Dynamic multicolor emissions of multimodal phosphors by Mn2+ trace doping in self-activated CaGa4O7

The manipulation of excitation modes and resultant emission colors in luminescent materials holds pivotal importance for encrypting information in anti-counterfeiting applications. Despite considerable achievements in multimodal and multicolor luminescent materials, existing options generally suffer from static monocolor emission under fixed external stimulation, rendering them vulnerability to replication. Achieving dynamic multimodal luminescence within a single material presents a promising yet challenging solution. Here, we report the development of a phosphor exhibiting dynamic multicolor photoluminescence (PL) and photo-thermo-mechanically responsive multimodal emissions through the incorporation of trace Mn2+ ions into a self-activated CaGa4O7 host. The resulting phosphor offers adjustable emission-color changing rates, controllable via re-excitation intervals and photoexcitation powers. Additionally, it demonstrates temperature-induced color reversal and anti-thermal-quenched emission, alongside reproducible elastic mechanoluminescence (ML) characterized by high mechanical durability. Theoretical calculations elucidate electron transfer pathways dominated by intrinsic interstitial defects and vacancies for dynamic multicolor emission. Mn2+ dopants serve a dual role in stabilizing nearby defects and introducing additional defect levels, enabling flexible multi-responsive luminescence. This developed phosphor facilitates evolutionary color/pattern displays in both temporal and spatial dimensions using readily available tools, offering significant promise for dynamic anticounterfeiting displays and multimode sensing applications.

Low-Coordination Trimetallic PtFeCo Nanosaws for Practical Fuel Cells

Developing high-performance catalysts for fuel cell catalysis is the most critical and challenging step for the commercialization of fuel cell technology. Here 1D trimetallic platinum-iron-cobalt nanosaws (Pt₃ FeCo NSs) with low-coordination features are designed as efficient bifunctional electrocatalysts for practical fuel cell catalysis. The oxygen reduction reaction (ORR) activity of Pt₃ FeCo NSs (10.62 mA cm^-2 and 4.66 A mg^-1 _Pt at 0.90 V) is more than 25-folds higher than that of the commercial Pt/C, even after 30 000 voltage cycles. Density functional theory calculations reveal that the strong inter-d-orbital electron transfer minimizes the ORR barrier with higher selectivity at robust valence states. The volcano correlation between the intrinsic structure featured with low-coordination Pt-sites and corresponding electronic activities is discovered, which guarantees high ORR activities. The Pt₃ FeCo NSs located in the membrane electrode assembly (MEA) also achieve very high peak power density (1800.6 mW cm^-2 ) and competitive specific/mass activities (1.79 mA cm^-2 and 0.79 A mg^-1 _Pt at 0.90 V_iR-free cell voltage) as well as a long-term lifetime in specific H₂ O₂ medium for proton-exchange-membrane fuel cells, ranking top electrocatalysts reported to date for MEA. This work represents a class of multimetallic Pt-based nanocatalysts for practical fuel cells and beyond.

Artificially steering electrocatalytic oxygen evolution reaction mechanism by regulating oxygen defect contents in perovskites

The regulation of mechanism on the electrocatalysis process with multiple reaction pathways is more efficient and essential than conventional material engineering for the enhancement of catalyst performance. Here, by using oxygen evolution reaction (OER) as a model, which has an adsorbate evolution mechanism (AEM) and a lattice oxygen oxidation mechanism (LOM), we demonstrate a general strategy for steering the two mechanisms on various La_xSr_1-xCoO_3-δ. By delicately controlling the oxygen defect contents, the dominant OER mechanism on La_xSr_1-xCoO_3-δ can be arbitrarily transformed between AEM-LOM-AEM accompanied by a volcano-type activity variation trend. Experimental and computational evidence explicitly reveal that the phenomenon is due to the fact that the increased oxygen defects alter the lattice oxygen activity with a volcano-type trend and preserve the Co⁰ state for preferably OER. Therefore, we achieve the co-optimization between the activity and stability of catalysts by altering the mechanism rather than a specific design of catalysts.

Exposed facet-controlled N2 electroreduction on distinct Pt3Fe nanostructures of nanocubes, nanorods and nanowires

Understanding the correlation between exposed surfaces and performances of controlled nanocatalysts can aid effective strategies to enhance electrocatalysis, but this is as yet unexplored for the nitrogen reduction reaction (NRR). Here, we first report controlled synthesis of well-defined Pt3Fe nanocrystals with tunable morphologies (nanocube, nanorod and nanowire) as ideal model electrocatalysts for investigating the NRR on different exposed facets. The detailed electrocatalytic studies reveal that the Pt3Fe nanocrystals exhibit shape-dependent NRR electrocatalysis. The optimized Pt3Fe nanowires bounded with high-index facets exhibit excellent selectivity (no N2H4 is detected), high activity with NH3 yield of 18.3 μg h-1 mg-1 cat (0.52 μg h-1 cm-2 ECSA; ECSA: electrochemical active surface area) and Faraday efficiency of 7.3% at -0.05 V versus reversible hydrogen electrode, outperforming the {200} facet-enclosed Pt3Fe nanocubes and {111} facet-enclosed Pt3Fe nanorods. They also show good stability with negligible activity change after five cycles. Density functional theory calculations reveal that, with high-indexed facet engineering, the Fe-3d band is an efficient d-d coupling correlation center for boosting the Pt 5d-electronic exchange and transfer activities towards the NRR.

Analysis of Ultrahigh Apparent Mobility in Oxide Field-Effect Transistors

For newly developed semiconductors, obtaining high-performance transistors and identifying carrier mobility have been hot and important issues. Here, large-area fabrications and thorough analysis of InGaZnO transistors with enhanced current by simple encapsulations are reported. The enhancement in the drain current and on-off ratio is remarkable in the long-channel devices (e.g., 40 times in 200 µm long transistors) but becomes much less pronounced in short-channel devices (e.g., 2 times in 5 µm long transistors), which limits its application to the display industry. Combining gated four-probe measurements, scanning Kelvin-probe microscopy, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and device simulations, it is revealed that the enhanced apparent mobility up to several tens of times is attributed to the stabilized hydrogens in the middle area forming a degenerated channel area while that near the source-drain contacts are merely doped, which causes artifact in mobility extraction. The studies demonstrate the use of hydrogens to remarkably enhance performance of oxide transistors by inducing a new mode of device operation. Also, this study shows clearly that a thorough analysis is necessary to understand the origin of very high apparent mobilities in thin-film transistors or field-effect transistors with advanced semiconductors.

"Energy Relay Center" for doped mechanoluminescence materials: a case study on Cu-doped and Mn-doped CaZnOS

We unraveled the mechanisms of transition metal-doped mechanoluminescent materials through a case study of CaZnOS. We found that the native point defect levels in Cu or Mn-doped CaZnOS system acted as energy relay centers for luminescence energy transfer. In combination with native point defect levels, discussed in a previous study [Phys. Chem. Chem. Phys., 2016, 18, 25946], we found that phosphor luminescence belongs to two different mechanisms. For Cu-doping, it occurs by the path via the conduction band minimum to the Cu-t_2g level of the 3d orbital localized in the band gap. The hole-drifting effect was found to support the reported red-shifting of the emission. Both reversible and irreversible mechanical quenching were attributed to the spatially separated electrons recombining with the hole localized on the Cu-t_2g level within the gap at levels below or above respectively. For Mn-doping, this occurs by a collaborative luminescence assisted by native point defects, and the excited states of Mn²⁺ overlap with the conduction band edge. The coexistence of Mn_Zn and Mn_Ca was confirmed, but was relatively low in Mn_Ca. The concentration quenching effect, as well as the red-shift of absorption, shows a strong correlation with native point defect levels and the relative position of the 4T₁(⁴G) state for both Mn_Zn and Mn_Ca. Further simplified approximations were used for modeling such concentration quenching effects.

Unravelling the energy transfer of Er3+-self-sensitized upconversion in Er3+-Yb3+-Er3+ clustered core@shell nanoparticles

Unravelling upconversion (UC) energy transfer mechanisms is significant for designing novel efficient anti-Stokes phosphors. We have studied the correlation of different lanthanide dopants within Er³⁺-self-sensitized core@shell upconversion nanoparticles (UCNPs). Here, our focus will be on high-concentration dopants that are able to sufficiently produce the clustering effect, especially within the interplay between Er³⁺ and Yb³⁺. We demonstrate that whatever the amount of the self-sensitizer (e.g., Er³⁺), abnormal absorption enhancement will occur as long as Yb³⁺ clusters are present. This effect originates from the substantial energy transfer between Yb³⁺-Yb³⁺ clusters despite the increased energy transfer from Yb³⁺ to Er³⁺. Therefore, the energy transfer efficiency is still constrained. However, we conversely used one of the aforementioned quench-paths of UC energy transfer to easily transfer the energy from the in-shell shell layer to the in-core area with the assistance of the energy potential reservoir, which was given by the homogeneous core@shell band offset at the interface region. Indirectly, we actualize the Er³⁺ UC luminescence with self-sensitization through an extended energy transfer path. This work provides a solid support and analytic theory for unraveling the energy transfer mechanism from recent works on Er³⁺ self-sensitized UC luminescence.

Confining Excitation Energy in Er3+ -Sensitized Upconversion Nanocrystals through Tm3+ -Mediated Transient Energy Trapping

A new class of lanthanide-doped upconversion nanoparticles are presented that are without Yb³⁺ or Nd³⁺ sensitizers in the host lattice. In erbium-enriched core-shell NaErF₄ :Tm (0.5 mol %)@NaYF₄ nanoparticles, a high degree of energy migration between Er³⁺ ions occurs to suppress the effect of concentration quenching upon surface coating. Unlike the conventional Yb³⁺ -Er³⁺ system, the Er³⁺ ion can serve as both the sensitizer and activator to enable an effective upconversion process. Importantly, an appropriate doping of Tm³⁺ has been demonstrated to further enhance upconversion luminescence through energy trapping. This endows the resultant nanoparticles with bright red (about 700-fold enhancement) and near-infrared luminescence that is achievable under multiple excitation wavelengths. This is a fundamental new pathway to mitigate the concentration quenching effect, thus offering a convenient method for red-emitting upconversion nanoprobes for biological applications.

Charge transfer induced energy storage in CaZnOS:Mn – insight from experimental and computational spectroscopy

A spectroscopic study shows that energy storage prior to mechanoluminescence and thermoluminescence in CaZnOS:Mn can be effectuated by a ligand-to-Mn charge transfer.

Energy conversion modeling of the intrinsic persistent luminescence of solids via energy transfer paths between transition levels

The energy transfer mechanism for persistent luminescence. The thermodynamic transition levels (TTLs) and single-particle levels (SPLs) are correlated with phonons.

Doping of RE ions in the 2D ZnO layered system to achieve low-dimensional upconverted persistent luminescence based on asymmetric doping in ZnO systems

The Smith-charts feature a range of 15 lanthanide dopant ions in ZnO for modulating the output emission luminescence properties (Ln²⁺: left; Ln³⁺: right).

Energy harvesting and conversion mechanisms for intrinsic upconverted mechano-persistent luminescence in CaZnOS

Vacancy defects acting as native activators, e.g. V2+ZnO and V2+CaZnOS, function as energy conversion centers to transfer energy into photons.