We fabricated ytterbium-doped yttrium aluminum oxide (Yb:Y–Al–O) thin films by radio-frequency magnetron sputtering and evaluated their crystallinity and anti-Stokes photoluminescence (PL) properties for optical refrigeration. The Yb:Y–Al–O films that were grown on c-sapphire substrates had better transparency than the films deposited on fused-quartz substrates. The better transparency is considered to be a result of the smaller mismatch between the thermal expansion coefficients of Yb:Y–Al–O and c-sapphire. We found that the thin films on the c-sapphire substrates consist of densely packed sub-micron columnar crystals that are aligned perpendicular to the substrate. In these films, we confirmed the existence of perovskite, garnet, and monoclinic phases despite using a single-phase sputtering target. The excitation wavelength dependence of anti-Stokes PL is used to investigate the energy transfer process between trivalent Yb ions in neighboring columnar crystals. The data indicate that the resonant energy transfer from Yb3+ ions at a specific seven-coordinated site of the monoclinic phase to Yb3+ ions in neighboring columnar crystals is faster than the radiative relaxation at the energy-donor site.We fabricated ytterbium-doped yttrium aluminum oxide (Yb:Y–Al–O) thin films by radio-frequency magnetron sputtering and evaluated their crystallinity and anti-Stokes photoluminescence (PL) properties for optical refrigeration. The Yb:Y–Al–O films that were grown on c-sapphire substrates had better transparency than the films deposited on fused-quartz substrates. The better transparency is considered to be a result of the smaller mismatch between the thermal expansion coefficients of Yb:Y–Al–O and c-sapphire. We found that the thin films on the c-sapphire substrates consist of densely packed sub-micron columnar crystals that are aligned perpendicular to the substrate. In these films, we confirmed the existence of perovskite, garnet, and monoclinic phases despite using a single-phase sputtering target. The excitation wavelength dependence of anti-Stokes PL is used to investigate the energy transfer process between trivalent Yb ions in neighboring columnar crystals. The data indicate that the resonant energy transfer from Yb3+ ions at a specific seven-coordinated site of the monoclinic phase to Yb3+ ions in neighboring columnar crystals is faster than the radiative relaxation at the energy-donor site.

AIP AdvancesFeb 1, 20221 citation

Luminescence and stimulated emission of Yb 3+ ions in aluminum garnets

Kh. S. Bagdasarov, G. A. Bogomolova, Dmitrii N. Vylegzhanin +4 more

SPhDDec 1, 19746 citations

Low-Temperature Stabilization of $δ$ -NbN Superconducting Thin Films through Energy-Selective Ion Beam SputteringLow-Temperature Stabilization of $δ$-NbN Superconducting Thin Films through Energy-Selective Ion Beam Sputtering

Yifan Liu, Junwoo Lee, Mingyu Xu +3 more

Achieving high-quality superconducting thin films at low temperatures is a central challenge for scalable quantum device integration and Complementary Metal-Oxide-Semiconductor (CMOS)-compatible fabrication. Here, we demonstrate a room-temperature magnetron sputtering approach for synthesizing niobium nitride (NbN) thin films using a novel energy-selective ion source that enables independent control of ion energy and ion flux. This capability provides a powerful route to precisely tailor surface kinetics and crystallization pathways, overcoming longstanding limitations in stabilizing high-quality NbN at reduced temperatures. The resulting films were characterized by superconducting transport measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Compared with conventional reactive sputtering, ion beam-assisted growth yields a substantial narrowing of the transition width at the superconducting temperature, indicating improved phase purity and electronic homogeneity. Furthermore, this work introduces energy-selective ion control as a general, non-equilibrium route to stabilize metastable superconducting phases at low temperatures, offering a new design paradigm for thin-film quantum materials.Achieving high-quality superconducting thin films at low temperatures is a central challenge for scalable quantum device integration and Complementary Metal-Oxide-Semiconductor (CMOS)-compatible fabrication. Here, we demonstrate a room-temperature magnetron sputtering approach for synthesizing niobium nitride (NbN) thin films using a novel energy-selective ion source that enables independent control of ion energy and ion flux. This capability provides a powerful route to precisely tailor surface kinetics and crystallization pathways, overcoming longstanding limitations in stabilizing high-quality NbN at reduced temperatures. The resulting films were characterized by superconducting transport measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Compared with conventional reactive sputtering, ion beam-assisted growth yields a substantial narrowing of the transition width at the superconducting temperature, indicating improved phase purity and electronic homogeneity. Furthermore, this work introduces energy-selective ion control as a general, non-equilibrium route to stabilize metastable superconducting phases at low temperatures, offering a new design paradigm for thin-film quantum materials.

arXiv:2609.35091Sep 28, 20260 citations

Microstructural and optical characterization of Erbium-doped calcium tungstate films on yttria-stabilized zirconia

Sagar Kumar Seth, Bonnie Y.X. Lin, Ignas Masiulionis +7 more

Er3+-doped bulk CaWO4 has been demonstrated to be a promising platform for quantum repeaters. However, the use of bulk crystals presents challenges for device integration and scalability. In this paper, we address the scalability of this platform by realizing thin-film CaWO4 growth on yttria-stabilized zirconia wafers, a step toward a CMOS-compatible heterogeneous platform. The films were deposited via radio-frequency magnetron sputtering, a scalable method, followed by postdeposition annealing and were in situ doped with Er. Optical characterization of the Er3+ ions in these films reveals lifetimes of 2.28 ± 0.16 ms, inhomogeneous linewidths of 48.29 ± 0.96 GHz, and a spectral-diffusion-limited homogeneous linewidth of 12.61 ± 2.79 MHz. These results are comparable to previously reported Er3+ in rare-earth oxide thin film hosts. The results highlight the potential of sputtered Er3+-doped CaWO4 thin films for quantum coherent applications.Er3+-doped bulk CaWO4 has been demonstrated to be a promising platform for quantum repeaters. However, the use of bulk crystals presents challenges for device integration and scalability. In this paper, we address the scalability of this platform by realizing thin-film CaWO4 growth on yttria-stabilized zirconia wafers, a step toward a CMOS-compatible heterogeneous platform. The films were deposited via radio-frequency magnetron sputtering, a scalable method, followed by postdeposition annealing and were in situ doped with Er. Optical characterization of the Er3+ ions in these films reveals lifetimes of 2.28 ± 0.16 ms, inhomogeneous linewidths of 48.29 ± 0.96 GHz, and a spectral-diffusion-limited homogeneous linewidth of 12.61 ± 2.79 MHz. These results are comparable to previously reported Er3+ in rare-earth oxide thin film hosts. The results highlight the potential of sputtered Er3+-doped CaWO4 thin films for quantum coherent applications.

Journal of Vacuum Science & Technology A Vacuum Surfaces and FilmsOct 21, 20260 citations

Thermally up-converted photoluminescence of Er3+ ions in KY0.9Er0.1F4 crystal by level crossing

Ta-Ryeong Park

Current Applied PhysicsMar 5, 20113 citations

Low-Temperature Stabilization of

δ

-NbN Superconducting Thin Films through Energy-Selective Ion Beam Sputtering