Upconversion nanoparticle (UCNP) thermometers are widely studied for their high sensitivity, compact size, and stability. Enhancing their performance remains a challenge. Here, we demonstrate a novel approach to modulate their thermal sensitivity using Yb3+/Er3+/Tm3+ tri-doped UCNPs, which emit strong green bands centered at 520 nm and 539 nm. These UCNPs are coated onto polystyrene (PS) microspheres and assembled into ordered arrays (PS@UCNPs). Under 980 nm laser excitation, the fluorescence intensity ratio (FIR) of two green emission peaks (520 nm and 539 nm) exhibits temperature dependence. Varying the laser incident angle (15 degrees-165 degrees), the thermal sensitivity shows nonlinear behavior and unique polarization, peaking at 45 degrees with a relative sensitivity of 0.0182 K--(1)-58 % higher than unassembled UCNPs. Finite-difference time-domain (FDTD) simulations reveal enhanced 980 nm light localization on PS@UCNPs at 45 degrees, explaining the maximal sensitivity. This work provides a new strategy to optimize UCNP thermometers through structural design.

Lanthanide doped upconversion nanoparticles (UCNPs) can be considered as nano-thermometer in monitoring temperature in nanoscale region due to their unique optical properties and abundant thermal-coupled energy levels. However, current optical thermometers mostly work on the single mode of intensity ratio and suffer the limitation of weak signal intensity. Here in this work, we propose a four-layer plasmonic metasurface composite structure composed of gold nanoring/nanowire array, UCNPs, a gold film, and a SiO2 substrate for dual-mode and non-contact temperature sensing. The optical signal intensity of UCNPs can be numerically enhanced by over 5 orders of magnitude. And the local field was found sensitive to both the structural parameters and the environmental temperature, which will eventually affect the optical signal intensity of UCNPs. Different from the traditional sensing mode of intensity ratio, here the hybrid plasmonic metasurface offers a dual mode temperature sensing by emission intensity enhancement factor and NIR absorption variation. The signal intensity in such a nanoscale temperature sensing platform can be dramatically enhanced. This sensing platform can be flexible in choosing the detecting signal. And the dual mode will improve the temperature sensing accuracy since these modes can be self-correcting for each other. And the dual-mode sensing strategy can be promising in high efficient and switchable nano thermometer.

Accurate temperature sensing at the nanoscale is critical for applications in cellular thermometry and micro-electromechanical systems (MEMS), yet it remains challenging due to the low quantum yield and signal attenuation of conventional upconversion nanothermometers. To address this limitation, we developed an innovative platform integrating gold microsphere arrays with core–shell upconversion nanoparticles (NaGdF4:Yb,Er@NaYF4). This design leverages localized surface plasmon resonance and thermal confinement effects to enhance both optical excitation and thermal response. Experimental results demonstrate a 4200

By constructing a SiO 2 sphere array@Au film@UCNPs composite structure, the upconversion fluorescence was amplified by 10.4-fold through the plasmonic effect, enabling efficient dye degradation under 980 nm near-infrared light excitation.

Non-contact and highly sensitive nanoscale temperature measurements are crucial for micro-nano devices, human health monitoring, and disease diagnosis applications. Although optical thermometry using upconversion nanoparticles (UCNPs) has advanced, the low efficiency and significant fluorescence intensity decay with temperature rise became a challenge. This study reported an optical thermometer based on a gold triangle nanoarray (AuTNA) and NaGdF4: Yb, Er@NaYF4 Core–Shell UCNPs (C-S UCNPs) with simultaneously enhanced signal intensity and sensitivity. The near-infrared (NIR) pump of UCNPs can be localized and enhanced within the AuTNA, and local thermal effects induced by plasmon hot carriers amplified the near field temperature further increased the sensitivity. Such a local heat amplification can also result in a population redistribution of thermal coupling energy level which can accelerate the fluorescent intensity ratio (FIR) variation. Compared with bare UCNPs-based thermometer, the fluorescence signal intensity and sensitivity of the proposed thermometer was simultaneously enhanced by over 1450% and 91%. Furthermore, such temperature sensor possessed other merits such as easy fabrication, good stability and cyclicity. The excitation power independent signal enhancement factors and temperature sensitivity make this thermometer promising for future applications in biodetection, heat management in microscale and even low-power threshold environments.

ABSTRACT Power‐tunable luminescent materials hold significant potential for applications in anti‐counterfeiting, information encryption, and displays. However, existing systems often suffer from limited color gamut, slow response, reliance on multi‐material composites, and poor photostability. To overcome these limitations, we present a novel class of multilayer upconversion nanoparticles featuring spatially separated emitter and sensitizer dopants combined with precise concentration control. In this architecture, high concentrations of Er 3+ and Tm 3+ are confined within distinct shell layers, effectively suppressing non‐radiative energy loss caused by inter‐ion cross‐relaxation. By systematically tuning the Er 3+ ‐doping concentration (10%–100%), we further regulate the cross‐relaxation dynamics and energy transfer from Er 3+ to Tm 3+ . Under single‐wavelength 980 nm excitation, the 20% Er 3+ ‐doped C‐SSS sample exhibits a continuous color transition from red to white to blue over a power density range of 4–277.5 mW/mm 2 , which is ascribed to a reversal of interfacial energy transfer, while the 40% Er 3+ ‐doped sample shows a shift from red to yellow to green, enabling full‐spectrum color tuning. This structure simultaneously achieves high upconversion quantum efficiency and excitation power sensitivity, overcoming the challenge of efficient broadband color modulation in upconversion systems. We demonstrate applications of the nanoparticles in power‐controlled anti‐counterfeiting tags and dual‐mode fluorescence encryption, which promise advanced information security.

High-precision refractive index sensors are pivotal for medical diagnostics, environmental monitoring, and bioanalysis. This study presents a dual-mode refractive index sensor integrating spectral shift detection and fluorescence enhancement through a gold nanodisk-UCNP heterogeneous metamaterial. By optimizing structural parameters (e.g., metal layer number, nanodisk radius), tunable multiplexed band absorption is achieved. The platform exhibits strong local field amplification at 808, 980, 1064, and 1550 nm wavelengths, significantly boosting UCNP optical signals while accommodating diverse sensitizer doping configurations. Beyond conventional refractive-index-induced spectral shifts, a linear correlation between local field strength and refractive index is revealed, enabling a dual-mode mechanism that concurrently links spectral shifts and luminescence intensity to refractive index variations. Demonstrating broad compatibility with UCNP with different dopant ions, this design advances sensing technology through synergistic spectral-intensity modulation, with applications spanning diabetes detection, tunable nanolight sources, and high-sensitivity environmental monitoring systems.

Rare earth-doped upconversion nanoparticles (UCNPs) can convert low-energy photons (NIRs) into high-energy photons (visible light), offering advantages such as low background signal, good stability, and excellent biocompatibility. However, exploring a strategy to combine the advantages of high efficiency, low cost, and easy fabrication of a plasmonics–UCNPs system is still a challenge. Here, we reported a metal–dielectric–metal (MDM)-type plasmonic platform based on the aluminum metasurface, which can efficiently enhance the luminescence intensity of magnetic and non-magnetic rare earth-doped UCNPs. Attributed to the strong local field effect of the nanocavities formed by the aluminum anti-transmission layer at the bottom, the fluorescence of the two types of UCNPs in such a platform can be enhanced by over 1000 folds compared with that in the conventional substrate. It is found that the deposited UCNPs amount and the aluminum pillar size can both impact the enhancement. We confirmed that the constructed MDM nanocavities could enhance and regulate the local field strength, and the optimum enhancement can be achieved by choosing proper parameters. All these findings provide an efficient way of exploring the plasmon-enhanced UCNPs luminescence system with low cost, high efficiency, and easy fabrication and can be promising in the fields of biosensing and photovoltaic devices.

Generating white luminescence at the nanoscale is highly desirable for applications in cell imaging and optical sensing, where nanoscale photon sources are essential. However, achieving efficient white upconversion luminescence (UCL) remains a substantial challenge. In this study, we propose a method to achieve ultrastrong white UCL by spatially separating Yb3+/Er3+ and Yb3+/Tm3+ ion pairs into distinct layers within a core/multishell nanoparticle (NaYF4@NaYbF4:1.375%Tm@NaYF4@NaYbF4:20%Er@NaYF4, denoted as C-SSSS). The introduction of an inert NaYF4 interlayer (second shell) is critical, as it controls energy transfer between Er3+ and Tm3+ ions and suppresses nonradiative cross-relaxation. Under 980 nm excitation, the C-SSSS nanoparticles exhibit white emission intensity 37.1 times greater than that of core-only nanoparticles (NaYbF4:0.5%Tm, 0.5%Er). Furthermore, optimizing the inert core size to 85 nm maximizes the effective excitation volume of the Yb-Tm-doped active layer, enabling precise control of luminescence intensity and strong white light emission. The C-SSSS nanoparticles also demonstrate exceptional thermal sensitivity, with a thermometry sensitivity 2.5 times higher than that of core-only nanoparticles, attributed to lattice distortion at the NaYF4@NaYbF4 interface. This work highlights the dual functionality of ultrastrong white UCL and high-performance luminescent thermometry in a single-nanomaterial system.

Toxic gas leakage, such as ammonia, pose significant threats to the human nervous system and environmental safety. Considering the limitations of common semiconductor-based sensors, hypersensitive, stable, recyclable and room-temperature workable ammonia sensor is urgently needed. This study proposed an efficient optical sensing platform based on a multi-hotspot plasmonic structure with high signal to noise ratio (SNR) and stability. The sensing platform consists of polystyrene(PS) microsphere arrays@Au@lanthanide-doped upconversion nanoparticles(UCNPs) composite materials. Assisted by surface plasmon resonance (SPR) effects, the excitation light is circlewise localized and amplified, leading to a significant enhancement in the upconversion fluorescence signals. The ammonia sensing performance was evaluated at room temperature, and the linear correlation with detection limit of 7.49 ppm between emission intensity and ammonia concentration was established. Compared with bare UCNPs based sensing platform, the proposed plasmonic hybrid system demonstrates improvements in sensitivity, fluorescence intensity, detection limit and SNR by 263 %, 1400 %, 500 % and 1600 %, respectively. Additionally, the sensor is easy to fabricate, highly stable, and reusable. All these findings not only improve the fluorescence signal intensity of UCNPs but also significantly enhance its gas sensing performance, providing a new sensing strategy in environmental monitoring and bio-analysis.

The utilization ratio of solar energy is the key factor affecting the external quantum efficiency (EQE) of photovoltaic (PV) devices, especially for the near-infrared (NIR) which account for nearly half of solar energy. In this paper, we proposed a material design of multilayered metasurface composing of upconversion nanoparticles (UCNPs) and Ti film for high-efficient solar collector and converter application. The Fabry-Perot (F-P) cavity formed by adjacent Ti layers can localize the incident NIR light, achieving ultrahigh absorption of nearly 100 % and acting as a perfect solar collector. This adjustable absorption spectrum and hotspots distribution of the proposed structure remarkably facilitate NIR conversion by UCNPs. The proposed metasurface design provided an efficient strategy to enhance the energy harvesting ability of common perovskite solar cells as they can extend the solar utilization spectrum range to NIR. By combining the superiority of plasmonic perfect absorber and UCNPs in such hybrid metasurface, solar energy can be efficiently harvested and the NIR part can be simultaneously converted into visible light, which is quite promising to enhance the performance of traditional perovskite solar cells. In addition, the solar collector and converter still maintaining the high mechanical intensity, low cost, and stable properties. This bifunctional metasurface design have the potentials in solar cells, photodetectors and sensors.

Fluorescent microspheres exhibit unique emissions at the microscale and have been widely used as probes for immunoassays and advanced micro-sensors.

Lanthanide-doped upconversion nanoparticles (UCNPs) were found promising in photovoltaic devices and nanoscale sensing due to their excellent optical properties. However, the low quantum yields severely limit their practical applications. In this work, we reported the enhanced upconversion emission by near-field modulation on all dielectric interfaces. The flexible polystyrene (PS) sphere array @UCNPs composite was fabricated by self-assembly and the NIR excitation can be highly localized and amplified in the array with proper sphere size, thus promoting the upconversion process. Based on this efficient upconversion composite film, the sensing performance on acetic acid gas were discussed in detail. The good linear relationship between the upconversion luminescence intensity and acetic acid concentration can be achieved with a detection limit of 5.2 ppm at room temperature, which is comparable with the best level reported so far. In addition, such optical signal-based sensors possessed other unique advantages such as easy fabrication, high sensitivity, long-term stability, reusability and flexibility. And the fluorescence signal enhancement factor showed less dependence on the excitation power and can emit effectively at low pump power. This all dielectric fluorescent composite with high efficiency and sensing performance can be helpful in biosensor and flexible security label applications.

Bound states in the continuum (BICs) have emerged as a powerful platform for boosting light–matter interactions because they provide an alternative way of realizing optical resonances with ultrahigh quality( Q -) factors, accompanied by extreme field confinement. In this work, we realized an optical biosensor by introducing a quasi-BIC (qBIC) supported by an elaborated all-dielectric dimer grating. Thanks to the excellent field confinement within the air gap of grating enabled by such a high- Q qBIC, the figure of merit (FOM) of a biosensor is up to 18,908.7 RIU −1 . Furthermore, we demonstrated that such a high- Q grating can help push the limit of optical biosensing to the single-particle level. Our results may find exciting applications in extreme biochemical sensing like COVID-19 with ultralow concentration.

A multi-functional thermal management strategy to tackle the thermal-induced self-degradation and recombination loss issues of inverted perovskite solar cells.

An efficient monodisperse MDM upconversion composite with a theoretical enhancement factor of four orders of magnitude is proposed. This design provides strategies and possibilities for dual-mode temperature sensing and other applications.

Lanthanide-doped upconversion nanoparticles have unique optical properties that can absorb low-energy infrared photons and then emit higher-energy visible ones, which have been widely used for advanced optical sensors and fluorescent probes. Efficiently tailoring the upconversion emission is desirable for meeting the wavelength requirement in various application fields. However, up to now, optimizing the composition combining with core/shell structure is still the predominant way to reach this goal. Here, we show that the relative intensities of the emission peaks of upconverting nanoparticles can be tuned by coupling to single microcavity mode with specific symmetry. Theoretical calculation based on the finite-difference method in time-domain (FDTD) indicates that the symmetries of the microcavity modes dominate their resonant absorption properties in the visible region. As a result, the upconversion emission peaks vary in these microcavities with different symmetries. This route can be developed for tailoring the emission spectra of other luminescent materials, such as quantum dots and fluorescent dyes.

We have achieved a tunable triple plasmon-induced transparency (PIT) effect on a metasurface aligned with continuous graphene strips. We also introduce coupled mode theory (CMT) as an explanation of the triple-PIT, obtaining theoretical calculation data consistent with time-domain finite-difference method (FDTD) simulations. A five-frequency asynchronous switch is developed by exploiting the sensitivity of the PIT to polarized light, and the modulation depths at the five resonance frequencies can reach 85.5 %, 83.03 %, 84.7 %, 87.5 %, and 79.8 %, respectively. Notably, altering the length of certain bright modes within the structure, either increasing or decreasing the length, will lead to the degradation of the triple-PIT to a double-PIT. Furthermore, it is demonstrated that the structure exhibits outstanding slow-light performance, possessing a group refractive index above 1000. Our findings thus offer a theoretical foundation for further investigation into high-performance slow light devices as well as multi-frequency modulators operating at terahertz frequencies.

Active manipulation on absorption takes an essential place in nanophotonic light modulators, which always suffer from static tuning ability, limited depth, and insufficient modulating efficiency. In this study, we propose an alternative strategy utilizing the symmetry -protected -type bound state in the continuum (SPBIC) to satisfy a tunable critical -coupling absorber with high modulating mobility. To demonstrate our concept, we illustrate an ultrathin critical -coupling absorbing system composed of germanium metasurface and monolayer graphene through elaborately maneuvered quasi-SPBIC, which provides substantial local field enhancement to boost the light absorption of graphene. The intensity of such critical -coupling absorption can be efficiently tuned by modulating the polarization of the incident waves with an efficiency of 97.1%. Via this polarization control, we demonstrate digital switch "0-1" and switchable and selectable image -displaying functions in simulation. Such functions are obtained in one single -designed array by incident polarization while requiring no additional structural change. Our results may pave the way for next-gen nanophotonic metadevices.