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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Reverse Polarizability of Rare Earth Ions (La 3+ , Gd 3+ , Lu 3+ , Y 3+ ) in Tellurite Glasses and Glass Ceramics for Optical Limiting

All-optical modulation using inherent third-order optical nonlinearity of a medium has garnered considerable interest in photonics and optoelectronics. Herein, nonlinear optical (NLO) properties of tellurite glasses and glass ceramics (GCs) containing four different rare earths (RE = La, Gd, Lu, and Y) have been deliberated in near-infrared regions under an ultrafast regime. The La-based glass exhibits ~10 times higher nonlinear refraction (n 2 ) and absorption (α 2 ) than reported NLO materials. The NLO susceptibility [χ (3) ] trend in the studied glasses is La > Gd > Lu > Y, matching with RE 3+ polarizability. Furthermore, Ln 2 Te 6 O 15 nanocrystallite-embedded transparent GCs exhibit a larger NLO coefficient due to the enhanced local field from oxygen vacancies in crystallites. Interestingly, the trend of χ (3) in GCs follows the sequence of Y > Lu > Gd > La, precisely opposite to the glasses. This observation challenges the general polarizability approach of RE 3+ ions, emphasizing that quadratic hyperpolarizability of RE 3+ is pivotal for NLO properties of GCs. Among the studied matrices, Y-containing GCs showed the lowest optical limiting (OL) threshold (5.4 mJ/cm 2 at 800 nm), much lower than those of the reported NLO materials, suggesting its potential as a femtosecond NIR-laser safety material. A combination of large α 2 and n 2 from the studied matrices indicates their advantage for harmonic generation, potentially aiding in the design of ultrafast signal processing devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Stable and Recyclable Photocatalysts of CsPbBr 3 @MSNs Nanocomposites for Photoinduced Electron Transfer RAFT Polymerization

All-inorganic metal halide perovskite CsPbX 3 (X = Cl, Br, I) nanocrystals (NCs) have demonstrated attractive optoelectronic characteristics. However, their photocatalytic properties are limited by their poor stability and easy recombination of photogenerated carriers. Herein, we introduced a CsPbBr 3 @MSNs nanocomposite (CsPbBr 3 NCs embedded in dendritic mesoporous silica nanospheres (MSNs)) as photocatalysts for photoinduced electron transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerization. In this study, the CsPbBr 3 nanocrystals (~8.1 nm; PLQY of 62 ± 2.1%) were embedded in dendritic MSNs using a nanoconfinement strategy. PET-RAFT polymerization was successfully initiated using the CsPbBr 3 @MSNs nanocomposite as the photocatalyst. Reaction variables, such as catalyst loading, monomer composition, and excitation light wavelengths, were varied to yield polymers with the desired control of molecular weight and dispersity as well as block copolymers with high chain-end fidelity. In addition, the perovskite-based photocatalysts could be readily separated and purified, which allowed effective and rapid recycling of the nanocomposites for multiple polymerization cycles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Ultrafast Carrier Drift Transport Dynamics in CsPbI3 Perovskite Nanocrystalline Thin Films

We study the early time carrier drift dynamics in CsPbI3 nanocrystal thin films with a sub 25 ps time resolution. Prior to trapping, carriers exhibit band-like transport characteristics, which is similar to those of traditional semiconductor solar absorbers including Si and GaAs due to optical phonon and carrier scattering at high temperatures. In contrast to the popular polaron scattering mechanism, the CsPbI3 nanocrystal thin film demonstrates the strongest optical phonon scattering mechanism among other inorganic-organic hybrid perovskites, Si, and GaAs. This ultrafast dynamics study establishes a foundation for understanding the fundamental carrier drift properties that drive perovskite nanocrystal optoelectronics.

CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS,S↗
DOE OSTI2024

Resonance plasmonic coupling: selective enhancement of band edge emission over trap state emission of CdSe quantum dots

The photoluminescence properties of quantum dots (QDs) are often enhanced by eliminating surface trap states through chemical methods. Alternatively, a physical approach is presented here for improving photoluminescence purity in QDs by employing frequency-specific plasmon resonance coupling. Emitter-bound plasmonic hybrids are designed by electrostatically binding negatively charged QDs in water to positively charged gold nanoparticles having a thin polymer coating. Herein, two types of QDs are used: (i) bare CdSe, which exhibits both band edge and trap state emission, and (ii) CdSe overcoated with a ZnS shell (CdSe/ZnS) devoid of trap state emission. Tuning the extinction spectrum of the plasmonic system to match the band edge emission of CdSe enables the selective enhancement of band edge emission over trap state emission. Excellent match in the extinction spectrum of the gold nanoparticle with both, experimentally calculated photoluminescence enhancement factor and theoretically calculated radiative rate enhancement signifies the role of frequency-specific plasmon resonance coupling. Plasmon-coupled photoluminescence of CdSe/ZnS is further investigated by varying the number density of emitter on the surface of plasmonic nanoparticle. An enhancement in the photoluminescence is observed at a lower emitter density of CdSe/ZnS and the photoluminescence enhancement factor closely follows the plasmon resonance. However, photoluminescence quenching occurs with an increase in CdSe/ZnS due to plasmon-assisted nonradiative energy transfer between nearby QDs, as indicated by a red shift in the PL maximum. These studies establish that resonance plasmonic coupling is a convenient physical strategy for tuning the intrinsic photoluminescence properties of QDs for various optoelectronic applications.

Paul, Livin↗
DOE OSTI2024

Effect of niobium doping on excitonic dynamics in MoSe 2

Abstract Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe 2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe 2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Anisotropic Thermal Transport in Quasi-2D Ruddlesden-Popper Hybrid Perovskite Superlattices

Two-dimensional hybrid metal-halide perovskites (2D-MHPs) have emerged as important solution-processed semiconductors with favorable optical and electronic properties for diverse applications in photovoltaics, optoelectronics, and spintronics. The quasi-2D layered structures, featuring large acoustic impedance mismatches between the organic and inorganic sublattices, are expected to result in distinct and anisotropic thermal transport properties along the cross-plane and in-plane directions. Here, we introduce transducer-free vibrational-pump-visible-probe (VPVP) approaches that enable accurate quantification of anisotropic thermal transport properties in various archetypical single-crystalline 2D-MHPs. Specifically, using VPVP spectroscopy and VPVP microscopy, we measure the anisotropic thermal diffusivities of 2D-MHPs with systematically varied Pb-I octahedral layer thicknesses, as well as organic spacer types and lengths, revealing how these structural parameters alter the cross-plane and in-plane thermal transport properties in distinct ways. While diffuse interface scattering plays an important role in dictating cross-plane thermal transport, in-plane thermal transport is primarily determined by phonon transport within interconnected inorganic layers. Density functional theory incorporating four-phonon scatterings provides further insight into the low thermal conductivity and modest thermal conduction anisotropy in 2D-MHPs. Our work demonstrates a new all-optical and noncontact method, which requires minimal sample preparation and allows direct visualization of cross-plane and in-plane thermal transport, potentially compatible with sample environments. The demonstrated VPVP approaches can advance understanding of thermal transport in 2D-MHPs as well as wide-ranging hybrid and polymeric semiconductors beyond 2D-MHPs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optically Induced Static Magnetization in Metal Halide Perovskite for Spin‐Related Optoelectronics

Abstract Understanding the feasibility to couple semiconducting and magnetic properties in metal halide perovskites through interface design opens new opportunities for creating the next generation spin‐related optoelectronics. In this work, a fundamentally new phenomenon of optically induced magnetization achieved by coupling photoexcited orbital magnetic dipoles with magnetic spins at perovskite/ferromagnetic interface is discovered. The depth‐sensitive polarized neutron reflectometry combined with in situ photoexcitation setup, constitutes key evidence of this novel effect. It is demonstrated that a circularly polarized photoexcitation induces a stable magnetization signal within the depth up to 7.5 nm into the surface of high‐quality perovskite (MAPbBr 3 ) film underneath a ferromagnetic cobalt layer at room temperature. In contrast, a linearly polarized light does not induce any detectable magnetization in the MAPbBr 3 . The observation reveals that photoexcited orbital magnetic dipoles at the surface of perovskite are coupled with the spins of the ferromagnetic atoms at the interface, leading to an optically induced magnetization within the perovskite’s surface. The finding demonstrates that perovskite semiconductor can be bridged with magnetism through optically controllable method at room temperature in this heterojunction design. This provides the new concept of utilizing spin and orbital degrees of freedom in new‐generation spin‐related optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A synergistic experimental and theoretical study elucidating the electronic and thermal properties in spinel CuInSnS 4

Quaternary chalcogenides of different structure types continue to be of interest due to the novel physical properties they exhibit and for applications ranging from optoelectronics to energy-related technologies. Herein we report on the electronic and thermal properties of spinel CuInSnS 4 . UV–vis–NIR spectroscopy indicates strong absorption in the visible-light region with an indirect bandgap of 1.52 eV. First-principles computations corroborate our experimental data and reveal that the band-edge electronic properties are due to strong p – d ands – p hybridization and antibonding interactions. Analyses of temperature-dependent thermal properties together with first principles simulations reveal strong anharmonicity and low-lying optical branches that hybridize with the acoustic modes effectively suppressing thermal conductivity. This intrinsically very low thermal conductivity is much lower than that of related chalcogenides. Finally, our findings are discussed in the light of ongoing interest in quaternary metal chalcogenide materials and may aid in the development of this and similar chalcogenides for applications of interest.

36 MATERIALS SCIENCE↗
DOE OSTI2023

α-Quartz Phase Stabilization, Surface Texturing, and Tunable Optical Properties of Nanocrystalline GeO 2 Films Made by Pulsed-Laser Deposition: Implications for Optical and Optoelectronic Applications

Germanium oxide (GeO 2 ) has great potential in multifunctional devices and next-generation power electronics due to its high thermal conductivity and ambipolar doping capability. However, the complexity of synthesizing the desirable polymorph with a controlled phase, surface/interface quality, microstructure, and functional properties is the main barrier to GeO 2 utilization in advanced applications. Here, in this regard, we present a method to realize the hexagonal (h) or a-quartz type GeO 2 with nano-textured surface morphology on sapphire substrates using a hybrid synthesis strategy that comprises pulsed laser deposition (PLD) and post-deposition thermal annealing. We performed a comprehensive study to investigate the effect of annealing temperature, which was varied in a wide range (600-1100 °C), on the crystal structure, phase, surface morphology, chemical stoichiometry, defect states, and optical properties of PLD-grown GeO 2 films. As-deposited GeO 2 films at 500 °C were amorphous. Upon annealing, the GeO 2 films induced an amorphous-to-crystalline phase transformation; GeO 2 films annealed at higher annealing temperatures (≥900 °C) stabilized in the hexagonal phase and demonstrated excellent crystal quality and chemical stability. Thermally activated growth process showed increased average crystallite size, which was varied in the range of 20-130 (±2) nm, while the surface roughness followed a similar trend. The spectral transmittance and band gap also increased with increasing annealing temperature. The resulting h-GeO 2 films, particularly those obtained at annealing temperatures in the 900-1100 °C range, had a higher band gap of 6.2-6.3 eV and displayed excellent optical transmittance in the visible region. Moreover, the absence of extended valence band maxima and reduced optical defect density support the quality improvement upon annealing. When considering phase-pure bulk and nanostructured GeO 2 as a possible candidate for ultra wide band gap semiconductors in cutting-edge technological applications, the results of the current work can be beneficial to realize high structural and optical quality a-quartz structured GeO 2 films.

GeO2↗
DOE OSTI2025

Exploring Cs 2 AgIn x Bi 1− x Cl 6 double perovskites for optoelectronics: insights from theoretical and photophysical approaches

Lead-free halide double perovskites (HDPs) have become attractive materials for optoelectronic applications owing to their nontoxicity, structural stability, and germane photoelectric properties. In this work, we report the synthesis of high-quality In-alloyed Cs 2 AgIn x Bi (1−x) Cl 6 nanocrystals (NCs) using the antisolvent recrystallization method and comprehensively investigate the effects of In alloying on the structural, morphological, optoelectronic, and temperature-dependent photoluminescence (TDPL) properties using the state-of-the-art experimental and computational tools. Both XRD and Raman spectroscopy analyses confirmed the synthesis of highly crystalline Cs 2 AgIn x Bi (1−x) Cl 6 materials, which exhibited cubic morphology, as confirmed by TEM analysis. Room-temperature photoluminescence (PL) measurements revealed a drastic increase in the intensity above 75% In concentration with dual emission, whereas the time-resolved PL (TR-PL) results show an increase in the average lifetime values with an increase in In content, suggesting that the materials have excellent optical properties and hence are suitable candidates for optoelectronics. The TDPL measurements revealed the smallest Huang–Rhys factor (18.6) for the Cs 2 AgIn x Bi (1−x) Cl 6 (x = 0.9) sample, indicating weak exciton–phonon coupling in this composition. When deployed in the fabrication of a photodetector device, the Cs 2 AgIn x Bi (1−x) Cl 6 (x = 0.9) sample exhibited significantly enhanced photoresponsivity and a faster response time, confirming its potential for photodetector applications. Complementary DFT calculations showed that In alloying modifies the band structure of Cs 2 AgIn x Bi (1−x) Cl 6 . Our results provide valuable insights for designing multifunctional Cs 2 AgIn x Bi (1−x) Cl 6 -based materials for next-generation energy and optoelectronic devices.

14 SOLAR ENERGY↗
DOE OSTI2023

Linear and Nonlinear Optical Properties of Iridium Nanoparticles Grown via Atomic Layer Deposition

Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical applications. While noble-metal nanoparticles, nanostructures, and thin films of silver and gold have been widely studied, iridium (Ir) nanoparticles and ultrathin films have not been investigated for nonlinear optical applications yet. Here, we present a combined theoretical and experimental study on the linear and nonlinear optical properties of iridium nanoparticles deposited via atomic layer deposition (ALD). Linear optical constants, such as the effective refractive index and extinction coefficient, were evaluated at different growth stages of nanoparticle formation. Both linear and nonlinear optical properties of these Ir ALD coatings were calculated theoretically using the Maxwell Garnett theory. The third-order susceptibility of iridium nanoparticle samples was experimentally investigated using the z-scan technique. According to the experiment, for an Ir ALD coating with 45 cycles resulting in iridium nanoparticles, the experimentally determined nonlinear third-order susceptibility is about χ Ir (3) = (2.4 – i2.1) × 10 –17 m 2 /V 2 at the fundamental wavelength of 700 nm. The theory fitted to the experimental results predicts a 5 × 10 6 -fold increase around 230 nm. This strong increase is due to the proximity to the Mie resonance of iridium nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ferroelastic Domain-Induced Electronic Modulation in Halide Perovskites

Lead halide perovskites have emerged as promising materials for optoelectronic applications due to their exceptional properties. In the all-inorganic CsPbBr 3 perovskites, ferroelastic domains formed during phase transitions enhance bulk transport and emissive efficiency. However, the microscopic mechanisms governing carrier dynamics remain poorly understood. In this study, we employ cathodoluminescence (CL) and micro-Raman spectroscopy to image and investigate the electronic properties of the ferroelastic domain walls in CsPbBr 3 single crystals. CL measurements reveal a reduced emissive yield and a slight redshift in emission at the domain walls. Further, micro-Raman studies provide spatially resolved mapping of vibrational modes, exhibiting second-order phonon modes localized at the domain boundaries. In conclusion, our findings suggest that electron–phonon coupling at the twin domain walls plays a critical role in facilitating efficient charge separation, thereby improving the optoelectronic performance of the CsPbBr 3 perovskites.

Carrier dynamics↗
DOE OSTI2022

Structural, Optical and Mechanical Properties of Nanocrystalline Molybdenum Thin Films Deposited under Variable Substrate Temperature

Molybdenum (Mo), which is one among the refractory metals, is a promising material with a wide variety of technological applications in microelectronics, optoelectronics, and energy conversion and storage. However, understanding the structure–property correlation and optimization at the nanoscale dimension is quite important to meet the requirements of the emerging nanoelectronics and nanophotonics. In this context, we focused our efforts to derive a comprehensive understanding of the nanoscale structure, phase, and electronic properties of nanocrystalline Mo films with variable microstructure and grain size. Molybdenum films were deposited under varying temperature (25–500 °C), which resulted in Mo films with variable grain size of 9–22 nm. The grazing incidence X-ray diffraction analyses indicate the (110) preferred growth behavior the Mo films, though there is a marked decrease in hardness and elastic modulus values. In particular, there is a sizable difference in maximum and minimum elastic modulus values; the elastic modulus decreased from ~460 to 260–280 GPa with increasing substrate temperature from 25–500 °C. The plasticity index and wear resistance index values show a dramatic change with substrate temperature and grain size. Additionally, the optical properties of the nanocrystalline Mo films evaluated by spectroscopic ellipsometry indicate a marked dependence on the growth temperature and grain size. This dependence on grain size variation was particularly notable for the refractive index where Mo films with lower grain size fell in a range between ~2.75–3.75 across the measured wavelength as opposed to the range of 1.5–2.5 for samples deposited at temperatures of 400–500 °C, where the grain size is relatively higher. The conductive atomic force microscopy (AFM) studies indicate a direct correlation with grain size variation and grain versus grain boundary conduction; the trend noted was improved electrical conductivity of the Mo films in correlation with increasing grain size. The combined ellipsometry and conductive AFM studies allowed us to optimize the structure–property correlation in nanocrystalline Mo films for application in electronics and optoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Order–Disorder Phase Stabilization by Pressure‐Induced Charge Transfer Enhances the Ferroelectric Photovoltaic Effect in Multiferroic BaFe 4 O 7

Abstract Multiferroic ferroelectric photovoltaic (FPV) materials, combining magnetic and ferroelectric properties, are of paramount importance for optoelectronic and photovoltaic applications. However, optimizing both the remanent polarization and the optical bandgap—key factors for enhanced FPV performance—presents a significant challenge due to their trade‐off. This work shows that pressure‐induced charge transfer between different metal sites can break this trade‐off. Above ≈20 GPa, charge transfer between different trivalent iron (Fe) sites in the multiferroic material BaFe 4 O 7 leads to Fe valence disproportionation, FeO 4 tetrahedra disorder, and Jahn–Teller distortion of FeO 6 octahedra. These changes reduce the bandgap, lower resistivity, and enhance ferroelectric polarization, resulting in a 2.5‐fold increase in photocurrent. Upon decompression, BaFe 4 O 7 retains an order–disorder structure, optimal ferroelectric and optical properties at ambient conditions. This work provides a novel pathway to simultaneously optimizing ferroelectricity and bandgap via pressure‐induced charge transfer, overcoming the traditional trade‐off in FPV materials, and offers a promising approach for developing high polarization performance, narrow‐bandgap FPV materials.

Chemistry↗
DOE OSTI2025

Unraveling the Atomic Mechanism of the Crystalline Phase‐Dependent Structural Features and Special Spectral Design of α‐, β‐, and Ɛ‐Ga₂O₃

Atomic‐scale phase transformations profoundly influence the functional properties of Ga₂O₃ polymorphs. By combining irradiation experiments with microstructure characterization and theoretical approaches, phase‐specific energy‐dissipation pathways in α‐, β‐, and ε‐Ga₂O₃ are uncovered and strategies for targeted property design are outlined. Competing antiphase boundaries (APBs) and twin domain boundaries (TDBs) promote irreversible α→ε interconversion through domain fragmentation. In β‐Ga₂O₃, defect‐induced stress gradients drive two distinct local transformations: surface Ga‐aggregated β→δ that stabilizes transient states, and latent‐track‐confined β→κ phase transition with recoverable distortions via cation reordering. Under electronic excitation, β‐Ga₂O₃ forms nanohillocks via robust GaO₆ octahedra (high density/strong Ga─O bonds), while α/ε‐Ga₂O₃ generates nanopores from tetrahedral Ga looseness (low bonding energy), highlighting phase‐dependent surface dynamics shaped by atomic packing and bonding anisotropy. Defect‐regulated recombination suppresses visible photoluminescence in α/β‐Ga₂O₃, whereas in ε‐Ga₂O₃ bandgap narrowing of ΔE: 0.30 eV is observed, enhancing emission. Linking phase‐dependent defect‐carrier interactions and metastable‐phase engineering in Ga₂O₃ enables property optimization for power‐electronics and optoelectronics devices.

electronic state configuration↗
DOE OSTI2025

Technical Routes to Achieve High Circular Polarized Luminescence in Chiral Perovskites: A Mini‐Review

Chiral hybrid organic-inorganic perovskites (HOIPs) have emerged as promising materials for optoelectronic and spintronic applications, leveraging unique properties such as circularly polarized luminescence (CPL), circularly polarized nonlinear optical (NLO) emission, and chiral-induced spin selectivity (CISS). However, challenges remain in stabilizing these materials under environmental stresses and precisely controlling chirality for scalable use. This review summarizes five main strategies to induce chirality in HOIPs, i.e., direct incorporation of chiral cations, surface modification with chiral ligands, ion doping, template-induced chirality, and chiral metasurfaces. Each approach offers distinct advantages for optimizing CPL efficiency and device stability, paving the way for next-generation applications in CPL detectors, information encryption, spintronic devices, etc.

14 SOLAR ENERGY↗
DOE OSTI2026

Stabilizing Ultrathin CsPbBr 3 Nanoplatelet Films for Deterministic Strong Light-Matter Coupling

While the excitons in perovskite nanomaterials possess interesting properties central to their use in optoelectronic technologies, their instability limits real world applicability. In this study, we describe a method to stabilize the structures of cesium lead bromide (CsPbBr 3 ) nanoplatelets (NPLs) in spin-casted films. We apply this method to design, fabricate, and characterize exciton cavity polaritons formed from these nanomaterials. These studies show that we can form exciton cavity polaritons from CsPbBr 3 in precisely designed Fabry−Perot microresonators and suggest that the structures of these materials can be stabilized toward their use in other solution-processed optoelectronic devices.

cavities↗