Diana Serrano

Enhancing the charging efficiency of persistent luminescence materials remains a key challenge for their practical implementation. Here, we report a hybrid strategy based on coupling ZnGa ₂ O ₄ :Cr ^{3 +} nanoparticles with TiO ₂ through a porous SiO ₂ interlayer to promote interfacial charge transfer and improve energy storage. The resulting architecture exhibits a twofold increase in both steady‐state and afterglow intensity under UV excitation. Through excitation‐dependent spectroscopy, we show that TiO ₂ ‐mediated excitation modifies the population pathway of Cr ^{3 +} centers, leading to enhanced vibronic emission characteristic of Cr ³⁺ in a distorted environment. Kinetic analysis using a rate equation model reveals that the hybrid system features an increased excitation rate, the activation of additional trapping states, and a reduced sensitivity to optically stimulated detrapping, demonstrating that TiO ₂ sensitization not only enhances carrier generation but also mitigates intrinsic loss processes during charging. These results establish interfacial engineering as a powerful approach to decouple light absorption from energy storage and to control trapping–detrapping processes, opening new pathways for the design of high‐performance persistent phosphors.

Rare‐earth‐ion‐doped solid materials have attracted considerable interest for quantum technologies. However, achieving robust spin coherence in polycrystalline systems remains challenging due to structural disorder and limited understanding spin environments. Here, we report high‐quality : optical ceramics with optical inhomogeneous of GHz and sub‐kHz homogeneous linewidths, indicating a spectrally quiet optical environment. At cryogenic temperatures, spin‐dynamics measurements show that decoherence is strongly influenced by the surrounding nuclear spin bath. Magnetic‐field‐dependent studies, combined with radio‐frequency spectroscopy, reveal the sensitivity of spin coherence to weak magnetic perturbations and enable selective addressing of the bath spins. By applying an all‐optical Raman dynamical decoupling protocol, we substantially prolong the observed nuclear‐spin coherence decay, yielding a slow decay component of 224 ms. These results establish : ceramics as a promising platform for solid‐state quantum memories and highlight the potential of spin‐bath engineering in polycrystalline rare‐earth‐ion systems.

Chemical substitution o!ers a powerful route to tune molecular quantum materials, but its e!ects on optical decoherence extend beyond the simple dilution of interacting emitters; here, we investigate these e!ects in the molecular crystal [Eu(III)(TMHD)3(phen)], its dilution series in the isostructural host [Y(TMHD)3(phen)], and a partially deuterated analogue. The optical inhomogeneous linewidth of the 7F0 ↔ 5D0 transition near 580.4 nm exhibits a pronounced concentration dependence, ranging from 6 to 20 GHz, while the transition frequency shifts by up to ↗25 GHz across the dilution series. In contrast, the homogeneous linewidth measured by two-pulse photon echoes remains in the 50–130 kHz regime at 1.4 K, and shows a non-monotonic dependence on Eu(III) content. Partial phenanthroline deuteration also leaves the homogeneous linewidth essentially unchanged. Spectral-di!usion and temperature-dependent photon-echo measurements identify non-magnetic fluctuations of the molecular environment as the dominant residual dephasing channel. In contrast to rigid inorganic rare-earth hosts, the molecular crystal lattice supports low-frequency lattice modes that can dynamically modulate the anisotropic Eu(III) crystal field, while the extrapolated zero-temperature linewidth is most likely limited by electric-field perturbations. These results establish Eu(III) molecular crystals as chemically tunable materials with robust optical coherence and show that chemical dilution simultaneously reshapes static disorder, lattice dynamics, and decoherence, identifying molecular-lattice rigidity and electrostatic stability as central design parame-

Understanding and modeling energy transfer mechanisms in rare-earth-doped nanomaterials are essential for advancing luminescent technologies used in bioimaging, optical thermometry, and solid-state lasers. In this work, we investigate the photoluminescence dynamics of Yb³⁺ and Er³⁺ ions in Y₂O₃ nanoparticles over a wide concentration range (0.5–17%), using both direct and up-conversion excitation. Luminescence decays of green, red, and near-infrared transitions were measured and analyzed using a single rate equation model incorporating radiative and non-radiative processes, energy transfer mechanisms, and defect-related quenching. Using specific measurements to determine each model parameter in a reliable way, we successfully reproduce experimental trends across most concentrations and excitation paths. This unified approach thus provides a sound and predictive framework for modeling energy transfer in rare-earth-doped materials and offers valuable insights for optimizing photoluminescent properties in nanostructured systems.

Nuclear magnetic resonance is a powerful tool for applications ranging from chemical analysis to quantum information processing. Achieving optical initialization and detection of molecular nuclear spins promises new opportunities—including improved nuclear magnetic resonance signals at low magnetic field, sensitivity down to the single-molecule level and full access to atomically precise molecular architectures for quantum technologies. Here we report the optical read-out of coherently controlled nuclear spins in a europium-based molecular crystal. By harnessing ultranarrow optical transitions, we achieve the optical initialization and detection of nuclear spin states. Through radio-frequency driving, we address two nuclear quadrupole resonances, characterized by narrow inhomogeneous linewidths and a distinct correlation with the optical transition frequency. We implement Rabi oscillations, spin echo and dynamical decoupling techniques, achieving nuclear spin quantum coherence with a lifetime of up to 2 ms. These results highlight the capabilities of optically detected nuclear magnetic resonance and underscore the promise of molecular nuclear spins for quantum information processing.

Optically addressable solid-state spins have been extensively studied for quantum technologies, offering unique advantages for quantum computing, communication, and sensing. Advancing these applications is generally limited by finding materials that simultaneously provide lifetime-limited optical and long spin coherences. Here, we introduce ¹⁷¹Yb³⁺ ions doped into a CaWO₄ crystal. We perform high-resolution spectroscopy of the excited state, and demonstrate all-optical coherent control of the electron-nuclear spin ensemble. We find narrow inhomogeneous broadening of the optical transitions of 185 MHz and radiative-lifetime-limited coherence time up to 0.75 ms. Next to this, we measure a spin-transition ensemble line width of 5 kHz and electron-nuclear spin coherence time reaching 0.15 seconds at zero magnetic field between 50 mK and 1 K temperatures. These results demonstrate the potential of ¹⁷¹Yb³⁺:CaWO₄ as a low-noise platform for building quantum technologies with ensemble-based memories, microwave-to-optical transducers, and optically addressable single-ion spin qubits.

We report a detailed investigation of spin relaxation dynamics in the rare-earth-doped crystal ¹⁷¹ Yb:Y ₂ SiO ₅ , a promising platform for quantum memory based on atomic frequency combs. The population dynamics among the four ground-state hyperfine levels were studied in the 50 mK–6 K temperature range by optically modifying the spin populations and monitoring their return to thermal equilibrium via absorption spectroscopy. Below 1 K, population rethermalization occurs on timescales of several hours and is governed by direct spin-phonon relaxation. In contrast, the lifetime of individual spin states is strongly reduced by spin-spin interactions, ranging from seconds in low-doped (2 ppm) samples to milliseconds at higher doping (10 ppm). These results provide clear guidelines for optimizing doping concentration and operating temperature, indicating that atomic frequency comb lifetimes on the order of one hour are achievable in ¹⁷¹ Yb:Y ₂ SiO ₅ crystals with Yb concentrations not much lower than 2 ppm and at temperatures at or below 1 K.