Optical Decay Research Articles

Correlation between thermoluminescence and optically stimulated luminescence of LiMgPO4:Tb,Sm,B phosphor

LiMgPO4:Tb,Sm,B is a promising material for dosimetry applications, particularly in optically stimulated luminescence (OSL). This study aimed to explore residual thermoluminescence (R-TL) glow curves after different light bleaching times to establish a connection between TL traps and OSL components for the first time. The OSL decay curves and R-TL glow curve intensities were analyzed using exponential decay functions to account for optical decay, enabling identification of the OSL components and bleaching decay rates of each TL peak. A correlation between the decay rates of OSL components and bleaching decay rates of TL peaks, as well as the relationship between increased OSL intensity and decreased TL intensity were studied for different irradiation doses. Various bleaching models were evaluated to determine the most appropriate one for LiMgPO4:Tb,Sm,B. A non-thermally sensitive deep electron trap is proposed to enhance the understanding of the luminescence mechanism in LiMgPO4:Tb,Sm,B.

Optical characterizations of densely doped Tm3+:KYW crystals at low temperatures

We investigate the optical lifetime, decay characteristics, spectral linewidth and energy level properties of thulium ions doped in a KY(WO 4 ) 2 crystal at 4 K temperature. High doping concentration of thulium ions with inhomogeneous broadening allow us to study nonradiative behaviors, instantaneous spectral diffusion, and spectral power broadening in this solid-state material. The theoretical consideration of ion–ion interactions is shown to accurately characterize the absorption, decay and other spectral behaviors of Tm 3+ ions. We observe more than ten-fold reduction in the decay time of 3H4 state and about three-fold reduction in the spectral-hole lifetime as we approach the center of the inhomogeneous broadening, corresponding to higher optical densities.

Continuous Solar Energy Conversion Windows Integrating Zinc Anode-Based Electrochromic Device and IoT System.

Integration of solar cells and electrochromic windows offers crucial contributions to green buildings. Solar-charging zinc anode-based electrochromic devices (ZECDs) present opportunities for addressing the solar intermittency issue. However, the limited energy storage capacity of ZECDs results in wasted harnessing of solar energy as well as overcharging. Herein, spectral-selective dual-band ZECDs that continuously transport solar energy to indoor appliances by remotely controlling the repeated bleached-tinted cycles during the daytime, are reported. Hexagonal phase cesium-doped tungsten bronze (h-Cs0.32WO3, CWO) nanocrystals are adopted for dual-band ZECDs due to their independent control ability of near-infrared (NIR) and visible (VIS) light transmittance (∆T=73.0%, 700nm; ∆T = 83.7%, 1200nm) and excellent cycling stability (0.8% optical contrast decay at 1200nm after 10000 cycles). The prototype device (i.e., CWO//Zn//CWO) delivers extraordinary thermal insulation capability, displaying a 10°C difference between "bright" and "dark" modes. Furthermore, an Internet of Things (IoT) controller to control the NIR and VIS lights of the CWO//Zn//CWO window wirelessly with a smartphone, empowering the continuous discharging of the solar-charged window during the daytime remotely, is developed. Such windows represent an intriguing potential technology whose future impact on green buildings may be substantial.

Ga/Al ratio induced afterglow behavior of Ce3+:GAGG scintillation ceramics

This work investigated the optical and scintillation properties of cerium-doped gadolinium aluminum gallium garnet (Ce:GAGG) ceramics with different gallium-to-aluminum (Ga/Al) ratios. The optical transmittance, fluorescence spectra, fluorescence lifetime, light yield, scintillation decay, and afterglow characteristics of the ceramic samples were studied. The experimental results reveal that the decay time of Ce:GAGG ceramic is significantly decreased with the increase of Ga content. The mean decay time of 60 ns is achieved when the Ga/Al ratio is 3:2 in our experiment. The light yield of ceramics varies from 12,140 to 44,825 ph/MeV with the change of Ga content, and the highest light yield is achieved when the Ga/Al ratio is 2.4:2.6. Noteworthy fluctuation in the afterglow performance is affected by the Ga content significantly. The afterglow intensity of the sample with Ga/Al = 2:3 is approximately 0.5 % of its initial intensity after the X-ray excitation was turned off for 5 s. The formation mechanism of defects which is related with the afterglow behaviors were investigated and discussed.

Structural, optical, luminescence spectroscopy and radiation shielding properties of Eu3+:borophosphotellurite glasses

Recently much effort is being paid to study the rare earth ions in multi component glass formers as they exhibit high enhancement in the efficiency of luminescence properties. In this direction, the present study focuses on the preparation and analysis of novel glass batches with composition of (in mol %) BPTCZEu: 40B2O3+20P2O5+15TeO2+ 10CaO+(15−x)ZnO + xEu2O3, x = 0.1, 0.5, 1.0, 1.5, 2.0 and 2.5. The important spectroscopic techniques such as optical absorption, luminescence, excitation and decay curves are taken to analyse the BPTCZEu glasses. Luminescence spectrum of BPTCZEu comprise of emission from excited (5D0) to the lower multiplets (7FJ (J = 0−4)), among these, 5D0 → 7F2 (red luminescence) at 612 nm found to be very intense. Judd−Ofelt characteristics, Ω2, Ω4 and Ω6, were derived from different constraints. To know the site symmetry around Eu3+, the fluorescence intensity ratio of 5D0 → 7F2 vs. 5D0 → 7F1 were analysed. Exciting 7F0 → 5L6 and monitoring 5D0 → 7F2, the lifetime of 5D0 level is determined to be 2 ms which is independent of Eu3+ content. The colour coordinates for all the Eu3+ concentrations are estimated to fall in the reddish−orange region. Theoretical radiation shielding results showed that substituting Eu2O3 for ZnO in the glasses lowers photon number that can pass via the material, enhancing the glass system's trend to shield high energy radiation. These stimulated results are compared with experimental measurements of mass attenuation coefficient with respect to energy up to 662 KeV using Cs−137 source. All these findings obtained from title glasses are compared and discussed with respect to reported Eu3+:glasses and no systematic variation has been noticed either with single, bi− or multi−component glass formers and therefore needs further systematic work to relate Eu−radiation−ligand interaction.

Strong plasmon-mechanical coupling through standing acoustic waves and antenna enhancement, toward mass transduction

Plasmon-mechanical resonators are frequently employed in sensor development. Here, I report the coupling of plasmon and mechanical modes in a multilayer architecture. In the experiment, the multilayer comprised indium tin oxide (ITO) and silver (Ag) mirrors placed on the top and bottom of a SiO2 substrate. By activating a Fabry–Pérot hybrid mode and surface plasmon polariton in a Kretschmann configuration, I demonstrated the generation of a hybrid plasmon-mechanical mode by plasmonic dispersion and through strong coupling, which resulted in mechanical distortion at multiple frequencies. Adsorption of rhodamine G6 on Ag modifies the optomechanical spectrum; it causes eigenmodes to split, resulting in a coupling rate greater than the optical decay rate (κ∗<g). Besides, the excitonic modes were observed to interact with plasmon-mechanical modes, especially on-resonance, where the plasmon-mechanical modes exhibited the higher intensity. For example, the out-of-phase flexural mode (iii, g0=427×2πkHz) became active because of the coupling of the dye. Meanwhile, after dye absorption, the strong in-phase compressional mode (iv, g0=560×2πkHz) exhibited the widest splitting and an increase in the side peaks, which merged when the pump power was raised. The system was then analyzed to determine the ideal experimental settings for detecting mass by the oscillator in a controlled experiment. The mass sensor responsivity was evaluated to be F=1017Hzg−1. Advantages and disadvantages of this approach are presented.

Study of temperature evolution of phonon anharmonicity in HfxSn1-xSe2 (x = 0, 0.05, 0.1, 0.15, 0.2) crystals

In this paper, we demonstrate the study of the vibrational mode of HfxSn1-xSe2 (x = 0, 0.05, 0.1, 0.15, 0.2) crystals as a function of temperature. The temperature-dependent Raman spectra were measured in the temperature range 80 K–300 K. We demonstrated the careful study of temperature-dependent behaviour of out-of-plane A1g vibrational mode of the 2H-type lattice structure of HfxSn1-xSe2 crystals. The Raman peak is shifted towards the higher frequency side on decreasing temperature. The first-order temperature coefficient and an anharmonic constant were evaluated by fitting temperature dependence Raman peak and FWHM. The non-linear behaviour in Raman shifting with temperature is explained by optical phonon decay into two or three acoustic modes. The present investigations can be utilized for further study of the optical and thermal properties of HfxSn1-xSe2 (x = 0, 0.05, 0.1, 0.15, 0.2) transition metal dichalcogenides.

Optical free induction decay emission carrying orbit angular momentum from ionic nitrogen enabled by multiple-photon resonance

Optical free induction decay emission carrying orbit angular momentum from ionic nitrogen enabled by multiple-photon resonance

Imaging of Evoked Cortical Depolarizations Using Either ASAP2s, or chi-VSFP, or Di-4-Anepps, or Autofluorescence Optical Signals.

Population voltage imaging is used for studying brain physiology and brain circuits. Using a genetically encoded voltage indicator (GEVI), "VSFP" or "ASAP2s", or a voltage-sensitive dye, Di-4-Anepps, we conducted population voltage imaging in brain slices. The resulting optical signals, optical local field potentials (LFPs), were used to evaluate the performances of the 3 voltage indicators. In brain slices prepared from VSFP-transgenic or ASAP2s-transgenic mice, we performed multi-site optical imaging of evoked cortical depolarizations - compound excitatory postsynaptic potentials (cEPSPs). Optical signal amplitudes (ΔF/F) and cEPSP decay rates (OFF rates) were compared using analysis of variance (ANOVA) followed by unpaired Student's t test (31-104 data points per voltage indicator). The ASAP2s signal amplitude (ΔF/F) was on average 3 times greater than Di-4-Anepps, and 7 times greater than VSFP. The optical cEPSP decay (OFF rate) was the slowest in Di-4-Anepps and fastest in ASAP2s. When ASAP2s expression was weak, we observed slow, label-free (autofluorescence, metabolic) optical signals mixed into the ASAP2s traces. Fast hyperpolarizations, that typically follow depolarizing cortical transients (afterhyperpolarizations), were prominent in ASAP2s but not present in the VSFP and Di-4-Anepps experiments. Experimental applications for ASAP2s may potentially include systems neuroscience studies that require voltage indicators with large signal amplitude (ΔF/F), fast decay times (fast response time is needed for monitoring high frequency brain oscillations), and/or detection of brain patches in transiently hyperpolarized states (afterhyperpolarization).

Er3+: B2O3-TeO2-ZnO-PbF2−M2O/MF (M = Li, Na, and K) glasses: An inspection of structural, thermal, optical, chromatic, and near-infrared luminescence traits for displays and potential C-band amplification

Six 1.0 mol% Er2O3-doped lead fluoride zinc borotellurite glasses comprising different alkali metal oxides and fluorides (K2O, Na2O, Li2O, KF, NaF, and LiF) have been synthesized via melting and quick-quench approach and structural, thermal, optical, chromatic, upconversion, and NIR (near-infrared) emission features and fluorescence decay times were explored. Main structural units BO3 and BO4, as well as TeO4 and TeO3, are affirmed in all glasses networks by Fourier transform infrared and Raman spectroscopy. For transition 4I13/2 →4I15/2, σemi (emission cross-section) has been assessed by applying Füchtbauer–Ladenburg and McCumber's theories. For Li2O and NaF constituting glasses, acquired peak absorption cross-section (4I15/2→4I13/2) values are 0.999 × 10−20 cm2 and 1.093 × 10−20 cm2, while σemiM (4I13/2→4I15/2) values are 1.064 × 10−20 cm2 and 1.174 × 10−20 cm2 individually. At various P (population inversion) values, calculated gain spectra revealed the C- band amplification from P = 40%.

Bias-dependent degradation of single quantum well on InGaN-based light emitting diode

This paper investigates the factors that influence the efficiency and the reliability of InGaN-based light emitting diodes. The devices under test have a single InGaN quantum well, with a nominal emission wavelength of 495 nm. From the preliminary characterization, the L-I curve shows an anomalous slope mainly due to: i) high Shockley Read Hall recombination rate, and ii) low electron densities in the explored range of injection, as also confirmed by simulation. The reliability of the devices was investigated by performing a constant current stress test at J = 80 A/cm2 at room temperature. Optical degradation occurs with different trends, depending on the injection regime. For low injection levels, the optical power decay is monotonic. In the high injection range, for I > 10 mA, we can recognize different degradation phases. The optical degradation can be ascribed to the generation and relocation of defects in the active region, as also confirmed by DLOS measurement. The origin of degradation was also investigated by a stress test with photoluminescence measurement. The results suggest that the variation of the optical characteristics can be related to the variation of the intrinsic characteristics of the material.

Radiochemical Oxygen Depletion Depends on Chemical Environment and Dose-Rate: Implications for FLASH Effect

FLASH (dose rates > 40 Gy/s) radiotherapy (RT) protects normal tissues from radiation damage, compared with conventional RT (∼Gy/min). Radiation-chemical oxygen depletion (ROD) has been the leading and most-studied mechanism to explain FLASH. Previous studies have reported low ROD values of ∼0.35 µM/Gy, however, they do not accurately model (utilizing water or oxidized substrates such as albumin) the intracellular environment. It has been proposed that the intracellular environment may support higher ROD values due to its specific chemical makeup. As chemical reducing agents, which play a critical role in the cell, may promote ROD, we measured ROD for several well-known cellular reducing agents. Precision polarographic oxygen sensors were used to measure ROD over a ∼100-0 µM oxygen concentration range in solutions containing various types of intracellular reducing agents, either alone or combined with glycerol (1M; to simulate the intracellular hydroxyl-radical-scavenging capacity). A Cs irradiator and a research proton beamline were used for radiation beam generation over a 10,000-fold (0.0085 to 100 Gy/s) dose rate range. Reagents were grouped generally into primary free-radical scavengers (glycerol & lysozyme) and reducing agents (cysteamine, cysteine, glutathione, dextrin-conjugated linoleic acid, NAD(P)H, ascorbate and uric acid). Reducing agents at 1 mM significantly altered ROD values. ROD, at 0.1 Gy/s varied from greater than 1 µM/Gy for NADPH to less than 0.1 µM/Gy for uric acid. Even higher RODs were found at lower dose rates and/or higher reducing agent concentrations. Although most greatly increased ROD, ascorbate and uric acid decreased ROD and additionally imposed an oxygen dependence of ROD at low oxygen concentrations. Interestingly, all agents having high rates of ROD at low dose rates show a decrease at FLASH dose rates and this seems to be a proportional response (i.e., the greater the ROD at low dose rate, the greater the inhibition by FLASH). At FLASH dose rates our data for a simple mixture of glycerol and glutathione showed the same trend as recent studies that, in general, FLASH had ∼25% lower ROD rates than conventional demonstrating agreement between polarographic sensors and optical phosphorescence decay methods. ROD was greatly augmented by some intracellular reducing agents but others effectively reversed this effect. Ascorbate had its greatest impact at low oxygen concentrations. ROD decreased with increasing dose rate and in all cases was less than 1 µM/Gy at 100 Gy/s, potentially posing a fundamental limit of max ROD for FLASH.

A Mechanism Underpinning the Bioenergetic Metabolism-Regulating Function of Gold Nanocatalysts.

Bioenergetic deficits are known to be significant contributors to neurodegenerative diseases. Nevertheless, identifying safe and effective means to address intracellular bioenergetic deficits remains a significant challenge. This work provides mechanistic insights into the energy metabolism-regulating function of colloidal Au nanocrystals, referred to as CNM-Au8, that are synthesized electrochemically in the absence of surface-capping organic ligands. When neurons are subjected to excitotoxic stressors or toxic peptides, treatment of neurons with CNM-Au8 results in dose-dependent neuronal survival and neurite network preservation across multiple neuronal subtypes. CNM-Au8 efficiently catalyzes the conversion of an energetic cofactor, nicotinamide adenine dinucleotide hydride (NADH), into its oxidized counterpart (NAD+ ), which promotes bioenergy production by regulating the intracellular level of adenosine triphosphate. Detailed kinetic measurements reveal that CNM-Au8-catalyzed NADH oxidation obeys Michaelis-Menten kinetics and exhibits pH-dependent kinetic profiles. Photoexcited charge carriers and photothermal effect, which result from optical excitations and decay of the plasmonic electron oscillations or the interband electronic transitions in CNM-Au8, are further harnessed as unique leverages to modulate reaction kinetics. As exemplified by this work, Au nanocrystals with deliberately tailored structures and surfactant-free clean surfaces hold great promise for developing next-generation therapeutic agents for neurodegenerative diseases.

Influence of the Bismuth Content on the Optical Properties and Photoluminescence Decay Time in GaSbBi Films.

We report the optical properties of GaSbBi layers grown on GaSb (100) substrates with different bismuth contents of 5.8 and 8.0% Bi. Fourier-transform photoluminescence spectra were determined to identify the band gaps of the studied materials. Further temperature- and power-dependent photoluminescence measurements indicated the presence of localized states connected to bismuth clustering. Finally, time-resolved photoluminescence measurements based on single-photon counting allowed the determination of characteristic photoluminescence decay time constants. Because of the increasing bismuth content and clustering effects, an increase in the time constant was observed.

Photoluminescence properties of Lu2Si2O7:Eu3+ sol-gel thin films obtained using GLYMO as a silicon source

Thin films of Lu2Si2O7:Eu3+ were prepared via sol-gel methods and dip coating using lutetium nitrate and (3-Glycidyloxypropyl)trimethoxysilane as precursors, and ethanol and ethylene glycol were used as solvents. Acetylacetone was used as a stabilizer, and the pH was adjusted using acetic acid. Lu2Si2O7:Eu3+ films were deposited on silica quartz substrates and exhibited a monoclinic structure with preferential orientation along the [012] direction after heat treatment at 1000 °C. The film’ morphology was characterized by scanning electron microscopy, and the photoluminescence spectrum revealed a strong emission at 612 nm (5D0→7F2), corresponding to the Eu3+ ions, under 254 nm excitation. Notably, both the optical yield and decay time increased with increasing SiO2 content.

Generation of Stable Entanglement in an Optomechanical System with Dissipative Environment: Linear-and-Quadratic Couplings

In this paper, we present a theoretical scheme for the generation and manipulation of bipartite atom–atom entanglement in a dissipative optomechanical system containing two atoms in the presence of linear and nonlinear (quadratic) couplings. To achieve the goal of paper, we first obtain the interaction Hamiltonian in the interaction picture, and then, by considering some resonance conditions and applying the rotating wave approximation, the effective Hamiltonian, which is independent of time, is derived. In the continuation, the system solution was obtained via solving the Lindblad master equation, which includes atomic, optical and mechanical dissipation effects. Finally, bipartite atom–atom entanglement is quantitatively discussed, by evaluating the negativity, which is a well-known measure of entanglement. Our numerical simulations show that a significant degree of entanglement can be reached via adjusting the system parameters. It is noticeable that the optical and mechanical decay rates play an important role in the quasi-stability and even stability of the obtained atom–atom entanglement.

Luminescence performance of Dy3+ ions incorporated modifier reliant boro-tellurite glasses for white light applications

A diverse array/unique set of Dysprosium (Dy3+) activated alkali boro-tellurite glasses were synthesized for the current study using the conventional approach of glass fabrication, and its potential for photonic applications were explored utilizing optical absorption, emission, and decay measurement methods. In the interest of assessing the Rare Earth (RE) ions bonding behavior with the neighboring metal ligand site, and to establish the glasses ionic/covalence nature, bonding parameters (δ) and Nephelauxetic ratios were computed from the absorption band locations. For the as-prepared samples, the Judd-Ofelt parameters and oscillator strengths were determined in order to scrutinize the uniformity of the ligands surrounding Dy3+ ions. The calculated JO values consistently pursue Ω2 > Ω4 > Ω6 pattern for all samples, indicating their asymptotic character. When excited at 387 nm, the emission spectra demonstrate three intense transitions; 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2. Among them, strong yellow emission was observed owing to the increased transfer of electrons to 6H13/2 level. Besides, using JO parameters, radiative parameters were determined which was followed by lifetime studies to actualize the novel applications. The photoluminescence spectra were employed to estimate the CIE coordinates (x, y) and Yellow/Blue ratio, furthermore the (x, y) values were used to calculate the colour purity followed by colour correlated temperature (CCT). This demonstrates that the prepared samples have the ability to emit neutral white light.

Scintillator‐oriented near‐infrared emitting Cs4SrI6:Yb2+, Sm2+ single crystals via sensitization strategy

AbstractIn this study, a new Cs4SrI6:Yb2+,Sm2+ near‐infrared (NIR) emitting scintillator was developed using sensitization strategy. It was found that Yb2+ sensitization significantly enhances the NIR radioluminescence (RL) of Sm2+, providing a new approach of designing highly emissive sensitized NIR scintillators. By studying the optical spectra and decay kinetics of Cs4SrI6:Yb2+,Sm2+, it was revealed that the energy transfer pathways involve both radiative and nonradiative processes. The gamma spectroscopy performance of Cs4SrI6:Yb2+,Sm2+ single crystals was studied by using the high‐quantum‐efficiency avalanche photodiode (APD) as the readout. Our results highlight the importance of using sensitization strategy of achieving NIR emitting scintillators and demonstrate the significant potential for radiation detection applications.

CREATION OF COMPOSITE SCINTILLATORS WITH A SHORT DECAY TIME

To date, LuAG:Ce crystals are one of the most common scintillators, since they have been known for a long time and there are technologies for mass production of large-volume crystals. However, the scintillation properties of such crystals can be improved by creating mixed crystals with the replacement of some ions by others. In this work, composite scintillators based on the grown LuYAG:Ce inorganic crystals were produced. For the obtained samples, studies of optical transmission, luminescence, light output, and decay time were carried out. The optimal conditions and sizes of crystalline grains for the creation of composite scintillators have been determined.

Comparative studies on CIELab, thermal and optical characteristics of Dysprosium (Dy3+) incorporated phospho-tellurite glasses for white light generation

Concentration dependence of Dy3+ activated strontium lead phospho-tellurite glass series have been synthesized by melt quenching process. To explore the structural, thermal and optical traits of the present glasses we have investigated XRD, FTIR, DTA, UV–Vis–NIR absorption, optical band gap, excitation band, luminescence emission, decay lifetime and CIE chromaticity diagram, and analysed the Judd-Ofelt intensity parameters Ωλ (λ = 2,4,6) and various radiative parameters in detail. The photoluminescence spectra exhibit highly intense blue and yellow emissions at around 483 and 573 nm. The better values of yellow/blue intensity ratio and branching ratio (βexp) suggest that the proposed glass series are efficient candidates for visible laser media. Emission quenching effect has been observed beyond 1 mol% Dy3+ doping concentration. The luminescence lifetime of the 4F9/2 excited level declines with increasing Dy3+ doping level. The experimental lifetime and quantum efficiency of 1 mol% Dy3+ activated glass are acquired to be 0.75 ms and 81%, respectively. The appearance of chromaticity coordinates as well as CIELab coordinates in the white region highlights that the present glass system could be most promising for white light generation.