Spectra Of Crystals Research Articles

Structural, elastic, electronic, optical and anisotropy properties of newly quaternary Tl2HgGeSe4 via DFPT predictions associated to XPES and RS experiments

In the present work, we report on theoretical studies of thermodynamic properties, structural and dynamic stabilities, dependence of unit-cell parameters and elastic constants upon hydrostatic pressure, charge carrier effective masses, electronic and optical properties, contributions of interband transitions in the Brillouin zone of the novel Tl2HgGeSe4 crystal. The theoretical calculations within the framework of the density-functional perturbation theory (DFPT) are carried out employing different approaches to gain the best correspondence to the experimental data. The present theoretical data indicate the dynamical stability of the title crystal and they reveal that, under hydrostatic pressure, it is much more compressible along the a-axis than along the c-axis. Strikingly, the charge effective mass values (me∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{e}^{{^{*} }}$$\\end{document} and mh∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{h}^{{^{*} }}$$\\end{document}) vary considerably when the high symmetry direction changes indicating a relative anisotropy of the charge-carrier’s mobility. Furthermore, the Young modulus and compressibility are characterized by the maximum and minimum values (Emax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E^{max}$$\\end{document} and Emin\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E^{\\min }$$\\end{document}) and (βmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta^{max}$$\\end{document} and βmin\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta^{\\min }$$\\end{document}) that are equal to (62.032 and 28.812) GPa and (13.672 and 6.7175) TPa–1, respectively. Additionally, we have performed calculations of the Raman spectra (RS) and reached a good correspondence with the experimental RS spectra of the Tl2HgGeSe4 crystal. The XPES associated to RS constitutes powerful techniques to explore the oxidized states of Se and Ge in Tl2HgGeSe4 system.

Analysis on the minimum structure of harmonic spectra from MgO crystals.

Recent theoretical and experimental findings have demonstrated the minimum characteristic in the harmonic spectrum of bulk MgO crystals subjected to intense laser pulses. However, the dominant mechanism behind this minimum structure is still under debate. This study simulates the harmonic spectrum from a MgO crystal in a linearly polarized laser pulse by solving multi-band semiconductor Bloch equations. The results show that the minimum feature at 20 eV in the MgO harmonic spectra from 1700 and 800 nm laser pulses is due to band dispersion and interference between interband harmonics. Notably, the disappearance of the minimum structure at 14 eV in the harmonic spectrum from the 800 nm laser is attributed to the intensity suppression of higher energy harmonics, caused by decreased electron population at the boundary of the first Brillouin zone in the multi-band case. These findings offer insights into the spectral structure of solid-state harmonics, contributing to the all-optical reconstruction of the crystal band based on its harmonic spectrum.

Sm3+ as effective deactivator for enhanced ∼3 μm laser emission in Er,Sm:SrLaAlO4 crystal

A promising mid-infrared (MIR) laser crystal with Er, Sm co-doped SrLaAlO4 (Er,Sm:SLA) crystal was successfully grown using the Czochralski (CZ) method. It was the first time that co-doped Sm3+ ion as deactivator for Er3+ activated ∼ 3.0 μm laser. The crystal structure, absorption spectra, emission spectra, and energy level lifetime were discussed in detail. The band structure and density of states were calculated by the density functional theory. The spectral parameters were calculated using Judd-Ofelt (J-O) theory and the deactivate effect of Sm3+ was systematically studied. The introduction of Sm3+ ions enhance the 2.7 µm mid infrared emission intensity by three times, and decrease the lifetime of 4I13/2 energy level of Er3+ ion from 4.35 ms to 0.98 ms. The lifetime ratio of upper and lower levels for 2.7 µm emission was calculated to be 0.63, which is 2.6 times of Er:SLA crystal and comparable to some commercial crystals. All the results indicate that the Sm3+ ion is an effective deactivator for ∼3 μm laser emission. The long upper level lifetime, as well as the large lifetime ratio, the broadening spectra characteristics and the appropriate emission cross-section show the Er,Sm:SLA crystal a good gain material for ultrafast and tunable lasers at ∼3.0 μm.

Defect studies in transition metal dichalcogenide MoSe1.8S0.2 using resonant Raman spectroscopy

Using resonant Raman spectroscopy with 632.8 nm (1.96 eV) laser, we describe the Raman spectra of single crystals of transition metal dichalcogenides with nominal composition MoSe(2−x)Sx for x = 0.2. Changes in Raman spectra at some regions of the sample indicated non-stoichiometry and, in particular, chalcogenide vacancies. At low temperatures around 77 K, we observed unusual temperature dependent enhancement in the intensity of non-zone center modes as well as overtones and combination modes in Raman spectra. This enhancement in the intensity is correlated to the resonance achieved in the non-stoichiometric regions of the crystal at low temperatures. Observed resonance is attributed to modification in the electronic structure due to defects. Energy dispersive x-ray spectroscopy measurements confirmed chalcogenide vacancies in the crystals. The change in the electronic structure due to defects is also corroborated by photoluminescence spectroscopy measurements.

INSPIRED: Inelastic neutron scattering prediction for instantaneous results and experimental design

Inelastic neutron scattering (INS) has unique advantages in probing how atoms vibrate and how the vibrations propagate and interact. Such dynamic information is crucial in understanding various material properties, from heat capacity, thermal conductivity, phase transitions, and chemical reactions to more exotic quantum behavior. The analysis and interpretation of the INS spectra often start from a model structure of the sample, followed by a series of calculations to obtain the simulated spectra to compare with experiments. The conventional way to perform such calculations usually requires significant time, computing resources, and specialized expertise. Here, we present a new program named INSPIRED (Inelastic Neutron Scattering Prediction for Instantaneous Results and Experimental Design), which enables users to perform rapid INS simulations in several different ways on their personal computers in just a few clicks, with the crystal structure as the only input file. Specifically, the users can choose a pre-trained symmetry-aware neural network (coupled with an autoencoder) to predict the phonon density of states (DOS), 1D S(E) and 2D S(|Q|,E) spectra for any given structure. One can also choose an existing density functional theory (DFT) calculation from a database (containing over 12,000 crystals), and quickly obtain the simulated INS spectra for single crystals and powders. It is also possible to use pre-trained universal machine learning force fields to relax a given crystal structure, calculate the phonon dispersion and DOS, and, subsequently, the INS spectra. All these functions are implemented with a PyQt graphic user interface. We expect these new tools will benefit broad user communities and significantly improve the efficiency of experiment design, execution, and data analysis for INS. Program summaryProgram Title: INSPIREDCPC Library link to program files:https://doi.org/10.17632/8g3s8f9n2p.1Developer's repository link:https://github.com/cyqjh/inspired (software), https://doi.org/10.5281/zenodo.11478889 (database, models files, and virtual machine appliance file)Licensing provisions: MITProgramming language: PythonNature of problem: How to easily and quickly assess the expected INS spectra for a given crystal structure has been a major challenge in the INS user community. It is a main bottleneck affecting almost every stage of the workflow, from experimental design and steering to data analysis and interpretation. The widely used approach involving DFT calculations is time-consuming, requires advanced computing resources, and has a steep learning curve. With the growing power of neutron sources and more high-throughput INS experiments, there is a pressing need to address this problem, preferably by taking advantage of the recent developments in machine learning and artificial intelligence.Solution method: We take a data-driven approach to tackle the problem. A symmetry-aware neural network is trained to make direct predictions from the crystal structure to either 1D spectra or latent space vectors, which can be decoded to reconstruct 2D spectra. The database used for the training contains over ten thousand crystals, which can also be used to calculate INS spectra for single crystals and powders. The recently emerging universal machine learning force fields provide another venue to accelerate the simulation significantly. All these solutions are implemented in a graphic user interface so that a user with no modeling/programming background or access to powerful computers can still easily run the workflow.

Raman study of the conformational instability of a ferrocene molecule at high pressure: Influence of a crystal field

AbstractThe Raman spectra of ferrocene crystals were measured at pressures up to 20 GPa, and an abnormally large bandwidth of intermolecular phonons at ambient pressure was found. With an increase in the pressure, the bandwidth increased to a maximum at ~2 GPa and then decreased to a minimum at ~4 GPa, which was equal to the pressure‐independent bandwidth of intramolecular phonons. The unusual behavior of the bandwidth was related to the instability of a ferrocene molecule caused by jumps between its D5d and D5h conformations. A decrease in the time of jumps between the conformations to the period of crystal lattice vibrations led to a loss of coherence and broadening of intermolecular phonon bands. The energy barrier between the conformations was determined to be ~17.6 meV/molecule under ambient conditions and 80 meV/molecule at 4.9 GPa. An increase in the barrier with pressure was due to the enhancement of the crystal field, which resulted in the inhibition of the jumps and the stabilization of the molecule in the D5d conformation.

Pressure-induced phase transition in nanostructured cation-deficient Zn0.34Fe2.53☐0.13O4 ferrite

The crystal structure and vibrational spectra of cation-deficient nanostructured zinс ferrite Zn0.34Fe2.53☐0.13O4 (where ☐ denotes the cation vacancies) have been studied using X-ray diffraction and Raman spectroscopy methods in the pressure range of 0–34 GPa. Our results indicate a phase transition from the initial cubic phase with space group Fd3‾m to a high-pressure phase with orthorhombic symmetry of Bbmm at pressures above 18 GPa. This phase transition is accompanied by changes in lattice parameters, unit cell volume, interatomic bond lengths, and vibration mode frequencies.

The Wannier-Mott Exciton, Bound Exciton, and Optical Phonon Replicas of Single-Crystal GaSe

We report the absorption and photoluminescence spectra of GaSe single crystals in the near-edge region. The temperatures explored the range from 17 to 300 K. Specifically, at a temperature of 17 K, the photoluminescence spectrum reveals an interesting phenomenon: the Wannier-Mott exciton separates into two states. These states are a triplet state with an energy of 2.103 eV and a singlet state with an energy of 2.109 eV. The energy difference between these two states is 6 meV. Furthermore, the bound exciton (BX) can be localized at an energy of 2.093 eV. It is worth noting that its phonon replicas (BX-nLO) can be clearly distinguished up to the fourth order. Interestingly, the energy gaps between these replicas exhibit a consistent spacing of 7 ± 0.5 meV. This intriguing finding suggests a high-quality crystalline structure as well as a strong coupling between the phonon and BX-nLO. Additionally, at low temperatures, both the ground state (n = 1) at 2.11 eV and the excited state (n = 2) at 2.127 eV of free excitons can be observed.

VIBRATIONAL AND X-RAY MEASUREMENTS OF La2Ti2O7 UNDER HIGH PRESSURE CONDITION

The present study focuses on investigating the impact of high-pressure conditions on the crystal structure and vibration spectra of the perovskite-like layered compound La2Ti2O7. To this end, X-ray diffraction and Raman spectroscopy techniques were employed to observe the behavior of the compound under pressure levels up to 30 GPa. The neutron diffraction at ambient pressure confirms that the structure of La2Ti2O7 is monoclinic P21. The results indicate that when the pressure attains 17.3 GPa, the original monoclinic phase of P21 symmetry undergoes a phase transition to the monoclinic phase of P2 symmetry. The observed pressure-induced phase transitions in La2Ti2O7 are associated with anomalous changes in both the unit cell parameters and the vibrational modes. Additionally, the study obtained the baric dependences of lattice parameters, unit cell volume and vibration frequencies, which were used to calculate the bulk modules for the initial and pressure-induced phases of La2Ti2O7.

Crystal growth and spectroscopic performances of Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystal as potential yellow laser gain mediums

Exploring new Dy3+-doped laser gain medium is still a challenge for constructing efficient yellow solid-state laser at current stage. In this paper, high quality Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystals were grown by the high temperature solution method. The crystal structure, chemical composition, phonon energy, polarized absorption and emission spectra, fluorescence lifetime were investigated. The obtained large FWHMs (6 nm) and absorption cross-sections (3.87×10−21 cm2) of Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystals at 454 nm indicate that they can be efficiently pumped by the commercial blue laser diodes. J-O intensity (Ω2, Ω4, Ω6), fluorescence branching rate and radiative lifetime of Dy3+ ions were calculated by J-O theory. Benefiting from the appropriate phonon energy, the emission cross-section of Dy3+: YPO4 crystal at 575 nm can reach 5.04×10−21 cm2. Moreover, after co-doping Tb3+ as deactivating ion, the emission cross-section of Dy3+/Tb3+: YPO4 crystal at 575 nm was promoted to 5.98×10−21 cm2 by a resonance energy transfer process between the Dy3+-6H13/2 and Tb3+-7F4. Therefore, both Dy3+:YPO4 and Dy3+/Tb3+:YPO4 crystals are potential candidates for yellow laser gain mediums.

Synthesis, Crystal Structure, and Optical and Magnetic Properties of the New Quaternary Erbium Telluride EuErCuTe3: Experiment and Calculation.

This paper reports for the first time on a new layered magnetic heterometallic erbium telluride EuErCuTe3. Single crystals of the compound were obtained from the elements at 1120 K using CsI as a flux. The crystal structure of EuErCuTe3 was solved in the space group Cmcm (a = 4.3086(3) Å, b = 14.3093(9) Å, and c = 11.1957(7) Å) with the KZrCuS3 structure type. In the orthorhombic structure of erbium telluride, distorted octahedra ([ErTe6]9-) form two-dimensional layers (Er(Te1)2/2e(Te2)4/2k-)∞2, while distorted tetrahedra ([CuTe4]7-) form one-dimensionally connected substructures (Cu(Te1)2/2e(Te2)2/1t5-∞1) along the [100] direction. The distorted octahedra and tetrahedra form parallel two-dimensional layers (CuErTe32-∞2) between which Eu2+ ions are located in a trigonal-prismatic coordination environment (EuTe610-). The trigonal prisms are connected by faces, forming chains (Eu(Te1)2/2(Te2)4/22-∞1) along the [100] direction. Regularities in the variations in structural parameters were established in the series of erbium chalcogenides (EuErCuCh3 with Ch = S, Se, and Te) and tellurides (EuLnCuTe3 with Ln = Gd, Er, and Lu). Ab-initio calculations of the crystal structure, phonon spectrum, and elastic properties of the compound EuErCuTe3 were performed. The types and wavenumbers of fundamental modes were determined, and the involvement of ions in the IR and Raman modes was assessed. The experimental Raman spectra were interpreted. The telluride EuErCuTe3 at temperatures below 4.2 K was ferrimagnetic, as were the sulfide and selenide derivatives (EuErCuCh3 with Ch = S and Se). Its experimental magnetic characteristics were close to the calculated ones. The decrease in the magnetic phase transition temperature in the series of the erbium chalcogenides was discovered.

Raman scattering of omphacite at high pressure: towards its possible application to elastic geothermobarometry

Abstract Due to their widespread occurrence in several geological settings, omphacite inclusions could be used for elastic Raman geothermobarometry. However, the Raman scattering of complex silicate minerals entrapped in a host depends on both the chemical composition and elastic strain developed during the metamorphic pathway, which makes the task very challenging. Here, as a very first step to probe the potential of omphacite to be used as a mineral inclusion in elastic geothermobarometry, we report the pressure dependence of the Raman spectra of omphacite crystals with the same composition, approximately Jd45Di55, but having different symmetry because of the existence (P2/n) or absence (C2/c) of chemical order at the six- and eight-coordinated cation sites. The experimental results are complemented by ab initio quantum mechanical simulations on fully ordered omphacite (Jd50Di50). We demonstrate that the position of the well-resolved Raman peak near 688 cm-1, arising from Si-O-Si bond bending, is very sensitive to pressure but independent of the state of chemical order, which makes it promising to be utilized in Raman geobarometry. The width of this peak varies with chemical order but not with pressure and therefore can be used to constrain the temperature of inclusion entrapment, because the chemical order is indicative of the closure temperature of the cation-exchange reaction. However, further detailed analyses on the compositional variation of the Raman spectra of omphacite is required before considering omphacite-in-garnet systems as suitable for Raman elastic geothermobarometry.

Lattice dynamics of the BaMg1/3Ta2/3O3 complex perovskite: DFT calculation and Raman spectroscopy

The article presents the results of studies of theBaMg1/3Ta2/3O3 (BMT) complex perovskite crystal using Raman spectroscopy and density functional theory (DFT) calculation. The polarized Raman spectra of a cubic BMT single crystal are obtained in two different geometries in a broad temperature range (5–580 K). The density functional theory calculations of the lattice dynamics and vibrational spectra of the BMT crystal in the Г point of the trigonal phase are carried out. The simulated Raman spectra are analyzed in comparison with the experimental spectra of cubic single crystals and those of ceramics in the trigonal phase. The Raman spectra peculiarities are observed and explained.

Does a “glycine magnesium chloride” crystal exist?

The authors of a recently published paper (J Mol Struct 1277 (2023) 134,839) report to have newly grown seeds of “glycine magnesium chloride” (GMC) crystal by slow evaporation of an aqueous solution containing equimolar ratios of glycine and magnesium chloride. A critical analysis of the unit cell data and infrared spectrum of the so-called GMC crystal reveals the total absence of magnesium chloride, as these correspond to the γ-modification of glycine. In this letter to the Editor, we prove that all papers reporting on so-called GMC, “coumarin doped GMC” CDGMC, and “methylene blue dye doped GMC” MDGMC crystals, are erroneous as the material studied in all cases is γ-glycine. Hence, the quantum mechanical studies on the non-existent GMC, CDGMC and MDCMG crystals have no scientific value.

Heat Capacity and Features of the Phonon Spectrum of Single Crystals of Solid Solutions of Yttrium–Lutetium Aluminum Garnets

The temperature dependences of the heat capacity were measured and the general patterns of the formation of the phonon spectrum of single crystals of solid solutions of yttrium-lutetium aluminum garnets Y3 – xLuxAl5O12 at 0 ≤ x ≤ 3 were investigated in the temperature range from 1.9 to 220 K. According to the data obtained at temperatures below 10 K, the Debye temperatures were calculated. The features of the phonon spectrum in the intermediate temperature range are interpreted as a superposition of optical modes for yttrium and lutetium garnets. It is shown that the low heat capacity values due to the contribution of acoustic phonons for Y2.25Lu0.75Al5O12 correlate with anomalies in the concentration dependences of the phonon transport, the absorption of acoustic waves, and the shape of the aluminum NMR line.

Syntheses and Spectroscopic Characterization of Selected Methyl Quinolinylphosphonic and Quinolinylphosphinic Acids; Rationalized based on DFT Calculation

Abstract: The quinoline derivatives arouse interest due to their broad spectrum of activity. The phosphorus compounds under investigation, quinolinylphosphonic and -phosphinic acids and aminophenylphosphonic and -phosphinic acids, possess potent bioactive properties, mimicking amino acids, phosphate esters, anhydrides, or carboxylate groups in enzymes. Despite its potential value, there is no reported example of quinolinylphosphonic or - phosphinic acids with phosphonic or phosphinic functional groups connected directly to the benzene ring in quinoline constitution. The selected quinoline derivatives have been synthesized by adopting the Skraup-Doebner-Von Miller reaction. To this end, the syntheses of aminophenylphosphonic and -phosphinic acids were conducted and afforded the target products with high yield. All structures have been proven by the combination of NMR, IR, MS, and HRMS techniques and were rationalized based on DFT calculation. The structures of triphenylphosphane oxide (TPO), diphenylphosphosphinic acid (1c), (tert-butyl)phenylphosphinic acid (1d) and bis(3-nitrophenyl)phosphinic acid (2c) were determined by single-crystal X-ray diffraction measurements. The Hirshfeld surface analyses for 1c, 1d and 2c were performed to analyze the intermolecular interactions in their crystal structures. According to our findings, the presence of numerous intermolecular PO•••H, NO•••H, and CH•••O contacts stabilizes the crystal structures. The NO•••H interactions manifest in the IR spectrum of 2c crystal as a narrow band with a maximum at 3088 cm-1. The PO•••H intermolecular interactions are attributed to a weak experimental band at 1288 cm-1.

Growth, optical and thermal properties of YbxHo1-xCa4O(BO3)3 crystals

YbxHo1-xCa4O(BO3)3 (Yb:HoCOB, x = 0, 0.1, 0.2, 0.3) crystals were grown by the Bridgman method for the first time. The crystal structure, rocking curve, transmission spectra, absorption spectra, band structure and thermal properties of Yb:HoCOB were characterized in detail. The maximum half peak width (FMHW) of Yb0.1Ho0.9COB and Yb0.2Ho0.8COB is 26.7″ and 23.8″, respectively, and the effective segregation coefficient is greater than 0.9. In addition, the transmittance of Yb:HoCOB is 88 %. New absorption peaks are introduced by doping Yb3+ at 850–1000 nm. The UV absorption cut-off edge of Yb:HoCOB is red-shifted with increasing Yb3+ doping. The thermal diffusivity and thermal conductivity of Yb:HoCOB decrease with increasing temperature. The specific heat increases with the increasing temperature and finally approaches a constant value. The specific heat of Yb:HoCOB crystal are above 0.670 J/gK at room temperature. Yb:HoCOB with good crystallization quality, high transmittance and high specific heat has the application potential in laser frequency and QPCPA. This work provides a useful exploration for the study of nonlinear optical materials in solid state lasers.

Depicting the Chemical Diversity of Bioactive Meroterpenoids Produced by the Largest Organism on Earth.

In this investigation, we explored the diversity of melleolide-type meroterpenoids produced by Armillaria ostoyae, one of the largest and oldest organisms on Earth, using extracts from liquid and solid fermentation media. The study unveiled three unprecedented dimeric bismelleolides and three novel fatty-acid-substituted congeners, along with 11 new and 21 known derivatives. The structures were elucidated by 1D and 2D NMR spectroscopy and HRESI-MS, and ROESY spectral analysis for relative configurations. Absolute configurations were determined from crystal structures and through ECD spectra comparison. A compound library of melleolide-type meroterpenoids facilitated metabolomics-wide associations, revealing production patterns under different culture conditions. The library enabled assessments of antimicrobial and cytotoxic activities, revealing that the Δ2,4 double bond is not crucial for antifungal activity. Cytotoxicity was linked to the presence of an aldehyde at C1, but lost with hydroxylation at C13. Chemoinformatic analyses demonstrated the intricate interplay of chemical modifications on biological properties. This study marks the first systematic exploration of Armillaria spp. meroterpenoid diversity by MS-based untargeted metabolomics, offering insight into structure-activity relationships through innovative chemoinformatics.

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.

Effect of thickness and applied pressure on quality factor in defective photonic crystals composed of polymer materials

In this work, we employed the transfer-matrix method to obtain the transmittance spectrum of a defective one-dimensional photonic crystal composed of polymer materials. We consider that the dielectric constant of the polymers is a function of the applied pressure, and the cavity is infiltrated by plasma cells. When blood plasma concentration and cavity thickness are increased, we observe a defective mode tuned to long wavelengths within the photonic band gap. By calculating the energy stored in the cavity, a maximization of the quality factor to [Formula: see text] for a 2350[Formula: see text]nm cavity was observed. In addition, we report that as the applied pressure increases, the defective mode shifts to shorter wavelengths, accompanied by a decrease in the quality factor to [Formula: see text] for a pressure of 100[Formula: see text]MPa.