Optical Cross Sections Research Articles

Structure, and opto-dielectric investigations of Cu2+ -doped calcium bismuth silicate glass ceramics

CuO inclusive silicate glasses are well known for various semiconductor applications. However, there is a lot of demand and necessity of high efficient opto-dielectric materials. In view of this, the glasses of chemical composition (30 – x) CaO + (10) Bi2O3 + (60) SiO2 + (x) CuO have been synthesized and studied for their structural, optical and dielectric characterization techniques. Glassy behaviour of CuO undoped glass and ceramic behaviour of all other CuO doped glasses conformed by structural characterization. The elastic modulus and micro hardness of glass and glass ceramics reveal their inter connected covalent structure. Trap depth parameters (Tm, Eτ, Eδ, Eω & μs) have been determined and analysed under irradiation, and found that 0.3 mol% CuO -doped glass ceramic under 30 kGy of irradiation dose exhibiting better TL output. Dielectric relaxation studies of the glass ceramics suggested that mixed conduction of both ionic and electronic. Observed dielectric results; dielectric constant (εr), dielectric loss (tanφ), temperature region of relaxation (ΔT), low activation energie's for conduction (Ea) and AC Conductivity (σac) suggesting that the glass ceramics are dielectric. Optical band gap (Eo), transition probability (At) and emission cross section (σ) corresponding to the emissive transition 3D1 → 1S0 assessed by optical techniques. All the results suggests that 0.3 mol% CuO -doped glass ceramic is a useful opto-dielectric resource.

High-Efficiency All-Polymer Solar Cells with Poly-Small-Molecule Acceptors Having π-Extended Units with Broad Near-IR Absorption

We report two new poly-small-molecule acceptors, PYN-BDT and PYN-BDTF, which serve, by virtue of their π-extended naphthalene rings, as broad optical cross-section macromolecular absorbers (extendi...

Quantitative morphometric analysis of single gold nanoparticles by optical extinction microscopy: Material permittivity and surface damping effects.

Quantifying the optical extinction cross section of a plasmonic nanoparticle has recently emerged as a powerful means to characterize the nanoparticle morphologically, i.e., to determine its size and shape with a precision comparable to electron microscopy while using a simple optical microscope. In this context, a critical piece of information to solve the inverse problem, namely, calculating the particle geometry from the measured cross section, is the material permittivity. For bulk gold, many datasets have been reported in the literature, raising the question of which one is more adequate to describe specific systems at the nanoscale. Another question is how the nanoparticle interface, not present in the bulk material, affects its permittivity. In this work, we have investigated the role of the material permittivities on the morphometric characterization of defect-free ultra-uniform gold nanospheres with diameters of 10 nm and 30 nm, following a quantitative analysis of the polarization- and spectrally-resolved extinction cross section on hundreds of individual nanoparticles. The measured cross sections were fitted using an ellipsoid model. By minimizing the fit error or the variation of the fitted dimensions with color channel selection, the material permittivity dataset and the surface damping parameter g best describing the nanoparticles are found to be the single crystal dataset by Olmon et al. [Phys. Rev. B 86, 235147 (2012)] and g ≈ 1, respectively. The resulting nanoparticle geometries are in good agreement with transmission electron microscopy of the same sample batches, including both 2D projection and tomography.

Fixed-size double-resonant nanolaminate plasmonic nanoantennas with wide spectral tunability and high optical cross-sections

Plasmonic nanoantennas can support localized surface plasmon (LSP) modes to concentrate light at the nanoscale. Although “single-resonant” plasmonic nanoantennas are sufficient for applications based on single-photon processes, “double-resonant” or “multiresonant” plasmonic nanoantennas are more favorable for multiphoton nonlinear processes or wavelength-multiplexing multifunctional operations. Despite significant efforts, current multiresonant plasmonic nanoantennas still face challenges in achieving wide spectral tunability and high excitability for multiple LSP modes under strict geometric size-footprint constraints. Here, we propose and numerically demonstrate that fixed-size nanolaminate plasmonic nanoantennas (NLPNAs) consisting of multiple metal/insulator layers can support two highly excitable LSP modes with electrical dipole (ED) and magnetic dipole (MD) characteristics. Notably, the resonant wavelength of both ED and MD modes are broadly tunable in the near-infrared range between ∼700 nm and ∼1000 nm by controlling the thickness ratio between individual metal and insulator layers without changing the overall size. While the ED mode in NLPNAs can have large scattering cross-sections suitable for applications based on plasmonic emission/scattering processes, the MD mode has large absorption cross-sections desirable for applications based on plasmonic photothermal effects. We further reveal that NLPNAs’ broad double-resonance tunability originates from the out-of-plane geometric dependence of the elementary ED/MD modes in the building blocks and their optical coupling.

An Ultrasensitive Gateless Photodetector Based on the 2D Bilayer MoS2-1D Si Nanowire-0D Ag Nanoparticle Hybrid Structure.

Atomically thin transition metal dichalcogenides (TMDC) have received much attention due to their wide variety of optical and electronic properties. Among various TMDC materials, molybdenum disulfide (MoS2) has been intensely studied owing to its potential applications in nanoelectronics and optoelectronics. However, two-dimensional MoS2 photodetectors suffer from low responsivity due to low optical cross section. Combining MoS2 with plasmonic nanostructures can drastically increase scattering cross section and enhance local light-matter interaction. Moreover, suspended MoS2 has been shown to exhibit higher photoluminescence intensity and strong photogating effect, which can be employed in photodetectors. Herein, we propose an approach to utilize plasmonic nanostructures and physical suspension for 2D MoS2 photosensing enhancement by hybridizing 2D bilayer MoS2, 1D silicon nanowires, and 0D silver nanoparticles. The hybrid structure shows a gateless responsivity of 402.4 A/W at a wavelength of 532 nm, which represents the highest value among the ever reported gateless plasmonic MoS2 photodetector. The great responsivity and large active area results in an exceptional detectivity of 2.34 × 1012 Jones. This study provides a new approach for designing high-performance 2D TMDC-based optoelectronic devices.

Phonon-Assisted Hot Carrier Generation in Plasmonic Semiconductor Systems.

Plasmonic materials have optical cross sections that exceed by 10-fold their geometric sizes, making them uniquely suitable to convert light into electrical charges. Harvesting plasmon-generated hot carriers is of interest for the broad fields of photovoltaics and photocatalysis; however, their direct utilization is limited by their ultrafast thermalization in metals. To prolong the lifetime of hot carriers, one can place acceptor materials, such as semiconductors, in direct contact with the plasmonic system. Herein, we report the effect of operating temperature on hot electron generation and transfer to a suitable semiconductor. We found that an increase in the operation temperature improves hot electron harvesting in a plasmonic semiconductor hybrid system, contrasting what is observed on photodriven processes in nonplasmonic systems. The effect appears to be related to an enhancement in hot carrier generation due to phonon coupling. This discovery provides a new strategy for optimization of photodriven energy production and chemical synthesis.

Inhibition of non-photochemical quenching increases functional absorption cross-section of photosystem II as excitation from closed reaction centres is transferred to open centres, facilitating earlier light saturation of photosynthetic electron transport.

Induction of non-photochemical quenching (NPQ) of chlorophyll fluorescence in leaves affords photoprotection to the photosynthetic apparatus when, for whatever reason, photon capture in the antennae of photosystems exceeds their capacity to utilise this excitation in photochemistry and ultimately in CO2 assimilation. Here we augment traditional monitoring of NPQ using the fast time resolution, remote and relatively non-intrusive light induced fluorescence transient (LIFT) technique (Kolber et al . 2005 ; Osmond et al . 2017 ) that allows direct measurement of functional (σ'PSII ) and optical cross-sections (a 'PSII ) of PSII in situ , and calculates the half saturation light intensity for ETR (E k ). These parameters are obtained from the saturation and relaxation phases of fluorescence transients elicited by a sequence of 270, high intensity 1 μs flashlets at controlled time intervals over a period of 30 ms in the QA flash at intervals of a few seconds. We report that although σ'PSII undergoes large transient increases after transfer from dark to strong white light (WL) it declines little in steady-state as NPQ is induced in shade- and sun-grown spinach and Arabidopsis genotypes Col , OEpsbs , pgr 5bkg , stn 7 and stn 7/8. In contrast, σ'PSII increases by ~30% when induction of NPQ in spinach is inhibited by dithiothreitol and by inhibition of NPQ in Arabidopsis npq 1, npq 4 and pgr 5. We propose this increase in σ'PSII arises as some excitation from closed PSII reaction centres is transferred to open centres when excitation partitioning to photochemistry (Y II ) and NPQ (Y NP ) declines, and is indicated by an increased excitation dissipation from closed PSII centres (Y NO , including fluorescence emission). Although E k increases following dissipation of excitation as heat when NPQ is engaged, it declines when NPQ is inhibited. Evidently photochemistry becomes more easily light saturated when excitation is transferred from closed RCIIs to open centres with larger σ'PSII . The NPQ mutant pgr 5 is an exception; E k increases markedly in strong light as electron transport QA → PQ and PQ → PSI accelerate and the PQ pool becomes strongly reduced. These novel in situ observations are discussed in the context of contemporary evidence for functional and structural changes in the photosynthetic apparatus during induction of NPQ.

Quantum dot clusters as self-assembled antennae with phycocyanine and phycobilisomes as energy acceptors.

In this study, we investigated an experimental and Monte-Carlo computational characterization of self-assembled antennae built using CdTe colloidal quantum dots (QDs). These clusters provide efficient excitation of phycocyanine (PC) or phycobilisomes (PBSs). PBSs are light-harvesting complexes (LHCs) of cyanobacteria, made of several PC units, organized in disks and rods. Each PC contains three separate cofactors. Therefore, we analyzed variations in multi-donor and multi-acceptor systems. The self-assembled QD clusters were formed mostly by electrostatic interactions, possibly due to the introduction of a positive charge on an originally negatively charged nanoparticle surface. Our results suggest that PC may accept energy from multiple nanoparticles localized at a distance significantly longer than the Förster radius. The excitation transfers between particular nanoparticles with possible delocalization. The maximal energy transfer efficiency was obtained for the PC/PBS : QD ratio from 1 to 20 depending on the QD size. This cannot be fully explained using computational simulations; hence, we discussed the hypothesis and explained the observations. Our self-assembled systems may be considered for possible applications in artificial light-harvesting systems because absorption spectra of QDs are different from the absorption characteristics of PC/PBS. In addition, huge clusters of QDs may effectively increase the optical cross-section of so-created nanohybrids.

Purcell-enhanced photoluminescence of few-layer MoS2 transferred on gold nanostructure arrays with plasmonic resonance at the conduction band edge.

Plasmonic coupling of metallic nanostructures with two-dimensional molybdenum disulfide (MoS2) atomic layers is an important topic because it provides a pathway to manipulate the optoelectronic properties and to overcome the limited optical cross-section of the materials. Plasmonic enhanced light-matter interaction of a MoS2 layer is known to be mainly governed by optical field enhancement and the Purcell effect, while the discrimination of the contribution from each mechanism to the plasmonic enhancement is challenging. Here, we investigate photoluminescence (PL) enhancement from few-layer MoS2 transferred on Au nanostructure arrays with controlled localized surface plasmon resonance (LSPR) spectral positions that were detuned from the excitation wavelengths. Two distinctive regimes in LSPR mode-dependent PL enhancement were revealed showing a maximum enhancement (∼40-fold) with zero detuning and a modest enhancement (∼10-fold) with the red-shift detuned LSPR from the excitation wavelength, which were attributed to LSPR-induced optical field enhancement and the Purcell effect, respectively. By applying the experimental parameters into the Purcell effect formalism, an effective mode volume of ∼0.016λ03 was estimated. Our work provides an insight into how to utilize few-layer MoS2 as a base material for optoelectronics by harnessing Purcell-enhanced optical responsivity.

OSL CHARACTERISTICS: THEORY AND EXPERIMENTS.

Fundamental effects such as the participation of crystal lattice vibrations should be taken into account while considering photo-ionisation in solids at measurement temperatures characteristic for dosimetric applications. The impact of these effects on the optically stimulated luminescence (OSL) can be recognised for example by changes in the optical cross-section of the trap with the stimulation energy and the temperature. The OSL signal observed during the stimulation with variable energy, during the linear heating of a sample or during the stimulation with modulation of the shape of a spectral band can provide important information about the properties of the trap. Moreover, such methods when applied with carefully selected experimental parameters enable the effective separation of the OSL signal originating from different traps. The consequences of such an approach to optical stimulation will be presented using the modelling of the OSL process and compared with experimental results.

SEQUENTIAL RETINAL THICKNESS ANALYSIS SHOWS HYDROXYCHLOROQUINE DAMAGE BEFORE OTHER SCREENING TECHNIQUES.

We sought to determine the earliest diagnostic signs of hydroxychloroquine retinopathy up to the point of clinical recognition. Retrospective series of 6 patients (5 parafoveal disease; 1 pericentral disease) with at least 3 examinations over 3.5 years or more preceding diagnosis of HCQ retinopathy. Spectral domain optical coherence tomography (sdOCT) cross-sections, fundus autofluorescence (FAF) and visual fields were generated clinically. Stored sdOCT data were re-examined later to generate topographic ellipsoid zone (EZ) maps, minimum intensity (MI) analysis and sequential plots of regional retinal thickness. Retrospective series of six patients (5 parafoveal disease; one pericentral disease) with at least three examinations over 3.5 years or more preceding diagnosis of hydroxychloroquine retinopathy. Spectral domain optical coherence tomography cross-sections and fields showed similar sensitivity; fundus autofluorescence was not helpful. In parafoveal cases, EZ topography and minimum intensity analysis were no more reliable. Sequential thickness plots from four parafoveal cases showed dramatic retinal thinning across the posterior pole beginning 4 years to 5 years before clinical diagnosis, with parafoveal regions thinning even faster. The pericentral case showed thinning only outside the central macula. Peripheral EZ loss was more dramatic with EZ topography than sdOCT cross-sections. Sequential retinal thickness plots reveal definitive thinning years before current diagnostic procedures. We hope that OCT manufacturers will develop software to display such measurements. Ellipsoid zone topography was not more sensitive than sdOCT cross-sections, but important for recognizing pericentral disease.

Enhanced optical cross-section of radiation induced defect centers under plasmon resonance conditions: Shifting stimulation wavelength of optically stimulated luminescence dosimeters

Plasmon-enhanced luminescence is an important tool for development of advanced sensing technologies but the mechanisms originating these enhancements are still in debate. In this work, we investigate plasmon-enhanced luminescence mechanisms using the Optically Stimulated Luminescence (OSL) from defect centers in X-ray irradiated sodium chloride nanocrystals deposited on silver nanoparticle (AgNP) films with varying plasmon properties upon blue, green, and red OSL stimulation. Although the absolute OSL intensity for NaCl crystals is higher upon blue stimulation, under plasmon resonance conditions, higher absolute OSL intensity occurs upon green stimulation and the largest OSL enhancements are observed by employing red stimulation. These results suggest that, as long as the OSL stimulation wavelength is well tuned with the film plasmon band, plasmonic coupling does not depend on the trap depth and that the largest luminescence enhancements are achieved in spectral regions where the optical cross-sections of the defect centers are smaller. In terms of radiation dosimetry applications, this result allows to shift the stimulation wavelength farther from the OSL emission window, improving the signal to noise ratio and the dose assessment sensitivity and accuracy.

Analytical Modeling and Design of a Graphene Metasurface Sensor for Thermo-Optical Detection of Terahertz Plasmons

Thermo-optic mechanism for plasmonics sensing of terahertz radiations is numerically and analytically investigated for metasurface formed from Graphene/SiO2 and simulated at room temperature. For this purpose, here, by considering coupling condition as well as strong light-matter interaction in graphene metasurface a very compact footprint in less than half of the wavelength is proposed. Also, for deep benchmark of structure at different temperature, tunable optical properties of graphene is considered. Subsequently, the numerical operation of the sensor fulfilled based 3-dimension finite-difference time-domain (3D-FDTD) and also, the transfer matrix method (TMM) modelling is introduced. In order to investigate the relationship between the temperature variation and tunable behavior of the structure on the performance parameters, temperature is increased from 0 to 600 K in steps of 300, whereas the other parameters were fixed. Numerical results show that the max sensitivity and figure of merit (FoM) are more than 1140 nm/RIU and 5.1, respectively. Then, we numerically simulate the optical cross-section including absorption, scattering and total of them. Also, by harnessing of graphene’s surface conductivity properties, we indicate the giant tunability and minimum transmittance of % 0.02 in frequency of 14 THz in which the best track of optical performance over a wide range of frequency is occurred. Eventually, a novel research direction of the software-defined metasurface is explained, which is tried to achieve the graphene-based metasurface toward unique in controllability and harnessing of the light. This proposed thermo-optical metasurface structure can be used as a nanosensor for exciting surface plasmons.

Absorption cross section of gold nanoparticles based on NIR laser heating and thermodynamic calculations

We present a method for measuring the optical absorption cross section (sigma_{abs}) of gold nanoparticles (GNPs) based on optically heating the solution of GNPs with an 808 nm near-infrared (NIR) laser and measuring the temperature increase of the solution. We rely on the theoretical calculations based on the heat diffusion equations and experimental measurements based on the energy balance equations to measure the sigma_{abs} and the temperature distribution of single GNPs. Several morphologies, including gold nanospheres (GNSs), spherical gold nanoparticle conjugate (AuNPC), which are 20 nm GNSs surface-functionalized with an IR 808 dye, gold nanorods (GNRs), and gold nanourchins (GNUs), were studied. The study found that a single 20 nm GNS has the lowest sigma_{abs} and temperature distribution as compared to 100 nm GNUs. By increasing the size of GNSs from 20 to 30 nm, the magnitude of sigma_{abs} as well as temperature distribution increases by a factor of 5. The sigma_{abs} values of 20 and 30 nm GNSs calculated by Mie theory and the experimentally measured are in a good agreement. GNRs with equivalent radius (R_{eq}) 9.16 nm show the second lowest sigma_{abs}. By increasing the R_{eq} by a factor of 2 to 19.2 nm, the measured sigma_{abs} and temperature distribution also increased by a factor of 2. We also estimated sigma_{abs} for GNUs with diameters at 80 and 100 nm, which also have higher sigma_{abs} values. This work confirms that we can use temperature to accurately measure the sigma_{abs} of a variety of GNPs in solution.

The Ångström Exponent and Single-Scattering Albedo of Black Carbon: Effects of Different Coating Materials

In this work, the absorption Ångström exponent (AAE), extinction Ångström exponent (EAE), and single-scattering albedo (SSA) of black carbon (BC) with different coating materials are numerically investigated. BC with different coating materials can provide explanations for the small AAE, small EAE, and large AAE observed in the atmosphere, which is difficult to be explained by bare BC aggregate models. The addition of organic carbon (OC) does not necessarily increase AAE due to the transformation of BC morphologies and the existence of non-absorbing OC. The addition of coating materials does also not necessarily decrease EAE. While the addition of coating materials can increase the total size of BC-containing particles, the effective refractive index can be modified by introducing the coating materials, so increases the EAE. We found that it is not possible to differentiate between thinly- and heavily-coated BC based on EAE or AAE alone. On the other hand, SSA is much less sensitive to the size and can provide much more information for distinguishing heavily-coated BC from thinly-coated BC. For BC with different coating materials and mixing states, AAE, EAE, and SSA show rather different sensitivities to particle size and composition ratios, and their spectral-dependences also exhibit distinct differences. Different AAE and EAE trends with BC/OC ratio were also found for BC with different coating materials and mixing states. Furthermore, we also found empirical fittings for AAE, EAE, SSA, and optical cross-sections, which may be useful for retrieving the size information based on the optical measurements.

Gold Nanorods as Contrast Agent for Photoacoustic Imaging (PAI) of Breast Cancer

Gold Nanorods (AuNRs) can play a fundamental role in the enhancement of photoacoustic imaging (PAI). This is due to their high and tunable optical absorption cross-section. Normally, the most convenient and highly stable AuNRs are synthesized using Cetyltrimethylammonium bromide (CTAB) as a surfactant. In this work, surface modification with poly ethylene glycol (PEGylation) and Silica coating (SiO2-coating) were applied to help in reducing toxicity of CTAB capped AuNRs. Breast cancer cell line (MDA-MB-231) was used to assess the modified AuNRs as contrast agents. A much brighter PAI of cells loaded with SiO2-coated AuNRs was obtained. Such an enhanced PA image is due to the larger cellular uptake, as observed from bright field microscope images taken for the cells. On the other hand, the corresponding PA image for cells with PEGylated AuNRs is diminished. The increase in cell uptake, in case of SiO2-coated AuNRs, could result due to the adsorption of protein, contained in the cell culture media, on the negatively charged silica surface, which increases intercellular uptake by receptor-mediated endocytosis. Moreover, the increase of the brightness of PAI of SiO2-coated AuNRs may be due to the lowering of the interfacial thermal resistance between gold and the surrounding solvent. This allows the particle to release more heat to its environment which increases the generated acoustic signals from these particles.

A Tutorial on the Classical Theories of Electromagnetic Scattering and Diffraction

AbstractStarting with Maxwell’s equations, we derive the fundamental results of the Huygens-Fresnel-Kirchhoff and Rayleigh-Sommerfeld theories of scalar diffraction and scattering. These results are then extended to cover the case of vector electromagnetic fields. The famous Sommerfeld solution to the problem of diffraction from a perfectly conducting half-plane is elaborated. Far-field scattering of plane waves from obstacles is treated in some detail, and the well-known optical cross-section theorem, which relates the scattering cross-section of an obstacle to its forward scattering amplitude, is derived. Also examined is the case of scattering from mild inhomogeneities within an otherwise homogeneous medium, where, in the first Born approximation, a fairly simple formula is found to relate the far-field scattering amplitude to the host medium’s optical properties. The related problem of neutron scattering from ferromagnetic materials is treated in the final section of the paper.

Optical Absorption Cross-Section of DNA Bases—Thymine and Guanine—in the Energy Region from 3.1 to 250 eV (5–400 nm)

(1) Background: Optical absorption cross-section—the absolute absorption intensity specific to each molecule—of nucleic acid bases enables us to estimate the reaction yields of DNA lesions induced by the exposure to not only photons but also ionizing radiations. However, it was unknown in the energy region exceeding ~10 eV (wavelength < ~120 nm). (2) Methods: Thin films of DNA bases—thymine and guanine—were prepared using a vacuum sublimation technique. Absorption spectra of these films were measured in the energy region from 3.1 to 250 eV (5–400 nm) at the synchrotron radiation facility UVSOR. (3) Results: The absorption spectra of both bases exhibited prominent absorption peaks around 20 eV and smaller peaks in the energy region below 10 eV. The determined optical oscillator strength distribution was verified to be reasonable based on the Thomas–Reiche–Kuhn oscillator strength sum rule. (4) Conclusion: Most of the oscillator strength distribution was positioned in the measured energy region, and therefore the absorption spectra significantly contributed to the quantitative study for the photo and radiation-chemical reactions of DNA.

Thermo-optical performance of iron-doped gold nanoshells-based nanofluid on direct absorption solar collectors

Nanofluids are potential working fluids for Direct Absorption Solar Collectors, mainly due to the enhancement of the optical absorption by the presence of metallic nanoparticle inclusions. For instance, Gold Nanoshells (Au NS) have absorption spectrums in the visible–NIR spectrum that can be tuned controlling their size in the chemical synthesis. The use of metallic nanoheaters in photo-thermal applications requires finding nanostructures with high optical absorption features and low optical scattering properties, which could be achieved by doping gold with transition metals impurities, such as Pt, Fe, or Ag. In this work, a numerical analysis is used to determine the proper fraction of Fe-doping Au NS to increase the solar energy efficiencies of plasmonic nanofluids. In our knowledge, it is the first time this kind of nanofluid is proposed for solar harvesting applications. The results show that the solar weighted absorption efficiency of Fe-doped Au NS based nanofluids is sensibly enhanced and improved the performance of direct solar absorption collectors by increasing the optical absorption cross-section of plasmonic nanoparticles. The collector using Fe-doped gold nanoshells based nanofluids can reach thermal efficiency above 95% at 1 kWm−2, and in a very dilute condition (volume fraction of p=2×10−5). This value is up to 20% superior to that of pure Au NS based working fluids. These results demonstrated that adjusting the proper fraction of Fe as a dopant into the Au layer of nanostructure provides a novel approach to harvesting solar energy flux under optimal conditions.

Primary intrinsic defects and their charge transition levels in β–Ga2O3

A steady-state photocapacitance (SSPC) setup directly connected to the beamline of a MeV ion implanter is utilized to study primary intrinsic defects in $\ensuremath{\beta}\text{--}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ generated by He implantation at cryogenic temperatures (120 K). At low temperatures, the migration of defects is suppressed, and hence the generation of primary intrinsic defects is expected to prevail. SSPC measurements reveal defect-related optical transitions in halide vapor-phase epitaxy (HVPE) -grown $\ensuremath{\beta}\text{--}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ thin films with onset energies at 1.3 $({T}_{1}),$ 1.7 $({T}_{2}),$ 1.9 $({T}_{3}),$ 2.6 $({T}_{4}),$ 3.7 $({T}_{5}),$ and 4.2 eV $({T}_{6})$. ${T}_{2},$ ${T}_{4},$ ${T}_{5},$ and ${T}_{6}$ were observed in as-received HVPE-grown $\ensuremath{\beta}\text{--}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ thin films, whereby ${T}_{2}$ is only sporadically observed. The introduction rates for ${T}_{3},$ ${T}_{4},$ as well as ${T}_{6}$ indicate an origin related to primary intrinsic defects. Notably, ${T}_{1}$ and ${T}_{3}$ are only observed after He implantation at cryogenic temperatures. Hybrid-functional calculations were performed to estimate the optical absorption cross-section spectra for the gallium $({\mathrm{Ga}}_{\mathrm{i}})$ and oxygen $({\mathrm{O}}_{\mathrm{i}})$ interstitials as well as the corresponding vacancies (${V}_{\mathrm{Ga}}$ and ${V}_{\mathrm{O}}$, respectively), and compared with the measured onsets for optical absorption found by SSPC measurements. Indeed, we propose ${T}_{3}$ to be associated with ${\mathrm{Ga}}_{\mathrm{i}}^{(+/+2)}$ and/or ${V}_{\mathrm{GaI}}^{(\ensuremath{-}3/\ensuremath{-}2)}$, while ${T}_{4}$ is suggested to be related to ${V}_{\text{O}K}^{(0/+)}$ $(K=\mathrm{I}, \mathrm{II}, \mathrm{III})$ and/or ${V}_{\mathrm{GaII}}^{(\ensuremath{-}3/\ensuremath{-}2)}$. Additionally, several further charge-state transition levels associated with ${V}_{\mathrm{GaI}}$ and ${V}_{\mathrm{GaII}}$ may contribute to ${T}_{4}$ and ${T}_{6}$. We further studied the kinetics of the defects created with He implantation by exposing the sample to room temperature. The kinetics observed for ${T}_{3}$ and ${T}_{4}$ further support the proposed assignments of the corresponding defect signatures.