The team’s solution was to abandon the traditional measurement strategies altogether and instead interrogate the nucleus through its own electrons, stripped down to a bare handful. In a study published in Nature Communications, the researchers performed high-precision extreme ultraviolet spectroscopy of highly charged ions, atoms from which dozens of electrons have been removed, using the Tokyo-EBIT facility at the University of Electro-Communications. By measuring the emission line energies of lutetium ions carrying charges of 59+ and 60+ and ytterbium ions carrying charges of 58+ and 59+, and comparing those energies against state-of-the-art atomic structure calculations, they extracted the tiny influence of nuclear size on atomic energy levels. The verdict: the lutetium nucleus is actually slightly smaller than that of ytterbium, exactly as the expected odd-even staggering predicts.

To understand why this measurement required such an exotic approach, it helps to consider what a nuclear charge radius actually is and how it normally gets measured. The nucleus is astonishingly small compared with the cloud of electrons that surrounds it, typically by a factor of tens of thousands. When an electron orbits far from the nucleus, as it does in a neutral atom or a singly charged ion, it spends almost no time inside the nuclear volume, so the finite size of the nucleus barely perturbs its energy. The resulting energy shift, known as the volume shift, is real but minuscule, and teasing it out of optical spectra has historically required exquisite laser spectroscopy and careful comparisons, usually within a single element across a chain of isotopes. Comparing radii between different elements was notoriously difficult, because the atomic physics differences between neighboring elements swamp the nuclear signal.

Highly charged ions change the calculus dramatically. When an atom is ionized many times, the remaining electrons are pulled into tight orbits that lie close to the nucleus, in some cases penetrating deep into the nuclear interior. There they directly sample the distribution of nuclear charge, and the volume shift is amplified enormously relative to what a neutral atom would show. A nucleus that is a few percent larger or smaller than its neighbor leaves a measurable fingerprint on the extreme ultraviolet emission lines of these stripped ions. In effect, the highly charged ion acts as an exquisitely sensitive probe that has been threaded directly into the nucleus, converting a nuclear property into an atomic wavelength that can be measured with spectroscopic precision.

The instrument that made this possible is Tokyo-EBIT, an Electron Beam Ion Trap developed at the University of Electro-Communications in the 1990s and refined over decades of operation. Inside the device, a monoenergetic electron beam is compressed by a strong magnetic field to high current density, creating a laboratory plasma unlike any natural one. When atoms of a chosen element are injected into this beam, they collide repeatedly with the fast electrons and are stripped of their electrons in successive steps, climbing the charge-state ladder until they reach the desired ionization stage. Tokyo-EBIT boasts world-class performance in both electron beam energy and current, which allowed the team to generate and observe lutetium and ytterbium ions in the extremely high charge states around 58+ to 60+, where only a handful of bound electrons remain.

The experimental protocol demanded unusual care. The team alternately recorded high-resolution extreme ultraviolet emission spectra of the lutetium and ytterbium ions, switching between elements so that instrumental drifts and plasma conditions would affect both measurements equally. The emission line energies of Lu59+, Lu60+, Yb58+, and Yb59+ were then compared line by line. Because the ions in each pair share nearly identical electronic configurations, the differences in their emission energies could be attributed almost entirely to the nuclear volume shift rather than to ordinary atomic structure effects. The latest high-precision atomic structure calculations served as the theoretical bridge, converting the observed energy differences into differences in nuclear charge radii with a rigor that earlier techniques could not match.

The result settles a puzzle that has lingered through generations of nuclear data compilations. Earlier evaluations, built on electron scattering experiments, muonic atom spectroscopy, and laser spectroscopy of neutral atoms and singly charged ions, had implied that lutetium’s nucleus was larger than ytterbium’s, an apparent reversal of the odd-even staggering that governs nuclear sizes across the rare-earth region. The new measurement shows that no reversal exists. The nucleus of lutetium, with its odd number of protons, is slightly smaller than the even-proton nucleus of ytterbium, in keeping with the zigzag pattern that reflects the pairing tendency of protons and neutrons inside the nucleus. The long-debated reversal problem, as it came to be known, has been resolved.

Yet the resolution of one puzzle opens the door to another. The charge radii of rare-earth elements obtained in this study not only call into question the picture built on conventional experimental data but also suggest that the odd-even effects in this region may be significantly more pronounced than current nuclear structure theories can fully explain. Deformed nuclei, those whose shapes deviate from spherical, dominate the rare-earth region, and their radii encode rich information about collective rotation, pairing correlations, and the interplay of protons and neutrons in a strongly interacting quantum system. If the staggering is stronger than theory predicts, then something important about the nuclear force and the pairing of nucleons in deformed systems remains to be understood, and the rare-earth nuclei are pointing the way.

What makes the demonstration especially significant is its generality. Because the method compares emission line energies of highly charged ions of different elements directly, it enables the kind of cross-element comparison that laser spectroscopy of neutral atoms and singly charged ions could never easily provide. The researchers plan to extend the technique beyond lutetium and ytterbium to neighboring rare-earth elements and to radioactive nuclides, mapping out whether the enhanced odd-even staggering is a general feature of the region or specific to particular nuclei. Systematic measurements across a chain of highly charged ions could deliver a new, self-consistent dataset on nuclear charge radii in the heavy-element region, precisely where deformed nuclei make the physics richest and the traditional methods most strained.

The work also represents a striking repurposing of a technique born in a different corner of physics. Highly charged ion spectroscopy was cultivated over decades to advance relativistic atomic physics and to support nuclear fusion science, where the extreme plasmas of fusion devices strip atoms to high charge states and demand accurate atomic data for diagnostics. The present study shows that the same machinery, together with refined methods of high-precision wavelength analysis, rare-earth element injection into the trap, and high-precision atomic structure calculation, can serve as a precision tool for nuclear structure research. The researchers intend to pursue this line vigorously, with applications extending to fusion plasma diagnostics, astrophysics, and the development of short-wavelength light sources. A puzzle about the size of two adjacent nuclei, probed by electrons that orbit within a whisper of the nuclear surface, has thus become a demonstration that the boundary between atomic and nuclear physics is thinner, and more useful, than anyone had fully appreciated.

Subject of Research: Measurement of nuclear charge radii in rare-earth elements using extreme ultraviolet spectroscopy of highly charged ions

Article Title: Exploring nuclear properties by atomic spectroscopy

Article References: Exploring nuclear properties by atomic spectroscopy. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: nuclear charge radii, highly charged ions, atomic spectroscopy, extreme ultraviolet, Tokyo-EBIT, lutetium, ytterbium, odd-even staggering, rare-earth nuclei, nuclear structure, deformed nuclei, volume shift

Now a team at Rice University, working with collaborators at Duke University and the glass-microfabrication company Translume Inc., has unveiled a new device that could make this powerful technique far more accessible. Writing in the journal Physical Review Applied, the researchers describe a monolithic segmented three-dimensional ion trap, a single microfabricated structure that combines the strengths of two long-standing trap designs while, for the first time in this class of devices, supporting the use of heavy ions such as ytterbium. The work was led by Guido Pagano, associate professor of physics and astronomy at Rice, with graduate student Abhishek Menon serving as corresponding author and Roman Zhuravel, an assistant research professor in the Pagano lab, as a senior author.

To appreciate why the new trap matters, it helps to understand the two design families it draws from. Ion traps that use radio-frequency voltages have traditionally fallen into two camps. Blade-style traps, built from precisely machined metal electrodes arranged around the trapping region, deliver excellent performance, but their geometry is limited in precision and each device must be assembled by hand, making them difficult to reproduce at scale. Microfabricated chip traps, by contrast, are typically planar, two-dimensional structures produced with lithographic techniques. They offer superior geometric precision, high modularity, and easy reproducibility, which makes them attractive for laboratories that cannot devote years of engineering effort to trap construction. In many performance metrics, however, chip traps have lagged behind their blade-style counterparts.

Monolithic three-dimensional ion traps were conceived as a way to capture the best of both worlds: the high performance of blade traps and the scalability and modularity of chip traps, all in a single block of material. Until now, though, devices of this type had only been demonstrated with light ions such as calcium. That limitation mattered, because heavier ionic species like ytterbium are widely used in quantum simulation and quantum information experiments, with well-developed laser-cooling schemes and mature optical access. Extending monolithic three-dimensional architecture to heavy ions would open the platform to a much broader community of researchers.

That is precisely the gap the Rice-led team set out to close. In their monolithic ion trap, the researchers aimed to combine the high-performance features and accessibility of the blade trap with the scalability and modularity of the chip trap in a way that was compatible with heavier ions, as Menon explained. Solving the harder engineering problems associated with trapping heavier ionic species, he noted, also simplifies the trapping of lighter species and broadens the trap’s usefulness across a variety of quantum technologies. The design process began with a block of fusilica glass. Using lasers and chemical processes, the team marked out and created channels for the ions and trenches for the electrodes that had to be installed before the entire structure was coated with sputtered gold.

Those trenches proved to be a crucial element of the design. By isolating the electrodes from one another by construction, they prevented the electrodes from shorting together during the gold sputtering process, and they also protected the device from dielectric breakdown under the high-voltage conditions the trap experiences in vacuum. In a radio-frequency ion trap, voltages applied to the electrodes create a rapidly oscillating electric field that confines charged particles near a point where the field averages to zero. Any unintended electrical contact or breakdown between electrodes would destroy the carefully shaped fields that hold the ions in place, so the isolation strategy was essential to making a robust, high-voltage device in a compact monolithic package.

The path to a working device was anything but smooth. Menon described the development as an iterative process in which the first generation of the trap failed, although in a promising and informative way: it suffered from a significant thermal and electrical management problem, and the trap began to glow visibly when the desired high radio-frequency voltage was applied in vacuum. That glow was a sign that electrical energy was being dissipated somewhere it should not have been, heating the structure and threatening the stability of the trapping fields. The second generation fixed the first generation’s major flaws, but it introduced new problems, including considerable axial micromotion, an unwanted oscillation of the trapped ions driven by imperfections in the electric field, and high ion-heating rates that would degrade the quality of quantum simulations.

Only with the third generation did the team arrive at a viable trap. The final design incorporated a better heat sink to draw heat away from the trap structure, addressing the thermal failures of earlier versions. It minimized the axial micromotion of the ions, improving the precision with which the ions could be held and manipulated. And it employed a plasma-based surface treatment of the electrode surfaces, a technique known to reduce the anomalous heating that occurs when electric-field noise from contaminated or rough surfaces jostles the trapped ions. Beyond these fixes, the design had to balance several competing requirements: greater spacing between the ions in the chain, lower voltages in the system, and appropriate ion-heating rates, all without sacrificing the qualities that made the ion trap useful in the laboratory.

Once the design was finalized, the Pagano lab, together with collaborators at Duke University, individually tested the ion traps. The devices were confirmed to work as intended, and their measured performance agreed with computer simulations that had been run before fabrication. That agreement between model and experiment is an important validation for a microfabricated device, because it means future iterations can be designed and refined with confidence in the simulation tools, shortening the development cycle. It also means that other laboratories adopting the platform can expect reproducible behavior from trap to trap, one of the key promises of monolithic microfabrication.

The implications extend well beyond the device itself. As Zhuravel pointed out, the monolithic trap makes trapped-ion simulators more accessible to academic labs, allowing researchers to simplify challenging quantum problems into ones they can solve and then map those solutions onto bigger, more complex problems. Applications could include understanding charge transfer in photosynthesis, a process Pagano highlighted as an example of the complex phenomena these simulators can illuminate. The work was supported by the U.S. Department of Energy Office of Science, the Welch Foundation, the Office of Naval Research, the National Science Foundation, the Army Research Office, and the U.S. Army Research Laboratory. With a reproducible, high-performance, heavy-ion-compatible trap now demonstrated, quantum simulation with trapped ions may be poised to move from a handful of specialized laboratories to a much wider scientific community.

Subject of Research: Monolithic segmented three-dimensional ion traps for trapped-ion quantum simulation with heavy ions

Article Title: New monolithic ion trap developed for accessible quantum simulations

Article References: New monolithic ion trap developed for accessible quantum simulations. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: quantum simulation, ion trap, trapped ions, ytterbium, microfabrication, Rice University, Physical Review Applied, radio-frequency trap, ion heating, quantum technology, blade trap, chip trap

Heavy fermions are not new to physics. They have been studied for decades in certain bulk compounds, typically materials containing rare-earth elements such as cerium, ytterbium, or uranium. In these compounds, the electrons responsible for electrical conduction do not travel freely as they would in an ordinary metal. Instead, they become entangled with electrons that are tightly bound to individual atoms, and this entanglement slows them down dramatically. Because the effective mass of an electron is inversely related to its mobility, the conduction electrons in these materials appear enormously heavy. The consequences are profound: heavy-fermion systems are among the most fertile grounds for unconventional superconductivity, quantum criticality, and other exotic phenomena that remain poorly understood even after decades of research.

What has made heavy fermions difficult to harness, however, is that they usually emerge only in specific three-dimensional crystals whose chemistry is largely fixed by nature. If researchers want a heavy-fermion material with different properties, they generally cannot simply design one; they must search for it. The Osaka-led team’s result points toward a different philosophy. Rather than relying on bulk crystals, the researchers showed that a heavy-fermion state can be engineered at an interface, the planar boundary where two materials meet, by combining an atomic layer with a suitable substrate.

The material at the heart of the study is ytterbium copper, in the compound form YbCu2, deposited as a single-atom-thick layer on a copper crystal surface. Creating such a layer is far from trivial. At this scale, the quality of the film determines everything: defects, disorder, or unwanted chemical reactions at the surface can destroy the delicate quantum behavior the researchers hoped to observe. The team’s success rested on producing a high-quality, well-ordered two-dimensional Kondo lattice, an arrangement in which ytterbium atoms carrying localized magnetic moments form a regular grid within the atomic layer. The Kondo lattice is the canonical setting for heavy-fermion physics, because it is where localized moments and conduction electrons negotiate their quantum relationship.

To interrogate the electronic states of this system, the researchers turned to synchrotron radiation, the intensely bright light produced when electrons are accelerated around storage rings at nearly the speed of light. Synchrotron-based spectroscopy allows scientists to probe the energies and momenta of electrons in a solid with exceptional precision, effectively taking a picture of the material’s electronic structure. By applying these measurements to the YbCu2 layer on its copper substrate, the team could distinguish electrons residing in the atomic layer from those in the underlying metal, and, crucially, identify states that belonged to neither in isolation.

The measurements revealed not one but two distinct heavy-fermion states. The first was confined mainly to the two-dimensional YbCu2 layer itself, a heavy-electron state living within the plane of the atomic film. The second was more remarkable: it extended into the three-dimensional copper substrate below. This interfacial state arose from hybridization, the quantum mixing, between localized ytterbium 4f electrons in the atomic layer and the mobile conduction electrons of the copper crystal. The 4f electrons of ytterbium are the archetypal localized electrons of heavy-fermion physics, shielded deep within the atom and only weakly interacting with their surroundings. The observation that these electrons hybridize across the interface with conduction electrons in a different material constitutes direct evidence that a heavy-fermion state can be born at the boundary between two substances, rather than within the body of a single compound.

This distinction matters because it demonstrates that the interface itself is an active participant in creating quantum states, not merely a passive boundary. The electrons on each side of the boundary interact across it, and the resulting hybridized state inherits properties from both worlds: the strong correlations of the localized f electrons and the itinerant, three-dimensional character of the substrate metal. In effect, the researchers have shown that a quantum state with no counterpart in either constituent material can be assembled by stacking them together.

The implications for materials design are considerable. The authors suggest that by carefully combining atomic layers and substrates, and by precisely controlling the interfacial structure, the electronic orbitals involved, and even moiré patterns, the long-wavelength interference patterns that arise when two lattices are stacked with a twist or mismatch, researchers may be able to create and tune low-dimensional quantum phenomena that cannot be realized in conventional materials. Moiré engineering has already transformed the study of two-dimensional systems, most famously in twisted bilayer graphene, where small rotations between layers produce entirely new electronic phases. The Osaka result suggests that similar design principles, combined with the strong correlations of rare-earth f electrons, could open access to quantum states that have never been explored.

Among those potential states, the team has set its sights on unconventional superconductivity. Heavy-fermion compounds are celebrated for hosting superconducting phases that do not conform to the conventional theory of superconductivity, and their superconductivity is widely believed to be driven by the same strong electron correlations that create the heavy masses in the first place. If heavy-electron states can be engineered and controlled at interfaces, researchers may be able to tune them continuously, adjusting the strength of hybridization, the dimensionality of the electrons, and the geometry of the lattice, in ways that bulk crystals never allowed. That tunability is precisely what the field needs to test competing theories of unconventional superconductivity and, perhaps, to find new superconducting phases.

Senior author Professor Shin-ichi Kimura emphasized that the achievement grew out of a sustained effort to prepare materials of the highest quality and to measure their electronic states as precisely as possible. The team’s next goal, he noted, is to engineer and control such heavy-electron states deliberately, opening the way to previously unexplored quantum states, including unconventional superconductivity. The study, titled Interfacial heavy fermion formation in a two-dimensional Kondo lattice YbCu2 on Cu(111) substrate, was published in Communications Materials. As an experimental demonstration that one of physics’ most celebrated correlated-electron states can be assembled atom by atom at a designed boundary, the work marks a shift from searching for heavy fermions in nature to building them by intention, a shift that could define the next chapter of quantum materials research.

Subject of Research: Interfacial heavy-fermion formation in a two-dimensional Kondo lattice on a copper substrate

Article Title: Heavy Fermions emerge at an atomic-layer interface

Article References: Heavy Fermions emerge at an atomic-layer interface. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: heavy fermions, ytterbium, Kondo lattice, interfaces, synchrotron spectroscopy, quantum materials, unconventional superconductivity, two-dimensional materials, hybridization, moiré patterns, 4f electrons, low-dimensional systems

The material at the heart of the study belongs to a family called zero-dimensional metal halides. In the crystal Cs3GdCl6, negatively charged gadolinium-chlorine octahedra float in isolation, surrounded by cesium ions, with no continuous framework connecting them. This isolated architecture gives the compound exceptional chemical and thermal stability, a stark contrast to the moisture-fragile lead halide perovskites that have dominated optoelectronics research. Lead perovskites are brilliant light emitters, but their toxicity collides with regulations such as the Restriction of Hazardous Substances Directive, and their instability, while useful for sensing, ruins long-term device reliability. The cesium-gadolinium-chloride host sidesteps both problems while offering another crucial advantage: as a heavy halide lattice with low phonon energy, it suppresses the vibrational relaxation that normally kills upconversion, the nonlinear process by which materials absorb low-energy infrared photons and emit higher-energy visible light.

By replacing a fraction of the gadolinium ions with lanthanide emitters such as terbium, ytterbium, or erbium, the researchers created a versatile optical platform. X-ray diffraction with Rietveld refinement confirmed a pure monoclinic structure, and the unit cell contracted linearly with dopant concentration, exactly as Vegard’s law predicts for successful substitution. X-ray photoelectron spectroscopy verified that the dopants sat in their trivalent states within the halide coordination environment. The erbium-only composition Cs3Gd0.8Er0.2Cl6 emerged as the most interesting member of the family, because its emission color depended dramatically on which infrared laser was shining on it.

Under 1550-nanometer excitation, erbium ions absorb photons through the transition from their ground state to the first excited manifold, and a sequential three-photon process climbs the energy ladder to the green-emitting levels at 525 and 550 nanometers. Under 980-nanometer excitation, erbium’s absorption is inherently weak because the relevant transition has a low oscillator strength, and a two-photon pathway instead populates a higher level that relaxes nonradiatively, favoring red emission at 670 nanometers. Pump-power measurements confirmed the physics: intensity scaled with roughly the second power of laser power at 980 nanometers and between 2.5 and 3 at 1550 nanometers, matching the two- and three-photon mechanisms respectively.

Then came the surprise. When the erbium-only crystal was exposed to ambient air at 22 percent relative humidity, its bright green upconversion glow under 1550-nanometer light shifted to red within three minutes. Yet under 980-nanometer light, the same sample, in the same humid air, held a steady yellow hue with virtually unchanged spectra. Moisture alone, in other words, did not determine whether the material switched color. The deciding factor was whether the excitation wavelength could pump enough population into the moisture-sensitive excited states. This excitation selectivity is what the authors call hydrochromic upconversion, and it elevates the phenomenon from a simple wavelength-dependent color variation to a mechanistically defined optical response.

The mechanism hinges on water’s molecular vibrations. Adsorbed water molecules carry high-energy oxygen-hydrogen oscillations that act as exceptionally efficient quenching channels, draining energy nonradiatively from erbium’s green-emitting levels. But quenching can only occur if those levels are actually populated, which requires strong absorption at the excitation wavelength. Time-resolved photoluminescence sealed the argument. In a ytterbium-sensitized companion composition, where ytterbium absorbs 980-nanometer light strongly and transfers energy to erbium, the green emission decay curves showed a characteristic population buildup that vanished as moisture exposure progressed, alongside a shrinking lifetime, the classic signature of oscillation quenching. In the erbium-only crystal under 980 nanometers, no buildup existed and the decay curves stayed frozen throughout eight minutes of humidity exposure, because the excited-state population was simply too sparse for water to matter. Crucially, Raman spectra collected during exposure showed that the vibrational bands of the gadolinium-chloride octahedra never shifted or broadened, proving the color change involves no lattice disorder or defect formation, only surface-mediated energy quenching.

The absorption-coefficient explanation passed a decisive test. Quantified from diffuse-reflectance spectra, the ratio of absorbance at 1550 nanometers to that at 980 nanometers was 3.11 for the erbium-only crystal but inverted to 0.56 for the ytterbium-codoped one. When both compositions were excited at 1550 nanometers, a wavelength both absorb strongly, both showed the rapid green-to-red hydrochromic transition. The rule held at every level of the analysis: steady-state color, decay kinetics, and absorption strength all pointed to the same criterion. A secondary contribution from moisture-altered erbium-erbium cross-relaxation cannot be fully excluded, the authors note, but vibrational quenching by adsorbed water is clearly the dominant driver.

To showcase the practical power of this selectivity, the team arranged three compositions, the terbium emitter, the ytterbium-erbium codoped crystal, and the erbium-only crystal, into a single pattern plate that is completely invisible under daylight. Under 254-nanometer ultraviolet light, the terbium regions glow green in a circular pattern; under x-rays, the same circle appears on a CMOS sensor array, since the terbium emission at 548 nanometers matches the sensitivity of commercial imaging chips and scales linearly with x-ray dose. Under 1550-nanometer infrared light, both erbium compositions reveal a green comet pattern that turns entirely red when moisture arrives. Under 980 nanometers, however, a yellow heart shape appears, and it stubbornly refuses to change even in humid air. Because the heart is moisture-insensitive while the comet is not, the same plate carries an internal reference that separates genuine moisture signals from any general drift in emission, a built-in control that most single-stimulus sensors lack.

The researchers then pushed beyond qualitative color tricks into quantitative dosimetry. They built an automated analysis pipeline in Python that extracts video frames, detects the crystal region of interest, and converts emission colors into the CIE Lab* color space, tracking the a* coordinate that captures the green-to-red transition. The a* value climbs from minus 33.21 in the dry state to 20.37 at full saturation, defining fixed boundaries that normalize the response to a 0-to-100 percent saturation scale. Experiments across relative humidities from 11 to 93 percent, controlled with saturated salt solutions, showed that the color evolution follows the long-time solution of Fick’s second law of diffusion, with fitting quality above 0.97 under high humidity. The extracted diffusion coefficients rose exponentially with relative humidity, correlating above 0.96 across the entire range. Because the measured color reflects moisture that has already diffused into the lattice rather than the instantaneous external humidity, the sticker records cumulative exposure, so the readout remains meaningful even when humidity fluctuates unpredictably over time.

The end result is a smartphone-based dosimeter that requires no external power. A 1550-nanometer laser illuminates the sticker, the phone camera captures the emission, an inverse calculation based on Fick’s law converts the color coordinates into a saturation level, and the user receives a concrete number, say 68 percent, instead of a vague color warning. Unlike conventional binary indicators such as cobalt chloride, this system quantifies accumulated moisture uptake nondestructively through sealed packaging, making it attractive for precision chemicals, pharmaceutical storage, and heritage conservation. The luminescent material itself can even be regenerated by heating, although the assembled sticker is designed as a single-use record. Beyond the device, the deeper contribution is conceptual: the demonstration that hydrochromic switching in upconversion materials obeys an excitation-selective criterion, governed by whether the pump wavelength can populate moisture-sensitive excited states, gives materials designers a general principle for building optical sensors whose sensitivity can be switched on and off simply by changing the color of invisible light.

Subject of Research: Excitation-selective hydrochromic upconversion in lanthanide-doped zero-dimensional lead-free metal halides for optical moisture sensing

Article Title: Excitation‐Selective Hydrochromic Upconversion in Zero‐Dimensional Metal Halides

Article References: Han, J. H., Seo, J. M., Jang, S. W., Park, Y. M., Choi, S. H., Cha, J. H., & Im, W. B. (2026). Excitation‐Selective Hydrochromic Upconversion in Zero‐Dimensional Metal Halides. Advanced Science, Article e78059. https://doi.org/10.1002/advs.78059

Image Credits: AI Generated

DOI: 10.1002/advs.78059

Keywords: upconversion, metal halides, hydrochromic, lanthanide doping, erbium, ytterbium, moisture sensing, humidity dosimetry, Fick's second law, lead-free perovskite alternative, anti-counterfeiting, optical readout