Intensity Of Luminescence Band Research Articles

Excitonic feature in CsAg2I3 crystals prepared by Bridgman method

This study investigated the optical spectra of the CsAg2I3 crystals at low temperatures. In the reflection spectrum, remarkable reflection peaks owing to band-edge exciton transitions were observed at approximately 3.8 eV above the fundamental absorption edge at 3.6 eV. Under excitation in the energy region of exciton transitions, an intense luminescence band attributed to a self-trapped exciton (STE) was observed at 3.37 eV. In addition to STE luminescence, a weak luminescence line was observed at 3.77 eV. Because the value of 3.77 eV is practically equal to the lowest exciton transition energy estimated from the reflection spectrum, the luminescence line at 3.77 eV comes from a free exciton (FE). The intensities of the FE and STE luminescence peaks decrease with increasing temperature. The activation energies of the FE and STE were estimated from the quenching of luminescence intensities. The features of the exciton states in the CsAg2I3 crystals are presented.

Radiation modification of quartz and its spectral characteristics

The nature of the structural phase transition of quartz under neutron irradiation was studied by X-ray diffraction analysis. The kinetics of gamma luminescence (GL) bands in quartz crystals grown on seeds irradiated with neutrons with a dose of 5-1018..1019 and 5-1019 n/sm2 after additional neutron irradiation of 1016- 8.1020 n/sm2 in the temperature range 77-300 K. Based on experimental data, it is shown that all the structural characteristics of the seed are transferred to the grown crystal. This opens up the possibility of obtaining quartz crystals with predetermined properties. Diffraction parameters of quartz irradiated with neutrons and grown on neutron-irradiated seeds (n/sm2). Based on the results of studies of GL, the redistribution of the intensities of photoluminescence bands under illumination (λw = 300-340 nm) without heating and with heating in the temperature range 300-720 K, the dependence of the intensities of luminescence bands on the neutron fluence, it was assumed that the luminescence centers are at 550 and 660 nm are, respectively, peroxide radicals and non-bridging oxygen atoms located at the interfaces between the α- and β-phases of quartz.

Donor-acceptor pair transitions in MgAl2O4 spinel

The luminescence of the well-known spinel-structured functional compound MgAl2O4 was studied at cryogenic temperatures below 10 K in a wide spectral range from near-IR to VUV under synchrotron radiation and electron beam excitation. The most intense luminescence band at ∼5 eV, which origin remained largely unknown up to now, showed characteristic behaviour of the donor-acceptor pair (DAP) centres and was assigned to the so-called antisite defects. The antisite DAPs are formed by position-swapped cations AlMg● and MgAl′, which define the inversion degree of the spinel structure and, to the best of our knowledge, always exceed 10% (>1.5 × 1021 cm−3) in the synthetic solids. Full data set allowed confirming that extremely high concentration of these intrinsic defects is the main reason for the strong 5-eV luminescence, which mechanism includes the electron transfer from MgAl′ to AlMg● (excitation) following by that from VO● to MgAl× (emission). Irradiation with He + ions up to fluences of 1017 cm−2 randomly displaced cations to empty sites of the spinel lattice resulting in more intragap defect levels, which induce a non-radiative energy relaxation channel quenching closely spaced while unaffecting distant DAP luminescence.

Single-phase nanopowders of Sr0.85-xBaxEu0.15F2.15: Investigation of structure and X-ray luminescent properties

Novel scintillating and visualizing materials are an essential part of the development of high-power X-ray sources like synchrotrons and free-electron lasers. One of the latest approaches is the formation of composite materials composed of X-ray luminescent nanoparticles in a robust transparent matrix with high thermal conductivity. Here, such Sr0.85-xBaxEu0.15F2.15 nanopowders with a particle size of ≈50 nm were synthesized by precipitation from aqueous solutions. Single-phase solid solutions are formed up to a barium concentration of 70 mol.%. The most intense luminescence band is the band of trivalent europium with a maximum at 590.4 nm, corresponding to the 5D0 → 7F1 transition. The concentration dependence of the X-ray luminescence intensity on the barium content was revealed, and the most optimal composition Sr0.35Ba0.50Eu0.15F2.15 with the brightest luminescence response was determined. The obtained type of nanoparticles has potential applications for the fabrication of new scintillating and visualizing composites.

Effective ratiometric optical thermometry based on inverse temperature dependent dual near infrared emission of Cr3+ doped BaAl4Sb2O12 phosphor

The device of reliable non-contact ratiometric optical thermometry technique gradually became a cutting-edge research pot over decades due to its intriguing features of rapid response, high accuracy and simple operation. In which, Boltzmann-based optical thermometry has attracted widespread attention for its exceptional reliability. Here in, we put forward an effective ratiometric optical thermometry based on the highly sensitive and effective Boltzmann-based 2E→4A2/4T2→4A2 emission ratio of BaAl3.9Sb2O12:0.1Cr3+. The phosphor shows dual near-infrared luminescence lines at 698 nm and 710 nm (2E→4A2) and the luminescence band near 750 nm (4T2→4A2). With the temperature elevating from 170 to 470 K, the emission intensity of luminescence lines undergoes continuous enhancement and possess excellent anti-thermal quenching property (3.5-fold at 470 K, compared to 170 K). In contrast, the emission intensity of luminescence band shows a monotonic decline trend. The luminescence intensity ratio shows a good linear relationship in the Arrhenius diagram, and the relative sensitivity reaches 2.08 % K−1 at 170 K, which corroborates the BaAl3.9Sb2O12:0.1Cr3+ has the potential as the optical cryogenic thermometer. In the end, the work provides some insights into the development of novel Cr3+-doped thermometry materials based on the 2E and 4T2 energy level transitions in intermediate crystal field environments.

Energy transfer and color tunable up-conversion luminescence in PrF3 and YbF3 co-doped SrF2 transparent ceramics

Near-infrared pumped up-conversion luminescent PrF3 and YbF3 co-doped SrF2 ceramics were fabricated by the hot-pressing sintering technique, and the pellets were transparent with a primrose yellow appearance. The influence of YbF3 co-doping levels on the optical qualities and microstructures of ceramics was investigated. We identified the mechanisms to realize up-conversion luminescence in the visible range from 3P0,1 levels (Pr3+) under near-infrared wavelength pumping sources other than the near ultraviolet to blue region photons. Yb3+ ions inducing a broad and intense absorption band at the 900–1050 nm region, and the absorption coefficient and cross-section at 980 nm are 7.57 cm−1 and 4.19 × 10−21 cm2 in the ceramic co-doped with 15 wt% YbF3, respectively. The intense up-conversion luminescence bands at 480, 520, 540, and 600 nm under 980 nm excitation were attributed to 3P0→3H4, 3P1→3H5, 3P0→3H5 and 1D2→3H4 transitions of Pr3+ ions, respectively.

Photoluminescence and cathodoluminescence of CaCu(Si[formula omitted]O[formula omitted])[formula omitted

Photoluminescence, cathodoluminescence and light absorption spectra of CaCu(Si2O5)2 have been explored in the spectral range from ultraviolet to near infrared. The luminescence and light absorption spectral bands have been analyzed to determine their constituent peaks. In photoluminescence spectra, the main very intense luminescence band reaching maximum around the quantum energy of 1.42 eV has been found to be composed of six spectral components with the strongest one peaked near 1.41 eV. In cathodoluminescence, only three of six lines have been found to constitute this band, with the strongest one peaking also at 1.41 eV. Besides, two much weaker bands of cathodoluminescence—a narrower one peaked at about 2.2 eV and a broad one spreading from the blue–green spectral region to the near UV range—have been detected in the visible and UV spectral ranges at T=300 and 80 K and the e-beam energies of 10, 15 and 30 keV. The shape and peak composition of the latter band depend on the e-beam energy and sample temperature. The origin of the derived spectral peaks is discussed.

Diagnosis of the technology of titanium and hafnium oxides by luminescence methods

The article shows the role of oxygen vacancies in the formation of luminescence bands of titanium and hafnium oxides, and also demonstrates the relationship between the intensity of luminescence bands and the conditions for the synthesis of films of these materials. It is concluded that photoluminescence is a very sensitive method for diagnosing the composition of oxides. Luminescence bands at 2.45 eV in titanium oxide and 2.91 eV in hafnium oxide make it possible to analyze the change in the film composition under various technological conditions of their production. Keywords: oxygen vacancies, titanium oxide, hafnium oxide, photoluminescence.

Диагностика технологии оксидов титана и гафния методами люминесценции

The article shows the role of oxygen vacancies in the formation of luminescence bands of titanium and hafnium oxides, and also demonstrates the relationship between the intensity of luminescence bands and the conditions for the synthesis of films of these materials. It is concluded that photoluminescence is a very sensitive method for diagnosing the composition of oxides. Luminescence bands at 2.45 eV in titanium oxide and 2.91 eV in hafnium oxide make it possible to analyze the change in the film composition under various technological conditions of their production.

Рентгенолюминесценция нанопорошков SrF-=SUB=-2-=/SUB=-: Eu

Concentration series of single-phase SrF2:Eu solid solutions with a particle size of ≈50 nm were synthesized by precipitation from aqueous solutions. The bands of europium in the di- and trivalent states as well as a band of intrinsic exciton luminescence of strontium fluoride were identified in the X-ray luminescence spectra. The most intense luminescence band is the band of trivalent europium with a maximum at 585–590 nm which corresponding to the 5D0 →7F1 transition. The highest X-ray luminescence intensities upon excitation by an X-ray tube with silver and tungsten anodes are achieved for compositions containing about 15.0 mol.% and 7.5 mol.% europium, respectively.

Hydrothermal Synthesis and Micro-Structural, Optical and Luminescence Properties of Core-Shell Hetero Structure CdS/Zn3(PO4)2 Nanocomposite

The hydrothermal approach was used to make an inorganic semiconducting CdS/Zn3(PO4)2 nanocomposite at a mild reaction temperature of 100 ºC. The XRD data indicate peaks that correspond to CdS hexagonal structure and Zn3(PO4)2 monoclinic-phase with good crystalline character. Surprisingly, the phase shift from α-phase of Zn3(PO4)2 to γ-phase of Zn3(PO4)2 is observed under hydrothermal conditions due to the coupling of CdS with Zn3(PO4)2, as well as internal structural alterations leading to the formation of CdS/Zn3(PO4)2 nanocomposite. Debye-Scherrer and W-H methods were used to calculate average crystallite size, lattice strain and dislocation density. The average crystal lattice is 15-25 nm in size. The hexagonal spheres aggregated on rectangular flakes, indicating core-shell heterostructure, may be seen on the surface morphology of the prepared composite. Due to the quantum size effect, the absorption peak for the composite is in the visible wavelength. It also has a low optical band gap of 2.42 eV, which makes it useful for photocatalytic and photoelectrochemical applications. FT-IR spectrum shows all the fundamental vibrational modes of CdS/Zn3(PO4)2 nanocomposite. Colour coordinate values and CCT values of the prepared composites indicate that they are used for LED applications and the photoluminescence spectrum reveals a broad, intense luminescence band in the visible region with wavelengths ranging from 510 to 518 nm, in good agreement with the absorption wavelength and the CIE diagram.

Lead-Free MDABCO-NH4I3 Perovskite Crystals Embedded in Electrospun Nanofibers.

In this work, we introduce lead-free organic ferroelectric perovskite N-methyl-N'-diazabicyclo[2.2.2]octonium)-ammonium triiodide (MDABCO-NH4I3) nanocrystals embedded in three different polymer fibers fabricated by the electrospinning technique, as mechanical energy harvesters. Molecular ferroelectrics offer the advantage of structural diversity and tunability, easy fabrication, and mechanical flexibility. Organic-inorganic hybrid materials are new low-symmetry emerging materials that may be used as energy harvesters because of their piezoelectric or ferroelectric properties. Among these, ferroelectric metal-free perovskites are a class of recently discovered multifunctional materials. The doped nanofibers, which are very flexible and have a high Young modulus, behave as active piezoelectric energy harvesting sources that produce a piezoelectric voltage coefficient up to geff = 3.6 VmN-1 and show a blue intense luminescence band at 325 nm. In this work, the pyroelectric coefficient is reported for the MDABCO-NH4I3 perovskite inserted in electrospun fibers. At the ferroelectric-paraelectric phase transition, the embedded nanocrystals display a pyroelectric coefficient as high as 194 × 10-6 Cm-2k-1, within the same order of magnitude as that reported for the state-of-the-art bulk ferroelectric triglycine sulfate (TGS). The perovskite nanocrystals embedded into the polymer fibers remain stable in their piezoelectric output response, and no degradation is caused by oxidation, making the piezoelectric perovskite nanofibers suitable to be used as flexible energy harvesters.

Cool white light and tunable multicolor emission from Tb3+/Dy3+ co-activated glasses under different excitations for WLEDs

A set of co-doped (Tb3+/Dy3+) lithium zinc borate (LZB) glasses were developed by melt quenching. The structural evaluation was performed for synthesized glassy matrices. The Dy3+ and Tb3+ individually doped glasses exhibit intense yellow and green luminescence bands at 575 nm (4F9/2 → 6H13/2) and 543 nm (5D4→7F5), respectively. The sensitization effect of Dy3+ on Tb3+ was analyzed by increasing the Tb3+ content with respect to the optimum Dy3+ content (0.5 mol%) in Dy3+/Tb3+. The spectral overlay of Dy3+ luminescence and Tb3+ absorption profiles, Dy3+/Tb3+ PL spectra under different excitations 352, 362, 376, and 385 nm, shortening decay lifetimes of Dy3+ in Dy3+/Tb3+ co-activated glasses, energy transfer (ET) parameters, chromaticity coordinates and their corresponding correlated temperatures all help to explain ET from Dy3+ to Tb3+. At 385 nm of Dy3+ excitation, the optimized co-activated (0.5Dy3++1.0Tb3+):LZB glass displays cool white light emission. The non-radiative ET from Dy3+ to Tb3+ is dominated by electric dipole–dipole interaction and its ET efficiency was calculated to be 63%. At the same time, reverse ET from Tb3+ to Dy3+ was also analyzed. The shift in color coordinates from dominant yellow to greenish-yellow, green and white light emission suggests that Dy3+/Tb3+ co-activated LZB glasses can be a potential candidate for UV converted multicolor and white light emitting devices.

Assessment of optical and fluorescence aspects of Er3+-doped multicomponent B2O3 glasses as active media for 1.532 μm near-infrared optical amplifiers

Current work principally provides an idea on controlling the Er3+: NIR (near-infrared) emission characteristics by changing a glass constituent and finding a suitable glass host favorable to design a novel C-optical band (1.53–1.565 μm) amplifier. By melting and rapid quench route, six transparent Er3+ (1 mol%)-doped B2O3-rich glasses having different single and mixed alkali ions were fabricated, and optical and fluorescence (visible and NIR) traits including Er3+ ion upper-levels 4S3/2 and 4I13/2 decay dynamics were inspected for such samples. At 1.4–1.65 μm wavelength range, an intense and wide NIR luminescence band centered at 1.532 μm (Er3+: 4I13/2 → 4I15/2 transition) has been obtained by a 980 nm laser diode pumping (4I15/2 → 4I11/2). NIR fluorescence Δλeff (effective bandwidth) varied depending on added single or mixed alkali ions, and a maximum Δλeff ∼74.66 nm was acquired for Er3+: Li ions constituting glass. For the 4I13/2 → 4I15/2 transition, σemi (stimulated emission cross-section) was evaluated using both Füchtbauer–Ladenburg and McCumber's theories. In all glasses, comparably, higher gain bandwidth (= 5.384 × 10−26 cm3) and peak σemiM (= 1.692 × 10−20 cm2) values have been attained for 4I13/2 → 4I15/2 transition in Li ions containing sample, and also this glass possesses the largest σabs (absorption cross-section) (= 1.459 × 10−20 cm2) for 4I15/2 → 4I13/2 transition. Further, at distinctive P (population inversion) values, gain spectra were computed, and all samples show C-optical band amplification beginning from P = 50%. All analyzed NIR fluorescence results indicate that Li ions having glass could be a potential gain medium for fiber amplifiers.

Fabrication and optical characterizations of PrF3-doped SrF2 transparent ceramics

A series of PrF 3 -doped SrF 2 ceramics were fabricated by the hot-pressed (HP) sintering method. The influence of PrF 3 concentrations on the microstructure and optical characterizations of transparent ceramics was investigated. PrF 3 doping was found to have a positive effect on increasing optical transmittance. The luminescence intensity and lifetime quenching of Pr:SrF 2 ceramics at high doping concentrations were attributed to the Pr 3+ -Pr 3+ interactions through the intense CR process. The luminescence color of Pr:SrF 2 ceramics was tuned from the blue region to the reddish region, and finally to the orange region with increasing PrF 3 concentrations. The effect of sintering temperature on the optical transmittance and microstructure of Pr:SrF 2 ceramics was also measured and discussed. The highest transmittance of the Pr:SrF 2 ceramic (doped with 5 wt% PrF 3 and sintered at 950 °C) at 350 nm and 1200 nm were 90.4% and 91.9%, respectively. • High transparency Pr:SrF 2 ceramics were fabricated by HP sintering. • The highest transmittance reaches 90.4% at 350 nm and 91.9% at 1200 nm. • Intense visible luminescence bands under 443 nm excitation were detected. • The luminescence color is tuned from blue to reddish, and to orange region.

Transition Metals (Cr3+) and Lanthanides (Eu3+) in Inorganic Glasses with Extremely Different Glass-Formers B2O3 and GeO2.

Glasses containing two different network-forming components and doped with optically active ions exhibit interesting properties. In this work, glass systems based on germanium dioxide and boron trioxide singly doped with lanthanides (Eu3+) and transition metals (Cr3+) ions are research subjects. Optical spectroscopy was the major research tool used to record excitation and emission spectra in a wide spectral range for studied systems. The emitted radiation of glasses doped with Cr3+ ions is dominated by broadband luminescence centered at 770 nm and 1050 nm (4T2 → 4A2). Interestingly, the increase of concentration of one of the oxides contributed to the detectable changes of the R-line (2E → 4A2) of Cr3+ ions. Moreover, EPR spectroscopy confirmed the paramagnetic properties of the obtained glasses. The influence of molar ratio GeO2:B2O3 on spectroscopic properties for Eu3+ ions is discussed. The intensity of luminescence bands due to transitions of trivalent europium ions as well as the ratio R/O decrease with the increase of B2O3. On the other hand, the increase in concentration B2O3 influences the increasing tendency of luminescence lifetimes for the 5D0 state of Eu3+ ions. The results will contribute to a better understanding of the role of the glass host and thus the prospects for new optical materials.

ZnO – Yb2O3 composite optical ceramics: Synthesis, structure and spectral-luminescent properties

Zinc oxide optical ceramics containing 0–2 wt% ytterbium are prepared by uniaxial hot pressing of commercial oxides at 1150 and 1180 °C. The ceramics have the main crystalline phase of hexagonal wurtzite-type ZnO. Ytterbium ions do not enter the ZnO crystals but form a cubic sesquioxide phase of Yb2O3 located at the ZnO grain boundaries. Yb acts as an inhibitor for the ZnO grain growth. The ceramics exhibit transmittance up to 60 % in the visible. Their transmission in the infrared is determined by the free charge carrier absorption. The Yb3+ ions are found in C2 and C3i sites in Yb2O3 crystals. Under X-ray excitation, the ceramics exhibit intense luminescence bands in the blue (near-band-edge emission) and green (defect emission) whose positions, intensities and decay times depend on the Yb content. Yb2O3 causes a redistribution of luminescence intensity in favor of the near-band-edge emission and fastens the emission decay.

A Single Crystal Hybrid Ligand Framework of Copper(II) with Stable Intrinsic Blue-Light Luminescence in Aqueous Solution.

Single-crystal solid–liquid dual-phase hybrid organic–inorganic ligand frameworks with reversible sensing response facilitated by external stimuli have received significant attention in recent years. This report presents a significant leap in designing electronic structures that display reversible dual-phase photoluminescence properties from single-crystal hybrid ligand frameworks. Three-dimensional Cu(C3N2H4)4Cl2 complex frameworks were formed through the intermolecular hydrogen bonding and π⋯π stacking supramolecular interactions. The absorption band peaks at 627 nm were assigned to d–d transition showing 10Dq = 15,949 cm−1 and crystal field stabilization energy (CFSE) = 0.6 × 10Dq = 114.4 kJmol−1, while the ligand-to-metal charge transfer (LMCT) of complexes was displayed at 292 nm. The intense luminescence band results from LMCT present at 397 nm. Considering its structure, air stability, framework forming and stable luminescence in aqueous solution, the Cu(C3N2H4)4Cl2 complex shows potential for luminescence Cu-based sensors using emission intensity to detect heavy metal ion species.

Difference of Eu3+ luminescent properties in YOCl and YOBr oxyhalide hosts

The photoluminescence spectra and luminescence lifetimes of Eu3+-doped oxyhalides, YOX:Eu3+ (X = Cl or Br), and their temperature dependence on different halide species of mixed-anion coordinations were investigated and analyzed. In terms of the ionic and covalent nature of bonding, Eu3+ ions form different coordination polyhedra in the isostructural YOCl and YOBr hosts: a ninefold [Eu3+O4Cl5] and an eightfold [Eu3+O4Br4] polyhedra. The Judd–Ofelt Ω2 parameter for YOCl:Eu3+ takes a very large value (=8.81 × 10−20 cm2) due to the ninefold polyhedron with C4v symmetry. On the other hand, despite the same C4v symmetry, YOBr:Eu3+ shows a very small Ω2 parameter (=2.72 × 10−20 cm2) because of its structural similarity to the square antiprism polyhedron with D4 symmetry. The Ω4 parameters for YOX:Eu3+ are much larger than those for other Eu3+-doped oxides, possibly related to the covalency of halide anions, Cl− and Br−, showing an intense luminescence band (5D0 → 7F4) at around 700 nm. The Eu3+ ions in these YOX hosts were excitable by charge transfer bands in 270–280 nm regions. The relaxation pathways from the charge transfer states to the initial states for luminescence are discussed, using the configuration coordinate diagrams with the spectroscopic characterization.

Low temperature luminescence of mechanically exfoliated β-InSe nanoflakes near fundamental absorption edge

We show that the low-temperature (5 K) emission spectrum of InSe nanoflakes, obtained by mechanical exfoliation of β-InSe, is characterized by unusual luminescence bands that are not present in the source material. These bands were observed both in the center and at the edges of the flakes, and their location at 30–70 meV below the expected position of the excitonic band bottom rules out intrinsic emission. In addition, the most intense luminescence band exhibits line narrowing and a pronounced blue shift of ~40 meV with the increase of excitation power from 40 to 1000 W/cm2. The shift is not observed in the low-temperature emission spectra of ultra thin (four monolayers) InSe flakes. Our data suggest that producing InSe flakes using mechanical exfoliation leads to the generation of optically active structural defects, presumably associated with a violation of the layer sequence and/or layer spacing inherent to β-InSe. The simplest type of these defects are bubbles and/or folds, the formation of which is accompanied by an increase in the distance between InSe layers and, as a consequence, produces repulsive (attractive) potential for electrons (holes). At low temperatures, these defects govern the luminescent properties of the flakes up to 6 monolayers by suppressing the intrinsic (exciton) emission. Some qualitative changes were observed only in ultrathin flakes with a thickness of ~4 monolayers.