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The deterioration of mechanical properties and structural instability of coal–rock system under water–rock interaction seriously affect the efficient mining of coal and the safety of workers. The interlayer weak zone between coal seam and rock strata in coal–rock system is the main area of fracture distribution. The existence of fractures speeds the process of water–rock interaction, accounting for aggravating the damage of coal–rock system. Considering penetrating fractures and water–rock interaction, five kinds of coal–rock combined body with different fracture widths were prefabricated, and uniaxial compression tests under different soaking time were carried out. The research shows that: (1) The larger the fracture width and the longer the soaking time, the more obvious the compaction stage and the plastic stage, the less obvious the elastic stage, and the slower the damage. (2) With the increase of fracture width, the compressive strength, elastic modulus, pre-peak energy, post-peak energy and impact energy index decrease gradually, and there is a linear relationship between fracture width and each parameter. With the increase of soaking time, the compressive strength, elastic modulus, pre-peak energy, post-peak energy and impact energy index all decrease gradually, but there is a non-linear relationship between soaking time and each parameter. (3) The crack evolution law of coal–rock combined body under the influence of fracture width and soaking time is analyzed. It is found that the fracture width and soaking time have a certain influence on the wing crack, secondary inclined crack, secondary coplanar crack, inclined crack, secondary derivative crack, wing crack derivative crack, far field crack and flake phenomenon. (4) With the increase of fracture width and soaking time, the cohesion and internal friction angle decrease gradually. (5) Considering the influence of fracture width and soaking time, the D–P criterion is modified. Two parameters c (k , t) and φ (k , t) are introduced into the Drucker–Prager criterion, and the strength criterion considering fracture width and soaking time is constructed and verified. The error range of all samples is 2.48–9.30%, which indicates that the modified D–P strength criterion has high accuracy and good rationality. (6) The energy migration model of fractured coal–rock combined body is constructed, and the energy migration mechanism of intact and fractured coal–rock combined body is compared and analyzed. The two ends of the fracture are the main energy accumulation areas. When the fracture end of the coal component is destroyed, a part of the energy is transported from the coal component to the fracture end of the rock component, and released in the form of deformation or failure of the rock component. (7) The deterioration mechanism of mechanical properties of coal–rock combined body under water–rock interaction is analyzed. The physical, chemical and mechanical effects between water and coal–rock combined body lead to the damage inside the coal rock, and the continuous accumulation of damage leads to the macroscopic damage of the sample. The deterioration effect of mechanical properties under water–rock interaction is a process of continuous accumulation of damage. Highlights: Water–rock interaction. Mechanical properties of fractured coal–rock combined body. Drucker–Prager criterion considering fracture width and soaking time. The energy migration model of fractured coal–rock combined body. The deterioration mechanism of mechanical properties. [ABSTRACT FROM AUTHOR]

This study sought to identify a method for swiftly improving the correlation between sensory crispness and acoustic characteristics of puffed food. The sensory group was formed by selecting individuals adept at identifying brittleness through sequencing test, with sensory assessments conducted on various puffed food. Adopting 1000 Hz as the interval for energy segmentation, the Hilbert-Huang Transform (HHT) was utilized to segment the energy of the sound signal from puffed food to observe the process of energy migration. The relationship between sensory evaluation and acoustic properties of 10 varied puffed food types was studied. The results of sensory evaluation showed that samples with higher "crispness" were more likely to obtain higher evaluation scores. The pulse factor (r=0.937) and kurtosis (r=0.889) showed an extremely significant correlation with sensory crispness between different types of puffed food, revealing that the energy release characteristics remained consistent (P

Photoexcited energy migration is prone to causing luminescence quenching in Mn2+ luminescent materials, presenting a formidable challenge for optoelectronic applications. Although various strategies and mechanisms have been proposed to mitigate this issue, the role of spin alignment between adjacent Mn2+ ions has remained largely unexamined. In this study, we have elucidated the influence of spin alignment on energy migration within the one‐dimensional Mn2+‐metal halide compound (CH3)4NMnCl3 (TMMC) through variable‐temperature photoluminescence (PL) and magnetic‐optical spectroscopy. This investigation was conducted with reference to (CH6N3)2MnCl4 (GUA) with isolated [Mn3Cl12]6− trimers and Cd2+‐doped TMMC. The spin order in TMMC below approximately 55 K is demonstrated by the disorder‐order transition observed in the temperature‐dependent magnetic susceptibility. This finding is further corroborated by the negligible shift in the temperature‐ and field‐dependent emission peaks, a consequence of magnetic saturation. Our results indicate that the antiparallel spin alignment along the Mn2+ chain in TMMC effectively suppresses energy migration and multiphonon relaxation, thereby reducing nonradiative transitions and enhancing the photoluminescence quantum yield (PLQY). This research casts new light on the potential for developing high‐performance Mn2+‐doped phosphors for optoelectronic and spin‐photonic applications, offering insights into the manipulation of spin and energy dynamics in these materials. [ABSTRACT FROM AUTHOR]

Inspired by the spatiotemporally modulated metamaterials, we propose a one-dimensional autoparametric periodic structure induced by nonlinear inertia that is realized simply by constructing an array of pendula coupled to local oscillators. The mechanism of autoparametric modulation is revealed using a unit cell. The evolution equations for a superlattice describing the global dynamics of the wave-vibration coupling are obtained analytically by combining the Floquet-Bloch theorem and the multiple-time scales perturbation technique. The band structure exists corresponding to the fixed point in the phase space, wherein large amplitude local vibrations with distributed traveling phases modulate the inertial properties of the host pendula propagating with a small amplitude signal wave by playing the role of a pump wave. Non-reciprocal dispersion relations are demonstrated both by numerical results and perturbation results with two-order accuracy. Selective wave amplification with two-mode directional emission is observed in a two-port system which is composed of a sandwich composite medium. The present research based on the proposed autoparametric structure paves a way towards building tunable wave manipulators, vibration energy migrators and mechanical amplifiers. • A class of nonlinear inertia-induced autoparametric mechanical metamaterial is proposed. • Energy flow between longitudinal wave and attached vibration is driven by the autoparametric inertial coupling. • Small-on-large modulation is naturally created by degenerating the autoparametric system to a one-way coupling system. • Selective wave amplification with two-mode directional emission is realized in a sandwich composite medium. [ABSTRACT FROM AUTHOR]

Puffed-grain food is a crispy snack whose consumer satisfaction depends on snack crispness and crunchiness, which can be characterized by the sound and the acoustic signals of food breaking. This study aimed to evaluate whether acoustic characteristics can be used to predict the crispness of various puffed-grain food. Sensory evaluation was performed on puffed-grain products with varying hygroscopic durations and different types. The relation between sensory evaluation and acoustic characteristics of nine different types of food was examined. The Hilbert--Huang transform was used to perform energy segmentation of the acoustic signal of puffed-grain food and observe its energy migration process. The results showed that energy release was more concentrated in the low-frequency range for grain-puffed foods with different hygroscopic durations. No notable correlation was observed between the lowfrequency interval and sensory crispness for the different types of puffed-grain foods. However, the acoustic features extracted from their inherent low-frequency intervals showed a significantly improved correlation with sensory crispness. Therefore, it provides a theoretical reference for applying acoustic characteristics to describe food texture. [ABSTRACT FROM AUTHOR]

Single Dy3+ doped material is indispensable to establish single-phase white emission. However, concentration quenching (CQ) and poor stability limit its wider application. Herein, Dy3+-doped Ca 3 LuAl 3 B 4 O 15 (CLAB:Dy3+) is reported to be an advanced dual-emitting micro phosphor with promising optical properties making it a promising applicant with potential applications in thermometric and n-WLEDs. The host has a highly disordered crystal structure, suppressing the CQ phenomena of Dy3+, and attains a high doping level. Using the Kubelka–Munk equation, the optical bandgap Calculated for the matrix is 4.66 eV, which is ideal for n-WLEDs. Under 350 nm UV light, the prepared CLAB:Dy3+ displayed emissions at 476 nm and 569 nm with a CIE diagram of (0.382, 0.402) and IQE up to 18.3%. The Blass and Dexter model analyzed the energy migration (EM) mechanism. The dual emissions in CLAB:Dy3+ have distinct thermal reactions caused by thermal quenching. The temperature sensing properties of CLAB:0.08Dy3+ ranging from 300 to 500 K was examined and showed a superb Boltzmann distribution behavior between 455 nm and 476 nm fluorescence intensity ratio (FIR) and the optimum relative sensitivity S R value of 1.46% K−1. Employing the CLAB:Dy3+, a fabricated phosphor-converted white light-emitting diode (pc-WLED) emitted white light with CIE (0.36, 0.39), a color rendering index (CRI = 67.5), and a low color coordinate temperature (CCT = 4624 K). These findings suggest that this incredibly efficient single-phase white-emitting material has great potential for optical thermometric and pc-WLEDs. The structural-suppressing concentration quenching in Ca 3 LuAl 3 B 4 O 15 :Dy3+ photoluminescence and phosphor possess significant resistance to thermal quenching. Fabricated WLED devices exhibited white emissions with CIE (0.36, 0.39), a color rendering index (CRI = 67.5), and a low color coordinate temperature (CCT = 4624 K). [Display omitted] • Dy3+-doped Ca 3 LuAl 3 B 4 O 15 phosphors with high quenching concentration were synthesized. • CLAB:Dy3+ is an excellent candidate material for white LED. • The maximum relative sensitivity of this optical thermometer is 1.46 % K-1. • Fabricated WLED devices exhibited white emissions with CIE (0.36, 0.39) and a CCT ∼4624 K. [ABSTRACT FROM AUTHOR]

Multimode luminescent materials exhibit tunable photon emissions under different excitation or stimuli channels, endowing them high encoding capacity and confidentiality for anti-counterfeiting and encryption. Achieving multimode luminescence into a stable single material presents a promising but remains a challenge. Here, the downshifting/upconversion emissions, color-tuning persistent luminescence (PersL), temperature-dependent multi-color emissions, and hydrochromism are integrated into Er 3+ ions doped Cs 2 NaYbCl 6 nanocrystals (NCs) by leveraging shallow defect levels and directed energy migration. The resulting NCs display strong static and dynamic colorful luminescence in response to ultraviolet, 980-nm laser, and X-ray. Additionally, the NCs exhibit distinct luminescent colors as the temperature increases from 330 to 430 K. Surprisingly, it also demonstrates the ability of the reversible emission modal and color in response to water. Theoretical calculations and experimental characterizations reveal that self-trapped exciton state (STEs), chlorine vacancy defects, and ladderlike 4f energy levels of Er 3+ ions contribute to multimodal luminescence. More importantly, it has extremely remarkable environmental stability, which can be stored in the air for more than 18 months, showing promising commercial prospects. This work not only gives new insights into lanthanide-based metal halide NCs but also provides a new route for developing multimodal luminescent nanomaterials for anti-counterfeiting and encryption., (© 2025 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

We have designed and synthesized photochromic tetrathienyl corannulene compounds, 1,2,7,8‐tetrakis(2‐methyl‐5‐phenylthiophen‐3‐yl)corannulene (1) and 1,2,7,8‐tetrakis(2,4‐dimethyl‐5‐phenylthiophen‐3‐yl)corannulene (2), by fusing two units of photochromic terarylene with a curved aromatic corannulene with a promising antenna effect. Compound 1 exhibited highly sensitive photoreactivity, with a large molar absorption coefficient of 8.2×104 M−1 cm−1 and practically photon‐quantitative photocyclization. On the other hand, a terarylene derivative with a planar aromatic phenanthrene, 9,10‐bis(2,4‐dimethyl‐5‐phenylthiophen‐3‐yl)phenanthrene (4) showed no photoreactivity. The reason for such a difference was attributed to the predominance of the photoreactive atropisomers amplified by energy migration, and the shortened distance between reactive carbons induced by the curved structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microwave-assisted sol–gel method is used for synthesizing Eu3+-doped KYBO phosphors. • Li+ and Na+ co-doping enhances luminescence in Eu3+-doped KYBO phosphors. • Abnormal thermal stability is observed with Na+ co-doping in KYBO phosphors. • XRD and FTIR confirm structural integrity with effective dopant incorporation. • High activation energy (0.2536 eV) achieved with Na+ co-doping. Eu3+-doped and Li+/Na+ co-doped K 3 Y(BO 2) 6 (KYBO) phosphors were synthesized through a microwave-assisted sol–gel method, and their structural and photoluminescent (PL) characteristics were examined. X-ray diffraction (XRD) and Rietveld refinement confirm effective dopant incorporation and preservation of the crystalline structure. Fourier Transform Infrared (FTIR) spectroscopy indicates the maintenance of the borate structure, confirming the structural integrity of the phosphors upon doping. The addition of Li+ and Na+ co-dopants notably enhances luminescent efficiency and thermal stability, making these phosphors promising candidates for solid-state lighting (SSL) applications. PL analysis reveals strong red emission peaks at 612 nm, attributed to the 5D o → 7F 2 transition of Eu3+ ions. The study indicates that electric dipole-quadrupole interactions are the primary mechanism for energy migration, with a critical distance of approximately 22.68 Å. This mechanism contributes to concentration quenching at higher doping levels. High temperature PL measurements indicated an activation energy of 0.1389 eV for thermal quenching in the Li+ co-doped sample. Additionally, the Na+ co-doped sample exhibited an abnormal thermal stability behavior, with an even higher activation energy of 0.2536 eV. This suggests that Na+ co-doping significantly enhances the thermal resilience of the phosphor, making it more suitable for high-power light-emitting applications that operate under extreme conditions. CIE chromaticity diagrams highlight the potential for optimizing Eu3+ doping levels, combined with Li+ and Na+ co-doping, to improve luminescent performance and thermal stability for advanced SSL applications. [ABSTRACT FROM AUTHOR]

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations. [ABSTRACT FROM AUTHOR]

A series of Sm3+-activated Ca 3 Gd(AlO) 3 (BO 3) 4 red-emitting phosphors were prepared by a traditional high-temperature solid-state approach. They were characterized by XRD refinements, TEM, SEM, EDS, DRS, FTIR, Raman spectra, photoluminescence (PL) spectra, and fluorescence decay curves. The microstructure of the cation-borate phosphors and the presence of Sm3+ dopants, and their impact at the Ca and Gd sites were studied. All the samples exhibited bright red emissions caused by intra-4f transitions of Sm3+ ions when excited at 404 nm. The optimum dopant concentration was 4mol%, and the concentration quenching (CQ) process was driven by dipole-dipole interaction using Inokuti-Hirayama, and Dexter theories. Interestingly, the temperature-dependent PL spectra manifested that the resulting phosphor had excellent thermal stability with an activation energy of 0.234 eV. Ultimately, the investigated phosphor demonstrated excellent chemical stability. The Sm3+-doped CGAB:Sm3+ phosphor can convert NUV LED chips into intense red emission with Commission Internationale de l'Eclairage (CIE) diagrams of 0.615, 0.382 and high color purity of up to 95.6%. The WLED containing CG 0.96 AB:0.04Sm3+ merged with the commercial phosphors revealed low correlated color temperature (CCT≈4197 K) and high color rendering index (CRI≈89.7). EL spectrum of the fabricated Red-LED device. Inset exemplifies the coordination diagram and image for the red phosphor. UV excitation induced bright red emissions with high color purity and outstanding thermal-quenching (TQ) resistance. Luminescent pictures of the prepared Red–LED and White-LEDs device with the input current.▪ • UV excitation induced bright red emissions with high color purity up to 95.6%. • They possessed good chemical stability in an existing environment. • The CG 0.96 AB:0.04Sm3+ exhibited outstanding thermal-quenching (TQ) resistance of>90.8%. • Red LED and WLED devices were fabricated by using phosphor and UV LED chips. [ABSTRACT FROM AUTHOR]

Surface sensitivity of lanthanide-doped nanocrystals has a great utility in controlling their optical properties. Surface sensitivity can be principally promoted by energy migration. Herein, we demonstrate that cross-relaxation between lanthanides makes nanocrystals less sensitive to environmental changes. We show that by codoping ytterbium ions (Yb3+) and neodymium ions (Nd3+) in hexagonal-phase sodium yttrium fluorides, surface sensitivity can be manipulated by energy transfer from Yb3+ to Nd3+. These findings enhance our understanding of surface quenching of nanocrystals and offer new opportunities in developing highly luminous nanoprobes for molecular sensing and biomedical applications.

Ce3+ is proved to play a major role in improving the UV light excitation and thermal stability performance of Sm3+ via ET of Ce3+ to Sm3+. The SrLa 0.95 Al 3 B 4 O 15 :0.02Ce3+,0.03Sm3+ phosphors possess significant resistance to thermal quenching. Practical application such as UV-LED devices owned warm white emission with the low CCT 4503 K, high CRI~88. [Display omitted] • The synthesized phosphors possess significant resistance to the thermal-quenching. • The red emission intensity of Ce3+,Sm3+ is enhanced up to ~3.9 times compared to the pure SLAB:Sm3+. • Phosphors have satisfactory IQE (up to 74.3%) and absorption efficiency (76.5%). • LED devices were fabricated owned warm white emission with the low CCT 4503 K, high CRI (Ra~88). Ce3+ ion can effectively sensitize Sm3+ ion via energy transfer, and this phenomenon can led to the development of white light-emitting diodes (WLED). However, interestingly, high correlated color temperature (CCT), poor color-rending index (CRI), poor thermal stability, and low efficacy of available red phosphor still pose immense challenges. Herein, we undertook a combined analysis: X-ray diffraction (XRD), crystal refinement, electron spin resonance (ESR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflection spectroscopy (DRS). We also observed the optical properties of the resulting samples. The Ce3+ and Sm3+ dopants on the Sr2+ and La3+ sites in the mixed cation borate Sr 3 LaAl 3 B 4 O 15 (SLAB) phosphors were quantitatively evaluated. A cerium ion merged as a sensitizer, improving the red emission intensity by enhancing it 3.9 times. The energy transfer (ET) between Ce3+ and Sm3+ was examined experimentally and with theoretical models as a function of Ce3+ concentrations at ambient temperatures. Several theoretical models were employed to simulate the luminescence decays of Ce3+ and Sm3+ doped samples at different doping levels and their transfer mechanisms were studied depending on forced electric dipole at each ion. Notably, the electronic sites created by the oxygen vacancies around the Ln3+ ions can effectively justify the highly efficient bluish-red phosphor. Additionally, the SL 0.95 AB:0.02Ce3+,0.03Sm3+ exhibited outstanding thermal-quenching (TQ) resistance and has > 94.8% intensity at 425 K. WLEDs made with the use of SL 0.95 AB:0.02Ce3+,0.03Sm3+ furnished an exceptional CRI exceeding 88 and low at CCT 4503 K. These results are superior to the parameters of commercial WLED containing Y 3 Al 5 O 12 :Ce3+ phosphor and blue LED chip (CCT≈7746 K, CRI≈75), and they could be a cornerstone for the fabrication of warm WLEDs. [ABSTRACT FROM AUTHOR]

Abstract Anionic 9,10-diphenylanthracene chromophores electrostatically bound to cationic, chiral bilayer membranes show ordered self-assembly in water. The integrity of the chromophore-accumulated aqueous bilayer membranes is ensured by multiple hydrogen-bond networks introduced in the bilayer, which allowed adaptive accommodation of the guest chromophores at the inner surface of the bilayer while maintaining their cohesive interactions. The regular chromophore alignment in the aqueous assembly is confirmed by differential scanning calorimetry, circular dichroism, and circularly polarized luminescence spectra. Excitonic migration of triplet energy occurs among the chromophores densely organized at the inner surface of the bilayer, which lead to triplet–triplet annihilation-based photon upconversion (TTA-UC). This acceptor-bilayer self-assemblies show a notably long triplet lifetime of 8.0 ms, which allows TTA-UC at sufficiently low excitation light intensity. These results demonstrate the usefulness of the simple electrostatic accumulation approach for TTA-UC chromophores where the suitable molecular design of the TTA-UC chromophore-integrated bilayer membranes plays a key role.

Lanthanide‐based materials exhibit abundant emission colors under suitable infrared excitations; however, the dynamic control of orthogonal photon upconversion of lanthanide ions has remained challenging. Here, a novel mechanistic strategy to enable orthogonal upconversion emissions through energy migration in a simple core–shell nanostructure is reported. By constructing the migratory ytterbium‐sublattice shell layer outside the luminescent erbium matrix, the population of erbium emitters at their intermediate energy levels can be finely manipulated, and the red‐to‐green color‐switchable output has been achieved under separate 980 and 808 (or 1530) nm excitations. More interestingly, a tuning of the excitation pulse width also results in a gradual red‐to‐green color change. The mechanistic role of energy migration over ytterbium sublattice is also examined. A conceptual core–shell model for the excitation‐emission orthogonal upconversion output is provided, which is not only important for the fundamental research of photon upconversion but also helps in exciting new chances for the frontier applications such as information security. [ABSTRACT FROM AUTHOR]

Förster resonance energy transfer between identical chromophores (homo‐FRET) has been difficult to analyze since neither emission intensity nor lifetime changes with the occurrence of homo‐FRET. Herein we used a DNA scaffold to analyze homo‐FRET between pyrene moieties. The DNA scaffold was modified with two pyrenes and a quencher, anthraquinone. Homo‐FRET was detected by monitoring quenching of pyrene emission and the decrease in the fluorescence lifetime of pyrene. Homo‐FRET efficiencies could be calculated by excluding effects of hetero‐FRET. The experimentally determined efficiencies showed an excellent agreement with Förster theory. These results will inform design of novel molecular probes and light‐harvesting antennae. [ABSTRACT FROM AUTHOR]

The alignment of chromophores plays a crucial role in determining the optoelectronic properties of materials. Such alignment can make interpretation of fluorescence anisotropy microscopy (FAM) images somewhat ambiguous. The time-resolved emission behaviour can also influence the fluorescence anisotropy. This is particularly the case when probing excitation energy migration between chromophores in a condensed phase. Ideally information concerning the chromophoric alignment, emission decay kinetics and fluorescence anisotropy can be recorded and correlated. We report on the use of polarised transmission imaging (PTI) coupled with both steady-state and time-resolved FAM to enable accurate identification of chromophoric alignment and morphology in thin films of a conjugated polydiarylfluorene. We show that the combination of these three imaging modes presents a comprehensive methodology for investigating the alignment and morphology of chromophores in thin films, particularly for accurately mapping the distribution of amorphous and crystalline phases within the thin films, offering valuable insights for the design and optimization of materials with enhanced optoelectronic performance., (Creative Commons Attribution license.)

Abstract Individually and doubly doped Ce3+/Eu3+:CaLa 2 ZnO 5 (CLZO) phosphors were synthesized by a conventional sol-gel method as highly efficient luminescence-based phosphor materials. X-ray diffraction and field-emission scanning electron microscope were used to analyze the structural and morphological properties. The elements and their ionic states were determined by energy-dispersive spectroscopy and X-ray photoelectron spectroscopy studies, respectively. The assignment of the functional groups was analyzed using Fourier-transform infrared spectral studies. Bright red emission was obtained from Eu3+-doped CLZO phosphors due to its hypersensitive transition of 5D 0 →7F 2 at 626 nm with a royal blue excitation source. By increasing the Eu3+ content, the emission features were rapidly enhanced. Moreover, the red emission related to Eu3+ was further increased by the addition Ce3+ ions as a co-dopant along with Eu3+ in the CLZO matrix due to energy transfer. The energy migration from Ce3+ to Eu3+ is systematically illustrated by several fluorescent approaches, such as photoluminescence analysis, spectral overlap, CIE coordinates, lifetime dynamics, luminescence quantum yields, and color purity. Surprisingly, the CIE coordinates were very close to the NTSC coordinate values. Based on the results, these phosphors could be suitable materials for luminescence-based optoelectronic devices. Highlights • Dazzling red emission is obtained from Ce3+/Eu3+: CaLa 2 ZnO 5 phosphors. • Red emission of Eu3+ was remarkably enhanced by co-doping with Ce3+. • Effective sensitization of Ce3+ ions and enhanced quantum yield have been elucidated. • Energy transfer from Ce3+ to Eu3+ ions by several fluorescence dynamics. • Meritorious CCT, CIE coordinates and high red color purity have obtained. [ABSTRACT FROM AUTHOR]

The realization of upconversion at 808 nm excitation has shown great advantages in advancing the broad bioapplications of lanthanide-doped nanomaterials. In an 808 nm responsive system, Nd3+ and Yb3+ are both needed where Nd3+ acts as a sensitizer through absorbing the excitation irradiation. However, few studies have been dedicated to the role of Yb3+. Here, we report a systemic investigation on the role of Yb3+ by designing a set of core-shell-based nanostructures. We find that energy migration over the ytterbium sublattice plays a key role in facilitating the energy transportation, and moreover, we show that the interfacial energy transfer occurring at the core-shell interface also has a contribution to the upconversion. By optimizing the dopant concentration and surface anchoring the infrared indocyanine green dye, the 808 nm responsive upconversion is markedly enhanced. These results present an in-depth understanding of the fundamental interactions among lanthanides, and more importantly, they offer new possibilities to tune and control the upconversion of lanthanide-based luminescent materials.

Upconversion is a process in which one photon is emitted upon absorption of several photons of lower energy. Potential applications include super resolution spectroscopy, high density data storage, anti-counterfeiting and biological imaging and photo-induced therapy. Upconversion luminescence dynamics has long been believed to be determined solely by the emitting ions and their interactions with neighboring sensitizing ions. Recent research shows that this does not hold for nanostructures. The luminescence time behavior in the nanomaterials is confirmed seriously affected by the migration process of the excitation energy. This new fundamental insight is significant for the design of functional upconversion nanostructures. In this paper we review relevant theoretical and spectroscopic results and demonstrate how to tune the rise and decay profile of upconversion luminescence based on energy migration path modulation. [ABSTRACT FROM AUTHOR]

Efficient upconversion (UC)-downshifting (DS), dual-mode-emitting NaGdF4:Yb,Tm/NaGdF4:Tb/NaYF4 core/shell/shell (C/S/S) nanophosphors (NPs) were synthesized. The UC luminescence color changed from blue to sky blue after doping Tb3+ into NaGdF4 shell because Tb3+ emission peaks via 5D4 → 7FJ transition were observed with Tm3+ emission peaks via 1D2 → 3F4 and 1G4 → 3H6 transitions through the energy migration UC process of Yb3+ → Tm3+ → Gd3+ → Tb3+. Upon increasing the Tb3+ concentration in the NaGdF4 shell from 5 to 15%, the Commission Internationale de l’Éclairage (CIE) color coordinates changed from (0.2188, 0.2390) to (0.2616, 0.3654). When NaGdF4:Yb(49%),Tm(1%)/NaGdF4:Tb(15%)/NaYF4 NPs were excited using 273 nm ultraviolet light, the C/S/S NPs exhibited bright green light with CIE color coordinates of (0.3354, 0.5090) as a result of energy transfer from Gd3+ to Tb3+. These bright UC-DS, dual-mode-emitting C/S/S NPs could be applied in various applications, including multiplexed imaging and anticounterfeiting. [ABSTRACT FROM AUTHOR]

In this study, bundle-shaped β-NaYF 4 microrods with uniform morphology and good monodispersity were successfully synthesized via a facile, template-free and environmentally-friendly hydrothermal route. According to the time-dependent experimental results, the formation mechanism for the crystal phase and shape evolution process has been proposed via the Ostwald-ripening process. Under single wavelength irradiation at 250 nm, intense multi-color downconversion emissions can be obtained by co-doping Ce 3+ , Gd 3+ and X 3+ (X = Eu, Tb and Dy) into the as-synthesized β-NaYF 4 crystals, in which Gd 3+ plays an intermediate role in transferring the excitation energy from sensitizer Ce 3+ to activators X 3+ . Furthermore, the temperature-dependent emission behaviors of β-NaY 0.8 Gd 0.2 F 4 :Ce 3+ /X 3+ dual-emitting products have been systemically investigated to explore their possible application in self-calibrated optical thermometry. Impressively, the high temperature sensitivity, good signal discriminability and excellent thermal stability of the investigated dual-emitting phosphors making them a promising candidate for temperature sensing. [ABSTRACT FROM AUTHOR]

Abstract: Upconversion emission dynamics have long been believed to be determined by the activator and its interaction with neighboring sensitizers. Herein this assumption is, however, shown to be invalid for nanostructures. We demonstrate that excitation energy migration greatly affects upconversion emission dynamics. “Dopant ions’ spatial separation” nanostructures are designed as model systems and the intimate link between the random nature of energy migration and upconversion emission time behavior is unraveled by theoretical modelling and confirmed spectroscopically. Based on this new fundamental insight, we have successfully realized fine control of upconversion emission time behavior (either rise or decay process) by tuning the energy migration paths in various specifically designed nanostructures. This result is significant for applications of this type of materials in super resolution spectroscopy, high‐density data storage, anti‐counterfeiting, and biological imaging. [ABSTRACT FROM AUTHOR]

Energy transfer and migration from Coumarin102 to Coumarin6 in Poly (methylmethacrylate) have been investigated using steady-state and time domain fluorescence spectroscopy. It is found that the influence of energy migration in energy transfer can be described quite convincingly on the basis of theories of Loring, Anderson and Fayer (LAF) and Huber. At higher acceptor concentrations direct donor–acceptor transfer occurs through Förster mechanism. It is suggested to use a mixture of these two dyes in the LSCs. [ABSTRACT FROM AUTHOR]

The luminescence efficiency of lanthanide-doped upconversion nanoparticles is of particular importance for their embodiment in biophotonic and photonic applications. Here, we show that the upconversion luminescence of typically used NaYF4:Yb3+30%/Tm3+0.5% nanoparticles can be enhanced by ~240 times through a hierarchical active core/active shell/inert shell (NaYF4:Yb3+30%/Tm3+0.5%)/NaYbF4/NaYF4 design, which involves the use of directed energy migration in the second active shell layer. The resulting active core/active shell/inert shell nanoparticles are determined to be about 11 times brighter than that of well-investigated (NaYF4:Yb3+30%/Tm3+0.5%)/NaYF4 active core/inert shell nanoparticles when excited at ~980 nm. The strategy for enhanced upconversion in Yb3+/Tm3+-codoped NaYF4 nanoparticles through directed energy migration might have implications for other types of lanthanide-doped upconversion nanoparticles.

Processes of excitation energy migration in europium magnesium borate nanocrystals at different concentrations of neodymium and lanthanum ions were investigated by steady-state and time-resolved luminescence spectroscopy. Energy migration in neodymium doped mixed europium–lanthanum magnesium borate nanocrystals is well fitted by ∼t0.33dependence indicating one-dimensional transport to neodymium energy acceptors through europium chains. Variation of neodymium and lanthanum concentrations have shown that at room temperature excitation can migrate over the distances up to 100 nm that is comparable with the size of nanocrystal. [ABSTRACT FROM PUBLISHER]

Lanthanide-doped nanocrystals have shown great promise in bio-detection due to their outstanding luminescent properties, including large Stokes shift and sharp emission bands. Herein, we describe an in vitro detection of STAT3 by using an all-nanocrystal biosensing system that takes advantage of inter-particle energy transfer between two types of lanthanide-doped nanocrystals. We investigate the effect of nanocrystal size on the sensing performance and find that smaller nanocrystals offer a lower detection limit and larger dynamic range. As STAT3 is identified as an oncogene aberrantly activated and expressed in malignant transformation and tumorigenesis, our study thus holds promise for cancer diagnosis and therapy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Rare-earth-doped red upconversion nanocrystals (UCNPs) have shown excellent prospects for application in biological imaging, labeling and other fields. In this work, NaErF 4 @NaYF 4 core-shell (CS) UCNPs were successfully constructed to enhance red emission by introducing Yb3+ ions as energy trapping centers under different near-infrared excitation wavelengths. The experimental results showed that the red upconversion emission intensity of NaErF 4 @ NaYF 4 CS UCNPs doped with 15%Yb3+ ions in the core is nearly 202 times higher than that of NaErF 4 UCNPs under 980 nm excitation wavelength, with a red/green emission intensity ratio of 18.7. When Yb3+ ions were introduced into the core and shell of NaErF 4 @NaYF 4 CS UCNPs, NaErF 4 :15%Yb3+@NaYF 4 :10%Yb3+ CS UCNPs showed the best red emission due to the energy network characteristics of the Yb3+ ions. Furthermore, the enhancement mechanism of red emission in NaErF 4 @NaYF 4 CS UCNPs with different Yb3+ ion doping concentrations were discussed, based on the spectral characteristics and lifetime. It was found that doping of Yb3+ ions in NaErF 4 @ NaYF 4 CS UCNPs can significantly improve the red emission intensity of Er3+ ions through controlling energy migration (EM) and energy back transfer (EBT) processes, which has considerable potential for applications in bioimaging and anti-counterfeiting. [Display omitted] • The red UC emission intensity were enhanced 202 times by introducing Yb3+ ions in NaErF 4 @NaYF 4 CS UCNPs. • The optimal enhancement system was successfully constructed by varying the concentration of Yb3+ ions. • The enhancement mechanisms of red UC emission were carefully discussed based on EM model and lifetimes. [ABSTRACT FROM AUTHOR]