Positron Annihilation Spectroscopy Research Articles

Molecular design of free volume structure in thermally rearranged polybenzoxazole membranes for gas separation studied by positron annihilation

AbstractIn this work, 2,2‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane (APAF) was used as the fixed diamine monomer, and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), 3,3′,4,4′‐biphenyltetracarboxylic diandhydride (BPDA) and pyromellitic dianhydride (PMDA) were selected as four different dianhydride monomers, respectively, to prepare the thermally rearranged polybenzoxazole (TR‐PBO) gas separation membranes with different structures via a thermal rearrangement reaction at 450°C. The microstructure of TR‐PBO membranes was investigated using X‐ray diffraction and positron annihilation spectroscopy. All the TR‐PBO membranes exhibit bimodal free volume structure, containing ultramicropores (<0.7 nm) and micropores (<2 nm) with size of 3.6–4.6 and 7.6–8.4 Å, respectively. As the steric hindrance of the bridging groups in the dianhydride monomers increases, the radius and number of pores in the membranes increases, leading to an increase in fractional free volume (FFV). The pure gas permeation test shows a positive correlation between gas permeability and FFV in the TR‐PBO membranes, indicating that an increase in FFV is favorable for the diffusion of gas molecules. Particularly, the ultramicropores play a decisive role on the gas selectivity. All the TR‐PBO membranes exhibit excellent gas permeaselectivity. Among them, the H2/CH4 separation performance of APAF‐6FDA and APAF‐ODPA membranes approaches the 2008 Robeson upper bound, which is due to the high number of both micropores and ultramicropores. Our results demonstrate that the free volume structure of polymer membranes can be designed by selecting monomers with different structures and utilizing thermal rearrangement reactions, allowing for the preparation of gas separation membranes with high permeability and selectivity.

Impacts of vacancy complexes on the room-temperature photoluminescence lifetimes of state-of-the-art GaN substrates, epitaxial layers, and Mg-implanted layers

For rooting the development of GaN-based optoelectronic devices, understanding the roles of midgap recombination centers (MGRCs), namely, nonradiative recombination centers and deep-state radiative recombination centers, on the carrier recombination dynamics is an essential task. By using the combination of time-resolved photoluminescence and positron annihilation spectroscopy (PAS) measurements, the origins of major MGRCs in the state-of-the-art GaN epilayers, bulk crystals, and Mg-implanted layers were identified, and their concentrations were quantified for deriving the capture coefficients of minority carriers. In this article, potential standardization of the room-temperature photoluminescence lifetime for the near-band-edge emission (τPLRT) as the concentration of major MGRCs well below the detection limit of PAS is proposed. For n-GaN substrates and epilayers grown from the vapor phase, τPLRT was limited by the concentration of carbon on N sites or divacancies comprising a Ga vacancy (VGa) and a N vacancy (VN), [VGaVN], when carbon concentration was higher or lower, respectively, than approximately 1016 cm−3. Here, carbon and VGaVN act as major deep-state radiative and nonradiative recombination centers, respectively, while major MGRCs in bulk GaN crystals were identified as VGa(VN)3 vacancy clusters in Na-flux GaN and VGa or VGaVN buried by a hydrogen and/or VGa decorated with oxygen on N sites, VGa(ON)3–4, in ammonothermal GaN. The values of τPLRT in n-GaN samples are compared with those of p-GaN, in which τPLRT was limited by the concentration of VGa(VN)2 in Mg-doped epilayers and by the concentrations of VGaVN and (VGaVN)3 in Mg-implanted GaN right after the implantation and after appropriate activation annealing, respectively.

Defectivity of Al:ZnO thin films with different crystalline order probed by Positron Annihilation Spectroscopy

Three Positron Annihilation Spectroscopy (PAS) techniques have been employed to investigate the point defects of Al-doped Zinc Oxide (AZO) thin films grown by Radio Frequency (RF) magnetron sputtering with different substrates and deposition parameters. The films were grown with thickness varying from 100 to 300 nm, and their crystalline quality ranged from single crystalline epitaxial to partially amorphous. We found that the main defect in the crystalline samples is the 3VZn−VO four vacancy complex, with a concentration around 1018−1019 cm−3. In polycrystalline films larger vacancy clusters, within 10%−20% of the total concentration, were detected. These vacancy clusters are inferred to be most likely located at the grain boundaries. In partially amorphous films the concentration of these larger vacancy clusters, located either at grain boundaries or in the amorphous regions of the film, approached even the 40%, and also some sub-nano voids have been observed.

Formulation and Characterization of Chitosan-Based Mixed-Matrix Scaffold for Tissue Engineering

The use of scaffolds, three-dimensional porous, biodegradable and biocompatible structures, that can be produced from natural polymers, synthetics, ceramics and metals is crucial in the tissue engineering field. Chitosan is a polysaccharide of natural origin, found in the exoskeleton of marine arthropods and in the cell wall of fungi, with enormous popularity in the production of three-dimensional materials for Tissue Engineering, in particular bone repair. This polymer has several advantages in the production of these structures in bone regeneration and repair: biodegradability, biocompatibility, non-toxicity and antimicrobial properties. This study aimed to prepare porous scaffolds, for bone repair of degenerative diseases in the spine with better performance and less secondary effects, based on chitosan and another biopolymer (sodium alginate) with the incorporation of calcium phosphates (hydroxyapatite and β-tricalcium phosphate), for tissue engineering application. The obtained scaffolds were object of a detailed characterization, namely with regard to their porosity through the ethanol method, degradation, positron annihilation spectroscopy (PAS), mechanical properties, scanning electronic microscope (SEM), thermal stability through thermogravimetric analysis (TGA), chemical composition through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results obtained showed that the different scaffolds presented pores able to support osteoid matrix growth. The crosslinking of scaffolds was also evaluated and resulted in pores with smaller dimensions and higher regularity in the chitosan-sodium alginate polymer without calcium phosphate scaffold. It was also possible to observe the effect of inorganics on mixed-matrix scaffolds, both morphologically and chemically. These scaffolds showed promising results in terms of mechanical and chemical properties, along with promising porosity for tissue regeneration applications.

Hole and positron interaction with vacancies and p-type dopants in epitaxially grown silicon

The concentration of vacancies and impurities in semiconductors plays a crucial role in determining their electrical, optical, and thermal properties. This study aims to clarify the nature of the interaction between positrons and ionized p-type impurities, emphasizing the similarities they share with the interaction between holes and this type of impurity. An overall strategy for investigating defects in semiconductor crystals that exhibit a combination of vacancies and p-type impurities is presented. By using positron annihilation spectroscopy, in particular, Doppler broadening of the annihilation radiation, we quantify the concentration of vacancies in epitaxial Si crystals grown by low-energy plasma-enhanced chemical vapor deposition. The vacancy number densities that we find are (1.2 ± 1.0) × 1017 cm−3 and (3.2 ± 1.5) × 1020 cm−3 for growth rates of 0.27 and 4.9 nm/s, respectively. Subsequent extended annealing of the Si samples effectively reduces the vacancy density below the sensitivity threshold of the positron technique. Secondary ion mass spectrometry indicates that the boron doping remains unaffected during the annealing treatment intended for vacancy removal. This study provides valuable insights into the intricate interplay between vacancies and ionized impurities with positrons in semiconductor crystals. The obtained results contribute to advance the control and understanding of material properties in heterostructures by emphasizing the significance of managing vacancy and dopant concentrations.

Superior radiation resistance of ODS-RAFM steels revealed by Positron annihilation spectroscopy study

Oxide-dispersion-strengthened (ODS) reduced-activation ferritic/martensitic (RAFM) steels are considered as most promising structural materials for fusion reactors and other advanced nuclear systems due to its excellent irradiation resistance under high dose irradiations. However, the extreme complex synergistic effect between transmuted helium/hydrogen and displacement damage which most seriously affects the structure and mechanical properties of ODS-RAFM steels is very difficult to understand, especially the role of hydrogen still remains unclear. Taking advantage of very sensitive to small vacancy clusters of Positron annihilation spectroscopy (PAS) method, we conducted irradiation defect study on ODS-RAFM, RAFM and its corresponding model alloy Fe–9Cr and α-Fe to investigate their anti-swelling properties at the early stage of irradiation with hydrogen-helium synergism and the mechanism. Three distinct irradiation schemes including (1) single Fe ion beam, (2) simultaneous Fe and He (named Fe + He) ion beam, (3) subsequent H ion injection after Fe + He (named Fe + He/H) ion beam irradiation were performed. Hydrogen-helium synergistic effects on vacancy evolution within these steels were explored combining the first-principles calculation. The implantation of He was observed to significantly increase defect concentration among all four steels, while H exhibited interestingly complexity on affecting the evolution of helium bubbles. The H post-injection increased defect concentration obviously in the materials with abundant sinks, but improved poorly in ones with rare sinks. Through the systematic study of the interactions between H, He, and vacancies, it was revealed that even at the early irradiation stage, ODS-RAFM steels has already exhibited excellent irradiation resistance compared to other alloys across three irradiation schemes.

Positron annihilation spectroscopy evaluation of using proton irradiation as a surrogate for early neutron radiation damage

A positron annihilation spectroscopy investigation of early stages of radiation-induced damage in Chinese f/m (ferritic/martensitic) steel SIMP and strengthened variant of f/m steel ODS (oxide dispersion strengthened) EUROFER was conducted. Studied materials were irradiated by neutrons at the LVR-15 research reactor to 0.12 dpa at an average temperature of 260 ± 20 °C, and implanted by protons at the 6 MV Tandetron Accelerator of the Slovak University of Technology, to 0.0196 dpa at room temperature (RT) and 300 °C. The potential of using proton irradiation as a surrogate for early neutron radiation damage was investigated. A lifetime spectrometer and Doppler spectrometer was used to obtain simultaneously positron lifetime (PALS) and Doppler broadening spectra (DBS), which provided experimental data used to characterize the vacancy-type defect and their interaction with H atoms in the studied materials. The obtained results show an increase of mean positron lifetime (MLT) in the proton-implanted samples at RT when compared with high temperature irradiation. Similar trend was observed when comparing vacancy concentration of different irradiation conditions. The impact of temperature on mobility and recombination of defects, as well as effect of vacancy stabilization by H atoms, has been addressed. The effect of ODS microstructure on results has been examined. A methodology of comparing various irradiation conditions has been proposed, where the vacancy concentrations have been normalized by the dpa values. The potential application of proton implantation for evaluation of early stages of neutron damage was found to be promising.

Memory effect in photochromic rare-earth oxyhydride thin films studied by in situ positron annihilation spectroscopy upon photodarkening-bleaching cycling

Memory effect in photochromic rare-earth oxyhydride thin films studied by <i>in situ</i> positron annihilation spectroscopy upon photodarkening-bleaching cycling

Hydrogen-Induced Microstructure Changes in Zr/Nb Nanoscale Multilayer Structures

Zr/Nb nanoscale multilayer coatings (NMCs) were studied after hydrogenation in a gaseous environment at 400 °C. The hydrogen distribution and content were determined by pressure and hydrogenation time. Increasing the pressure from 0.2 to 2 MPa resulted in different hydrogen distribution within the Zr/Nb NMCs, while the concentration remained constant at 0.0150 ± 0.0015 wt. %. The hydrogen concentration increased from 0.0165 ± 0.001 to 0.0370 ± 0.0015 wt. % when the hydrogenation time was extended from 1 to 7 h. The δ-ZrH hydride phase was formed in the Zr layers with Zr crystals reorienting towards the [100] direction. The Nb(110) diffraction reflex shifted towards smaller angles and the interplanar distance in the niobium layers increased, indicating significant lateral compressive stresses. Despite an increase in pressure, the nanohardness and Young’s modulus of the Zr/Nb NMCs remained stable. Increasing the hydrogen concentration to 0.0370 ± 0.0015 wt. % resulted in a 40% increase in nanohardness. At this concentration, the relative values of the Doppler broadening variable energy positron annihilation spectroscopy (S/S0) increased above the initial level, indicating an increase in excess free volume due to hydrogen-induced defects and changes. However, the predominant positron capture center remained intact. The Zr/Nb NMCs with hydrogen content ranging from 0.0150 ± 0.0015 to 0.0180 ± 0.001 wt. % exhibited a decrease in the free volume probed by positrons, as demonstrated by the Doppler broadening variable energy positron annihilation spectroscopy. This was evidenced by opposite changes in S and W (S↓W↑). The microstructural changes are attributed to defect annihilation during hydrogen accumulation near interfaces with the formation of hydrogen–vacancy clusters and hydrides.

Investigation of vacancy-type defects in diamond-like carbon films using slow positron beam

Positron annihilation spectroscopy was used to investigate vacancy-type defects in diamond-like carbon (DLC) films. From Doppler broadening measurements of the γ-rays produced by annihilation and positron annihilation lifetime (PAL) using a slow positron beam on DLC films deposited by various deposition methods and conditions, it was found that there is a good correlation between the S parameter obtained by Doppler broadening and PAL. The result of PAL correlates well with film density and hardness, indicating that PAL measurements can be used as an indicator of these film properties. The hydrogen content in the DLC film was roughly proportional to the PAL. However, there were also cases in which PAL differed greatly even with almost the same hydrogen content, and the sp 2/(sp 2+sp 3) ratio of carbon in DLC films has no direct relationship with PAL.

Unraveling Precise Locations of Indium Atoms in g‐C3N4 for Ameliorating Hydrogen Peroxide Piezo‐Photogeneration

Increasing active sites in catalysts is of utmost importance for catalytic processes. In this regime, single‐atom dispersing on graphitic carbon nitrides (g‐C3N4) to produce fine chemicals, such as hydrogen peroxide (H2O2), is of current interest due to not only enhancing catalytic performance but also reducing the loading of necessary metals. Hence, we, in this research, engineered g‐C3N4 by atomically dispersing aluminum (Al) or indium (In) sites to provide catalytic active centers via one‐step thermal shock polymerization. The addition of Al and In sites can accelerate the catalytic efficacy owing to the Lewis acid‐base interactions between these metals and oxygen (O2). Under catalytic conditions, the formation of oxygenic radicals would strongly be associated with the enhanced formation of H2O2, confirmed by in‐situ electron paramagnetic resonance (EPR) spectroscopy. Furthermore, the empirical analyses from positron annihilation spectroscopy (PAS) show that In atoms would occupy the near positions of carbon vacancies (VC) to form N‐VC@In‐O bonds. This replacement would produce the highest formation energy based on the density functional theory (DFT) calculations, improving the stability of atom‐dispersive materials. Therefore, via the combination of experimental and theoretical proofs, this study suggests the exact location of In atoms in g‐C3N4 structures, which can help boost the catalytic production of H2O2.This article is protected by copyright. All rights reserved.

Damage recovery stages revisited: Thermal evolution of non-saturated and saturated displacement damage in heavy-ion irradiated tungsten

Establishing the correlation between damage recovery and temperature in nuclear materials is vital to understanding material property degradation. Among the handful of topics related, one long-standing concern is the differences in damage recovery caused by different initial defect concentrations, with respect to ranges below and beyond the damage saturation limit. In this study, the temperature dependence of damage recovery has been comprehensively elucidated for pure tungsten, irradiated with 6 MeV copper ions at room temperature (RT), up to 0.05 dpa (non-saturated damage, n-SD) and 0.6 dpa (saturated damage, SD), and followed by isochronal annealing. Coupled transmission electron microscopy and Doppler broadening positron annihilation spectroscopy characterizations provided a full-probe-range picture of defect evolution. The varied initial defect concentrations caused retaining differences in damage recovery, but no substantial influence on temperature-dependent defect evolution. Moderate and dramatic damage recovery were identified below 973 K and above 1123 K in n-SD and SD tungsten, respectively. Most strikingly, nano-sized voids were confirmed at 473 K in both samples. Annealing at 1873 K saw the complete removal of defects in n-SD tungsten, but survival of a few dislocations via void pinning in SD tungsten. Full damage recovery in SD tungsten was projected to be ∼2000 K. The current revisit of damage recovery stages demonstrated the significance of encompassing scenarios of non-saturated and saturated defect concentrations. Accordingly, four damage recovery stages were redefined for heavy-ion irradiated tungsten, namely stage I (20 K–RT), stage II (RT–653 K), stage III (653–1123 K), and stage IV (1123–2000 K).

Advanced Magnetocaloric Materials for Energy Conversion: Recent Progress, Opportunities, and Perspective

AbstractSolid‐state caloric effects as intrinsic thermal responses to different physical external stimuli (magnetic‐, uniaxial stress‐, pressure‐, and electric‐fields) can achieve a higher energy efficiency compared with traditional gas compression techniques. Among these effects, magnetocaloric energy conversion is regarded as the best available alternative and has been exploited extensively for promising application scenarios in the last decades. This review systematically introduces the magnetocaloric effect and its applications, and summarizes the corresponding representative magnetocaloric materials, as well as important progress in recent years. Specifically, the review focuses on some key understandings of the magnetocaloric effect by utilizing state‐of‐the‐art technical tools such as synchrotron X‐ray, neutron scattering, muon spin spectroscopy, positron annihilation spectroscopy, high magnetic fields, etc., and highlights their importance toward advanced materials design and development. An overview of the basic principles and applications of these advanced techniques on magnetocaloric materials is provided. Finally, the challenges and perspectives on further developments in this field are discussed. Further in‐depth understanding and manufacturing technology advancement combined with fast‐developed artificial intelligence and machine learning are expected to advance the magnetocaloric energy conversion technology closer to real applications.

Cold Sprayed Deposits Characterized by Positron Annihilation Spectroscopy

Cold Sprayed Deposits Characterized by Positron Annihilation Spectroscopy

He ion irradiation resistance of W-Ni-Fe alloys with variable Ni and Fe concentrations

Tungsten-nickel-iron (W-Ni-Fe) alloys, commonly known as W heavy alloys (WHAs), exhibit enhanced ductility, thermal conductivity, and mechanical attributes. These properties render WHAs highly suitable as plasma-facing materials in lieu of pure W. This investigation examines the irradiation resistance of two WHAs—97W-2Ni-1Fe and 90W-7Ni-3Fe—by subjecting them to He ion irradiation at doses reaching 5 × 1017 ions/cm2. The study establishes that low-dose irradiation (1 × 1017 ions/cm2) inflicted negligible surface damage on both WHA compositions. Nonetheless, increasing the radiation dose to 5 × 1017 ions/cm2 led to observable surface impairments, albeit at a reduced magnitude when compared to pure W. An array of analytical methods was employed to characterize irradiation-induced microstructures and void swelling, including positron annihilation spectroscopy, thermal desorption spectroscopy, and transmission electron microscopy. These analyses revealed that low-dose irradiated WHAs predominantly generated vacancy-type defects. Moreover, these defects evolved into HemVn and HemVn-NiFe complexes as the irradiation dose increased. Concurrently, He bubble density escalated with rising irradiation dosage. When subjected to an irradiation dose of 1 × 1017 ions/cm2, both alloys manifested desorption levels approximately 6.5 times greater than that observed in pure W. The findings of this investigation offer valuable insights to the understanding of WHA irradiation behavior in nuclear materials.

Ultrafast annihilation of irradiation-induced defects using pulsed electric current for damage performance regeneration

As the most important irradiation-induced defects, dislocation loop and copper-rich nanocluster are the major contributors to the embrittlement of the neutron-irradiated reactor pressure vessel steels. In this study, such nano-defects were introduced into the material by 3 MeV Fe ions up to the dose of 1 dpa at high temperature (290 °C) to simulate neutron irradiation. It was found that pulsed electric current can effectively reduce 95 % of irradiation-induced hardening. Correspondingly, the characterization results showed that almost all the dislocation loops disappeared and the quantity of copper-rich nanoclusters also reduced greatly at relatively low temperature (450 °C), and the process took only 20 min. Meanwhile, it was qualitatively proved by positron annihilation spectroscopy that the number of irradiation-induced vacancy-type defects and solute-enriched clusters was significantly decreased after electropulsing. Furthermore, under the pulsed electric field, the rapid annihilation of the dislocation loops due to their accelerated collision with vacancies can remove the nucleation sites of the copper-rich nanoclusters and make them become dispersed, further promoting the nanoclusters that lack nucleation sites dissolving faster. Therefore, this electropulsing treatment provides a practical ‘‘in-situ” performance repair technology to extend the service life of reactor pressure vessel steels by regulating the interaction between vacancies, interstitial atoms and irradiation-induced defects.

Transient positron annihilation spectroscopy under light irradiation at liquid nitrogen temperature: evaluation of defect states in single-crystal ZnO

Abstract A time-dependent measurement system has been developed for positron annihilation spectroscopy to study the effects of light irradiation at liquid nitrogen temperature. The system enables the measurement of positron annihilation lifetimes after pulse light irradiation, utilizing various time windows to investigate the transient changes of photo-excited vacancy-type defects. Additionally, this system facilitates coincidence Doppler broadening measurements during light irradiation at liquid nitrogen temperature. The system was successfully employed to analyze changes in positron lifetime and positron annihilation sites in electron-irradiated single-crystalline ZnO under light irradiation.

On the role of defects in modelling approaches for thin film gas barrier coatings on polymer substrates: I. Model development

We present a method to model the gas permeation through silicon-oxide thin film coatings that are afflicted with nanoscale defects. With it, we are able to give an estimation of the diffusion coefficient in bulk by subtracting the influence of the defects. The model is based on data obtained from positron annihilation spectroscopy, which is processed to yield possible defect allocation patterns of the coatings. For a systematic evaluation of these patterns, a path through the coating is calculated and then subjected to in-depth analysis to evaluate the used approach as well as to interpret the results for insights on the permeation mechanisms. The model appears to function as intended and no unexpected behaviour is observed. The defect volume share is overestimated, which can be retraced to the underlying algorithm, and a correction method is applied to the resulting bulk diffusion coefficient. The model gives reasonable results both for oxygen and water vapor permeation. These results can be used in following works that build on the presented model.

Co-evolution of point defects and Cr-rich nano-phase in binary Fe-20 at.% Cr alloy: A comprehensive investigation using positron annihilation spectroscopy and atom probe tomography

The role of point defects in temporal evolution of Cr-rich α′-phase separation in Fe-20 at.% Cr alloy is elucidated by intercepting the long term (upto 1000 h at 773 K) aging at regular intervals and probing by a combination of atom probe tomography (APT) and positron annihilation spectroscopy (PAS). Since the Cr concentration of nano-scale α′-phase in Fe-20 at.% Cr alloy increases continually on aging, the point defects play active role throughout the aging duration. The near-atomic resolution of APT and self-seeking ability of positrons towards point defects make this analysis possible. The difference of positron affinities between Fe and Cr enables identification of the Cr-rich nano-phases that are specifically associated with defects; they would otherwise be indiscernible in the absence of defect. Thus, the temporal evolution of Cr-rich nano-phase along with the associated point defects can be fully characterized at each stage of aging using APT and PAS, respectively. The combined APT-PAS study shows that Cr-rich α′-precipitation is preceded by vacancy-Cr complex that act as nucleation site for Cr-clusters, which in turn, cause an early rise in micro-hardness due to cluster hardening. Interestingly, this is accompanied by redistribution of the quenched-in vacancies and their trapping in Cr-clusters. Our results depict that the vacancies present in the core of the α′-precipitates migrate towards the precipitates’ interface during the course of aging and eventually get recovered resulting in virtually defect-free precipitates. This study chronicles the way the point defects shape the process of α′-phase separation throughout the entire length of aging.

Defects in layered boron nitride grown by Metal Organic Vapor Phase Epitaxy: luminescence and positron annihilation studies

Defects in two-dimensional boron nitride (BN) are candidates for a manifold of applications, for example, as single-photon emitters or optically addressable spin defects. However, the topic has proven to be complex and despite extensive research efforts, knowledge on midgap defects and their signature in photoluminescence (PL) remains fragmentary. Mass production of high-quality layered BN by Metal Organic Vapor Phase Epitaxy (MOVPE) is possible and effective, thus understanding the conditions of formation and identifying defects that arise in the material grown by this method is extremely important. Here, we present an analysis of the influence of the MOVPE growth conditions of layered BN on the occurrence of specific structural defects. PL spectra in the visible range were analysed involving the Huang-Rhys theory implemented in the fitting procedure for polycrystalline samples grown under various conditions. Such an approach allowed us to separate bands from individual entities. Two bands at 1.57 eV and 2.6 eV with phonon replicas were observed. The three additional bands are characterized by a broad emission centered at 1.38 eV, 1.9 eV and 2.24 eV. Further properties, including an analysis of the surface morphology, the impact of annealing and laser bleaching on the PL spectra and Positron Annihilation Spectroscopy (PAS) were considered to draw conclusions about the nature of the examined defects. The PAS analysis correlated with the PL of the BN layers allows us to classify the studied samples in terms of the concentrations of boron vacancies and their complexes. Based on the obtained results, we propose that the rich family of PL bands observed in various sp2-BN layers is associated with different defect complexes build of boron vacancies (VB), boron antisite defects (BN), substitutional carbon defects (CB, CN) and their donor-acceptor pairs. The main value of this paper is the transfer of knowledge gained about defects and the corresponding luminescent bands to characterize high-quality continuous epitaxial sp2-BN layers. The presented results constitute an important step toward the deterministic manipulation of defect concentrations in two-dimensional boron nitride, which opens up new pathways for future optoelectronic device application.