Absorption Of Single Crystals Research Articles

Influence of swift heavy ions irradiation on optical and luminescence properties of Y3Al5O12 single crystals

Optical and luminescence properties of Y3Al5O12 (YAG) single crystals preliminary irradiated by swift heavy ions were studied. Swift heavy Xe ions with fluences ranging from 6·1010 to 2·1012 ions/cm2 were utilized for the irradiation of nominally undoped YAG single crystals. A stable strong induced absorption observed in the 200–600 nm spectral range correlates with the irradiation fluence. It is suggested that several centers are responsible for this induced absorption in YAG single crystals and their possible origin (F-type centers) is proposed and discussed. The swift heavy ions irradiation strongly modifies the luminescence properties of YAG, namely, the excitonic emission at liquid helium temperature is drastically suppressed in heavily irradiated crystals.

Cu-MOF attached with pyrene-cored probes as a highly sensitive indicator for carbon monoxide in coal mine gas: Synthesis and performance

As a toxic component in coal mine gas, CO has both acute and long-term damages to human health. Suitable CO probes satisfying the requirement for long-distance real-time monitoring in confined space are still underdeveloped. In this work, a series of fluorescent probes derived from pyrene were synthesized and coordinated onto [Cu3(BTC)2(H2O)3]n (H3BTC meant 1,3,5-benzenetricarboxylic acid) via a coordination bond with Cu2+. These probes were carefully analyzed, including their single crystal structure, absorption spectra, excitation spectra, and emission spectra. Their emission response towards CO gas was analyzed, with a sensing mechanism of probe release which was triggered by a dynamic wagging between the trans- and cis- configuration of –C = N–N = C– moiety upon photoexcitation. These probes were attached onto a classic MOF (metal-organic framework) [Cu3(BTC)2(H2O)3]n, which was confirmed by SEM, fluorescence microscopy, XRD, N2 adsorption/desorption, and TGA. The resulting composite samples (denoted as Pm@CuBTC) showed emission recovery upon trace amount CO (LOD = 0.005 % vs N2, 50 ppm), with a short response time of 31 s at room temperature. High sensing selectivity over competing species of alkane was observed, with stable signal for 5 days.

Can thick metal-halide perovskite single crystals have narrower optical bandgaps with near-infrared absorption?

Metal-halide perovskite (MHP) single crystals are emerging as potential competitors to their polycrystalline thin-film counterparts. These materials have shown the specific feature of extended absorbance towards the near-infrared (NIR) region, which promises further extension of their applications in the field of photovoltaics and photodetectors. This notable expansion of absorbance has been explained by the narrower effective optical bandgap of MHP single crystals promoted by their large thickness over several micrometres to millimetres. Herein, the attributes of the material's thickness and the measurement technique used to estimate these characteristics are discussed to elucidate the actual origins of the extended absorbance of MHP single crystals. Contrary to the general belief of the narrower bandgap of the MHP single crystals, we demonstrate that the extended NIR absorption in the MHP single crystals mainly originates from the combination of unique below-bandgap absorption of MHPs, the thickness of single crystals, and the technical limitation of the spectrophotometer, with the key attributes of (i) significantly large thickness of the MHP single crystals by suppressing the transmitted light and (ii) the detector's limited dynamic range. Combining the theoretical and experimental characterizations, we clarify the significant role of the large thickness together with the limited sensitivity of the detector in promoting the well-known red shift of the absorption onset of the MHP single crystals. The observations evidently show that in some special circumstances, the acquired absorption spectrum cannot reliably represent the optical bandgap of MHP materials. This highlights some misinterpretations in the estimation of the narrower optical bandgap of the MHP single crystals from conventional optical methods, while the optical bandgap is an inherent property independent of the thickness. The proposed broad applications of the MHP single crystals are dictated by their fascinating properties, and therefore, a deep insight into these features should be considered besides device applications, because much of their property-function relationships are still ambiguous and a subject of debate.

Thermally induced effects on optical absorption in Ag-doped Bi12SiO20 single crystals

The spectral-temperature dependences of optical absorption of Bi12SiO20 crystals doped with Ag ions were measured in the visible range of photon energy hν. The temperature of the samples was varied in heating-cooling cycles in the interval T = 280 – 680 K. It was shown that the spectra fulfilled Urbach rule for hν > 2.1 eV at the forbidden zone width of 3.3 eV. The Urbach rule parameters, calculated within the frame of the electron-phonon interaction model, showed anomalous behavior in the interval T = 389 – 500 K. The observed peaks in the temperature dependences of optical absorption were attributed to the competition of thermally induced processes of color centers formation and destruction. The color centers were assumed in the form of Ag2+ – 2O- and Ag+ – O- complexes that are created due to thermal activation energy Ea1 = 0.1 eV and Ea2 = 0.145 eV, respectively. The spectrum of thermochromic effect characterizing non-reversible thermally induced weakening of optical absorption was detected and analyzed.

Growth and spectroscopic properties of a novel Tm3+-doped YSr3(PO4)3 disordered crystal

A novel Tm3+-doped YSr3(PO4)3 (Tm:YSP) crystal with a disordered crystal structure was grown by using the Czochralski pulling method. The single crystal growth, structure, absorption and emission spectra were systematically analyzed. The absorption bandwidth at ∼792 nm was found to be 21 nm, showing that the Tm:YSP crystal was very suitable for commercial laser diodes pumping of AlGaAs. Furthermore, the maximum emission cross section centering at 1835 nm was determined to be 0.86 × 10−20 cm2 with an emission bandwidth of 202 nm, which indicates the promising applications in the fields of ultrafast and tunable lasers. In addition, Spectroscopic parameters, containing Judd – Ofelt intensity, line strengths, radiative transition probabilities, fluorescence branching ratio and radiative lifetime, were analyzed by using the Judd – Ofelt theory. All above results showed that the Tm:YSP crystal with a disordered structure was a potential laser medium in the ⁓ 2 μm region.

Electric-dipole and magnetic absorption in TbFeO3 single crystals in the THz–IR range

Various mechanisms of absorption including both electric-dipole excitations and magnetic ones in a broadband (5–5000 cm−1) polarized transmission and reflection spectra were studied in orthoferrite TbFeO3 using a coherent submillimeter, pulsed THz, and IR Fourier transform spectroscopy. The classical oscillator model and generalized four-parameter model were used to analyze the spectra obtained, and the parameters of the models were determined. We analyzed main absorption processes, which include contributions of both phonons and multi-phonon processes as well as electron transitions in Tb3+ ions and two antiferromagnetic resonance modes in the Fe subsystem. As a result, the spectra of real and imaginary parts of permeability and permittivity were obtained. A distinctive feature of the studied electrodynamic response in TbFeO3 is a significant absorption in the THz range due to multi-phonon processes, which exceeds optical phonon contribution by an order of magnitude at room temperature.

An UV/Vis/NIR optical absorption spectroscopic and color investigation of transition-metal-doped gahnite (ZnAl2O4 spinel) crystals grown by the flux method

Abstract Synthetic flux-grown end-member gahnite, ZnAl2O4, and several different colored crystals doped with one or more transition metals including Mn, Ni, Cr, Co, and Fe were studied by electron microprobe methods and UV/Vis/NIR single-crystal optical absorption spectroscopy. The first major objective was to measure and assign the various electronic absorption features. The second was to analyze quantitatively the crystal colors using the experimental spectra and the CIE 1931 color-space-chromaticity diagram. The microprobe results show that the doped gahnites have transition metal concentrations between about 0.001 and 0.1 cations per formula unit. The spectrum of colorless, nominally pure ZnAl2O4 displays no absorption in the visible region. Microprobe analysis of a light-blue gahnite crystal reveals small amounts of Ni and Mn. The UV/Vis/NIR spectrum does not indicate any dd-electronic transitions relating to Mn. All absorption features also cannot be fully interpreted using Tanabe-Sugano diagrams for Ni2+ in either octahedral or tetrahedral coordination. A series of seven slightly different colored gahnites with differing concentrations of Cr3+ and most also containing smaller amounts of Ni was investigated. The spectrum of a one pink crystal shows two intense absorption features in the visible region. They are assigned to spin-allowed 4A2g → 4T2g (4F) and 4A2g → 4T1g (4F) transitions of VICr3+. Other spectra display additional weak bands and lines that are most probably spin-forbidden dd-transitions of Ni2+. These gahnites with Ni and Cr show varying purple colorations depending on the concentrations of both metals. Two more deeply blue gahnites contain Co2+ as demonstrated by their UV/Vis spectra but not by microprobe analysis. Two intense absorption features at ~7440 and ~16 850 cm–1 are observed and assigned to the spin-allowed transitions 4A2 → 4T1 (4F) and 4A2 → 4T1 (4P) of Co2+, respectively. Complex absorption fine structure, caused by spin-orbit and/or vibronic interactions, is also observed. Three different gahnites with yellow to orange colorations contain measurable Mn. Their spectra are similar in appearance and display several weak IVMn2+ spin-forbidden transitions located above 20 000 cm–1. The spectra of two green gahnites show several Fe spin-forbidden electronic transitions arising from single, isolated IVFe2+ and VIFe3+ cations between 10 000 and 25 000 cm–1. The intensities of some of the VIFe3+-related bands can be increased through exchange-coupled interactions with next nearest IVFe2+ neighbors. The colors of various doped gahnites and the end-member galaxite are analyzed using their single-crystal absorption spectra in the visible region. Their dominant wavelength, λk, and hue saturation, pc, values are given on the CIE 1931 color-space-chromaticity diagram and are discussed. The Hex colors of all crystals are calculated and can be compared to those of the studied crystals.

Differential-thermal analysis and a microscopic study of the effect of γ-radiation on CuTlSe2 single crystal

Herein, the X-ray phase analysis (XPA) and differential-thermal analysis (DTA) of the CuTlSe2 compound obtained by the Bridgman–Stockbarger method have been investigated. As a result of the study, the values of energy absorption and mass losses of CuTlSe2 single crystal have been estimated depending on the temperature given their change mechanisms. The surface morphology of single crystals of the ternary coppercopounds (Cu-Tl-X ([Formula: see text])) in the initial state, annealing and after exposure to gamma-radiation is studied by atomic force microscopy. It is shown that the surface relief undergoes modification in the absorbed dose region of [Formula: see text] 500[Formula: see text]krad.

Thermally induced effects in the optical absorption of pure and doped Bi12SiO20 single crystals

Thermally induced effects in the optical absorption of pure and doped Bi12SiO20 single crystals

Radiation effects in Gd3(Al,Ga)5:O12:Ce3+ single crystals induced by swift heavy ions

Radiation effects in cerium doped Gd3(Al,Ga)5:O12 (or GGAG) single crystals irradiated by swift heavy ions with fluences ranging from 6·1010 to 2·1012 ions/cm2 have been studied. A stable strong induced absorption observed in the spectral range 200–350 nm correlates with the irradiation fluence. It is suggested that several centers are responsible for this induced absorption in GGAG single crystals and their possible origin (F-type centers and V-centers or holes trapped near cation vacancies) is proposed and discussed. The swift heavy ions irradiation strongly modifies the luminescence properties of GGAG, namely, the excitation spectra of the Ce3+ emission, which have been measured over a wide spectral range including vacuum ultraviolet diapason. In particular, it was shown that the formation of the stable radiation defects under swift heavy ions irradiation leads to the effective Ce4+ → Ce3+ transformation in the Mg2+ co-doped GGAG single crystals. The reasons leading to the alteration in the luminescence properties of irradiated GGAG single crystals are elucidated and discussed.

Pbx(OH)y cluster formation and anomalous thermal behaviour in STI framework-type zeolites

For the first time, the structural investigation of a Pb-exchanged zeolite (Pb13.4(OH)10Al17.4Si54.6O144 ∙38H2O) with STI framework type, revealed a highly unusual and intriguing sudden volume increase under continuous heating. Understanding the fundamental mechanisms leading to such an unusual behaviour is essential for technological applications and interpretation of chemical bonding in zeolites. The dehydration was tracked in situ from 25 to 450 °C by single crystal X-ray diffraction, infrared and X-ray absorption spectroscopy. Further interpretation of the experimental observations was supported by ab initio molecular dynamics simulations. Initially, Pb-STI unit-cell volume contracts (ΔV = − 3.5%) from 25 to 100 °C. This agrees with the trend observed in STI zeolites. Surprisingly, at 125 °C, the framework expanded (ΔV = + 2%), adopting a configuration, which resembles that of the room temperature structure. Upon heating, the structure loses H2O but no de-hydroxylation occurred. The key mechanism leading to the sudden volume increase was found to be the formation of Pbx(OH)y clusters, which prevent the shrinking of the channels, rupture of the tetrahedral bonds and occlusion of the pores. This zeolite has therefore an increased thermal stability with respect to other STI metal-exchanged zeolites, with important consequences on its applications.

The role of defects on the transition from saturable absorption to nonlinear absorption of Bi12GeO20 single crystal under increasing laser excitation

This work reports defect and input intensity dependent nonlinear optical behaviors of Bi12GeO20 (BGO) single crystal. Open aperture (OA) Z-scan experiments were performed with 532 nm excitation wavelength under 4 ns and 100 fs pulsed laser irradiation. Obtained data were fitted with a theoretical model considering one-photon, two-photon and free carrier absorption contributions to nonlinear absorption due to longer lifetime of localized defect states than that of used laser pulse durations. At low input intensities, the BGO single crystal showed saturable absorption (SA) behavior and transition to nonlinear absorption (NA) behavior observed with further increase of the input intensities both of pulse durations. At low input intensity, the OPA mechanism is dominant and results in SA by filling of the defect states due to defect state at around one photon energy (2.32 eV). At higher input intensity, multi-photon, two-photon and free carrier absorption become dominant mechanisms, and nonlinear absorption behavior was observed. The lowest saturation threshold was found as 1.36 × 1010 W/cm2 with nanosecond pulses. We have revealed the mechanisms contributing both SA and NA, and determined saturation intensity threshold and effective nonlinear absorption coefficients. Our findings indicate that the tails of defect states overlap in the energy band gaps especially in sufficiently disordered crystal. With this way, the spectral range for saturable absorption and nonlinear absorption can be broadened.

Investigation on multiphoton absorption in MAPbBr3 and MAPbCl3 single-crystals under excitation wavelength up to mid-infrared

The multiphoton absorption (MPA) in MAPbBr3 and MAPbCl3 single-crystals (SCs) is experimentally investigated at the excitation wavelength from near-infrared to mid-infrared. A five-photon absorption (5PA) in MAPbBr3 is demonstrated at an excitation wavelength of 2400 nm for the first time, while that in MAPbCl3 demonstrated at 2100 nm via observing fluorescence as well as using Z-scan measurement. Meanwhile, a 5PA coefficient obtained is 8.4 × 10−13 cm7 GW−4 at 2400 nm for MAPbBr3, while that of MAPbCl3 is 8.7 × 10−11 cm7 GW−4 at 2100 nm. Our results reveal that mid-infrared is available wavelength for generating high-order MPA effect in MAPbBr3 and MAPbCl3 SCs.

Donors and polaronic absorption in rutile TiO2 single crystals

We have used a combination of optical absorption and electrical conductivity measurements to study the effect of the main donor on small polarons in rutile TiO2 single crystals rendered n-type conductive by hydrogenation or doping with Nb. The electrical conductivity measured at 295 K for hydrogenated samples shows a clear correlation with the interstitial hydrogen (Hi) concentration, which is consistent with reports that Hi is the main shallow donor in rutile TiO2. Conductive samples exhibit two distinct optical absorption bands in the IR spectral region, at ω1 = 6500 cm−1 (∼0.8 eV) and ω2 = 3100 cm−1 (∼0.4 eV), which are present in both hydrogen-rich and Nb-doped samples. The intensities of the absorption bands are proportional to the electrical conductivity, and they exhibit an Arrhenius-like temperature dependence for temperatures between 25–50 K and 50–100 K for H-doped and Nb-doped samples, respectively. The thermal activation energies (EAs) for the absorption bands depend strongly on the main donor: ω2 exhibits EA(H) and EA(Nb) of ∼4 and ∼10 meV, respectively, whereas ω1 shows EA(H) and EA(Nb) of ∼1 and ∼2 meV, respectively. The combination of temperature-dependent data for the optical absorption bands and interstitial deuterium (Di)-small polaron vibrational lines support a model where the thermal activation is associated with the reconfiguration of small polarons involving Ti sites far away from the donor. The thermal activation of the optical absorption bands gives us insight into the dynamics of donor-dependent small polaron reconfiguration in rutile TiO2.

Role of the ferroelastic strain in the optical absorption of BiVO4

Bismuth vanadate (BiVO4) has recently been under focus for its potential use in photocatalysis thanks to its well-suited absorption edge in the visible light range. Here, we characterize the optical absorption of a BiVO4 single crystal as a function of temperature and polarization direction by reflectance and transmittance spectroscopy. The optical bandgap is found to be very sensitive to the temperature, and to the tetragonal-to-monoclinic ferroelastic transition at 523 K. The anisotropy, as measured by the difference in the absorption edge for the light polarized parallel and perpendicular to the principal axis, is reduced from 0.2 eV in the high-temperature tetragonal phase to 0.1 eV at ambient temperature. We show that this evolution is dominantly controlled by the ferroelastic shear strain. These findings provide a route for further optimization of bismuth vanadate-based light absorbers in photocatalytic devices.

Two‐Photon Absorption of Butterfly‐Shaped Carbonyl‐Bridged Twistarene

AbstractThe single crystals of a butterfly‐shaped carbonyl‐bridged twistarene 3 were obtained by slow diffusion of methanol into its chloroform solution. The single‐crystal structure analysis indicated that 3 crystallized in a triclinic space group (P‐1). The two‐photon absorption (TPA) and nonlinear optical properties of single crystal of 3 were investigated in the range of 400 nm ∼650 nm. This is the first example of the TPA study based on single crystals made from the carbonyl‐bridged twistarene. The corresponding TPA cross‐section was found to be 3.69 GM at 800 nm.

Phenomena induced by UV irradiation in PbMoO4 single crystal

Electrical properties and optical absorption of PbMoO4 single crystal were studied after UV irradiation. Anomalies of permittivity ε and conductivity σ were detected and attributed to the dipole centers induced by UV light. It was proposed that dipole centers were created by photoelectrons trapped by Mo within oxygen tetrahedra distorted by an oxygen vacancy VO. At high temperatures conductivity was nearly insensitive to UV irradiation. Additional optical absorption was observed in PbMoO4 single crystal after UV irradiation. It was argued that transfer of photoelectrons from lead to molybdenum groups was responsible for the photochromic effect found.

Tridentate Schiff base and 4,4′‐bipyridine coordinated di/polynuclear Cu (II) complexes: Synthesis, crystal structure, DNA/protein binding and catecholase activity

Abstract4,4′‐bipyridine bridged two Cu (II) complexes, [Cu2L12(4,4′‐bipy)(H2O)2](ClO4)2 (1) and [Cu2L22(4,4′‐bipy)]n·(2H2O)n (2) (where, HL1 = 2‐[(3‐methylamino‐propylimino)‐methyl]‐phenol, H2L2 = 3‐[(2‐hydroxy‐3‐methoxy‐benzylidene)‐amino]‐propionic acid, and 4,4′‐bipy = 4,4′‐bipyridine) have been synthesized and characterized by single crystal structure determination, mass spectrometry, FT‐IR, electronic absorption, and emission spectroscopy. Complex 1 is dinuclear cationic compound and counter balanced by perchlorate anion, whereas complex 2 possesses 1D poly‐nuclear structure. Both the complexes crystallize in monoclinic system with P21/c space group and the copper centers possess square pyramidal geometry. H‐bonding, C‐H···π, π···π interactions results the formation of two dimentional supramolecular structure for both the complexes. Interactions of complexes with bovine serum albumins (BSA) and human serum albumins (HSA) have been studied by using electronic absorption and emission spectroscopic technique. The calculated values of binding constants (Kb) are (9.22 ± 0.26) × 105 L mol−1 (1‐BSA), (7.19 ± 0.16) × 105 L mol−1 (1‐HSA), (5.05 ± 0.20) × 105 L mol−1 (2‐BSA) and (3.56 ± 0.25) × 105 L mol−1 (2‐HSA). The mechanism of serum albumins‐complex interactions have been investigated by fluorescence lifetime measurement. Fluorescence spectroscopic studies indicate that both the complexes interact with calf thymas‐DNA. Catecholase activity of the complexes has been studied in methanol using 3,5‐di‐tert‐butylcatechol (3,5‐DTBC) as substrate and the result show that both the complexes are active for catalytic oxidation of 3,5‐DTBC to 3,5‐di‐tert‐butylquinone (3,5‐DTBQ) in presence of molecular oxygen. Calculated values of turnover numbers are 71.81 ± 1.04 h−1 and 69.45 ± 0.74 h−1 for 1 and 2, respectively.

Quantification of the mixed-valence and intervalence charge transfer properties of a cofacial metal-organic framework via single crystal electronic absorption spectroscopy.

Gaining a fundamental understanding of charge transfer mechanisms in three-dimensional Metal–Organic Frameworks (MOFs) is crucial to the development of electroactive and conductive porous materials. These materials have potential in applications in porous conductors, electrocatalysts and energy storage devices; however the structure–property relationships pertaining to charge transfer and its quantification are relatively poorly understood. Here, the cofacial Cd(ii)-based MOF [Cd(BPPTzTz)(tdc)]·2DMF (where BPPTzTz = 2,5-bis(4-(pyridin-4-yl)phenyl)thiazolo[5,4-d]thiazole, tdc2− = 2,5-thiophene dicarboxylate) exhibits Intervalence Charge Transfer (IVCT) within its three-dimensional structure by virtue of the close, cofacial stacking of its redox-active BPPTzTz ligands. The mixed-valence and IVCT properties are characterised using a combined electrochemical, spectroelectrochemical and computational approach. Single crystal electronic absorption spectroscopy was employed to obtain the solid-state extinction coefficient, enabling the application of Marcus–Hush theory. The electronic coupling constant, Hab, of 145 cm−1 was consistent with the localised mixed-valence properties of both this framework and analogous systems that use alternative methods to obtain the Hab parameter. This work demonstrates the first report of the successful characterisation of IVCT in a MOF material using single crystal electronic absorption spectroscopy and serves as an attractive alternative to more complex methods due to its simplicity and applicability.

Development of a Tethered Palladium–BODIPY Dual Catalyst for Enhanced Photo- and Thermally Activated Catalysis, and for Promoting Sequential Reactivity

In recent years there has been a growing interest in merging different types of catalysis to create new multistep catalytic processes. However, the majority of reported dual catalysis strategies use a mixture of individual catalysts, with limited reports of dual catalysis reactions where the different catalysts are combined in a single compound. This work reports the synthesis of a tethered palladium-BODIPY dual catalyst to enable increased synergistic interactions between the catalytic centres. Detailed analysis, including single crystal X-ray crystallography, absorption, fluorescence, and phosphorescence measurements, and kinetic analyses to determine singlet oxygen quantum yields, confirm that chemical tethering results in a significant increase in the photocatalytic potential of the palladium-BODIPY dual catalyst, relative to the parent BODIPY chromophore. Interestingly, the palladium-BODIPY complex also exhibited rare long-lived room temperature phosphorescence. Catalytic applications of the palladium-BODIPY dual catalyst indicate that chemical tethering increases the reactivity of the catalytic centres for both photocatalytic oxidation of thioanisole and palladium catalysed Suzuki–Miyaura cross coupling, highlighting that enhancements in both photo and thermally activated catalysis can be achieved on chemical tethering. In addition, the dual catalytic potential of the palladium-BODIPY catalyst was demonstrated using a representative sequential photocatalytic oxidation–cross coupling reaction.