Recently, infrared (IR) light-emitting diodes (LEDs) have attracted considerable interest in the research field worldwide. IR phosphors, the basic materials utilized in LEDs, have become a research hotspot as well. Here, we introduce the high-quantum-efficiency IR ScBO 3 :Cr 3+ phosphor, which provides a spectral range of emission from 700 to 1000 nm with a peak maximum at 800 nm. Electron paramagnetic resonance spectroscopy, with high element selectivity, was used to elucidate the unusual small peak in the photoluminescence spectrum. Phonon structure and electron−lattice interaction were well observed and discussed via temperature-dependent measurements. Moreover, the high quantum efficiency of 72.8% was achieved. To evaluate their potential practical application, phosphor-converted LED packages were designed, which revealed high stability and high output power of 39.11 mW. Furthermore, the fabricated IR LED demonstrated a remarkable ability to penetrate biological tissues. This study provides insights into the luminescent properties and the practical applications of IR LEDs.

High harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, to date the shortest subfemtosecond (attosecond, 10 −18 s) pulses have been produced only in the extreme UV region of the spectrum below 100 eV, which limits the range of materials and molecular systems that can be explored. Here we experimentally demonstrate a remarkable convergence of physics: when midinfrared lasers are used to drive high harmonic generation, the conditions for optimal bright, soft X-ray generation naturally coincide with the generation of isolated attosecond pulses. The temporal window over which phase matching occurs shrinks rapidly with increasing driving laser wavelength, to the extent that bright isolated attosecond pulses are the norm for 2-μm driving lasers. Harnessing this realization, we experimentally demonstrate the generation of isolated soft X-ray attosecond pulses at photon energies up to 180 eV for the first time, to our knowledge, with a transform limit of 35 attoseconds (as), and a predicted linear chirp of 300 as. Most surprisingly, advanced theory shows that in contrast with as pulse generation in the extreme UV, longduration, 10-cycle, driving laser pulses are required to generate isolated soft X-ray bursts efficiently, to mitigate group velocity walk-off between the laser and the X-ray fields that otherwise limit the conversion efficiency. Our work demonstrates a clear and straightforward approach for robustly generating bright isolated attosecond pulses of electromagnetic radiation throughout the soft X-ray region of the spectrum.ultrafast | coherent | nonlinear optics H igh-order harmonic generation (HHG) is the most extreme nonlinear optical process in nature, making it possible to coherently upconvert intense femtosecond laser light to much shorter wavelengths (1, 2). High harmonics are radiated as a result of a coherent electron recollision process that occurs each half-cycle of the driving laser field while an atom is undergoing strong-field ionization. The short pulse duration of HHG (which must be shorter than the driving laser pulse) has made it possible to directly access the fastest timescales relevant to electron dynamics in atoms, molecules, and materials. The unique properties of attosecond HHG in the extreme UV (EUV) have uncovered new understanding of fundamental processes in atoms, molecules, plasmas, and materials, including the timescales on which electrons are emitted from atoms (3), the timescale for spin-spin and electron-electron interactions (4, 5), the timescale that determines molecular dissociation and electron localization (6-9), the timescale and mechanisms for spin and energy transport in nanosystems (10-12), as well as new capabilities to implement EUV microscopes with wavelength-limited spatial resolution (13).The temporal structure of HHG is related to the number of times a high-energy electron undergoes a coherent recollision process, as well as the time window over which bright harmonics emerge. Usi...

High-harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, thus far, the shortest isolated attosecond pulses have only been produced with linear polarization, which limits the range of physics that can be explored. Here, we demonstrate robust polarization control of isolated extreme-ultraviolet pulses by exploiting non-collinear high-harmonic generation driven by two counter-rotating few-cycle laser beams. The circularly polarized supercontinuum is produced at a central photon energy of 33 eV with a transform limit of 190 as and a predicted linear chirp of 330 as. By adjusting the ellipticity of the two counter-rotating driving pulses simultaneously, we control the polarization state of isolated extreme-ultraviolet pulses-from circular through elliptical to linear polarization-without sacrificing conversion efficiency. Access to the purely circularly polarized supercontinuum, combined with full helicity and ellipticity control, paves the way towards attosecond metrology of circular dichroism.

To segregate accurately during meiosis in most species, homologous chromosomes must recombine 1 . Small chromosomes would risk missegregation if recombination were randomly distributed, so the double-strand breaks (DSBs) initiating recombination are not haphazard 2 . How this nonrandomness is controlled is not understood, although several pathways ensuring that DSBs occur at the appropriate time, number, and place are known. Meiotic DSBs are made by Spo11 and accessory “DSB proteins,” including Rec114 and Mer2, which assemble on chromosomes 3 – 7 and are nearly universal in eukaryotes 8 – 11 . Here we demonstrate how Saccharomyces cerevisiae integrates multiple temporally distinct pathways to regulate chromosomal binding of Rec114 and Mer2, thereby controlling the duration of a DSB-competent state. Engagement of homologous chromosomes with one another regulates the dissociation of Rec114/Mer2 later in prophase I, whereas replication timing and proximity to centromeres or telomeres influence Rec114/Mer2 accumulation early. Another early mechanism boosts Rec114/Mer2 binding specifically on the shortest chromosomes, subject to selection pressure to maintain hyperrecombinogenic properties of these chromosomes. Thus, an organism’s karyotype and risk of meiotic missegregation influence the shape and evolution of its recombination landscape. Our results create a cohesive view of a multifaceted and evolutionarily constrained system that ensures DSB allocation to all pairs of homologous chromosomes.