Energy Level Diagram Research Articles

Observation of up conversion/ down conversion luminescence and structural analysis of La2Zr2O7: Pr3+ nano phosphors

Charge transfer band (CTB) transition significantly improves the photoluminescence properties of phosphor materials due to its higher absorption efficiency than the characteristic excitations of rare-earth ions. La2Zr2O7 (LZO): Pr3+ phosphors with varying doping concentrations of Pr3+ were synthesized through the hydrothermal method. The formation of the pure pyrochlore phase was confirmed from powder X-ray diffraction (XRD). The structural analysis was performed from Rietveld refinement of the XRD data. Field emission electron microscope (FESM) equipped with EDX spectroscopy was used to study the surface morphology and elemental compositions. X-ray photoelectron spectroscopy (XPS) analysis of the optimized sample provides the bonding state of the compositions. Under 257 nm CTB excitation, the photoluminescence emission spectra (PL) exhibit all the characteristic emission peaks of Pr3+ ion. The transitions involved in the excitation and emission process have been shown in the energy level diagram of Pr3+ ions. The Concentration quenching effect was explained from Bless relation and Dexter energy transfer theory between activator ions. Decay curves of the prepared phosphors show bi-exponential behavior. The up-conversion emission spectra were recorded under 980 nm laser excitation. The optical transition in the UV–Vis range was investigated based on the diffuse reflectance spectra, and the results match well with the excitation spectra. The photometric study informs the color and the quality of the emitted light. The outcomes produce a new synthesis method to prepare La2Zr2O7:Pr3+ nano phosphor that can be an excellent candidate for solid-state lighting and UV/NIR to the visible converter in solar cell applications.

Electron transfer behaviour of green synthesized carbon quantum dot sensor towards VOC and heavy metal ion sensing

Present day world, the leakage of volatile organic compound (VOC) such as ethanol in industries, as well as presence of heavy metal ions in drinking water pose a serious threat to human health. This research develops a quantum dot sensor (nitrogen-doped carbon quantum dots (n-CDs)) for multifaceted applications. n-CDs were synthesized using hydrothermal from Citrus medica fruit and analysed using XPS, HRTEM, Zeta-potential, PL, and EDS. The study is unique, which employs the Scanning Kelvin Probe microscope (SKP) technique to investigate VOC sensing by n-CDs with contact potential difference mapping for ethanol gas sensing. n-CDs were first-ever characterized by SKP to resolute work function, and VOC interactions were examined. Energy level diagrams were used to study electron transitions. The luminescence quenching caused by electron transfer from n-CDs to receptors was manipulated to detect Fe3+ metal ions with a detection limit of 1.2 µM, which is well below the WHO’s acceptable limit.

18.55% Efficiency Polymer Solar Cells Based on a Small Molecule Acceptor with Alkylthienyl Outer Side Chains and a Low-Cost Polymer Donor PTQ10

18.55% Efficiency Polymer Solar Cells Based on a Small Molecule Acceptor with Alkylthienyl Outer Side Chains and a Low-Cost Polymer Donor PTQ10

Full understanding of K3GaF6:Cr3+ properties under hydrostatic pressure based on the Tanabe−Sugano energy-level diagram

The aim of this study is to make clear the photoluminescence (PL) properties of Cr3+-activated phosphors under the application of hydrostatic pressure (p). A determination of the excited-state zero-phonon line (ZPL) energies in the 3d3-configuration ions is possible from a set of Racah (B and C) and crystal-field splitting parameters (Dq), and vice versa. Detailed analyses of PL and PL excitation spectra are demonstrated to make possible exact determination of the excited-state ZPL energies, E (2Eg)ZPL and E (4T2g)ZPL, as a function of p. Inputting such pressure-dependent ZPL energies into a newly proposed set of Racah parameter expressions, it is possible to obtain reliable metal−ligand field parameters for 3d3 activator ions in red-emitting phosphors. An example of the analysis method is given on the Cr3+-activated K3GaF6 fluoride phosphor and suggests a change in its phosphor nature from type F–Cr-A [E (2Eg)ZPL > E (4T2g)ZPL] to type F–Cr–B [E (2Eg)ZPL < E (4T2g)ZPL]. The present analysis method can be used to obtain broad perspectives and insight for deeply understanding metal−ligand chemistry and related phenomena in the various 3d3 ion-activated phosphors under the application of external perturbation like hydrostatic pressure or lattice temperature.

White upconversion emission and color tunability of Y2O3:R(R=Yb3+, Er3+, Tm3+) nanophosphors

The Y2O3:R(R = Yb3+, Er3+, Tm3+) nanophosphors were synthesized by a solvothermal method and the temperature dependence of the white upconversion emission was studied using a 975 nm LD. The upconversion emission spectra in 1 mol% Er3+/5 mol% Yb3+/xTm3+ tri-doped Y2O3 nanophosphors were sintered at 1000 °C with x from 0 to 0.5 mol%. The blue emission intensity increases increasing Tm3+ concentration from 0 to 0.5 mol%, because the Tm3+ state can be easily reached due to the 2F7/2 → 2F5/2 transition of Yb3+ near 10,000 cm−1. The Y2O3: Er3+/Yb3+/Tm3+ nanophosphors exhibit upconversion emission from white to green with increasing sintering temperature. The calculated CIE coordinates are located in the white region at a pump power of 700 mW at 1000 °C, and the color coordinates were very similar to the standard white light emission. Their upconversion process was described through energy level diagrams and results of upconversion emission spectra and pump power dependence.

Up-conversion luminescence performance of Tm3+/Yb3+ co-doped strontium cerate phosphors

Tm3+/Yb3+ co-doped Sr2CeO4 phosphors were fabricated via a high-energy ball milling technique. The structural, morphological, and luminescence characteristics were analyzed by XRD technique, field emission scanning electron microscopy, and up-conversion luminescence spectra, respectively. The structural X-ray diffraction patterns indicate their orthorhombic structure. Under excitation at 975 nm, the up-conversion luminescence spectra of Sr2CeO4:Tm3+/Yb3+ samples with various concentrations of Yb3+ were observed. The phosphor containing 10 mol% Yb3+ ions exhibited optimal up-conversion luminescence. All the samples show emission peaks at 478, 652, and 801 nm, which are assigned to the 1G4 → 3H6, 1G4 → 3F4, and 3H4 → 3H6 transitions of Tm3+. A detailed analysis of the up-conversion mechanisms is proposed based on simplified energy level diagram. The results show that the Sr2CeO4:Tm3+/Yb3+ phosphor has potential application prospects in wide-range and light emitting devices.

Electronic transition pathways in energy transfer processes for upconversion photoluminescence of Yb3+/Ho3+ co-doped NaLa(MoO4)2 microcrystals

In recent years, upconversion photoluminescent micro/nanocrystals with unique anti-Stokes luminescence properties have shown high application value in many relevant fields. In this work, pure tetragonal phase NaLa(MoO4)2:Yb3+/Ho3+ microspheres have been synthesized by a solvothermal method in the presence of oleic acid and 1-octadecene. Under the excitation of 980 nm laser, NaLa(MoO4)2:Yb3+/Ho3+ microcrystals emit red, green and near infrared upconversion luminescence with peak wavelengths at 660/643 nm, 541 nm, and 756 nm. Based on the analysis of excitation power-dependent upconversion luminescence intensities and energy level diagram of Yb3+/Ho3+, electronic transition pathways in the energy transfer processes for upconversion luminescence of NaLa(MoO4)2:Yb3+/Ho3+ microcrystals are studied. For red upconversion luminescence at 660/643 nm, the predominant population pathway to state 5F5 (Ho3+) is “Yb3+ (2F5/2) + Ho3+ (5I7) → Yb3+ (2F7/2) + Ho3+ (5F5)”. While, “Yb3+ (2F5/2) + Ho3+ (5I6) → Yb3+ (2F7/2) + Ho3+ (5F4/5S2)” process accounts for the population of state 5F4/5S2 (Ho3+) for radiative transitions of upconversion luminescence at 541 and 756 nm. Energy back transfer contributes to the intense red upconversion luminescence at 660/643 nm. These electronic transition pathways in energy transfer processes are further confirmed by the analyses based on energy level mismatch and luminescent lifetimes.

Metallic Nitride and Carbide Perovskites: History and Prospects

Energy-level diagrams for cubic metallic Fe4N and Mn4N were proposed by Goodenough in the late 1960s. Fe4N is ferromagnetic, but Mn4N is ferrimagnetic with a large moment on Mnc at the cube corner site and a much smaller antiparallel contribution from Mnf at the three face-centre sites. Neutron diffraction revealed noncollinear ferrimagnetism with no compensation where the Mnf moments form 120° triangular antiferromagnetic sublattices but are tilted out of the kagome (111) planes to give the small net sublattice moment. A rich variety of magnetic ordering exists in the ternary Mn3−xM′xN metallic perovskites. Partial substitution of nonmagnetic M′ on Mnc sites leads to a tunable ferrimagnetic compensation point. Two possible antiferromagnetic modes in the kagome planes are a topological Γ4g mode, and a nontopological Γ5g mode where the in-plane components of the Mnf spins lie, respectively, perpendicular and parallel to the edges if the triangles in the kagome planes . Interest in the metallic perovskites has revived with the availability of high-quality thin films that facilitate measurements of magneto-transport properties, strain effects and spin wave velocity. The range of magnetic structures, magnetotransport, magnetocaloric and magnetovolume effects is exceptionally large. The topological ferrimagnets exhibit large anomalous Hall effects. The magnetism is compared with materials where N is replaced by C.

Upconversion photoluminescence and radiative properties of Ba2CaWO6: Er3+ phosphors for photonic applications

Trivalent erbium doped Ba2CaWO6 phosphors were synthesized by the solid-state reaction method. Nephelauxetic ratio and bonding parameter were calculated from the absorption spectrum in order to understand the nature of Er3+ ion-ligand bonds in the prepared phosphor samples. The phenomenological Judd-Ofelt (JO) analysis has been implemented to the recorded absorption spectrum of Ba2CaWO6: Er3+ phosphors for evaluating the JO parameters. Under 980 nm laser diode excitation, Ba2CaWO6: Er3+ phosphor exhibits strong green (4S3/2 →4I15/2) and weak red (4F9/2 →4I15/2) upconversion (UC) emissions centered at 566 and 680 nm and an intense downconversion NIR emission at 1.5 μm. The UC process were assessed on the basis of power dependence of upconversion emission intensity. The significant luminescence features observed from the photoluminescence spectra of Ba2CaWO6: Er3+ phosphors that comprise of both up conversion and down conversion luminescence were discussed in detail with the aid of partial energy level diagram. The better values of radiative properties, luminescence features and CIE color coordinates suggest the suitability of Er3+ doped Ba2CaWO6 material for various photonic applications.

Adjustable luminescence properties of Eu3+ and Bi3+ codoped Ca3Zn3Te2O12 phosphor

Ca3Zn3Te2O12:Bi3+, Ca3Zn3Te2O12:Eu3+, Ca3Zn3Te2O12:Eu3+/Bi3+ are prepared successfully in air. The crystal phase, microscopic image, and optical properties of samples are investigated by the X-ray difractometer, scanning electron microscopy, and edinburgh steady-state FLS 980 spectrograph. The green emission of Ca3Zn3Te2O12:Bi3+ phosphor with excitation at 314 nm is observed and its broad emission spectrum in the range of 360 - 790 nm is attributed to the 3P1 → 1S0 transition of Bi3+ ion. Under excitation at 395 nm, the red emission of Ca3Zn3Te2O12:Eu3+ is found, the chromaticity coordinates are (0.6392, 0.3605), and its PL spectrum is in the rang of 575 - 750 nm because of the 5D0 → 7F0,7F1, 7F2, 7F3, and 7F4 transations of Eu3+ ion. The doping Bi3+ ion can affect the luminescence properties of Ca3Zn3Te2O12:Eu3+ phosphor. The adjustable color light from green to yellow of Ca3Zn3Te2O12:Eu3+, Bi3+ phosphor with excitation at 314 nm is revealed when Eu3+ concentration is changed from 0 to 12 mol%. When the excitation wavelength is 395 nm, Ca3Zn3Te2O12:Eu3+, Bi3+ phosphor only emits red light with emission spectrum in the rang of 575 - 750 nm. The energy level diagrams of Eu3+ and Bi3+ in Ca3Zn3Te2O12:Eu3+, Bi3+ are drawn, which is used to analyze the luminous mechanism of samples.

Synthesis and tunable emission from yellow-green to red-orange of Ca3MgSi2O8:Eu3+, Dy3+ phosphor

In this work, Ca3MgSi2O8:R (R = Dy3+, Eu3+, and Eu3+/Dy3+) phosphors are synthesized in air by using the high-emperature solid-state reaction method. The crystal phase, crystal structures, lifetimes, and luminescence properties are investigated. Ca3MgSi2O8:Eu3+ phosphor with excitation at 394 nm emits red-orange light and its emission spectrum covers the region from 575 nm to 720 nm due to the 5D0 → 7F0, 7F1, 7F2, 7F3, and 7F4 transitions of Eu3+ ion. Ca3MgSi2O8:Dy3+ phosphor under excitation at 350 nm exhibits yellow-green emission with four emission bands in the range of 460–500 nm, 550–600 nm, 650–680 nm, and 740–775 nm, which are attribuited to the 4F9/2 → 6H15/2, 6H13/2, 6H11/2, and 6H9/2 transitions of Dy3+ ion, respectively. The energy transfer from Dy3+ to Eu3+ ions in Ca3MgSi2O8:Eu3+, Dy3+ phosphor can be confirmed by the spectral properties. The tunable emission properties of Ca3MgSi2O8:Eu3+, Dy3+ phosphor from yellow-green to red-orange can be fulfilled by the change of the excitation wavelength or the concentration proportion between Dy3+ and Eu3+ ions. The luminous mechanism and energy transfer of Ca3MgSi2O8:Eu3+, Dy3+ phosphor are explained by the energy level diagrams of Eu3+ and Dy3+ ions.

Luminescence Spectroscopy of 3d3 (Mn4+, Cr3+) Ions in Multiple Octahedral-Site Phosphors

Investigating spectroscopic properties of luminescent ions in multiple sites of host materials is not only of scientific interest, but also technological importance. The present investigation focuses on this problem and reports the analysis results of the optical properties of 3d 3 ions in the multiple octahedron sites. The phosphor materials considered are double-perovskite La4Ti3O12:Mn4+ and Ca3−x Lu x Hf2Al2+x Si1−x O12:Cr3+ (x = 0−1.0) phosphors. An analysis method is demonstrated for obtaining reliable and site-dependent crystal-field (Dq) and Racah parameters (B and C) based on a ligand field theory with paying an attention to difficulty in the exact estimation of such important crystal-field-related parameters. For example, the difference in the crystal-field splitting energies between the slightly and highly-distorted octahedron sites determined are ΔDq ∼ 1615 and 405 cm−1 (x = 0) for the [MnO6]8− and [CrO6]9− octahedrons, respectively. All results are in satisfactory agreement with the Tanabe−Sugano energy-level diagram plots, promising good understanding of such 3d 3-ion-activated phosphors with multiple octahedron sites.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

A General Synthetic Approach of Organic Lateral Heterostructures for Optical Signal Converters in All-Color Wavelength

A General Synthetic Approach of Organic Lateral Heterostructures for Optical Signal Converters in All-Color Wavelength

Energy transfer and broad-band luminescence of Nd3+-Er3+ co-doped Lithium Fluorophosphate (LFP) glasses

Nd3+-Er3+co-doped lithium fluorophosphate (NdEr) glasses with broad-band emission were made by the traditional melt quenching technique. These glasses were characterized through physical, absorption spectra, NIR luminescence properties and structural studies using XANES. The absorption spectra of this work showed an increase with the increasing concentration of Er2O3 in the glass. The Near-Infrared (NIR) luminescence spectra were obtained from several excitation sources. The energy level diagram studied the interraction process and energy transfer mechanism. The emission intensity of Er2O3 increases up to 1.5 mol%, the concentration quenching effect makes the emission 4F3/2 → 4I9/2, 4I11/2 and 4I13/2 Nd3+ intensity weaken, which means Nd3+→Er3+ energy transfer enhanced. The Judd-Ofelt (JO) theory investigations have been applied for Nd3+ ions and found that the trend follows Ω6>Ω4>Ω2. The stimulated emission cross-section is calculated in two ways: F u¨ chtbaueer Ladenburg (FL) method and Mc-Cumber theory. The decay time is found to be bi-exponential when monitored at λex = 581 nm and λem = 1061 nm. The XANES spectra of Nd LIII-edge were investigated and the absorption band showed at ∼6209.8 eV, confirming the presence of Nd3+. The XANES spectra of Er LIII-edge were investigated and the absorption band showed at ∼8362.5 eV, confirming the presence of Er3+.

Synthesis and Characterization of an α-Fe2O3-Decorated g-C3N4 Heterostructure for the Photocatalytic Removal of MO.

This study describes the preparation of graphitic carbon nitride (g-C3N4), hematite (α-Fe2O3), and their g-C3N4/α-Fe2O3 heterostructure for the photocatalytic removal of methyl orange (MO) under visible light illumination. The facile hydrothermal approach was utilized for the preparation of the nanomaterials. Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), and Brunauer–Emmett–Teller (BET) were carried out to study the physiochemical and optoelectronic properties of all the synthesized photocatalysts. Based on the X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance (DRS) results, an energy level diagram vs. SHE was established. The acquired results indicated that the nanocomposite exhibited a type-II heterojunction and degraded the MO dye by 97%. The degradation ability of the nanocomposite was higher than that of pristine g-C3N4 (41%) and α-Fe2O3 (30%) photocatalysts under 300 min of light irradiation. The formation of a type-II heterostructure with desirable band alignment and band edge positions for efficient interfacial charge carrier separation along with a larger specific surface area was collectively responsible for the higher photocatalytic efficiency of the g-C3N4/α-Fe2O3 nanocomposite. The mechanism of the nanocomposite was also studied through results obtained from UV-vis and XPS analyses. A reactive species trapping experiment confirmed the involvement of the superoxide radical anion (O2•−) as the key reactive oxygen species for MO removal. The degradation kinetics were also monitored, and the reaction was observed to be pseudo-first order. Moreover, the sustainability of the photocatalyst was also investigated.

Eu2+ activated novel eulytite Na3Bi5(PO4)6: Eu3+ phosphors: Enhanced luminescence and thermal stability for photonics application

For the first time, novel eulytite-like Eu2+/Eu3+: Na3Bi5(PO4)6 phosphor was synthesized via high temperature solid-state reaction method in reduction environment, and the structure, luminescence performances and thermal stability were investigated and discussed using various techniques. X-ray refinement diffraction and Raman spectra revealed the around 200 nm well-crystallized eulytite-type (I43d space group) phosphors were synthesized, and a diagram of crystal structure of Na3Bi5(PO4)6 was proposed. X-ray photoelectron spectroscopy analysis confirmed the co-existence of Eu2+ and Eu3+ ions which exhibited characteristic 4f65d→8S7/2 transition of Eu2+ and 7F0→5D0,1,2,3,4 transitions of Eu3+ ions. On the other hand, due to the activation of Eu2+, samples displayed good tunability on excited and emission behaviors under different excited laser. The JO parameters, emission cross-section, branching ratio and asymmetric ratio indicated that the Eu doping increased the covalency and asymmetry of host. Thermal quenching was studied and the reasons were discussed. Through the comparison of phosphors prepared in different conditions, the thermal stability& repeatability, radiative lifetime, color purity and activation energy were remarkably superior due to the Eu doping and in particularly Eu2+ activation. Finally, the energy level and CIE chromaticity diagrams were plotted to explain the mechanism of Eu2+ activation and energy transfer between Eu2+ and Eu3+ ions. The 0.5%Eu doped Na3Bi5(PO4)6 exhibited promising tunable red-emission performance with quantum efficiency of 92%, activation energy of 0.24 eV, red color purity of 93.74% and very low non-radiative transfer ratio 44.20 s−1 with smaller CCT (<2200 K).

A comprehensive understanding of multiple emissive states in S and N doped carbon dots and the highly selective detection of Cr(VI)

Although exceptional progress has been observed in enhancing the quantum yield and tuning the emission of carbon dots (CDs) in the recent past, the origin of photoluminescence is hazy due to the structural complexity. In this work, we synthesised luminescent S and N co-doped CDs, termed as SNCDs, via hydrothermal carbonisation of glutathione. We performed detailed photophysical studies, including fluorescence excitation, emission and time resolved analysis to understand its pH dependence luminescence in the SNCDs. Based on the results, a comprehensive energy level diagram for the SNCDs has been proposed, explaining the origin of multiple emissive states in SNCDs, contributed by core, surface, and edge states. The results are useful in tuning the emission properties of CDs and related materials for various optical applications. We demonstrate a highly selective fluorescence detection strategy for the Cr(VI) using the SNCDs as a fluorophore.

Influence of tantalum composition on mechanical behavior and deformation mechanisms of TiZrHfTax high entropy alloys

The effects of metastability engineering on tuning deformation behavior and deformation mechanisms in TiZrHfTaX (x = 1.00, 0.80, 0.60, 0.50) refractory body-centered cubic (BCC) high entropy alloys were investigated, with specific emphasis on elucidating the underlying interplay between phase stability, mechanical property, and deformation twins. It was found that in proper thermomechanical treated samples, a variation of tantalum content can effectively tune the activation of various deformation mechanisms. Detailed electron back-scattered diffraction and transmission electron microscopy analyses revealed for the first time that {332}<113̅>BCC twinning, deformation-induced α’’ phase, {111}α’’ type I and <2̅11>α’’ type II twinning can be sequentially activated in TiZrHfTaX (x = 1.00, 0.80, 0.60, 0.50) high entropy alloys with decreasing the content of tantalum. The comprehensive strengthening effect of transformation induced plasticity and twinning induced plasticity, was discussed and attributed as the pivotal factor for the improved work hardening capability and mechanical performances, especially for alloys with lower tantalum contents. Consequently, we extended the conventional bond order and d‐orbital energy level diagram that was originally developed for body-centered cubic titanium alloys for deformation mechanism evaluation to body-centered cubic high entropy alloys on the basis of current results, which sheds light on the design of ductile body-centered cubic high entropy alloys with expected deformation mechanisms and optimized mechanical performance.

Synthesis, photophysical, electrochemical, and DFT examinations of two new organic dye molecules based on phenothiazine and dibenzofuran.

New dyes were developed and produced utilizing distinct electron donors (phenothiazine and dibenzofuran), a π-spacer, and an electron acceptor of cyanoacetohydrazide, and their structures were studied using FT-IR and NMR spectroscopy. Following the synthesis of dye molecules, the photophysical and photovoltaic characteristics were investigated using experimental and theoretical methods. The photosensitizers have been exposed to electrochemical and optical property experiments in order to study their absorption performance and also molecular orbital energies. The monochromatic optical conversion efficiency of (Z)-N-((5-(10H-phenothiazin-2-yl)furan-2-yl)methylene)-2-cyanoacetohydrazide (PFCH) was found higher than that of (Z)-2-cyano-N'-((5-(dibenzo[b,d]furan-4-yl)furan-2-yl)methylene)acetohydrazide (BFCH), with IPCEs of 58 and 64% for BFCH and PFCH, respectively. According to the photosensitizer molecular energy level diagram, the studied dye molecules have strong thermodynamically advantageous ground and excited-state oxidation potentials for electron injection into the conduction band of titanium oxide. It was observed that the ability to attract electrons correlated favorably with molecular orbital energy. While density functional theory calculations were used to examine molecule geometries, vertical electronic excitations, and frontier molecular orbitals, experimental and computed results were consistent. Natural bond orbital and nonlinear optical properties were also calculated and discussed.