Emission Yield Research Articles

Synthesis and Chiroptical Activity of π-Expanded Electron-Rich Heterohelicenes Based on the 1,4-Dihydropyrrolo[3,2-b]pyrrole Core.

Herein, we report the synthesis and chiroptical characteristics of the first (double) helicenes possessing the 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) moiety as their central core. We have developed a three-step synthesis with 6π-electrocyclization accompanied by HBr elimination as its key step. We found that, whereas for smaller peripheral arms double 6π-electrocyclization occurs smoothly forming a double helicene, in the case of longer polycyclic aromatic hydrocarbons the reaction becomes less efficient and mono-helicenes are the only products. The electron density distribution analysis of LUMO explains the different regioselectivity of 6π-electrocyclization. The synthesized heterohelicenes are characterized by greenish-blue emission, distinct solvatofluorochromism and good fluorescence quantum yields (up to 42 %). Moreover, the chiroptical measurements reveal that unsymmetrical double heterohelicene exhibits excellent circularly polarized luminescence brightness (BCPL) reaching 30 M-1 cm-1. The combined experimental and computational study has revealed that a charge-transfer state is responsible for the observed emission (hence the solvatochromism), while low-energy absorption derives from multiple transitions.

Carbazole-Based Eu3+ Complexes for Two-Photon Microscopy Imaging of Live Cells.

Lanthanide(III) complexes with two-photon absorbing antennas are attractive for microscopy imaging of live cells because they can be excited in the NIR. We describe the synthesis and luminescence and imaging properties of two Eu3+ complexes, mTAT[Eu·L-CC-Ar-Cz] and mTAT[Eu·L-Ar-Cz], with (N-carbazolyl)-aryl-alkynyl-picolinamide and (N-carbazolyl)-aryl-picolinamide antennas, respectively, conjugated to the TAT cell-penetrating peptides. Contrary to what was previously observed with related Eu3+ complexes with carbazole-based antennas in a mixture of water and organic solvents, these two complexes show very low emission quantum yield (ΦEu < 0.002) in purely aqueous buffers. A detailed spectroscopic study on mTAT[Eu·L-Ar-Cz] reveals that the quantum yield of emission is strongly polarity dependent─the less polar the medium, the higher the quantum yield─and that the emission quenching in water is likely due to a photoinduced electron transfer between the excited carbazole-based antenna and Eu3+ that efficiently competes with the energy transfer process. Nevertheless, mTAT[Eu·L-Ar-Cz] shows a significant two-photon cross-section of 100 GM at 750 nm, which is interesting for two-photon microscopy. The live cell imaging properties of mTAT[Eu·L-Ar-Cz] and the two other conjugates were investigated. Cytosolic delivery was clearly evidenced in the case of mTAT[Eu·L-Ar-Cz] when cells are coincubated with this compound and a nonluminescent dimeric TAT derivative, dFFLIPTAT.

Red-Shifted and Enhanced Photoluminescence Emissions from Hydrogen-Bonded Multicomponent Nontraditional Luminogens.

Nontraditional luminogens (NTLs) without large π-conjugated aromatic structures have attracted a great deal of attention in recent years. Developing NTLs with red-shifted and enhanced emissions remains a great challenge. In this work, we developed a NTL composed of three components, i.e., polymaleic acid (PMA), arginine (Arg), and polyacrylamide (PAM), and investigated its photoluminescent behavior and mechanism. Compared with the single components and binary components, the PMA/Arg/PAM solid exhibited two red-shifted emission peaks at 510 and 562 nm and higher quantum yields. Structural characterizations demonstrated that hydrogen bonds formed between the nonconventional chromophores in PMA and Arg lead to more extended through-space conjugation and rigidified conformations, which is the fundamental reason for the red-shifted emission and higher quantum yield of the PMA/Arg/PAM solid. In addition, theoretical calculations proved that excited-state proton transfer occurs between the carboxyl groups of PMA and amino groups of Arg via photoexcitation, resulting in dual emissions in the PMA/Arg/PAM solid. This work provides a deeper understanding of the photoluminescence mechanism of NTLs based on multiple hydrogen bonds and is helpful in guiding the design of NTLs with red-shifted and enhanced emissions.

Meso-Substituted AB3-type phenothiazinyl porphyrins and their indium and zinc complexes photosensitising properties, cytotoxicity and phototoxicity on ovarian cancer cells.

New meso-substituted AB3-type phenothiazinyl porphyrins and ferrocenylvinyl phenothiazinyl porphyrin were synthesised by Suzuki-Miyaura and Mizoroki-Heck cross-coupling reactions, respectively. The free porphyrins were further used in the synthesis of new indium(iii) or zinc(ii) porphyrin complexes. All porphyrins exhibit red fluorescence emission in solution, a property that remains unimpaired following internalisation in ovarian A2780 cancer cells, as evidenced by fluorescence microscopy images. The In(iii) phenothiazinyl porphyrin complexes show a higher quantum yield of fluorescence emission (2aΦ F = 30%, 4aΦ F = 29%, 5aΦ F = 28%) compared to the free base porphyrin precursors, or Zn(ii) complex 4b (Φ F = 10%). The potential of novel phenothiazinyl porphyrins to act as photosensitisers was evaluated using two distinct approaches. The first was through the measurement of the singlet oxygen quantum yield Φ Δ(1O2), while the second employed in vitro measurements of metabolic activity, oxidative stress, nuclear factor-erythroid 2 related factor 2 (Nrf-2) activation and tumour necrosis factor-alpha (TNF-α) under both dark and light irradiation conditions. As reflected by the IC50 values, the most potent cytotoxicity of the phenothiazinyl porphyrins against the A2780 cells was observed for In(iii) ferrocenylvinyl phenothiazinyl porphyrin 4a (36.38 μM), the remaining compounds are less cytotoxic. The reduction in metabolic activity was observed in A2780 ovarian tumour cells treated with 4a and 6a and exposed to light compared to treatment in the absence of light. The oxidative stress, TNF-α and Nrf-2 transcription factor were particularly notable when A2780 cells were treated with 4a and subsequently photoirradiated, the oxidative stress was linked to the highest value of Φ Δ(1O2) recorded for 4a (60%).

The impact of encapsulation in cyclodextrin nanocavities on the participation of hydrogen bond assisted intramolecular charge transfer in fluorescence emission

This study investigates how incorporation of D-π-A derivatives in various cyclodextrin structures affects the identification of excited-state emission characteristics, focusing on the contribution of intramolecular charge transfer and hydrogen bond-assisted intramolecular charge transfer emissive states. In this context, the photophysical properties of 4-(5-(4-methoxyphenyl)thiophen-2-yl)benzamidine (I) and 2-fluoro-4-(5-(4-methoxyphenyl)thiophen-2-yl)benzamidine (II) in neutral aqueous solution and upon inclusion in various cyclodextrin derivatives were investigated by steady state and time-resolved measurements. Despite the very limited changes in the absorption spectra of the guest molecules upon addition of CDs, significantly large changes were observed in their steady-state fluorescence spectroscopy, both in the quantum yield of the fluorescence emission and their fluorescence lifetime results. Fluorescence decay profiles of (I) and (II) exhibited good fits with biexponential decay functions both in the presence and absence of the investigated CDs, with their respective contributions significantly dependent on the concentration of added cyclodextrin. The association constants derived from fluorescence decay measurements closely matched those obtained from steady-state fluorescence measurements. Inclusion of I and II in α-CD, β-CD, Mβ-CD, or HPβ-CD was confirmed using 1H NMR measurements, with notable 2D NOESY effects observed specifically for II..HPβ-CD complexes.

Effects of wheat straw mulching and wet treatment on soil improvement, greenhouse gas emission, nitrogen leaching, and vegetable yield

Effects of wheat straw mulching and wet treatment on soil improvement, greenhouse gas emission, nitrogen leaching, and vegetable yield

The role of rumen microbiome in the development of methane mitigation strategies for ruminant livestock.

Ruminants play an important role in global food security and nutrition. The rumen microbial community provides ruminants with a unique ability to convert human indigestible plant matter, into high quality edible protein. However, enteric CH4 produced in the rumen is both a potent GHG and a metabolizable energy loss for ruminants. As the rumen microbiome constitutes 15-40% of the inter-animal variation in enteric CH4 emissions, understanding the microbiological mechanisms underpinning ruminal methanogenesis and its interaction with the host animal, is crucial for developing CH4 mitigation strategies. Variation in the relative abundance of different microbial species has been observed in cattle with contrasting residual CH4 emission and CH4 yield with up to 20% of the variation in inter-animal CH4 emissions attributable to the presence of a small number of microbial species. The demonstration of ruminotypes associated with high or low CH4 emissions suggests that interactions within complex microbial consortia and with their host are a major source of variation in CH4 emissions. Consequently, microbiome-assisted genomic approaches are being developed to select low CH4 emitting cattle, with breeding values for enteric CH4 being included as part of national breeding programmes. Generating rumen microbiome data for use in selection programs is expensive, therefore, identifying microbial biomarkers in milk or plasma to develop predictive models which include microbial predictors in equations based on animal related data, is required. A better understanding of the rumen microbiome has also aided the development and refinements of anti-methanogenic feed additives. However, these strategies, which increase the amount of reducing equivalents in the rumen ecosystem, do not generally result in an enrichment of propionate or an improvement in animal performance. Current research aims to provide alternative sinks to reducing equivalents and to stimulate activity of commensal microbes or the supplementation of direct fed microbials to capture lost energy. Furthering our knowledge of the rumen microbiome and its interaction with the host, will aid in the development of CH4 mitigation strategies for ruminant livestock.

Introducing Methoxy Functionality to Modulate the Lead Halide Dimensionality in Robust Metal–Organic Frameworks for Enhanced Broadband Emission

AbstractAchieving hybrid lead halides with high stability and tunable dimensionality is essential for advancing their optoelectronic applications. While numerous studies have investigated ligand functionality to modulate lead halide dimensionality and enhance photoluminescence (PL) efficiency, most efforts remain limited to labile, ionically bound structures with stability issues. Herein, two new members of lead halide‐based metal–organic frameworks are successfully synthesized by employing dimethoxy‐functionalized benzenedicarboxylate acid (2,5‐dmbdcH2) as a bridging linker. This functionalization increases steric hindrance, effectively isolating 1D lead halide chains into 0D lead halide units. The 0D [Pb4X2]6+ (X = Cl, Br) cluster‐type units, are coordinatively linked by 2,5‐dmbdc to form two robust 3D frameworks, Pb4X2(2,5‐dmbdc)3. The structural deformation of the 0D lead halide units enhances photoluminescence quantum yields (PLQYs) of broadband emissions, increasing from 1.5–8.0% for TMOF‐5 to 33.4–34.6% for TMOF‐15, while maintaining excellent long‐term photostability and environmental durability. Mechanistic studies reveal that the strong interaction between charge carriers and phonons within the deformable [Pb4X2]6+ clusters promotes the formation of self‐trapped excitons (STEs), leading to the enhanced broadband emission observed in TMOF‐15. This work presents an effective linker‐functionalization strategy for synthesizing lead halide MOFs with both high stability and excellent PL performances.

Design, Synthesis, and Antibacterial Activities of Multi-Functional C2-Functionalized 1,4-Naphthoquinonyl Organoseleniums.

A practical and efficient reaction for C2-selenylation of 1,4-naphthoquinones has been explored. This coupling reaction of two redox structural motifs, such as 2-bromo-1,4-naphthoquinone with diaryldiselenide/ebselen has been achieved by using sodium borohydride reducing agent at room temperature. Using this approach, several 2-selenylated-1,4-naphthoquinones were obtained in moderate to good yields and thoroughly characterized by multinuclear (1H, 13C, and 77Se) NMR, cyclic voltammetry, and mass spectrometry. Further, light-irradiated thiolation of the synthesized selenazinone was also performed to show the utility of the synthesized compound for post-functionalization. Several 2-selenylated-1,4-naphthoquinones were studied by SC-XRD in which intramolecular Se⋅⋅⋅N (from quinolinyl ligand) non-bonded interactions were observed. Photophysical studies (UV-visible, emission, solvatochromism, and quantum yield) were also performed on selected C2-selenylated naphthoquinones. The naphthoquinonyl organoseleniums were also screened for their antibacterial properties and quinonyl organoselenium 5 d shows good antibacterial potential against S. aureus ATCC 29213 with MIC 0.5 μg/mL and a Selectivity Index of >200. Moreover, it also exhibited equipotent activity against various strains of S. aureus and Enterococcus faecium, including strains resistant to vancomycin and meropenem. From structure-activity correlation, it seems that nice blend of oxidant properties from quinone and antioxidant properties from selenium moiety makes it better candidate for antibacterial activity.

Converting Biochar Into Biochar‐Based Urea Promotes Environmental and Economic Sustainability in Rice‐Wheat Rotation System

ABSTRACTBiochar amendments in rice‐wheat systems are sustainable for reducing GHGs (greenhouse gases) and improving soil health but the widespread adoption of biochar faces economic challenges. To address limitation, a novel biochar‐based urea was formulated for environmental and cost advantages. A pot experiment within a rice‐wheat rotation was conducted to evaluate comparative effects of biochar‐based urea (CKBU), biochar + urea (BCU), and biochar‐based urea + biochar (BCBU) over conventional mineral fertilizer (CKU) on soil ammonia (NH3) volatilization, GHG emissions, soil structure, and crop productivity. Furthermore, fertilizer N fate was tracked using the 15N isotope during wheat season. The results indicated that compared to CKU, CKBU, BCU, and BCBU treatments significantly mitigated NH3 volatilization by 22%–31% during the rice season, and a 19% reduction was observed under the BCBU treatment during the wheat season due to the response of N‐cycling microorganisms. Regarding GHG emissions, the CKBU, BCU, and BCBU treatments significantly decreased the global warming potential (GWP) value by 49%–55% during the rice season and by 26%–45% during the wheat season, compared to CKU. Additionally, CKBU enhanced 15N use efficiency by 29% during wheat season, without affecting the rice season. The economic performance indicated that applying BU alone offered a net economic benefit, whereas biochar amendment led to a net economic loss. However, biochar amendment improved SOC and aggregation structure, with a significant increase in macroaggregate distribution over 50% compared to CKU and CKBU. Therefore, BU with small portions of biochar can be as effective in reducing NH3 emissions and mitigating GHG emissions as the use of a large quantity of biochar. Additionally, the BCBU did not show additional synergistic benefits regarding emission reduction or yield enhancement. Therefore, shifting biochar to BU could be a cost‐effective approach to achieving sustainable productivity in rice‐wheat crop rotation systems.

The Dual-Role of Benzothiadiazole Fluorophores for Enabling Electrofluorochromic and Electrochromic Devices.

Three unsymmetric fluorophores differing in their flanking electron acceptor (-NO2, -CN, -CHO) were investigated for their electrofluorochromism and electrochromism. The emission yield of the -NO2 substituted fluorophore in the solid state was ca. 9-fold less than its -CN and -CHO counterparts. Visible color changes of the fluorophores were observed with an applied potential. The intensity of the near-infrared absorption at ca. 1500 nm formed upon electrochemical oxidation was contingent on the electron-withdrawing group: 2-fold more intense with the -CN substitution than its -H counterpart. The coloration efficiency was upwards of 655 cm2 C-1 and the bleaching kinetics (tb; 22 s) of the NIR band decreased according to -NO2>-CN>- CHO ≈ -H. The electrochemically generated states could be reversibly formed during 120 min of switching the applied potential. The contrast ratio of the radical cation and the NIR absorption was near unity and 60-82 %, respectively. The photoemission intensity of the fluorophores could also be modulated with applied potentials. The collective electrochemically mediated color switching and emission intensity modulation along with their solid-state emission demonstrate that benzothiadiazole fluorophores can play a dual role in chromic devices both as the color switching and photoemission intensity modulating material.

Probing Luminescence in the Collisions of Furan Molecules with Dihydrogen Cations Using Collision-Induced Emission Spectroscopy

Optical spectroscopic studies of furan molecules (C4H4O) impinged by dihydrogen cations (H2+) were for the first time performed employing collisioninduced emission spectroscopy at ions incident energy range of 25–1000 eV corresponding to the velocities from 49 to 311 km/s. The recorded spectra reveal strong luminescence of atomic hydrogen Balmer lines whose intensities weaken with rising principal quantum number n. The spectra also display emission bands of CH radicals excited to the first A2Δ and second B2Σ− electronic states. The emission yield curves of these excited products were additionally measured by recording resultant intensities at different projectile energies. Impact processes are unveiled based on these results.

Steric and Distance Effect on Electron Transfer in Dibenzo-Fused BODIPY-Based Photoredox Catalysts.

π-Extended BODIPY compounds are a compelling class of fluorophores known for their red or near-infrared (NIR) emission and high quantum yields, which are crucial for applications in materials science, solar cells, and biomedical imaging. Our recent study shows that we can use a dibenzo-fused BODIPY as a singlet-driven red photoredox catalyst by installing a simple electron donor group. Despite their potential in these applications, knowledge of electron transfer reactions involving dibenzo-fused BODIPY is still scarce. This paper presents the synthesis and systematic photophysical investigations of donor-acceptor (D-A) and donor-bridge-acceptor (D-bridge-A) series of dibenzo-fused BODIPY with N,N'-diethylaniline fragments serving as an electron donor. We examined the effects of methyl substituents and bridge length on the rates of photoinduced electron transfer (PeT). Through steady-state and time-resolved optical spectroscopy, electrochemistry, and density functional theory calculations, we elucidated how these simple structural modifications controlled the PeT rates and examined their impacts on catalytic activities in atom transfer radical addition (ATRA) reactions. Our results support previous studies on the (D-A) design of red heavy atom-free photocatalysts.

Modeling of influence of the insulating film thickness non-uniformity along the cathode surface on its emission properties in glow gas discharge

A model of the cathode sheath of glow gas discharge at the existence of an insulating oxide film on the cathode surface, which thickness has non-equal values at its different sections, is formulated. An influence of the film thickness non-uniformity on the cathode effective ion-electron emission yield and discharge cathode sheath characteristics is investigated.

Effects of cashew nutshell extract inclusion into a high-grain finishing diet on methane emissions, nutrient digestibility, and ruminal fermentation in beef steers.

By 2050, the U.S. beef industry must produce an extra 40 million tons of beef to satisfy the global demand. Such an increase in inventory will undoubtedly enhance methane (CH4) production from livestock, which should be reduced by over 20%. The addition of plant secondary metabolites, such as anacardic acid present in cashew nutshell extract (CNSE), has shown promising results in reducing CH4 yield, although its effects seemed to be diet dependent. This study evaluated the addition of CNSE to a high-grain diet (85:15 Grain: forage) on in vivo CH4 emissions, nutrients digestibility, performance, feeding behavior, and ruminal fermentation parameters of beef steers. Sixteen Angus crossbred steers [599 ± 40kg of bodyweight (BW)] and six ruminally cannulated crossbred steers (490 ± 51kg of BW) were utilized in a crossover design with 2 experimental periods of 56 d each, composed by 14 d of adaptation, 35 d of measurement, and 7 d of washout. Following adaptation, steers were sorted by BW, and assigned to receive no additive (CON) or CNSE at 5g/steer/d. Data were analyzed using the MIXED procedure of SAS. Inclusion of CNSE increased (P < 0.05) propionate concentration and molar proportion (MP; mol/100mol), tended to decrease acetate MP (P = 0.10), reduced the acetate: propionate (A:P) ratio (P = 0.05), and MP of branched chain volatile fatty acids (P < 0.01). Neither in vitro organic matter digestibility nor in vitro CH4 yield were affected by CNSE inclusion (P > 0.05). Steers receiving CNSE exhibited greater (P < 0.05) final BW, dry matter intake (DMI), and average daily gain (ADG) but lesser (P < 0.05) in vivo CH4 emission rate (g/d), yield (g/kg of DMI), and intensity (g/kg of ADG). Meal length, bunk visit duration, and apparent total tract digestibility of DM increased (P < 0.05) after CNSE addition. Considering CNSE-supplemented steers spent more time in the feedbunk and exhibited higher DMI, CH4 mitigation was unlikely associated with intake reduction. The addition of CNSE to a high-grain diet in beef steers demonstrated significant improvements in animal performance and reduced CH4 emissions, as the result of shifts in ruminal fermentation patterns, favoring propionate instead acetate concentration, leading to a reduction in the A:P ratio. CNSE shows promise as a strategy to enhance beef industry sustainability.

Effects of nitrogen fertilizer and biochar levels on soil CO2 emission and wheat yield in irrigation region

Effects of nitrogen fertilizer and biochar levels on soil CO2 emission and wheat yield in irrigation region

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]+ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

New experimental methodology for determining the second crossover energy in insulators under stationary e-irradiation in a SEM

A new experimental methodology is proposed which uses the electrostatic influence method (EIM) in scanning electron microscope (SEM) in order to estimate the second crossover energy EC2 for uncharged insulators. This experimental methodology based on simultaneous time measurement of the displacement and leakage currents, is approached to the short pulse irradiation technique but under stationary e-irradiation and allows determining the intrinsic secondary electron emission yield, σ0 (σ0 is the value of the total secondary electron yield just at the beginning of the irradiation before significant charge accumulation or before the formation of a surface potential). The obtained value of EC2 for soda-lime glass is confirmed by two additional experiments based on secondary electron imaging. This value is in good agreement with those previously obtained by other studies based on the surface potential measurement or the pulsed irradiation technique.

Mechanism exploration of ion-implanted epoxy on surface trap distribution: An approach to augment the vacuum flashover voltages

Abstract The augmentation of the epoxy (EP) resin surface to advance flashover performance has become a pivotal point of global interest. This research introduces a novel surface modification method and its mechanism for insulation materials. The research follows an electron cyclotron resonance ion implantation system to subject the surface of EP insulation to ion beams with diverse energies, i.e., 6, 10, 20, 40, 50, and 60 keV for a consistent time of 300 s at an angle of 90°. The experimental phase includes the DC flashover examination under negative polarity. Besides, the simulation phase includes the Monte Carlo model constructed using SRIM software to examine the range and distribution of bombarded ions in the targeted insulation. Results reveal that the flashover properties are affected by the surface potential, surface conductivity, trap distribution, water contact angle, and elemental composition. Likewise, based on the outcomes and theoretical point of view, it is revealed that the bombardment of energetic ions enhances the trap depth, assisting in a reduction in surface conductivity, confining the surface charge movements, and extensively suppressing the secondary electron emission yield. Also, the enhanced trap depth induces homo-charge formation near triple junctions. Synergistically, the factors contribute to high flashover voltages.

Efficient Blue Emission in Organic–Inorganic Metal Halide (TEA)2InCl5 Triggered by Bi3+‐Doping

AbstractLead‐free 0D In‐based organic–inorganic metal halides (OIMHs) have attracted tremendous attention because of their nontoxicity, environmental stability, and excellent photoluminescence properties. However, it remains controversial and unclear whether the luminous division exists in ns2 doping In‐based materials, as the majority of In‐based materials are considered non‐luminous. Herein, a series of Bi3+‐doped (TEA)2InCl5 (TEA = tetraethylammonium) crystals are synthesized and it is determined that the blue emission stemmed from Bi ions. Remarkably, the photoluminescence quantum yield (PLQY) of the blue emission at 469 nm reached 69.69% under 371 nm excitation, exceeding those of previously reported Bi3+‐doped OIMHs. In addition, pristine and Bi3+‐doped compounds exhibited excellent structure and optical stability under humid conditions. This study provides new insights into the photoluminescence properties of In‐based OIMHs, especially regarding the high‐efficiency emission of Bi3+‐doped materials.