV for 2.0% Ce-doped sample.

Structural, Thermal, Optical, Mechanical, and Antibacterial Properties of PLA/Nanoclay/TiO2 Nanocomposite Films

In this report, Polylactide/Nanoclay/TiO2 nanocomposite films with two different weight percentages (2wt% and 5wt %) of clay and TiO2 nanoparticles were prepared by a cost-effective approach. A solvent casting process with the help of a cost-effective film applicator was used to prepare nanocomposite films. The surface morphology investigations revealed the agglomeration of fillers at higher weight percentages and uniform mixing of fillers at lower weight percentages. The crystallinity of the prepared films did not alter much with the nanofiller addition. Nanofillers with a 2wt% concentration in the PLA matrix enhanced thermal and mechanical properties significantly. The PLA nanocomposite films have exhibited an intense broad emission band in violet color with a wavelength of ≈420 nm. In addition, the antibacterial activity of polylactic acid nanocomposite films was investigated against Gram-positive S. aureus and Gram-negative E. coli bacteria. The enhanced antibacterial activity is observed for a 5wt% concentration of nanofillers. The results showed that the antibacterial activity increases with nanofiller concentration. This study presents a simple and cost-effective approach to preparing nanocomposite films with tuneable properties of mechanical, thermal, and antibacterial activity.

Model for Nitric oxide and its dayglow emission in the martian upper atmosphere using NGIMS/MAVEN measured neutral and ion densities

A comprehensive study of Nitric oxide (NO) chemistry in the Martian upper atmosphere is restricted due to the lack of requisite measurements. NO is an abundant form of odd nitrogen species in the Martian lower atmosphere and its density depends on several photochemical processes. We have developed a photochemical model to study the NO density in the dayside of Martian upper atmosphere by accounting for various production and loss mechanisms. By utilizing the Neutral Gas and Ion Mass Spectrometer (NGIMS) on-board Mars Atmosphere and Volatile Evolution (MAVEN) mission measured neutral and ion densities during deep dip 8 and 9 campaigns, we modelled NO number density in the Martian sunlit upper atmosphere for the altitudes between 120 and 200 km. The modelled NO densities are employed to calculate NO (1,0) γ band emission intensity profiles in the dayside upper atmosphere of Mars. The calculated NO density and its γ band intensity profiles are found to be consistent with Imaging Ultraviolet Spectrograph (IUVS) onboard MAVEN observations and also with other modelling studies. We found that the local CO2 and N2 density variations can lead to a change in NO density and consequently its dayglow intensity by a factor of 2 to 5. Since NO is a trace constituent and also its dayglow emissions are strongly obscured by CO Cameron band emissions, we suggest that the derivation of NO number density based on our approach can constrain its abundance in the dayside upper atmosphere of Mars. More observations of (1-0) γ band emission along with modelling will help to study the global distribution of NO in the Martian atmosphere.

Tunable multicolor luminescence and energy transfer mechanism in Eu3+/Dy3+ co-doped Ca2Sb2O7 phosphor under UV excitation

A series of Ca(2-x-y)Sb2O7:xDy3+,yEu3+ phosphors with tunable multicolor luminescence were synthesized via solid-state reaction method. The XRD, EDX and HR-TEM analysis confirmed the phase purity and the crystallinity of the samples. Under ultraviolet (UV) excitation, Ca(2-x-y)Sb2O7:xDy3+,yEu3+ phosphors exhibit characteristic emission bands of both Dy3+ and Eu3+ ions, along with an intense blue emission band of the host. The emission peaks at 575 and 660 nm correspond to 4F9/2 →6H13/2 and 4F9/2 →6H11/2 transitions of Dy3+ ions, and the peaks at 528 and 612 nm originate from 5D1 →7F1 and 5D0 →7F2 transitions of Eu3+ ions, respectively. There exists efficient energy (ET) transfer from host to Eu3+/Dy3+ ions, as well as from Dy3+ to Eu3+ ions. The decay lifetime of host and Eu3+/Dy3+ emissions were calculated to be in the microsecond range. By properly modulating the concentration of Eu3+/Dy3+ ions, the CIE chromaticity coordinates of the samples vary from (0.144, 0.097) to (0.446, 0.312). Hence, multicolor emission which can be tuned from blue to bluish-white and eventually to reddish-white can be obtained in the warm CCT region. The results indicate that Ca2Sb2O7:Dy3+,Eu3+ phosphor could be a promising candidate for UV excited WLEDs and multicolor displays.

Bi(III) I-Complexes of Porphyrins for Biomedicine: Synthesis and Spectral-Optical Properties

Bismuth complexes of porphyrins are of interest for IR luminescence diagnostics of cancer, since rather intense emission bands in the range of 800–920 nm have been found. In connection with the COVID-19 pandemic, bismuth compounds are also of interest in the treatment of coronavirus infection. Bismuth complexes of porphyrins of various spatial configurations have been synthesized, and several spectral-optical properties have been investigated. The influence of various substituents on the spectral characteristics was evaluated by methods of studying electronic absorption spectra, luminescence spectra, IR-, and 1H NMR spectroscopy.

Screen printing strategy for fabricating flexible crystallized perovskite nanocomposite patterns with high photoluminescence

Organohalide perovskites have been witnessed as an emerging class of solution processable semiconductor with huge potential for applications in optoelectronic devices. However, a low-cost and high-yield patterning of these materials needs to be further improved. Herein, we demonstrated a facile approach to pattern perovskite nanocrystals embedded in polymer matrix by screen printing strategy. Importantly, this strategy achieves a champion photoluminescence quantum yield up to 96.5% and exhibited an intense green emission band centered at 517 nm with narrow full width at half-maximum of 20 nm. In addition, the composite films show an extraordinary stability in various environments, such as air, water, high temperature (80 °C), and Ultraviolet -radiation. The photoluminescence intensity of composite films decreases only 1.4% after being stored in air with 85% relative humidity for 3 months and remains 81.6% of initial values after being submerged in water for 3 months. Finally, we printed high-resolution patterns of 175 µm, demonstrating that the screen printing is very promising for patterning perovskite composite microarrays.

Tunable luminescent chromaticity of CaZnOS: Bi3+, Eu3+ with white emitting based on energy transfer

A series of Bi3+ or Eu3+ ion single doped and Bi3+ and Eu3+ co-doped CaZnOS phosphors were synthesized via high temperature solid state method. Under ultraviolet (UV) excitation, CaZnOS: Bi3+ has an intense emission band ranged from 400 to 600 nm owing to the 3P1,0 → 1S0 transition of Bi3+. And CaZnOS: Eu3+ shows superior red emissions due to the characteristic 5D0 → 7FJ (J = 1, 2, 3, 4) transitions of Eu3+. Tunable emission chromaticity from cyan, white, yellow to red is obtained by regulating the proportion of Eu3+ in CaZnOS Bi3+, Eu3+. The energy transfer mechanism from Bi3+ to Eu3+ was confirmed to be a quadrupole-quadrupole interaction based on the overlap of emission band of Bi3+ and excitation band of Eu3+ combined with the luminescent lifetime measurement. In addition, CaZnOS: 2.5 mol% Bi3+, 3 mol% Eu3+ phosphor with optimized concentrations has standard white light chromaticity coordinates (0.315, 0.323) and activation energy about 0.372 eV, which reflects its potential application in ultraviolet-chip excited white light emitting diodes (W-LEDs).

White light emission and energy transfer in Pr3+/Er3+ co-doped InF3-based glass

Pr3+/Er3+ co-doped glasses based on InF3 were synthesized and then studied for white light emission. The emission spectra consist of several bands corresponding to characteristic 4f-4f electronic transitions of Pr3+ and Er3+ ions. The relative intensities of emission bands depend on the selective excitation wavelengths. The energy transfer process from Pr3+ to Er3+ ions was confirmed by the excitation and emission spectra measurements. From emission spectra, the CIE chromaticity coordinates, the correlated color temperature (CCT) and the color purity (CP) were determined. The results indicate that Pr3+/Er3+ co-doped glasses based on InF3 are excellent fluoride candidate to achieve warm white light emission.

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.