Persistent luminescence (PersL) materials offer emission for long time after stopping excitation, benefiting in noncontact thermometry, imaging, sensor, anticounterfeiting and other applications. However, PersL materials emitting in the red and deep-red range for advanced applications remain scarce. In this study, one reports europium doped SrSc2O4 (Eu:SSO) phosphors exhibiting dual Eu2+/Eu3+ red photoluminescence (PL) and deep-red PersL respectively. By evaluating the trap distribution that governs storage and release processes, one demonstrates a high-speed, time-resolved dynamic anti-counterfeiting platform capitalizing on the distinct decay kinetics of the two valence states. Furthermore, based on the dual PL features, one introduces an AI-assisted hyperspectral thermometry (AI-HySpec-T) method capable of operating across an extended temperature range of 20–450 K. By mapping complete spectral-thermal manifolds, this approach successfully circumvents the high-temperature performance constraints of conventional ratiometric methods. This work paves the way to the next generation of predictive optical materials for anticounterfeiting and noncontact thermometry applications.

Fractionalized excitations are among the most striking signatures of emergence in quantum matter. While widely sought in frustrated magnets, their detection and characterization remain challenging, motivating the exploration of new probes. Meanwhile, Spintronics offers versatile tools for probing spin-related phenomena. In particular, the spin Seebeck effect (SSE) converts thermally driven magnetic excitations into a voltage in an adjacent metal, providing electrical access to the underlying dynamics and transport properties. Here we employ the SSE to probe emergent magnetic monopoles in the non-collinear Ising magnet Dy$_2$Ti$_2$O$_7$, a rare instance of a three-dimensional fractionalized magnet. We observe an SSE signal featuring a pronounced peak at monopole proliferation, accompanied by characteristic frequency and angular dependence. Our results broaden the scope of spintronic methods for detecting exotic excitations, provide new insights into magnetic insulators generally and monopole physics specifically, and suggest the potential of quantum materials as functional interfaces.

Ensuring the thermal reliability of luminescent materials is a key requirement for next-generation lighting, display, and sensing technologies. The intricate interplay of thermal crossover and thermal ionization in lanthanide-doped phosphors often obscures their individual contributions. We present a frequency-domain photoluminescence analysis that disentangles these competing mechanisms. Using single crystals of SrAl2O4:Eu2+,Dy3+ (SAO:Eu,Dy) and (Gd0.33Y0.67)3Al2.4Ga2.6O12:Ce3+,Cr3+ (GYAGG:Ce,Cr) as model systems, we extract temperature-dependent trapping efficiencies and decay rates by analyzing the phase and amplitude response of luminescence under modulated excitation. Our approach reveals distinct signatures of thermal ionization and enables the direct quantification of ionization barriers and crossover rates. We demonstrate that SAO:Eu,Dy exhibits dominant trapping behavior with high ionization efficiency, while GYAGG:Ce,Cr shows significant competition between ionization and crossover. This method provides a powerful framework for resolving overlapping quenching pathways and offers new insights for the design of thermally robust luminescent materials.

The pyrochlore vanadates are compelling candidates for next-generation dissipationless devices. and are ferromagnetic insulators (T 70 K) that are believed to exhibit the magnon Hall effect and are expected to host topological magnons. Their completely dissipationless magnon edge states could be harnessed to realize low-power information transport in spintronic or magnonic devices. As a crucial step in the realization of devices, we synthesize the first thin films of pyrochlore on isostructural substrates and explore the evolution of their magnetic properties down to the ultrathin limit. All films are insulating ferromagnets with transition temperatures of up to the bulk value (T 68 K) that decrease with thickness according to finite-size effects. Our films also exhibit a change in anisotropy from in-plane to out-of-plane easy axis coincident with the development of partial strain relaxation and nonzero magnetic hysteresis in an applied field. This evolution demonstrates the impact of strain on magnetic anisotropy and paves the way to tunable magnon topology.

Frequency-domain techniques offer a powerful means to disentangle overlapping physical processes with distinct characteristic timescales-yet remain underexplored in the context of complex photoluminescent materials. Here, frequency-domain analysis is applied to persistent luminescence (PersL) materials, which exhibit long-lasting emission following excitation due to charge trapping and detrapping processes spanning wide temporal ranges. Using SrAl2O4:Eu2(+),Dy3(+) (SAO:Eu,Dy) as a model system, a general framework is developed for frequency-domain characterization of PersL and reports, for the first time, a direct measurement of the trapping rate in such a material. This approach also enables quantitative assessment of trapping probability, efficiency, and overall PersL performance. This work opens a new pathway for rational optimization of afterglow materials based on mechanistic insights beyond conventional time-domain approaches.

In persistent luminescent materials, energy can be stored under irradiation by controlled traps/defects. This energy is released at ambient temperature for long time by light emission once the excitation has been stopped. The search for innovative materials with improved properties is at the heart of the work and has recently led to several new persistent luminescence materials either as nanomaterials for sensors - and in biosensing and bioimaging- or as single crystals for various applications data storage or as jewels-. These persistent luminescent materials require identification and control of the depth of the traps and the studies of charge/discharge mechanisms.

We investigated the pressure- and temperature-dependent phase transitions in KTN40 (KTa0.6Nb0.4O3) and KNbO3, two members of the perovskite-type ferroelectric solid solution system KTN (KTa x Nb1-x O3), by heat capacity measurements, Raman spectroscopy, and second harmonic generation (SHG). The phase transition temperatures for the rhombohedral -> orthorhombic -> tetragonal -> cubic sequence in KTN40 were determined to be 180(2) K, 225(2) K, and 295(2) K, respectively, by heat capacity measurements. For KNbO3, SHG measurements revealed orthorhombic -> tetragonal -> cubic transitions at 460(3) K and 720(3) K. In both compounds, SHG experiments indicated the presence of polar nanoregions within the cubic phase above the Curie temperatures of KTN40 and KNbO3. The dynamics and stability fields of these polar nanoregions were analyzed, resulting in Burns temperatures T d of 510(5) K for KTN40 and 1000(5) K for KNbO3. Intermediate temperatures, T*, where polar nanoregions begin to merge into larger domains, were identified for KTN40 and KNbO3 to be 350(5) K and 775(5) K, respectively. The pressure-dependent tetragonal -> cubic phase transition was observed at 1.3(1) GPa for KTN40 and 15(0.5) GPa for KNbO3 using SHG. SHG measurements further confirmed polar nanoregions occurring in the cubic phase above the Curie pressures of KTN40 and KNbO3. Burns pressures p d were determined to be 6(1) GPa for KTN40 and 24(1) GPa and intermediate pressures p* were found at 1.8(2) GPa and 17(1) GPa, respectively. The known phase boundaries in temperature- and pressure-dependent phase diagrams could be reproduced and extended and phase diagrams could be enhanced by the addition of stability fields of polar nanoregions. It could also be shown that the dynamics of the polar nanoregions depend on chemical composition, as temperature-induced polar nanoregions in KTN40 appear to be smaller than in KNbO3. In addition, this study contains thermodynamic data for KNbO3, KTN40 and KTaO3. Based on the excess entropy for KTN40, these show that the formation of solid solutions tends to be favored in the KTN system compared to segregation.

Persistent luminescent (PersL) materials have garnered significant attention for applications in signaling, bioimaging, and anti-counterfeiting due to their long-lasting emission after excitation stoppage. Achieving both extended afterglow durations and stable luminescence remains challenging. This study investigates the effects of crystalline composition on the PersL properties of two polycrystalline ceramics namely Sr4Al14O25:Eu2+, Dy3+, B3+ (blue-emitting, SAO-B) and SrAl2O4:Eu2+, Dy3+,B3+ (green-emitting, SAO-G). Through various characterization techniques such as thermoluminescence (TL), radioluminescence (RL), and photoluminescence (PL) as well as persistent luminescence (PersL) excited by different sources such as X-ray, UV and visible lights, one demonstrates that SAO-B exhibits deeper traps which offer much longer afterglow duration than SAO-G, whereas SAO-G provides higher initial emission intensity and higher quantum yield. By leveraging structural PersL properties in Eu2+, Dy3+, B3+ co-doped compounds, color-tunable emission is observed. This allows for the proposal of various novel "temperature resolved" and "time resolved" anti-counterfeiting patterns, driven by the differing decay times of these aluminates. This establishes a streamlined, scalable approach to persistent phosphor design, advancing applications in security, safety lighting, and dynamic displays.

The pressure-dependent polarization of single-crystal and polycrystalline BaTiO3 and of BaTiO3-based solid solutions, was studied using second harmonic generation (SHG) to probe polarization directly. In single-crystal BaTiO3, the SHG intensity persisted above the Curie pressure, with remaining intensity attributed to polar nanoregions. Based on these findings, the pressure-temperature phase diagram of BaTiO3 was extended to include a stability field for polar nanodomains above the Curie point. In polycrystalline BaTiO3 and related solid solutions, a positive correlation between Curie pressure and temperature was observed. Complementary DFT calculations confirmed a pressure-induced reduction in SHG activity, linked to the symmetrization of the position of Ti in the structure.

Persistent luminescent (PersL) materials have garnered significant attention for applications in visualization, signaling, bioimaging, and anti-counterfeiting due to their long-lasting emission after pre-excitation. However, achieving both extended emission durations and stable luminescence remains challenging. In this study, we propose two previously lab-synthesized ceramics: Sr4Al14O25:Eu2+, Dy3+, B3+ (blue-emitting@490 nm, SAO-B) and SrAl2O4: Eu2+, Dy3+, B3+ (green-emitting@520 nm, SAO-G) belonging to strontium aluminate phosphors. This work demonstrates a comprehensive experimental approach involving detailed thermoluminescence (TL) and PersL characterizations. Under various excitation sources (UV and visible light), we identified that SAO-B exhibits deeper traps and longer decay times, whereas SAO-G shows stronger initial emission intensity. Furthermore, the video records two novel 'temperature-resolved' and 'time-resolved' dynamic anti-counterfeiting technologies within a wide time scale from a few seconds to minutes. The provided methodology serves as a valuable reference for researchers aiming to optimize persistent phosphors for security, safety lighting, and dynamic display applications.

Single crystals of yttrium aluminum borate YAl3(BO3)4 (YAB) are grown in high temperature solutions using different ratio of LaB3O6 - LiF flux. A partial ternary diagram of the system YAB - LaB3O6 - LiF is constructed using the results of slow cooling and single crystal growth experiments to identify the most suitable composition for YAB crystal growth. The growth defects (cracks, inclusions, and twins) observed in the as-grown crystal boule are discussed using several techniques including XRD and SEM observations. The substitution of Y by La was evidenced by ICP chemical analysis, Rietveld structural refinement and EXAFS analysis whereas the presence of Fe impurities at ppm levels was revealed by GDMS chemical analysis, optical absorption spectroscopy and EPR. The refractive indexes were determined showing that substitution by La faintly modifies angle phase matching conditions.

Magnetic monopoles, elusive in high-energy physics, have been realised as emergent quasiparticles in solid-state systems, where their unique properties hold promise for novel spintronic applications. Magnetic monopoles have been invoked in diverse platforms, including skyrmion lattices, chiral magnets, soft ferromagnets, aritifical nanomagnets. Yet, a demonstration of their role in magnetic transport has remained elusive. Here, we report such an observation via the spin Seebeck effect in the bulk insulating pyrochlore oxide, spin ice Dy_2Ti_2O_7. By applying a thermal gradient perpendicular to a [111]-oriented magnetic field, we detect a transverse spin Seebeck voltage marked by a dominant peak at the onset of monopole proliferation, accompanied by a secondary feature and frequency-dependent behavior. Our findings establish a direct link between monopole dynamics and magnetic transport in an insulating medium, establishing a new pathway for probing fractionalized excitations and advancing towards novel spintronic applications.

Persistent luminescent (PersL) materials have garnered significant attention for applications in signaling, bioimaging, and anti‐counterfeiting due to their long‐lasting emission after excitation stoppage. Achieving both extended afterglow durations and stable luminescence remains challenging. This study investigates the effects of crystalline composition on the PersL properties of two polycrystalline ceramics namely Sr 4 Al 14 O 25 :Eu 2+ , Dy 3+ , B 3+ (blue‐emitting, SAO‐B) and SrAl 2 O 4 :Eu 2+ , Dy 3+ ,B 3+ (green‐emitting, SAO‐G). Through various characterization techniques such as thermoluminescence (TL), radioluminescence (RL), and photoluminescence (PL) as well as persistent luminescence (PersL) excited by different sources such as X‐ray, UV and visible lights, one demonstrates that SAO‐B exhibits deeper traps which offer much longer afterglow duration than SAO‐G, whereas SAO‐G provides higher initial emission intensity and higher quantum yield. By leveraging structural PersL properties in Eu 2+ , Dy 3+ , B 3+ co‐doped compounds, color‐tunable emission is observed. This allows for the proposal of various novel “temperature resolved” and “time resolved” anti‐counterfeiting patterns, driven by the differing decay times of these aluminates. This establishes a streamlined, scalable approach to persistent phosphor design, advancing applications in security, safety lighting, and dynamic displays.

Accurate quantification of efficiency enables rigorous comparison between different photoluminescent materials, providing an optimization path critical to the development of next-generation light sources. Persistent luminescent materials exhibit delayed and long-lasting luminescence due to the temporary storage of optical energy in engineered structural defects. Standard characterization methods do not provide a universal comparison of phosphor performance, hindering the evaluation of the efficiency of the various processes involved in afterglow. Here, a protocol is established to determine the quantum yield of persistent phosphors by considering the ratio of photons emitted in the afterglow and during charging to those absorbed. The method is first applied to transparent single crystals of the most common persistent phosphors, such as SrAl2O4:Eu2+,Dy3+ and Y3Al2Ga3O12:Ce3+,Cr3+. The versatility of the methodology is demonstrated by quantifying the quantum yield of a ZnGa2O4:Cr3+ thin film, a material widely used in in vivo imaging. The high efficiency of strontium aluminate is confirmed, and a strong dependence of the obtained values on the illumination conditions is revealed, highlighting a trade-off between efficiency and brightness. The results contribute to the development of standardized protocols for analyzing afterglow mechanisms and assessing overall efficiency, facilitating rigorous comparison and optimization of persistent materials beyond trial-and-error approaches.

We report on the polarized spectroscopy of Ho3+-doped CALGO crystals in the spectral range of 2-3 μm, confirming observed trends in recent mode-locking experiments. The role of multiphonon-assisted processes is discussed.

Single-crystals of potassium gadolinium double tungstate KGd(WO4)2 doped with Sm3+ ions up to 20 at.% were grown from the flux using K2W2O7 as a solvent and a detailed polarization-resolved spectroscopic study of Sm3+ ions was performed with the goal of developing novel materials emitting in the visible spectral range. Polarized absorption spectra were measured and 4f-4f transition intensities of Sm3+ ions were calculated using a modified Judd-Ofelt theory yielding the intensity parameters of Ω2 = 8.027, Ω4 = 7.210 and Ω6 = 2.322 [10−20 cm2] and α = -0.017 [10-4 cm]. Polarized stimulated-emission properties of Sm3+ ions were studied. For the 4G5/2 → 6H9/2 transition in the red, the maximum σSE is 0.55×10-20 cm2 at 649.0 nm for light polarization E || Np (luminescence branching ratio: 40.2%). The radiative lifetime of the 4G5/2 state is 734 μs. The luminescence dynamics from this manifold was analyzed using the Inokuti-Hirayama model. The possible role of 4f – 4f excited-state absorption from the 4G5/2 level in preventing laser operation in the orange and deep red is analyzed. A 0.8 at.% Sm:KGd(WO4)2 laser generated an output power of 37.8 mW at 649 nm, with a laser threshold of 87 mW and a slope efficiency of 17.6%.

In persistent luminescence materials, energy can be stored in controlled traps/defects located within the bandgap of the material. The materials can be “charge” under brief irradiation, namely few minutes under various wavelengths ranging from natural daylight to x-rays [1]. This energy is then released at room temperature for several hours via light emission once the excitation is stopped. The present work is focused on the analysis of the persistent luminescence properties on single crystals of Ce 3+ and Cr 3+ co-doped gadolinium-yttrium-aluminum-gallium garnets of general formula Y 3-x Gd x Al 2 Ga 3 O 12 (GYAGG), to promote new applications of the persistent materials. Such single crystals can be very useful to study and better understand the persistent luminescence phenomena and can be elaborated by the Czochralski method. Some pictures of the obtained crystals are presented in Figure 1.

Despite significant interest in persistent luminescence materials, the focus of all recent works remains on the exploitation of materials in powder form. Here, a new point of view based on persistent luminescence in single crystals is presented. The garnet crystals [(Gd0.67Y0.33)3-xCex)](Al2-yCry)Ga3O12 and [(Gd0.33Y0.67)3-xCex](Al2-yCry)Ga3O12 (GYAGG) codoped with Ce3+ and different concentrations of Cr3+ have been elaborated and their persistent luminescence properties are fully characterized within this work. The persistent luminescence of Ce3+, Cr3+-codoped GYAGG single crystals is optimized due to their high optical quality, very good crystallinity and a volume effect where the whole material can be excited and charged by the excitation light. Furthermore, thanks to their transparency, robustness and homogeneity; in-depth optical spectroscopy characterization is possible, shedding light on the mechanism responsible for the afterglow.

In this work 1.6 MW peak power at 266 nm were obtained with 32% power conversion efficiency using YAl3(BO3)4 single crystal to generate the fourth harmonic of a Nd3+:YAG/Cr4+:YAG microchip laser.