Rare Earth Doping Research Articles

Density Functional Theory Study of Electronic Structure and Optical Properties of Ln3+-Doped γ-Bi2MoO6 (Ln=Gd, Ho, Yb)

Based on density functional theory (DFT), theoretical models of three kinds of lanthanide rare earth metal ion-doped γ-Bi2MoO6 were constructed (Ln-BMO (Ln=Gd, Ho, Yb)). The geometric structure, electronic structure, and optical properties of the model were calculated, and the influence of doped Ln3+ ions on the structures and properties of the system was analyzed. The results revealed that the substitution of smaller ionic radius Ln3+ ions for Bi3+ ions caused a contraction of the lattice parameters. At the same time, the contribution of the [Ln]4d near valence band and conduction band reduced the bandwidth of γ-Bi2MoO6, forming the Ln-O ionic bond with different strengths to obtain higher charge conductivity and charge-separation ability. Secondly, Ln3+ ions have a strongly ionic charge, which leads to the appearance of optical absorption bands in the infrared region and part of the visible region. This reduces the reflection in the visible region, improves the utilization rate, delays the loss of electron energy, and promotes phase matching in the visible region. And the Gd3+-doped system has better photocatalytic activity than the other Ln3+-doped system. This research provides theoretical insights into doped lanthanide rare earth ions and also provides strategies for the modification of γ-Bi2MoO6 nanomaterials.

Tunable Photoluminescence of Bismuth‐ and Trivalent‐Lanthanide‐Doped Monolayer Perovskite Oxide Nanosheets

AbstractMulticolor photoluminescent Bi0.4Ln0.1Na0.5Ta2O72− nanosheets (Ln = Eu, Tb, Dy, Sm, La) are prepared by delaminating an Aurivillius‐phase layered perovskite, Bi2.4Ln0.1Na0.5Ta2O9. Both Bi3+ and Ln3+ (except La3+) successfully function as luminescent centers under UV‐light illumination (λex. = 240–340 nm), which result in a photoluminescence color that can be tuned by changing the lanthanide doping. The emission spectra are influenced by pH because the energy distribution to Ln3+ or to Bi3+ is different in acidic or in basic solutions. Freestanding Bi0.4Ln0.1Na0.5Ta2O72− nanosheet membranes are prepared by vacuum filtration, and the relationship between the photoluminescence and structural properties of the nanosheet membranes is investigated. The results indicate that differences in the electron orbitals involved in the photoluminescence of Bi3+ (6s2–6s6p) and Ln3+ (4fn–4fn) influence the responsiveness to changes in the environment surrounding those luminescent centers.

Photocatalytic Performance of Zinc Oxide and Metal‐Doped Zinc Oxide for Various Organic Pollutants

AbstractZinc oxide (ZnO) has a high photocatalytic potential to decompose volatile organic pollutants into CO2 and H2O which depend on their physical properties, such as particle shape and size, band gap, type of dopant, and optical and structural properties. Using 93 references listed in this review, the relationship between metal dopant and synthesis methods to the efficiency of ZnO and composite ZnO‐metal in degrading pollutants for photocatalyst applications is studied. The basic principles of the photocatalyst process is described when the electrons at the valence band of ZnO get the energy from solar spectrum, generate the charge (electron and hole), and then continue to react with superoxide and water, resulting in radical atoms which break the bonds of organic pollutants. Rare earth dopants have the highest efficiency up to 100 % at 15 min irradiation. Conclusions and future prospects of ZnO and metal‐doped ZnO are also discussed. Perspectives and challenges of the future development of ZnO‐based photocatalysts are evaluated.

Cross Relaxation Channel Tailored Temperature Response in Er3+‐rich Upconversion Nanophosphor

AbstractRecently high doping of lanthanide ions (till 100 %) is realized unprecedentedly in nanostructured upconversion (UC) phosphors. However, oddly enough, this significant breakthrough did not result in a corresponding UC enhancement at ambient temperature, which hinders the otherwise very interesting applications of these materials in various fields. In this work, taking the Er3+‐rich UC nanosystem as an example, we confirm unambiguously that the phonon‐assisted cross relaxation (CR) is the culprit. More importantly, combining the theoretical modeling and experiments, the precise roles of different CR channels on UC energy loss are quantitatively revealed. As a result, lowering the temperature can exponentially enhance the relevant UC luminescence by more than two orders of magnitude. Our comprehension will play an important role in promoting the UC performance and further application of high doping rare earth materials. As a proof of concept, an Er3+‐rich core/multi‐shell nanophosphor is exploited which demonstrates the great potential of our finding in the field of ultra‐sensitive temperature sensing.

Cross Relaxation Channel Tailored Temperature Response in Er3+ -rich Upconversion Nanophosphor.

Recently high doping of lanthanide ions (till 100 %) is realized unprecedentedly in nanostructured upconversion (UC) phosphors. However, oddly enough, this significant breakthrough did not result in a corresponding UC enhancement at ambient temperature, which hinders the otherwise very interesting applications of these materials in various fields. In this work, taking the Er3+ -rich UC nanosystem as an example, we confirm unambiguously that the phonon-assisted cross relaxation (CR) is the culprit. More importantly, combining the theoretical modeling and experiments, the precise roles of different CR channels on UC energy loss are quantitatively revealed. As a result, lowering the temperature can exponentially enhance the relevant UC luminescence by more than two orders of magnitude. Our comprehension will play an important role in promoting the UC performance and further application of high doping rare earth materials. As a proof of concept, an Er3+ -rich core/multi-shell nanophosphor is exploited which demonstrates the great potential of our finding in the field of ultra-sensitive temperature sensing.

Facile synthesis of graphene anchored rare earth doped mixed metal ferrite nanorods: A potential candidate for azo dye mineralization

Bandgap tuning using rare earth metals as dopants in ferrite-based photocatalytic materials has received a lot of interest because the Fermi 4f energy of these metals generates a sub-energy state in the bandgap generated by the overlapping of Fe-3d and O-2p orbitals. Herein, dysprosium-doped cobalt-nickel mixed ferrite (D-CNFO) and its graphene-reinforced composite (D-CNFO@G) were prepared and an ideal photocatalyst material for azo dye mineralization was proposed. A cost-effective combination of wet-chemical and ultrasonication methods was used to prepare the doped and composite samples. Advanced characterization methodologies were used to scrutinize the optical, compositional, structural, morphological, and photocatalytic characteristics of as-prepared materials. The X-ray diffraction analysis identified the spinel phase's (cubic) structure, while the electronic spectroscopy examination confirmed the prepared samples' rod-like morphology. The UV/visible absorbance spectrum shows the higher light harvesting behavior of the D-CNFO@G in the visible region. The mineralization performance of the D-CNFO and D-CNFO@G composites was analyzed using Congo-red (an anionic dye), a well-known azo dye. The D-CNFO@G sample removes Congo-red dye at a rate almost 2.4% faster than the D-CNFO sample. The experiment involving trapping free radicals indicates that hydroxyl radical plays a crucial role in dye degradation. Since the D-CNFO@G catalyst is magnetic and can be isolated easily from the photocatalytic system, it shows an awkward cycle activity of more than 96% after five mineralization tests. The as-prepared D-CNFO@G composite is proved as an excellent option for azo dye mineralization because of the combined impacts of rare earth doping, graphene reinforcement and nanotechnology.

Effects of framework dopants on luminescent properties of red nitride phosphors via band structure modelling

Currently, researchers have been able to manipulate the luminescent properties and thermal stability of nitride red phosphor Sr2Si5N8:Eu2+ through rare earth doping. However, there is limited research on the doping of its framework. This work investigated the crystal structure, band structure, and luminescence properties of Sr2Si5N8: Eu2+ and its framework doped systems. We selected B, C, and O as doping elements because the corresponding formation energies of these elements doped structures are relatively low. Then, we calculated the band structures of various doped systems in both the ground and excited states. This analysis aimed to investigate their luminescent properties using the configuration coordinate diagram. The results show that doping with B, C, or O has minimal effect on the emission peak width. The thermal quenching resistance of the B- or C-doped system was enhanced due to the increased energy differences between the 5d energy level of the electron-filled state in the excited state and the bottom of the conduction band, compared to the undoped system. However, the thermal quenching resistance of the O-doped system varies depending on the position of the silicon vacancy. The work indicates that framework doping can also improve the thermal quenching resistance of phosphors besides rare earth ions doping.

Development of colour tunable phosphor via rare earth doping in eulytite type Ba3Bi2(PO4)4 host material

Development of colour tunable phosphor via rare earth doping in eulytite type Ba3Bi2(PO4)4 host material

Study of low-temperature magnetic properties of the antiferromagnetic topological insulator Sm-doped MnBi2Te4

MnBi2Te4 is the first discovered intrinsic magnetic topological insulator. It has great research significance and is related to new phenomena such as topological magneto-electric effect and quantum anomalous Hall effect (QAHE). We report first doping of rare-earth elements in MnBi2Te4 crystals. MnBi2Te4 crystalline samples with different Sm doping ratios were synthesized, and Sm atoms may enter the lattice and replace Mn atoms. Low-temperature magnetization measurements show that, in addition to the antiferromagnetic (AFM) transition of MnBi2Te4, some doped samples undergo small-scale ferromagnetic transitions at around 15 K. Doping furthermore reduces the magnetic field required for the transition to the canted AFM (CAFM) state and slightly increases the Néel temperature of the crystal. Our results suggest that doping rare-earth elements may be a feasible method for tuning the magnetism of MnBi2Te4 and for future applications of magnetic topological insulators.

Multiple spin switching and magnetocaloric effects in orthoferrite Yb0.25Tb0.75FeO3 single crystal

YbFeO3 exhibits spin switching (SSW) and spin reorientation transition (SRT) at low temperatures, but its mediocre magnetocaloric properties limit its further applications. As for TbFeO3 showing a large magnetocaloric effect, its SSW is missing. Motivated by this, we chemically put Yb and Tb with a ratio of 1:3 on the rare-earth site. Potential applications of magnetic and magnetocaloric properties are both preserved in one single phase Yb0.25Tb0.75FeO3, which is exceptional among the rare-earth orthoferrites. Spin switching temperature (TSSW) in the field-cooled-cooling mode increases to around 100 K compared with YbFeO3. A novel multiple SSW emerges in the field-cooled-warming mode originating from the complex competing magnetic interactions between Yb/Tb and Fe sublattices. We also addressed the mechanism of spin modification of magnetic ions with temperatures. Arrott plots created from the isothermal magnetization curves demonstrate that SRT is a second-order phase transition. The negative entropy change (refrigeration capacity) vs. temperatures [−∆Sm(RC) vs. T] diagrams indicate that the −∆Sm(RC) are effectively increased compared with YbFeO3 by rare-earth doping. The pronounced magnetic refrigeration performance and SSW effect with a low-field dependence make it promising to be employed in both magnetic sensing and refrigeration devices.

Multifunctional n-type [Sm3+-Eu3+-Tm3+] - doped SnO2 semiconductor system steered electrochemical and photovoltaic efficiency enhancement in energy applications

BackgorundCurrent study developed a sustainable and an efficient energy system by triply doping tin oxide (SnO2) host with the different lanthanides forming an n-type [Sm3+-Eu3+-Tm3+]: SnO2 heterostructure. MethodsNovel system was synthesized via chemical co-precipitation and thin films were fabricated. Significant findingsThe synergistic electronic coupling of the rare earth dopants and SnO2 host based heterostructure was marked by band gap reduction spanning in the range of 3.48 – 3.59 eV and an average particle size of 47.7 nm with tetragonal rutile geometry. Its electro-catalytic activity for producing O2 and H2 excelled over the conventional catalysts with lower overpotential for O2 / H2i.e. 260 and 143 mV and Tafel slope values of 89.8 and 66.9 mV dec−1, respectively. [Sm3+-Eu3+-Tm3+]: SnO2 is an auspicious electrode material for supercapacitors with the specific capacitance of 592.5 F g − 1 in 0.1 M NaCl, indicative of the characteristic pseudocapacitive behavior. This electrode is intact for an extended duration with the potential of acquiring higher current densities. Additionally, [Sm3+-Eu3+-Tm3+]: SnO2 electron transport layer in perovskite solar cell device ensued an efficiency of 14.23% and a fill factor of 66.94%. The improved photovoltaic parameters are expressive of the excellent connection between different layers enhancing the performance.

Comparison of rare earths doping (neodymium and samarium) on structural and magnetic properties of Ni–Zn–Bi nanoferrites

Excellent magnetic properties in ferrites are required for high-frequency applications and for wastewater treatment. Thus, the present study shows the comparison of magnetic and structural properties of Nd and Sm substituted Ni–Zn–Bi ferrites with the series Ni0.5Zn0.5Bi0.04NdxFe1.96–xO4 (with step size 0.002) and Ni0.5Zn0.5Bi0.04SmxFe1.96–xO4 (with step size 0.02) prepared using citrate precursor method. The impact of the substitution of rare earth ions (Nd and Sm) on magnetic properties of the synthesized samples is observed using a vibrating sample magnetometer (VSM). The saturation magnetization values enhance considerably from 52 to 58 emu/g for Nd3+ ions and 39 to 57 emu/g for Sm3+ ions, thus, making these materials magnetically hard. Further, the higher value of coercivity is also observed ranging from 133 to 167 Oe for Nd3+ ions and 81 to 155 Oe for Sm3+ ions. The shape of hysteresis loops indicates a super paramagnetic and ferromagnetic behavior in the obtained samples. The squareness ratio value is <0.5, suggesting the uniaxial anisotropy of particles and hence, these ferrites are suitable for microwave-absorbing and in permanent magnetic materials. The X-ray diffraction (XRD) pattern shows the formation of pure cubic crystallites, where, lattice parameters range from 0.840 to 0.839 nm and from 0.838 to 0.839 nm for Nd3+ and Sm3+ ions substitution, respectively. The crystallite size ranges between 28.63 to 29.89 nm and 18.33 to 26.23 nm, for substitution of Nd3+ and Sm3+ ions, respectively. Field emission scanning electron microscopy (FESEM) shows the formation of homogeneous grains, whereas, energy dispersive spectrometer (EDS) counts describe the purity of the samples. The Sm concentration x = 0.10 has the maximum surface area with value of 42.6 m2/g which proves to be having good data storage application due to high surface area. The zero-field cooled (ZFC) and field cooled (FC) data show that Nd-doped Ni–Zn–Bi nanoferrites show superparamagnetic behaviour in the room temperature range which makes them suitable for practical applications.

Lanthanide-doped MoS2 with enhanced oxygen reduction activity and biperiodic chemical trends

Molybdenum disulfide has broad applications in catalysis, optoelectronics, and solid lubrication, where lanthanide (Ln) doping can be used to tune its physicochemical properties. The reduction of oxygen is an electrochemical process important in determining fuel cell efficiency, or a possible environmental-degradation mechanism for nanodevices and coatings consisting of Ln-doped MoS2. Here, by combining density-functional theory calculations and current-potential polarization curve simulations, we show that the dopant-induced high oxygen reduction activity at Ln-MoS2/water interfaces scales as a biperiodic function of Ln type. A defect-state pairing mechanism, which selectively stabilizes the hydroxyl and hydroperoxyl adsorbates on Ln-MoS2, is proposed for the activity enhancement, and the biperiodic chemical trend in activity is found originating from the similar trends in intraatomic 4f–5d6s orbital hybridization and interatomic Ln–S bonding. A generic orbital-chemistry mechanism is described for explaining the simultaneous biperiodic trends observed in many electronic, thermodynamic, and kinetic properties.

Effect of multi-component rare-earth doping on maintaining structure stability of RE2Zr2O7 (RE = La, Sm, Gd, Y, Yb) coatings under thermal cycling

Inspired by the high entropy effects of high-entropy components, a novel high-entropy rare-earth zirconate (La1/5Gd1/5Y1/5Sm1/5Yb1/5)2Zr2O7 (HEC-LZ) was designed and successfully synthesized in this work. In addition, two binary rare-earth doped zirconates (RE-LZ), (La1/3Sm1/3Yb1/3)2Zr2O7 (LSYZ) and (La1/3Gd1/3Y1/3)2Zr2O7 (LGYZ), were proposed using the same rare-earth elements for comparison. The thermal barrier coatings with LZ-based ceramic top layer were prepared by spray granulation, solid-phase synthesis and atmospheric plasma spraying techniques. The as-synthesized LZ-based ceramics are all dominated by the pyrochlore phase. Under 1000 °C, the thermal cycling performances of the three coatings were studied. The microstructure evolution and crack expansion during the failure process were investigated in detail. The strengthening mechanism and the cause of coating spallation are proposed in combination with mechanical properties and thermal matching analysis. The results showed that compared with the undoped LZ coating, the thermal shock life of LGYZ coating, LSYZ coating and HEC-LZ coating is improved by nearly 46%, 27% and 57%, respectively. Due to the characteristics of high randomness, HEC-LZ ceramic has a large lattice distortion than RE-LZ ceramics, resulting in a higher coefficient of thermal expansion and fracture toughness, which contributes to maintaining the structure stability of coatings under thermal stress.

Mn2+ as an “Optical Energy Shutter” to Regulate Red‐to‐NIR Luminescence in Rare Earth Doped Layered Quadruple Perovskites

AbstractMetal halide perovskites (MHPs) have shown great application prospects in the field of optoelectronics owing to their superior optical and optoelectronic properties. Bandgap engineering and impurity doping are effective ways to achieve regulation of luminous properties in the visible light region. However, realizing efficient deep red and wide‐range tunable near‐infrared (NIR) emission remains a challenge. Here, a series of rare earth (RE3+) ions (RE = Nd, Dy, Ho, Er, Tm, Yb) doped Cs4Cd1−xMnxSb2Cl12 (0 ≤ x ≤ 1) quadruple perovskites are designed. An efficient tunable luminescence from red to NIR light is achieved based on the energy transfer (ET) from Mn2+ to RE3+ by building the Mn2+ energy bridge, which covers the NIR‐I (650–900 nm) and NIR‐II (900–1700 nm) regions. Moreover, the ET efficiency is availably influenced by the doping concentration of Mn2+. Interestingly, the energy bridge from Mn2+ to RE3+ is cut off because of the increased bandgap when Bi3+ is introduced into the RE3+‐doped Cs4Cd0.4Mn0.6Sb2−yBiyCl12 (0 ≤ y ≤ 2) lattice. Through bandgap engineering, the ET from Mn2+ to RE3+ resembles an “optical energy shutter” which quenches the NIR emission of RE3+ owing to the mismatched energy level but enhances the emission of Mn2+.

Sustainability Consolidated Ln3+(Ce3+‐Pr3+‐Nd3+):SnO2 System for Variegated Electrochemical and Photovoltaic Applications

AbstractThis work for the first time develops and employs the novel cerium‐praseodymium‐neodymium oxide co‐doped tin oxide (Ln3+(Ce3+‐Pr3+‐Nd3+):SnO2) system for varied energy applications including electro‐catalytic, super‐capacitive, and photovoltaic conversion potential. The outstanding optical, compositional, crystalline, and morphological aspects of the synthesized material express its effectiveness for energy related micro‐electrochemical applications. Bandgap narrowing due to lanthanide doping and acquiring cassiterite crystalline phase results in the auspicious output. O2 and H2 evolution of the developed electro‐catalyst expresses superior energy production with lower overpotential values of 95 mV for O2 and 131 mV toward H2. Fabricated electrode expresses an impressive charge storage potential with the specific capacitance of 151.62 F g−1. Also, this electrode has an extended service life for 100 min showing its ultra‐durability for commercial applications. Ln3+(Ce3+‐Pr3+‐Nd3+):SnO2 is used as an electron transport layer in the cesium based solar cells with the power conversion efficiency of 12.49%, short circuit current of 19.63 mA cm−1, and open circuit voltage of 1.2 V under artificial sun with negligible hysteresis. Ln3+(Ce3+‐Pr3+‐Nd3+):SnO2 is an effective material with the perfect bandgap tuned exceeding the pristine material for diverse energy applications marked by profound sustainability and economic viability.

First principles investigation of the substitutional doping of rare-earth elements and Co in La4MgNi19 phase

RE-Mg-Ni alloys, including AB3, A2B7, A5B19 and AB4 types, have received extensive attention due to their excellent hydrogen storage properties. La4MgNi19 is the one of the outstanding candidate for hydrogen storage. In this work, the structure, phase stability and electronic structure of the different La-site partial substituted by Pr, Sm, Gd, Nd and NI-site substituted by Co have been investigated by means of the density functional theory.The calculation results show that La4MgNi19 alloy shows the negative enthalpy of formation, indicating the more stable in the thermodynamic. When the substitution of La occurs, among the two sites La(2c) and La(4f), Pr, Nd, Sm and Gd preferentially occupy the La(4f) site. And the addition of the four doping elements will reduce the stability of the phase. Among them, Pr substituted La4MgNi19 has the highest structural stability. When Co substituting Ni, a single Co atom occupies the Ni(12k) preferentially among the seven different Ni positions. During this process, the crystal structure will be destabilized. The DOS results show that the system still puts up the metallic character after substitution. Sm(La(4f)) has the maximum valence band width. The stability of four doped alloys from high to low is: Pr, Nd, Sm, Gd, which is consistent with the enthalpy of formation results. The enthalpy of formation of hydrides shows that, the bounding hydrogen capacity of the system can be obtained as Nb > Sm > Pr > Gd.

Eco-friendly synthesis of Eu3+, Sm3+, and Dy3+-doped monticellite-based ceramic powders: effects of rare-earth dopants and synthesis temperature

Eco-friendly synthesis of Eu3+, Sm3+, and Dy3+-doped monticellite-based ceramic powders: effects of rare-earth dopants and synthesis temperature

Recent progress in lanthanide-based metal halide perovskites: Synthesis, properties, and applications

Metal halide perovskites (MHPs) have recently attracted significant interest, owing to their excellent optoelectronic properties and diverse applications, including photovoltaics, solid-state lighting emitting diodes (LEDs), and other optoelectronic applications. However, owing to the toxic nature of lead-based MHPs, lanthanide-based MHPs have recently emerged as an alternative, leading to new opportunities for emerging applications, such as in near-infrared (NIR) imaging, NIR cameras, white LEDs, photovoltaics, and information encryption. Moreover, lanthanide doping significantly enhances the stability and optical properties of MHPs. In this review, we have attempted to overview state-of-the-art synthesis strategies and investigate the structural, and optical properties of MHPs. Furthermore, several applications of MHPs, white LEDs, solar cells, and temperature sensors are discussed along with outlooks and future directions.

Rare earth (Sm/Eu/Tm) doped ZrO2 driven electro-catalysis, energy storage, and scaffolding in high-performance perovskite solar cells

Current work presents the first report on the modification of zirconia (ZrO2) by doping it with the lanthanides oxides i.e. [samarium, europium, and thulium] forming a [Sm/Eu/Tm] co-doped ZrO2 system. Lanthanide doping tailored the structure of host material by causing considerable bandgap energy shrinkage from 4.04 to 3.57 eV and reduction in the crystallite size from 67.92 to 45.23 nm. Profound electro-catalytic potential was reflected analyzed via linear sweep voltammetry showing the excellent of developed catalytic towards H2 evolution with lower overpotential i.e. 133 mV and Tafel slope of 119.3 mV dec−1. While for O2 evolution, the electro-catalyst succeeded in gaining overpotential and Tafel slope values of 310 mV and 294.8 mV dec−1, respectively. With such values, this material has surpassed the conventional electro-catalysts and is proved to be an excellent hydrogen producing electro-catalyst. The electrical charge storage potential was analyzed for [Sm/Eu/Tm] co-doped ZrO2 decorated nickel foam electrode for development into a super-capacitor. This electrode was impressively stable for 10 cycles after 20 days checked through cyclic voltammetry. Furthermore, an augmented specific capacitance of 447 F g−1 was achieved by the doped electrode when compared with the pristine one approaching 83.69 F g−1. The electrical energy storage capacity of [Sm/Eu/Tm] co-doped ZrO2 is even higher than the conventionally used metal oxides. In terms of the interfacial electrode-electrolyte, electrochemical impedance spectroscopy was done expressing the excellent ionic diffusion and electrochemically active sites for [Sm/Eu/Tm] co-doped ZrO2 electrode with minimal resistance. The developed doped system was used a spacer layer in a cesium lead halide perovskite solar cells having planar architecture. The spacer layer containing solar cell device succeeded in gaining a power conversion efficiency of 16.31% and a fill factor of 78% evaluated via photo-current measurements carried out under artificial solar irradiance. The impressively higher fill factor shows the effective passivation and scaffolding by the [Sm/Eu/Tm] co-doped ZrO2. The associated device was also marked by negligible hysteresis. Chrono-potentiometry and chrono-amperometry expressed commendable accelerated service lives for 100 min inside an electrolyte. The lanthanide co-doped ZrO2 is an effective material for the utilization in energy systems associated with the electro-catalysis of water, charge storage electrode for super-capacitors, and photovoltaic solar to electrical energy conversion.