Luminescence Excitation Spectra Research Articles

Codoped Lithium Sodium Iodide With Tl+ and Eu2+ Activators for Neutron Detector

Investigations of high-efficiency neutron-sensitive scintillators are very important for a wide variety of applications including special nuclear material detection, fundamental research, radiation safety, and industrial monitoring, among others. Responding to this need, we have been studying the Li x Na(1– x )I (conventionally called LNI) crystal system, using enriched 6Li because of its high neutron cross section. We have successfully grown single crystals of LNI with $x$ values in the range of 4%–20%, by the vertical Bridgman technique. Sodium iodide (NaI) and lithium iodide (LiI) have the same rock salt crystal structure capable of forming a monolithic solid solution over the entire concentration range. These LNI crystals are codoped with a few mol percent of Tl+ and Eu2+ activator to achieve the desired scintillation properties. X-ray excited luminescence spectra of LNI crystals show nearly identical main emission peaks around 440 nm independent of Li concentration. Neutron detection measurements using an americium/beryllium (AmBe) source show that increasing Li concentration from 4 to 20 mol% causes the neutron light yield (LY) to drop from 150 000 to 50 000 photons/neutron, while the gamma equivalent energy (GEE) for neutrons rises from 3.65 to 4.8 MeV. When measured at 662 keV (137Cs), the gamma ray LY behaves similarly, decreasing with the increase of Li content. This can be attributed to the lower fraction of Na, which affects both stopping power and scintillation efficiency. Pulse-shape discrimination measurements show well-defined differences between the gamma and neutron scintillator response.

Emission of Light by CdMnTe/CdMgTe Heterostructure with Narrow Quantum Wells

The optical properties of the Cd0.4Mn0.4Te/Cd0.5Mg0.5Te heterostructure with quantum wells of 7 monolayers in thickness are studied. The temperature dependences of the integral intensity of luminescence of the barrier layer and quantum well and intracenter luminescence of manganese ions are determined, and the luminescence excitation spectra are measured. Numerous components corresponding to LO phonons of the CdTe, MgTe, and MnTe types are observed in the Raman scattering spectra.

Ultraviolet-light emission enhancement and morphology stability for ZnO:Ga nanorod array treated by hydrogen plasma

Vertically aligned and highly uniform ZnO:Ga (1 mol%) nanorod array was fabricated by hydrothermal reaction method and then treated by hydrogen plasma. The results show hydrogen plasma treatment could drastically enhance ultraviolet light emission of ZnO:Ga nanorod arrays with maintaining their morphology, which is extremely important for X-ray imaging with high spatial resolution. Under the excitations of 266 nm laser and X-ray, a red-shift of ultraviolet light emission was observed and confirmed to be the internal absorption of ZnO:Ga. A visible light emission in X-ray excited luminescence spectrum revealed that the diffusion of hydrogen in the array had a limited penetration depth. Furthermore, the decay time of the ultraviolet light emission was measured to be less than 1.0 ns. The present work shows the hydrogen plasma treated ZnO:Ga nanorod array can be used as a potential scintillator for the ultrafast and high-spatial-resolution X-ray imaging detectors.

Effect of silver co-doping on enhancement of the Sm3+ luminescence in lithium tetraborate glass

Luminescent properties of the Sm3+-doped and Sm3+-Ag co-doped glasses with Li2B4O7 (or Li2O–2B2O3) basic composition are investigated and analysed. Spectroscopic properties of the obtained Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses were studied using measurements of optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics), and quantum yield (QY) via an absolute method. Optical absorption spectra exhibit absorption bands related with transitions from the ground 6H5/2 state of Sm3+ ions to several excited states. Photoluminescence spectra of the Sm3+-doped glasses reveal emission bands, which correspond to the 4G5/2 → 6HJ (J = 5/2–13/2) transitions of Sm3+ ions. Luminescence excitation spectra and decay curves of the Sm3+ luminescence also have been analysed. The EPR study confirms presence of Ag species in the Sm3+-Ag co-doped samples. Photoluminescence emission and excitation spectra and luminescence decay kinetics of the Ag+ ions and small non-plasmonic molecule-like silver (ML-Ag) nanoclusters are observed and discussed. Enhancement of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass has been observed. Measurements confirm the increasing of external QY of the Sm3+ luminescence in 1.43 times in the Ag co-doped glass. Such enhancement of the luminescence is attributed to the excitation energy transfer from Ag+ ions and ML-Ag nanoclusters to the Sm3+ ions. The obtained high QY of the Sm3+ luminescence shows that Li2B4O7:Sm, Ag glasses belong to promising luminescent materials.

Dy3+-doped BaLaMgSbO6 double perovskite highly efficient white phosphor

Abstract Trivalent dysprosium (Dy3+)-doped matrix BaLaMgSbO6 phosphors with a quenching concentration of 10% were obtained by using the perovskite BaLaMgSbO6 as a white phosphor matrix and the rare earth element Dy as an excitation center. BaLa1-xMgSbO6: xDy white phosphors were obtained by using the solid-state reaction method. The phase and structure information were determined via X-ray diffraction analysis, and the results showed that pure BaLaMgSbO6 was obtained. Luminescent properties for the phosphors were investigated by measuring the excitation, emission and total luminescence spectra. The emission spectra consisted of two strong peaks at 478 nm (blue) and 571 nm (yellow), as well as a weak peak at 660 nm (red). The color of the phosphors could be changed by controlling the Dy3+ doping concentration. The CIE coordinates for BaLa0.9Dy0.1MgSbO6 were calculated to be (0.387, 0.439) according to the emission spectra. All of these results prove that the UV-excited double perovskite white phosphor has very promising potential for application.

Energy relaxation from STE to In+ centers in NaI:In+ crystals

The energy relaxation from host crystals to impurity centers has been investigated by measuring the absorption and excitation spectra and the temperature dependence of the luminescence spectrum of NaI:In+. In the absorption spectrum, the A, B, and C bands due to the In+ centers are confirmed at 3.8, 4.0, and 4.5 eV, respectively. The excitation spectrum for the AT luminescence due to the In+ centers responds to the energy position of the A, B, and C bands and also the energy region above the exciton transition of NaI. The fact suggests the existence of the energy relaxation from host crystals to the In+ centers. The total intensity of the AT and AX luminescence due to the In+ centers exhibits different temperature dependence between the excitations at the C band and host crystals. Under excitation at the C band, the total intensity of the AT and AX luminescence monotonously declines with increasing temperature from 10 to 300 K. On the other hand, under excitation at host crystals, the total intensity of the AT and AX luminescence exhibits an increase with increasing temperature from 10 to 50 K, and a decrease with increasing temperature from 50 to 100 K. We discuss the temperature dependence of the total intensity of the luminescence under excitation at host crystals in relation to free excitons and self-trapped excitons.

Europium and terbium pyrrole-2-carboxylates: Structures, luminescence, and energy transfer

Lanthanide pyrrole-2-carboxylates [{Ln(L)3(H2O)2}·H2O]n (Ln = Eu, Gd, Tb) were synthesized and investigated using single crystal X-ray diffraction and optical spectroscopy (luminescence, luminescence excitation and vibrational IR spectra). The europium pyrrole-2-carboxylate crystallizes as a 2D network structure in the P21/c space group. The Eu3+ coordination polyhedron formed by five carboxylic groups and two water molecules can be described as a distorted single-capped square antiprism. The luminescence spectra indicate a low symmetry of the charge distribution around the Ln3+ ion that corresponds to the C1 symmetry of the coordination environment of Eu3+ ion in the [{Eu(L)3(H2O)2}·H2O]n crystal lattice. The low-energy ligand–metal charge transfer (LMCT) state was identified in the europium compound. The shortening of the 5D0 (Eu3+) lifetime in the 230–295 K temperature region, when the compound is heated from 77 to 295 K, and the low luminescence intensity of the europium pyrrole-2-carboxylate are caused by the participation of the LMCT state in quenching processes. The energy of activation determined for the 5D0 – LMCT crossover is 3900 ± 100 cm−1.

The Pr3+ and Tb3+ ground state locations in compounds obtained from thermoluminescence and intervalence charge transfer studies

The location of the lanthanide ground states with respect to the host valence band or to the vacuum level always follow characteristic zigzag patterns with the number of electrons q in the 4f orbital. The patterns that are used today evolved over the years by combining experimental data from different techniques, and they are in first approximation independent on the type of compound. Here we will demonstrate that the ground state locations for Pr3+ and Tb3+ in the currently used pattern for trivalent lanthanides appear, when inspected on the ± 0.1 eV accuracy level, not consistent with two independent sets of experimental data. One set is from data on the intervalence charge transfer (IVCT) from Pr3+ and Tb3+ to the conduction band (CB) observed in luminescence excitation spectra. The other set is from the release of holes from Pr4+ and Tb4+ to the valence band observed in thermoluminescence (TL). In addition to the inconsistency, TL based evidence for a slight compound dependence in the characteristic zigzag patterns is found.

Size effects and radiation resistance of BaF2 nanophosphors

Abstract The stationary X-ray excited luminescence (XEL) spectra at 80 and 294 K as well as the thermally stimulated luminescence (TSL) in the 80–300 К range of a single crystal and nanoparticles of BaF2 with various grain sizes of 20–113 nm were studied. Under the influence of size effects in BaF2 nanophosphors, a short-wave displacement of self-trapped excitons emission band was observed compared to the corresponding single crystal, and its splitting into two components peaked at 324 and 305 nm for 294 K, and at 321 and 305 nm – for 80 K. A slight decrease of radiation resistance of BaF2 nanophosphors was observed in comparison to single crystal, which led to additional band of X-ray excited luminescence at ∼410 nm that may be associated with emission of exciton localized in the vicinity of anionic vacancies of the matrix. At the same time, it was established that radiation resistance of BaF2 nanophosphors is much higher compared to the corresponding CaF2 nanophosphors. With the use of integral TSL curves and TSL spectra, it has been shown that VH-centers with delocalization temperature of ∼140 K are the main hole centers that occur in BaF2 nanoparticles under X-ray irradiation influence, while in ВаF2 single crystals – these are Vk - and H-centers with delocalization temperatures at 113 and 198 К, respectively. Significant long-wave displacement of emission bands associated with (VH-F)- and (H-F)- recombinations, compared to the spectra of corresponding single crystal, was observed in BaF2 nanophosphors.

Relaxation of intrinsic and extrinsic electronic excitations in nano- and micro-size alumina

Nanopowders consisting of mixed α-alumina and transition alumina phases were prepared by combustion synthesis and investigated using low temperature time-resolved cathodoluminescence and photoluminescence spectroscopy under VUV excitation. The onsets of the intrinsic absorption for different alumina phases were revealed in mixed phase nanopowders by analysing luminescence excitation spectra. All synthesized nanopowders possessed the intrinsic luminescence band with a maximum at 4.6 eV, which is assigned to the radiative decay of triplet self-trapped excitons with ∼750 μs decay time at 78 K. A red shift by 0.3 eV was revealed for the peak of the O2− – Cr3+ charge transfer band near 7 eV as a function of particle size. This shift is correlated with the decrease of α-alumina particle size from 180 to 80 nm. Its origin is discussed in the framework of the Kroning-Penney model.

FLUORESCENT PROPERTIES OF PAPER INSULATION OF OIL-FILLED TRANSFORMERS

The effect of paper thermal destruction on its luminescence spectra and luminescence excitation spectra in the spectral ranges of 400-550 nm and 250-450 nm, respectively, was studied. It is proposed to use the characteristic changes in the intensity and shape of the luminescence spectra as a criterion for the state of paper insulation of power transformers. On the basis of the analysis performed, it was concluded that when luminescence is excited at a wavelength of 360 nm, none of the main components of the paper can contribute to the recorded luminescence spectra. It is assumed that the resulting luminescence spectra are due to the emission of various impurities that enter the paper during its production.

Luminescence and electron-phonon interaction characteristics of radiation-induced point defects in magnesium fluoride nanocrystals

Nanocrystals of magnesium fluoride have been irradiated by γ-rays at 77 K or electrons at room temperature. Three types of radiation-induced defects (color centers) with previously unknown characteristics, such as luminescence and excitation luminescence spectra, luminescence lifetime, and Huang-Rhys parameters, have been observed and studied in these nanocrystals. It has been established that the luminescence excitation spectra of these centers contain two closely spaced bands with slightly different intensities. It was shown that pre-irradiation annealing of nanocrystals at temperatures above 823 K for one hour leads to the impossibility of observing all three new types defects in irradiated samples. It has been found that during the post-radiation annealing of samples, one of the new types of color centers is transformed into a well-known defect described earlier in the literature. It is concluded that new types of defects are generated near the nanoclusters which are formed during nanocrystals production. It has been found that defects previously known and referred to as M (C1) consist of two modifications which differ in luminescence and excitation luminescence spectra, and in dependencies of their concentrations upon temperature annealing.

Structure variation and luminescence enhancement of BaLaMg(Sb, Nb)O6:Eu3+ double perovskite red phosphors based on composition modulation

A series of BaLaMgSb1-xNbxO6:Eu3+ double perovskite red phosphors was successfully obtained. X-ray diffraction ans Rietveld refinement analyses were conducted to determine the phase information and the detailed structure parameters. The coordinate variations of both La3+/Eu3+ and Sb5+/Nb5+ were discussed to elucidate the influence of B-site ion doping on the lattice variation. Luminescence properties, excitation and emission spectra, were presented to show the advantages of doping with Nb5+ ion. Ultraviolet-vis diffuse reflectance spectra were performed to reveal the reason for the decreased emission intensity under the charge transfer band excitation. Moreover, band gap energy was estimated to clarify the relationship between the increased intensity (λex = 395 and 465 nm) and Nb5+ concentration. Intensity ratios of I(615)/I(590) were performed to show the symmetry variation of the lattice. Thermal quenching property was also investigated and the quenching mechanism was discussed in detail based on the ionization process.

Спектрально-люминесцентные свойства разнолигандных комплексных соединений европия(III) с n-метилбензойной кислотой

Abstract The spectral-luminescent properties of europium(III) complexes with p -methylbenzoic acid and nitrogen- and phosphorus-containing neutral ligands of compositions [Eu( p -MBA)_3 · D]_2 · x H_2O and [Eu( p ‑MBA)_3 · 2H_2O]_ n , where p -MBA is the anion of p -methylbenzoic acid and D is 1,10-phenanthroline (phen), 2,2' dipyridyl (dipy), triphenylphosphine oxide (tppo) ( х = 0), hexamethylphosphortriamide (hmpa) ( x = 1), or benzotriazole (bt) ( x = 2) are studied. The electronic absorption spectra, the luminescence excitation spectra, and the Stark structure of ^5 D _0−^7 F _ j ( j = 0–2) electronic transitions in low-temperature luminescence spectra of complex europium(III) p -methylbenzoates are analyzed. It is found that the excitation energy transfer to europium ions occurs from the levels of both p -methylbenzoic acid and neutral ligands.

Излучение света гетероструктурой CdMnTe/CdMgTe с узкими квантовыми ямами

AbstractThe optical properties of the Cd_0.4Mn_0.4Te/Cd_0.5Mg_0.5Te heterostructure with quantum wells of 7 monolayers in thickness are studied. The temperature dependences of the integral intensity of luminescence of the barrier layer and quantum well and intracenter luminescence of manganese ions are determined, and the luminescence excitation spectra are measured. Numerous components corresponding to LO phonons of the CdTe, MgTe, and MnTe types are observed in the Raman scattering spectra.

Экситонные эффекты и примесно-дефектное излучение в GaAs/AlGaAs-структурах, применяемых для изготовления детекторов среднего ИК-диапазона

AbstractA series of undoped GaAs/Al_ x Ga_1 –_ x As multiple quantum well heterostructures, whose doped analogs are used for the production of photodetectors operating in the spectral range 8–12 μm, is fabricated by molecular-beam epitaxy. For the heterostructures, the spectral position of absorption lines corresponding to the allowed transitions between quantum-confined electron and hole levels in GaAs layers is established. The influence of impurity–defect states on the luminescence and absorption spectra of quantum wells is studied. The excitonic corrections for the allowed transitions are determined in relation to the quantum-well width and the aluminum content in the barrier layers. The role of excitonic effects in restoring the structure of single-electron states from interband-absorption spectra (luminescence-excitation spectra) and the relationship between these states and the working region of IR photodetectors based on GaAs/Al_ x Ga_1 –_ x As quantum wells are discussed.

Photoluminescence of crystalline and glassy lead thiogermanate

Purpose: The interest to glasses Ge–Pb–S system is due to the opening possibilities of using them as a three-dimensional optical coating for active devices of integrated optics and multifunctional devices of semiconductor photonics, as well as electrophoto-graphic layers characterized by small value of the limit charging potentials and fast kinetics of dark half-decay. Methods: This paper presents the comparative study results of radiative recombination and photoluminescence excitation (PLE) spectra, temperature dependence of photoluminescence, lux-brightness characteristics (LBC) of crystalline ( c- ) and glassy ( g -) PbGeS 3 in the temperature range 77–300 K. Results: The PL spectra of ordered and disordered phases are qualitatively similar; they contain one intense broad radiation band, the energy position of its maximum at T = 77 K is hv max = 1.04 eV for the crystal and it lies within 1.13–1.18 eV for the glass. The luminescence excitation spectrum is a bell-shaped curve with a maximum at the photon energy of 2.7 eV for the crystal and 2.26 eV for the glass, which are close to the band gap of ordered and disordered phases, it indicates on the band-type excitation character. The Stokse shift W S = E PLE – E PL for the crystal phase W Sс = 1.65 eV is much larger than for the glassy phase W Sg = 1.07 eV. Lux-brightness characteristics (LBC) have the linear character for both PbGeS 3 phases. Only slight shift of the maximum in PL spectra into the high energy region is observed with the intensity excitation increasing. Linear LBCs along with the exponential decay of PL indicate to the monomolecular character of recombination in both phases. The similarity of PL and luminescence excitation spectra of c - and g -PbGeS 3 as well as their comparison to the known results for c - and g -GeS 2 (GeSе 2 ) allow to conclude that the radiative processes in lead thiogermanate are determined primarily by the chemical nature of luminescence centers and poorly depend on the presence of long-range order, while the nonradiative processes are very sensitive to the structure disordering. Conclusion: For the first time, in the photoluminescence spectra of both PbGeS 3 phases, a wide band with a Gaussian-shaped contour was detected, with the emission band for glassy samples shifted by ~0.1 eV towards higher energies. The relatively large half-widths and the absence of the oscillatory structure of the luminescence bands indicate that in both phases a high heat release occurs, and the energy position of the band maxima in the emission spectra indicates the impurity nature of the luminescence and high stokes losses.

Fluorescent Silver Clusters on Protein Templates: Understanding Their Structure

Luminescent metal nanoclusters (NCs) stabilized by natural proteins are of special interest in bioimaging applications. However, the detailed structure of the protein-templated NCs and the nature of their emissive states remain poorly understood. A fair amount of nonluminescent metal ions and clusters complexed to the proteins hinders probing of the structure of the emitting clusters using mass spectroscopy, infrared, or other conventional spectroscopy methods. In this respect, only luminescent excitation spectra distinguish the emitting NCs. In this experimental and theoretical joint study, we modeled the fluorescent excitation and excitation anisotropy spectra of protein-based silver (Ag) NCs. We varied the synthesis conditions and studied the spectral properties of Ag clusters on bovine serum albumin (BSA) and lysozyme, which had already been used as templates, as well as on HMG box (HMGB1) and histone H1 (H1) proteins. We also calculated the electronic spectra of quantum mechanics-optimized Ag–thiolat...

Luminescence properties of Ce3+ and Eu2+ doped M3MgSi2O8 (M = Ca, Sr) phosphors for potential detecting applications

A series of phosphors M3–xLnxMgSi2O8 (M = Ca, Sr; Ln = Ce, Eu; x = 0.005, 0.01, 0.03, 0.05, 0.07, 0.10, 0.15) were synthesized. The luminescence properties in the vacuum ultraviolet-ultraviolet visible spectral range and the X-ray excited radioluminescence were investigated in detail. The results reveal that the M3–xLnxMgSi2O8 (M = Ca, Sr; Ln = Ce, Eu) phosphors exhibit typical broad excitation and emission bands, which are ascribed to the 4f–5d transitions of the Ce3+ and Eu2+ ions. Finally, X-ray excited luminescence (XEL) spectra were measured to evaluate the possibility of Sr3MgSi2O8:Ce3+ and Sr3MgSi2O8:Eu2+ as scintillation materials.

The valence and ion-pair states of the N2I2 van der Waals complex

The N2I2(E0g+) van der Waals complexes have been observed and studied for the first time. Analysis of the luminescence excitation spectra as well as luminescence spectra themselves in the spectral ranges, where the I2(D0u+ → X0g+, β1g → A1u and D’2g → A’2u) transitions can occur, has been carried out. Branching ratios of the iodine molecule state formation and vibronic level population have been determined. Ab initio calculations of the N2I2(X0g+) complex ground state at complete basis set limit are performed. It is shown that it has two stable, parallel and linear, isomers separated by an energy barrier. The parallel isomer is observed in our experiments. Binding energies of the N2I2(X0g+,vX = 0,nX = 0, B0u+,vB = 19,nB = 0) as well as the some spectroscopic parameters of the N2I2(E,vE = 0, 3) complexes have been also estimated.