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Bright yellow upconversion emission spectra at 595 nm were investigated in Nd3+ ions doped gadolinium orthovanadate (GdVO 4) single crystals. 556-fold enhancement of the intensity of upconversion emission at 595 nm was investigated at the sample temperature of 400 °C, which followed the exponential increase with temperature. The lg-lg relationships of the detected upconversion emission spectra and the input pumping laser were discussed, which dropped to 2.28 at high temperature from 5.98 at low temperature and implied fewer photons are required at higher temperatures. Thermal phonon-assisted excitation and electron-phonon coupling activities played important roles in the one photon upconversion emission excited by the laser centered at 1064 nm, and over 3700-fold enhancement of the emission peaks at 756 nm was observed. The finding in this work provides thermal stability analysis in Nd3+ ions doped laser materials and expands rare earth ions upconversion mechanisms. [ABSTRACT FROM AUTHOR]

Er3+ -doped CaYA1O4 crystals with the doping concentration (atomic fraction) of 15% and 30% were successfully grown by Czochralski method. The polarized spectral and laser properties of Er:CaYA1O4 crystals were studied. The polarized absorption spectra, polarized emission spectra and fluorescence decay curves were measured at room temperature. The disorder of CaYA1O4 crystal results in broadband characteristics of absorption and emission spectra. The emission cross section of 15% Er:CaYA1O4 is determined to be 1. 22 x 10-20 cm² at 2 712 nm for σ polarization and 0. 71 x 10-20 cm² at 2 754 nm for π polarization, with a full width at half maximum (FWHM) of 152 and 167 nm, respectively. As Er3+ concentration increases, fluorescence lifetime of 4I11/2 and 4I13/2 energy levels decreases in different degrees, and lifetime ratio ( τlower/τupper) greatly reduces. The energy transfer upconversion ETU1 not only suppresses self-termination effect but also improves quantum efficiency of 2. 7μm radiative transition. Under 974 nm LD excitation, laser property for output couple mirror with a transmittance of 1. 5% is best. The maximum output power is 358 mW at 2 720 nm with a slope efficiency of 15.4% in c-cut 15%Er:CaYAlO4 crystal. [ABSTRACT FROM AUTHOR]

The Sc3+ ions doped NaYF4: Yb3+, Er3+ upconversion (UC) nanoparticles are synthesized by thermal decomposition method. We successfully obtained the upconversion luminescence (UCL) nanoparticles from green emission to red emission through doping Sc3+ ions with different concentrations. Based on the XRD, the phase change process of Sc3+ ions doped NaYF4 nanocrystalline phase were demonstrated. More importantly, through the analysis of UC spectrum data, the change in the phase of the NaY/ScF4: Yb3+, Er3+ nanocrystalline corresponds to the change in its luminous properties. It determines that the change of crystal field will lead to the change of luminescence, and then modulate the luminescence. NaScF4: Yb3+, Er3+ UC nanoparticles exhibit strong red light emission. In addition, the temperature-sensitive properties of the optimal doping concentration of Sc3+ ion were tested. The sensitivity of NaYF4: Yb3+, Er3+ nanoparticles doped with Sc3+ ion reached the maximum value of 0.024 K− 1 at 498 K. The nanocrystalline has great application value in the fields of optical temperature measurement, biomedicine, bioprobes and colorful display. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) is a promising technique for the readout of immunochemical assays utilizing indirect detection of labels (Tag-LIBS), typically based on nanoparticles. We have previously demonstrated that Tag-LIBS immunoassay employing yttrium-based photon-upconversion nanoparticles (UCNPs) can reach sensitivity similar to commonly used enzyme and fluorescence immunoassays. In this study, we report on further increasing the sensitivity of UCNP-based Tag-LIBS immunoassay by employing magnetic microbeads (MBs) as the solid phase in the determination of cancer biomarker prostate-specific antigen. Due to the possibility of analyte preconcentration, MBs enabled achieving a limit of detection (LOD) of 4.0 pg·mL−1, representing two orders of magnitude improvement compared with equivalent microtiter plate-based assay (LOD of 460 pg·mL−1). In addition, utilizing MBs opens up the possibility of an internal standardization of the LIBS readout by employing iron spectral lines, which improves the assay robustness by compensating for LIBS signal fluctuations and bead-bound immunocomplexes lost throughout the washing steps. Finally, the practical applicability of the technique was confirmed by the successful analysis of clinical samples, showing a strong correlation with the standard electrochemiluminescence immunoassay. Overall, MB-based Tag-LIBS was confirmed as a promising immunoassay approach, combining fast readout, multiplexing possibilities, and high sensitivity approaching upconversion luminescence scanning while avoiding the requirement of luminescence properties of labels. [ABSTRACT FROM AUTHOR]

Conventional photodetectors overly pursue high light‐to‐electric conversion efficiency under weak light stimulation, while disregarding the saturated absorption‐induced blinding effect upon strong light, and achieving efficient photodetection covering a large power range remains a great challenge. In this work, MoS2/BaTiO3 heterostructures are constructed through a low‐cost exfoliation and transfer method combined with spin‐coating. The photoresponse behaviors before and after assembling the BaTiO3 nanoparticles onto the MoS2 nanoflake are investigated, indicating that the high conductivity of MoS2 and ferroelectricity of BaTiO3 can complement each other to improve the photoresponse of the hetero‐integrated device, acquiring a high photoresponsivity of 17402 A W−1 under 0.2 nW irradiation, and a significant 570 µA photocurrent under 8 mW irradiation, realizing a large linear dynamic range index of 152 dB, which is at the top level among layered semiconductor‐based detectors. Moreover, strong power near‐infrared light can be up‐converted to the visible band through the nonlinear effect of BaTiO3, subsequently absorbed by the MoS2 and contributing to the photocurrent, providing a solution to combat and alleviate the saturated absorption issue in photodetection. This work marks a significant advancement in achieving robust high‐performance photodetection by hetero‐integrating 2D materials with ferroelectrics. [ABSTRACT FROM AUTHOR]

[Display omitted] • The design of active and inert shell in NaYF 4 :Yb,Er @ NaYF 4 UCNPs exhibits the superior luminescence under 980 nm excitation. • NaYF 4 @NaYF 4 :Yb,Nd,Er core–shell UCNPs demonstrate optimized luminescence under 808 nm laser excitation because the inert core can bring the activators into closer proximity with each other. • NaYbF 4 as an active layer improves temperature sensitivity with S r = 1.12 %K−1 under 808 nm excitation. Research on the core–shell design of rare earth-doped nanoparticles has recently gained significant attention, particularly in exploring the synergistic effects of combining active and inert shell layers. In this study, we successfully synthesized 8 types of spherical core–shell Na-based nanoparticles to enhance the efficiency of core–shell design in upconversion luminescence and temperature sensing through the strategic arrangement of inert and active layers. The most effective upconversion luminescence was observed under 980 nm and 808 nm laser excitation using NaYF 4 inert shell NaYF 4 :Yb3+, Er3+@ NaYF 4 and NaYF 4 @ NaYF4:Yb3+, Nd3+ core–shell nanostructures. Moreover, the incorporation of the NaYbF 4 active shell structure led to a significant increase in relative sensitivity in ratio luminescence thermometry. Notably, the NaYF 4 :Yb3+, Nd3+, Er3+@ NaYbF 4 core–shell structure demonstrated the highest relative sensitivity of 1.12 %K−1. This research underscores the crucial role of inert shell layers in enhancing upconversion luminescence in core–shell structure design, while active layers play a key role in achieving high-sensitivity temperature detection capabilities. [ABSTRACT FROM AUTHOR]

Understanding the interfacial composition in heterostructures is crucial for tailoring heterogenous electrochemical and photoelectrochemical processes. This work aims to elucidate the structure of a series of Co−Fe Prussian blue analogue modified ZnO (PBA/ZnO) electrodes with interface‐sensitive vibrational sum frequency generation (VSFG) spectroscopy. Our measurements revealed, for the first time, a cyanide linkage isomerism at the PBA/ZnO interface, when the composite is fabricated at elevated temperatures. In situ VSFG spectro‐electrochemistry measurements correlate the CoII→CoIII oxidation with the flip of the bridging CN ligand from Co−NC−Fe coordination mode to a Co−CN−Fe one. Photoluminescence measurements and X‐ray photoelectron spectroscopy reveal that this unprecedented linkage isomerism originates from surface defects, which act as oxidation sites for the PBA. The presence of such surface defects is correlated with the fabrication temperature for PBA/ZnO. Thus, this contribution identifies the interplay between the surface states of the ZnO substrates and the chemical composition of PBA at the ZnO surface, suggesting an easily accessible approach to control the chemical composition of the interface. [ABSTRACT FROM AUTHOR]

Cubic and hexagonal structured SrTa4O11(STO):Er3+/Yb3+ phosphors were synthesized by a solid state reaction (SSR) and molten salt synthesis (MSS). The upconversion luminescence (UCL) intensity of these samples was investigated. Hexagonal STO:Er3+/Yb3+ with much or a little β-Ta2O5 can be synthesized by SSR in air or vacuum, respectively, and the UCL intensity of the sample synthesized by SSR in a vacuum is higher. Cubic STO:Er3+/Yb3+ can be synthesized by MSS with KCl flux, and hexagonal STO:Er3+/Yb3+ can be synthesized by MSS with B2O3 flux, which has the strongest UCL intensity among all the samples compared with samples prepared by SSR. The sample by MSS with B2O3 flux was acid pickled (AP) with HCl solution, and the green UCL intensity increased by 2.18 times, which reached 32.95% for β-NaYF4:Er3+/Yb3+. The UCL intensity of the hexagonal STO:Er3+/Yb3+ is much higher than that of the cubic structure, which is due to the layered structure and the non-central symmetry of the Er3+/Yb3+ doped sites in hexagonal STO:Er3+/Yb3+. The temperature sensitivity of samples is evaluated by luminescence intensity ratio (LIR) technology. The maximum relative sensitivity is 0.0099 K−1 at 303 K. All the results show that hexagonal STO:Er3+/Yb3+ has excellent pure green UCL intensity and high temperature sensitivity, which can be used in UCL display and temperature sensing. [ABSTRACT FROM AUTHOR]

Lanthanide‐doped nanoparticles (NPs) exhibit temperature‐dependent luminescence, enabling the design of luminescent nanothermometers for industrial and medical applications. This research demonstrates the temperature‐sensing properties of NaYF4:7.5%Er3+@NaYF4 and NaErF4@NaYF4 NPs, which have a hexagonal shape and average size of 17 nm. Their core@shell structure is confirmed using high‐resolution transmission electron microscopy, and they exhibit intense upconversion (UC) emission under 1532 nm excitation in H2O and D2O colloids. The recorded spectra show Er3+ emission bands with varying intensity ratios depending on the Er3+ concentration, chosen solvent, and temperature. The spectroscopic properties of the studied NPs allow for their excitation and observation of emission within biological windows, which makes them useful for bio‐related applications. The emission of prepared NPs is analyzed as a function of temperature from 298 up to 358/363 K in H2O and D2O. The ratios for thermally‐coupled levels  and non‐TCLs and their relative sensitivities are studied. For the high dopant concentration sample in water, the O─H vibrations and blue shift in the absorption spectrum lead to a record relative sensitivity of 2.50% K−1 (at 363 K) for the 2H11/2/4I11/2 ratio. The use of synthesized NPs for bioimaging under 1550 nm excitation is also demonstrated to observe their accumulation in the guts of Daphnia magna. [ABSTRACT FROM AUTHOR]

NaBiF 4 :Yb3+(20 mol%),Er3+(2mol%) phosphors (NBF:Yb,Er) were synthesized by a simple precipitation method. Several NBF:Yb,Er samples were made with different Na/F ratios (from 2/16 to 6/16 and 6/24). XRD and SEM measurements indicated that all the NBF:Yb,Er phosphors presented an hexagonal phase and morphology of microbars with sizes of 1–2 μm, respectively. According to the photoluminescence measurements, these phosphors emitted red/green emission bands at 541/655 nm and their emission intensity increased ⁓10.5 and 21 times for the green and red bands, respectively, after increasing the Na/F ratio from 2/16 to 4/16. In addition, the emission color was tuned from deep-green to yellow. Moreover, the Na/F ratio was decreased from 6/16 to 6/24, this in turn, changed the color emission from deep-green to orange. This last change of color occurred because the red emission was mainly favored by the following two cross relaxation (CR) processes CR 1 : 4I 11/2 (Er3+)+ 4F 7/2 (Er3+)→4F 9/2 (Er3+)+ 4F 9/2 (Er3+) and CR 2 : 4S 3/2 (Er3+)+ 2F 7/2 (Yb3+)→4I 13/2 (Er3+)+ 2F 5/2 (Yb3+). The second CR 2 process also promoted the NIR emission at 1527 nm. Additionally, the lifetimes for the green and red bands increased from 393 to 420 μs and from 428 to 518 μs with the Na/F ratio, respectively. Thus, we presented here a new strategy to enhance the photoluminescence intensity and to control the emission-color/lifetimes without using extra co-dopants (as previously reported in literature). [ABSTRACT FROM AUTHOR]

Visible‐to‐ultraviolet (UV) upconversion provides a fascinating strategy to achieve deep UV emission through readily accessible visible light. However, the intensity of deep UV emission obtained through visible‐to‐UV upconversion progress is still far from satisfactory, severely constraining its practical applications. Herein, a novel class of praseodymium ion (Pr3+)‐doped rare‐earth oxyhalides (YOCl, YOBr, and LuOBr) to achieve efficient upconverted deep UV emission in the spectral range of 250–350 nm is developed. The upconverted UV emission intensity of LuOBr:Pr3+ is determined to be 56.7 times stronger than that of the well‐established Lu7O6F9:Pr3+. When employed as a photon‐converter to activate photocatalytic water splitting reactions, upconverted deep UV emission enables H2 generation under visible light (λ > 420 nm) excitation from a xenon lamp. The efficient deep UV upconversion stems from tuning 4f15d1 state of Pr3+ by oxyhalide constituent which both facilitates the absorption of excitation photons in long‐lived intermediate 4f2 states and suppress the probability of nonradiative relaxation from 4f15d1 state. These findings not only provide new insights into a mechanistic understanding of the host effect on upconversion process but also make a breakthrough in developing efficient deep upconversion materials that will expand their further applications. [ABSTRACT FROM AUTHOR]

Triplet‐triplet annihilation upconversion (TTA‐UC) is a photophysical process in which two low‐energy photons are converted into one higher‐energy photon. This type of upconversion requires two species: a sensitizer that absorbs low‐energy light and transfers its energy to an annihilator, which emits higher‐energy light after TTA. In spite of the multitude of applications of TTA‐UC, few families of annihilators have been explored. In this work, we show dipyrrolonaphthyridinediones (DPNDs) can act as annihilators in TTA‐UC. We found that structural changes to DPND dramatically increase its upconversion quantum yield (UCQY). Our optimized DPND annihilator demonstrates a high maximum internal UCQY of 9.4 %, outperforming the UCQY of commonly used near‐infrared‐to‐visible annihilator rubrene by almost double. [ABSTRACT FROM AUTHOR]

The security monitoring of valuables is a crucial concern to ensure the stable development of human social business activities, scientific research, production, and daily life. The implementation of security precautions has traditionally involved the mere placement of items in safes. However, the formidable task of ascertaining whether valuables have been compromised during storage remains a significant challenge. Photochromic materials are important intelligent substances that can be employed as a potential candidates for security monitoring. However, previous studies have predominantly focused on achieving prominent photochromism by utilizing specific light sources such as ultraviolet, laser, and X‐ray radiation. In light of these existing challenges, a design strategy engaging high entropy is proposed to improve the photochromic performance. By selecting a diverse range of volatile metal elements, the A‐site high entropy is realized within the ABO3 perovskite structure, enabling the construction of various defects. This results in the successful realization of the material's sensitive response to sunlight, thereby validating the feasibility of the photochromism boosted by a high entropy strategy. The developed photochromic materials for intrusion indication demonstrate the capability to operate autonomously, making it a crucial component in high‐level security monitoring systems and presenting a novel approach toward enhancing security protection in traditional domains. [ABSTRACT FROM AUTHOR]

Excitation wavelength controllable lanthanide upconversion allows for real-time manipulation of luminescent color in a composition-fixed material, which has been proven to be conducive to a variety of applications, such as optical anti-counterfeiting and information security. However, current available materials highly rely on the elaborate core–shell structure in order to ensure efficient excitation-dependent energy transfer routes. Herein, multicolor upconversion luminescence in response to both near-infrared I and near-infrared II (NIR-I and NIR-II) excitations is realized in a novel but simple NaYGeO4:Yb3+/Er3+ phosphor. The remarkably enhanced red emission ratio under 1532 nm excitation, compared with that under 980 nm excitation, could be attributed to the Yb3+-mediated cross-relaxation energy transfers. Moreover, multi-wavelength excitable temperature-dependent (295–823 K) upconversion luminescence realizes a ratiometric thermometry relying on the thermally coupled levels (TCLs) of Er3+. Detailed investigations demonstrate that changing excitation wavelength makes little difference for the performances of TCL-based ratiometric thermometry of NaYGeO4:Yb3+/Er3+. These findings gain more insights to manipulate cross-relaxations for excitation controllable upconversion in single activator doped materials and benefit the cognition of the effect of excitation wavelength on ratiometric luminescence thermometry. [ABSTRACT FROM AUTHOR]

[Display omitted] Optical information encryption with high encoding capacities can significantly boost the security level of anti-counterfeiting in the scenario of guaranteeing the authenticity of a wide scope of common and luxury goods. In this work, a novel counterfeiting material with high-degree complexity is fabricated by microencapsulating cholesteric liquid crystals and triplet–triplet annihilation upconversion fluorophores to integrate structural coloration with fluorescence and upconversion photoluminescence. Moreover, the multimode security ink presents tailorable optical behaviors and programmable abilities on flexible substrates by various printing techniques, which offers distinct information encryption under different optical modes. The advanced strategy provides a practical versatile platform for high-secure-level multimode optical inks with largely enhanced encoding capacities, programmability, printability, and cost-effectiveness, which manifests enormous potentials for information encryption and anti-counterfeiting technology. [ABSTRACT FROM AUTHOR]

(Ti 1-x Si x)O 2 :Er/Yb (0 ≤ x ≤ 0.3) phosphor was synthesized using spray pyrolysis, and the upconversion (UC) properties were optimized by varying the calcination temperature and Si content (x). By introducing Si into the TiO 2 matrix, the thermal stability of titania was effectively improved, allowing the anatase phase to be maintained even when the (Ti,Si)O 2 :Er/Yb phosphor was calcined at temperatures above 800 °C. From investigating the effect of crystal size on the UC emission of (Ti,Si)O 2 :Er/Yb, it was found the optimal crystal size of Antase to achieve the highest UC emission intensity is approximately 5.5 nm, beyond which the UC intensity decreases rapidly. With increasing Si content, the crystalltie size decreased linearly and more amorphous SiO 2 domains were formed in the anatase TiO 2 matrix, which could consume Er/Yb ions to form SiO 2 :Er/Yb with low UC emission. Resultently, the UC emission intensity was significantly affected by Si content. The optimal calcination temperature and Si content to obtain the highest UC luminescence were determined as 700 °C and 10 %, respectively. The optimized (Ti,Si)O 2 :Er/Yb showed approximately 2.7 times improved UC luminescence than TiO 2 :Er/Yb. [ABSTRACT FROM AUTHOR]

Y 2 O 3 : 5%Yb3+, 0.5%Tm3+, z%Ho3+ (z = 0, 0.1, 0.5, 1.0) upconversion luminescent materials were synthesized by CO 2 laser zone melting method. The upconversion luminescence (UCL) spectra of the samples were recorded with the excitation of 980 nm laser, and the energy transfer processes among doped rare earth (RE) ions were analyzed. The introduction of Ho3+ ions into Y 2 O 3 : 5%Yb3+, 0.5%Tm3+ gave the samples four distinct UCL bands, including blue, green, red, and infrared emission bands. The temperature sensing characteristics based on the fluorescence intensity ratio (FIR) of non-thermally coupled levels (NTCLs) of Tm3+ and Ho3+ ions were studied, and the derived maximum relative sensitivity (S R) reached impressive value of 0.0138 K-1 (298 K). Compared to the materials doped with single emission center of either Tm3+ or Ho3+ ions, the luminescent material co-doped with both Tm3+ and Ho3+ ions exhibited higher sensitivity while maintaining a wide temperature measurement range. The research results indicate that Y 2 O 3 : Yb3+, Tm3+, Ho3+ upconversion phosphor promises broad application prospects in optical temperature measurement. [ABSTRACT FROM AUTHOR]

Thio-benzothioxanthene imide (BTXI) exhibits long excited state lifetime (τT = 17.7 μs) and high ISC efficiency (ΦΔ = 97%). For the first time, BTXI derivatives were used as photosensitizers for triplet–triplet annihilation upconversion, achieving the highest efficiency of 13.8%. In addition, thio-BTXI derivatives were used as photoinitiators for photopolymerization, resulting in a series of green light-activated radical polymerization systems. [ABSTRACT FROM AUTHOR]

Spatial and temporal precisely control of direction and speed is crucial for nanomotors to enable complex operations and applications in microsurgery, drug delivery, isolation of biological targets, and so on. Judicious material design involving Janus nanoparticles has been popular over the past decades, however, precise and customizable modulation of Janus structure with a specific asymmetric ratio for motion control is still challenging. In this study, a universal "interface allocation" strategy is developed for efficient and controllable preparation of Janus mesoporous silica‐coated upconversion nanoparticles (Janus UCNP@mSiO2) with precisely tuned asymmetric ratio to achieve near‐infrared (NIR)‐controlled active mobility for relieving vessel plaque. Mesoporous silica with a thickness of 50 nm is precisely coated onto the nanoparticles' surface with an optimal coverage ratio of 50% to encapsulate gas propellant. Upon exposure to upconverted blue light, the nanomotors release nitric oxide, facilitating their motion and pathologically improving atherosclerosis through endothelium‐dependent vasodilation. Experimental and theoretical simulation results demonstrate the advantages of NIR‐controlled Janus upconversion nanomotors in atherosclerosis treatment, including enhanced nanoparticle‐transmittance rate (34.83% to 85.57%) and excellent in vivo therapeutic efficacy. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation of the green ionic liquid [C₄mim][PF₆] mixed with polar benzonitrile (BNZ) solvent provides detailed insights into their structural and dynamic properties, essential for electrochemistry and materials science applications. The simulations we carried out at varying mole fractions (XBZN) reveal the mixtures' physical, structural, and dynamic properties, with radial, spatial, and combined distribution functions, highlighting the effective interaction through H-bonding involved. The simulation indicates that BZN stacks on the cation butyl tail, providing a significant explanation for the unique experimental observations (following). Adding BZN causes the mixture's liquid dynamics to increase linearly at low XBZN and exponentially at high XBZN, with a notable singular transition at 0.5XBZN. Comprehensive efforts were made to verify and support experimental sum frequency generation (SFG) spectroscopy by simulating the surface structure of the mixtures. Consequently, the simulated BZN stacking structure explains (1) the absence of the C≡N vibrational mode in the SFG spectrum for XBZN < 0.8, and (2) the gradual diminishing of the CH3 SFG signal, which disappears as XBZN approaches 0.5. Finally, this research removes a persistent ambiguity, proving that only the molecular moieties on the surface generate the SFG vibrational signal, while those in the subsurface do not. [ABSTRACT FROM AUTHOR]

Infrared up‐conversion imaging is used for frequency conversion of near and mid‐infrared photons to the visible or shorter near‐infrared wavelength range where high‐performance silicon sensors can be used for imaging in‐lieu of the cumbersome infrared counterparts. Nonlinear optical crystals are used for up‐conversion imaging, however, this typically requires long lengths, high pump power, and careful phase matching between interacting waves. To miniaturize the up‐conversion imaging device and eliminate stringent phase‐matching requirements, sub‐wavelength size optical metasurfaces are being explored as the nonlinear optical medium supporting resonances in the near‐infrared, albeit being prone to higher‐order diffraction at the up‐converted wavelengths. Here, a novel two‐dimensional (2D) layered material‐based nonlinear optical mirror (NLOM) based wide‐field up‐conversion imaging device is demonstrated with only 45 nm thick Gallium Selenide (GaSe) layer on a gold reflector with a suitable dielectric spacer. Near‐infrared input at 1550 nm is up‐converted to 622 nm visible output in the presence of a pump beam at 1040 nm through a sum frequency generation (SFG) process. The NLOM stack is optimized using particle swarm optimization algorithm for maximizing the detected SFG signal. Image up‐conversion experiments are performed demonstrating real, Fourier‐plane imaging, and real‐time Fourier‐domain processing with good imaging fidelity and efficiency. [ABSTRACT FROM AUTHOR]

The exploration of photon avalanching (PA) luminescence in different lanthanide emitters has profound implications in plentiful frontier applications. However, studies for universal mechanisms at the nanoscale to exhibit giant nonlinear responses in various avalanching emitters are limited. Here, record‐breaking nonlinear responses up to 60th‐order in high‐lying emitting levels of various emitters at room temperature are generated by proposing a universal mechanism named energy relay‐mediated photon avalanche (enrePA). By harnessing energy from the avalanching nano‐engine through the energy relay of Yb3+ ions, the brightness of blue emissions from Tm3+ and Ho3+ can be enhanced with giant optical nonlinearity up to 60th and 38th order, respectively. Further incorporating gadolinium‐based systems, more emitters (Tb3+, Eu3+, Dy3+, Nd3+) can be activated with extreme optical nonlinearities up to 48th‐order. By expanding PA into the full‐spectrum range, the enrePA mechanism opens exciting avenues for flexible and high‐efficiency PA modulation in multilayer nanostructures, enabling the applicability of PA in more technologies such as super‐resolution imaging, lithography, and optical detection. [ABSTRACT FROM AUTHOR]

Lanthanide-ion-doped red upconversion (UC) fluorescent materials with excellent signal-to-noise ratio, stability, and red-green luminous intensity ratio have proven of tremendous research importance for biomedical, three-dimensional (3D) displays, sensors, and other sectors. In this study, xYb, 1Er: Sr 5 (PO 4) 3 F (S-FAP) (x=0–5 at%) transparent ceramics with outstanding optical quality were fabricated by hot pressing the co-precipitation powder with high sintering activity. The energy dispersive X-ray (EDX) results showed that the trivalent lanthanide ions were evenly doped into the S-FAP ceramic lattice. Increased Yb3+ doping considerably restricted the growth of ceramic grain size, which should be attributable to a decrease in sintering activity under high Yb doping conditions. The co-doping of Yb3+ successfully resulted in a significant improvement in up/down conversion efficiency via effective energy transfer mechanisms and the optimization of the electron population at the energy level of red-green emission. Furthermore, single-band red upconversion luminescence with the greatest red-green upconversion luminescence integral intensity ratio of 125.74 was discovered under 980 nm laser pumping at room temperature. The energy transition process involved in the phenomenon of the up-conversion luminescence intensity shift of red-green emission has been thoroughly examined. Finally, the noncontact optical thermometric ability based on fluorescence intensity ratio (FIR) technology showed that the maximum absolute sensitivity (Sa) of the 5Yb1Er sample in the temperature range of 320–556 K is 1.1×10−3 K−1, implying the possible use of Yb/Er-doped S-FAP transparent ceramics in the field of optical thermometers. [ABSTRACT FROM AUTHOR]

The exceptional optoelectronic properties of lead halide perovskite nanocrystals (PeNCs) in the ultraviolet and visible spectral regions have positioned them as a promising class of semiconductor materials for diverse optoelectronic and photovoltaic applications. However, their limited response to near‐infrared (NIR) light due to the intrinsic bandgap (>1.5 eV) has hindered their applications in many advanced technologies. To circumvent this limitation, it is of fundamental significance to integrate PeNCs with lanthanide‐doped upconversion nanoparticles (UCNPs) that are capable of efficiently converting low‐energy NIR photons into high‐energy ultraviolet and visible photons. By leveraging the energy transfer from UCNPs to PeNCs, this synergistic combination can not only expand the NIR responsivity range of PeNCs but also introduce novel emission profiles to upconversion luminescence with multi‐dimensional tunability (e.g., wavelength, lifetime, and polarization) under low‐to‐medium power NIR irradiation, which breaks through the inherent restrictions of individual PeNCs and UCNPs and thereby opens up new opportunities for materials and device engineering. In this review, we focus on the latest advancements in the development of PeNCs‐UCNPs nanocomposites, with an emphasis on the controlled synthesis and optical properties design for advanced optoelectronic applications such as full‐spectrum solar cells, NIR photodetectors, and multilevel anticounterfeiting. Some future efforts and prospects toward this active research field are also envisioned. [ABSTRACT FROM AUTHOR]

Three carbazole‐substituted anthracene 2CbzAn, 26CbzAn, and 246CbzAn have been developed. The introduction of these carbazole substituents could generate more triplet states with energy levels close to 2× E(T1) that could successfully facilitate the triplet‐triplet annihilation upconversion (TTA‐UC) process to achieve high upconversion quantum yield (UCQY). This observation aligns with the Adachi theory about TTA‐UC mechanisms. In organic light‐emitting diode (OLED) device investigation, in a non‐doped state show an external quantum efficiency (EQEmax) of 5.82% with exceptional pure‐blue emission (CIEy of 0.101), and the DPaNIF doped DMPPP/26CbzAn bilayer structure reaches an impressive EQEmax of 11.12%. [ABSTRACT FROM AUTHOR]

Recent vibrational sum frequency generation spectroscopic experiments [Sengupta et al., J. Phys. Chem. Lett. 13, 11391–11397 (2022)] demonstrated synergistic interfacial adsorption effects between the anionic dodecyl sulfate (DS−) and the polar, but charge-neutral hexaethylene glycol monododecyl ether (C12E6), surfactants. In this study, the interfacial adsorption thermodynamics underlying these synergistic effects are analyzed through free energy decompositions. A general decomposition method utilizing alchemical intermediate states is outlined. Combining free energy decompositions with the potential distribution theorem illuminates the statistical interpretations of correlated effects between different system components. This approach allows for the identification of the physical effects leading to synergistic adsorption thermodynamics of DS− binding to the air-C12E6-water interface. The binding properties are found to result from a combination of effects predominantly including energetic van der Waals stabilization between DS− and C12E6, as well as competing energetic and entropic effects due to changes in the interfacial water structure as a result of introducing a C12E6 monolayer into the bare air–water interface. [ABSTRACT FROM AUTHOR]

[Display omitted] Switchable emulsifiers are commonly studied at the macroscopic scale without significant insight into the molecular properties and processes underpinning their behaviour. This work aims to investigate on the molecular scale a switchable emulsifier comprising poly(methacrylic acid) (PMAA) and poly(ethylene glycol) methacrylate (PEGMA). This emulsifier forms stable oil/water emulsions at pH > 10, but the emulsion becomes unstable at pH < 3 due to droplet aggregation. It has been suggested that H-bonding between the MAA (methacrylic acid) and EG (ethylene glycol) groups is central for the switching behaviour. However, no detailed molecular understanding of the surface of the emulsifier coated droplets has been developed so far. Using sum frequency generation spectroscopy, we compared the spectra of the PMAA/PEGMA polymer deposited on a water surface under acidic (pH 2.5) and basic (pH 11.5) conditions. We found that at pH 2.5, both MAA-EG H-bonds and MAA = MAA cyclic dimers contribute to droplet aggregation in the emulsion. In contrast, at pH 11.5 deprotonation and solvation of the PMAA component lead to a polymer restructuring. As a result, the PMAA chains form a negative shell around the droplets, electrostatically stabilising the emulsion in alkaline conditions. [ABSTRACT FROM AUTHOR]

The expulsion of protein-coupled water and protein hydration enhance and attenuate the aggregation propensity of Amyloid β(1–42), respectively, leading to different degrees of aggregation. [Display omitted] Protein hydration water is essential for protein misfolding and amyloid formation, but how it directs the course of amyloid formation has yet to be elucidated. Here, we experimentally demonstrated that femtosecond sum frequency generation vibrational spectroscopy (SFG–VS) and the femtosecond IR pump–SFG probe technique can serve as powerful tools for addressing this issue. Using amyloid β(1–42) peptide as a model, we determined the transient misfolding intermediates by probing the amide band spectral features and the local hydration water changes by measuring the ultrafast vibrational dynamics of the amide I band. For the first time, we established a correlation between the dynamic change in protein hydration water and aggregation propensity. The aggregation propensity depends on the dynamic change in the hydration water, rather than the static hydration water content of the initial protein state. Water expulsion enhances the aggregation propensity and promotes amyloid formation, while protein hydration attenuates the aggregation propensity and inhibits amyloid formation. The suppression of water expulsion and protein hydration can prevent protein aggregation and stabilize proteins. These findings contribute to a better understanding of the underlying effect of hydration water on amyloid formation and protein structural stability and provide a strategy for maintaining long–term stabilization of biomolecules. [ABSTRACT FROM AUTHOR]

Thin-film lithium niobate (TFLN), also known as lithium niobate on insulator, is an important integrated optical platform due to its broad transparency window (from ultraviolet to mid-infrared) and exceptional nonlinear optical (NLO) properties. TFLN is a revolutionary technology that revitalizes micro/nano photonics based on LN, which holds prime importance in on-chip frequency conversion owing to its remarkable NLO properties. This review focuses on the optical nonlinearity of thin film lithium niobate and its applications in integrated optics. We commence with a brief overview of the TFLN platform. Followed by an introduction to the common device structures. We then present the recent advancements of TFLN in NLO frequency conversion, including χ (2) based optical frequency generation processes (second harmonic generation, sum frequency generation, and difference frequency generation, etc), frequency comb generation, and supercontinuum generation, etc. Finally, we propose future prospects for nonlinear photonic integrated circuits based on the TFLN platform. [ABSTRACT FROM AUTHOR]

A novel ratiometric luminescent nanoprobe based on UCNPs-CuMnO 2 nanoassemblies has been successfully applied to the detection of ROS in vitro and in vivo. [Display omitted] • A ratiometric luminescent nanoprobe based on UCNPs-CuMnO 2 nanoassemblies has been constructed for ROS sensing. • CuMnO 2 acts as an effective quencher to the upconversion luminescence and recognition unit for ROS. • The redox reaction between CuMnO 2 and ROS under acidic conditions, that would induce the recovery of luminescence signal. • The synthesized nanoprobe has been proved to monitor ROS level in living cells and tumor sites. • The luminescent sensor is capable of excellent performance in sensitivity, selectivity, stability, and response time. Here, we designed a ratiometric luminescent nanoprobe based on lanthanide-doped upconversion nanoparticles-CuMnO 2 nanoassemblies for rapid and sensitive detection of reactive oxygen species (ROS) levels in living cells and mouse. CuMnO 2 nanosheets exhibit a wide absorption range of 300–700 nm, overlapping with the visible-light emission of upconversion nanoparticles (UCNPs), resulting in a significant upconversion luminescence quenching. In an acidic environment, H 2 O 2 can promote the redox reaction of CuMnO 2 , leading to its dissociation from the surface of UCNPs and the restoration of upconversion luminescence. The variation in luminescence intensity ratio (UCL 475 /UCL 450) were monitored to detect ROS levels. The H 2 O 2 nanoprobe exhibited a linear response in the range of 0.314–10 μM with a detection limit of 11.3 nM. The biological tests proved the excellent biocompatibility and low toxicity of obtained UCNPs-CuMnO 2 nanoassemblies. This ratiometric luminescent nanoprobe was successfully applied for the detection of exogenous and endogenous ROS in live cells as well as in vivo ROS quantitation. The dual transition metal ions endow this probe efficient catalytic decomposition capabilities, and this sensing strategy broadens the application of UCNPs-based nanomaterials in the field of biological analysis and diagnosis. [ABSTRACT FROM AUTHOR]

Understanding the electric double layer (EDL) of the metal electrode–electrolyte interface is essential to electrochemistry and relevant disciplines. In this study, potential-dependent electrode Sum Frequency Generation (SFG) intensities of polycrystalline gold electrodes in HClO4 and H2SO4 electrolytes were thoroughly analyzed. The potential of zero charges (PZC) of the electrodes was −0.06 and 0.38 V in HClO4 and H2SO4, respectively, determined from differential capacity curves. Without specific adsorption, the total SFG intensity was dominated by the contribution from the Au surface and increased similar to that of the visible (VIS) wavelength scanning, which pushed the SFG process closer to the double resonant condition in HClO4. However, the EDL contributed about 30% SFG signal with specific adsorption in H2SO4. Below PZC, the total SFG intensity was dominated by the Au surface contribution and increased with potential at a similar slope in these two electrolytes. Around PZC, as the EDL structure became less ordered and the electric field changed direction, there would be no EDL SFG contribution. Above PZC, the total SFG intensity increased much more rapidly with potential in H2SO4 than in HClO4, which suggested that the EDL SFG contribution kept increasing with more specific adsorbed surface ions from H2SO4. [ABSTRACT FROM AUTHOR]

We computed the IR, Raman, and sum frequency generation spectra of water in the OH-stretch region by employing the quantum/classical mixed approach that consists of a vibrational spectroscopic map and molecular dynamics (MD) simulation. We carried out the MD simulation with the TIP4P, TIP4P/2005, and TIP4P/Ice models and applied the map designed for TIP4P by Skinner et al. to each MD trajectory. Although the map is not tuned for TIP4P-like models, TIP4P/2005 and TIP4P/Ice provide the best reproduction of the experimental vibrational spectra of liquid water and crystalline ice, respectively. This result demonstrates the transferability of the map from TIP4P to TIP4P/2005 and TIP4P/Ice, meaning that one can choose an appropriate TIP4P-like model to calculate the vibrational spectra of an aqueous system without rebuilding the map. [ABSTRACT FROM AUTHOR]

We design a multi-effective nanoplatform (CeO2:Nd@SiO2@CeO2:Yb,Er@SiO2-RB/MB/CD36) with down/upconversion dual-mode emissions and targeting ability in foam macrophages. Under NIR excitation, this nanoplatform can realize in vivo NIR-II imaging and PDT/PTT coordinated therapy for early AS simultaneously. [ABSTRACT FROM AUTHOR]

Upconversion detectors monolithically combining a detection unit and a light emitting unit, enables light detection and visualization in a compact structure, promising great advances in miniaturized multifunctional optoelectronics. The detection range of upconversion detectors usually covers a broadband spectrum, limiting their use in spectroscopic fields. This work investigates two wavelength‐selective upconversion detectors made with organic semiconductors to realize narrowband near‐infrared (NIR) light detection and visualization dual function. Two non‐fullerene‐based NIR‐sensitive bulk‐heterojunctions (BHJs) are exploited to make wavelength‐selective upconversion detectors, achieving peak sensitivity at 860 and 890 nm, with full width at half maximum of 125 and 170 nm, respectively. Each NIR‐sensitive BHJ comprises a donor polymer and a non‐fullerene acceptor, both of which are selectively sensitive to NIR light. The cumulative analysis of the optical properties of the absorber and current–voltage characteristics of the device indicates that the wavelength selectivity stems mainly from the wavelength‐dependent absorption. In particular, the upconversion detectors exhibit wavelength‐selective electronic and optical dual‐readouts, which are appealing for miniaturized spectroscopic applications, including health monitoring, optical communication, and microbead imaging, paving the way for practical applications. [ABSTRACT FROM AUTHOR]

Er3+/Yb3+ doped YVO4 and GdVO4 phosphors were prepared through the combustion technique and were characterized through various techniques. XRD has revealed a tetragonal structure for YVO4 and GdVO4 phosphors. The 980 nm excited upconversion emission has resulted in intense green upconversion emission from both samples. However, the GdVO4 sample has shown higher emission intensity. Photoacoustic heat generation in samples has been studied using the same 980 nm excitation, and in this case, the YVO4 phosphor has shown higher heat generation. The YVO4 phosphor again has shown lower heat dissipation and, hence, higher photo-thermal conversion efficiency upon irradiation of the sample. [ABSTRACT FROM AUTHOR]

Upconversion luminescence presents obvious advantages in optical temperature sensing, nevertheless the application in complex scenarios is limited by luminescence thermal quenching. Herein, NaYS 2 :Yb3+,Nd3+ phosphors are synthesized by the solid-gas reaction method and used for temperature sensing. A series of emissions for Nd3+ from visible to near-infrared region are achieved based on energy transfer from Yb3+ to Nd3+ under 980 nm excitation. With elevating the temperature, significant thermal enhancement effect of nearly three orders of magnitude is detected in near-infrared emission of 4F 7/2 → 4I 9/2 , which is attributed to phonon-assisted energy transfer of Yb3+→Nd3+ and the corresponding thermal population effect. The thermal behaviors of thermally coupled energy levels for 4G 7/2 /2G 9/2 and 4F 7/2 /4F 5/2 in NaYS 2 :Yb3+,Nd3+ are evaluated by luminescence intensity ratio technique. Remarkably, the optical thermometer based on the enhanced emission of 4F 7/2 /4F 5/2 shows excellent temperature measurement performance, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing. These results not only provide a pathway to realize high performance temperature sensing, but also heighten the understanding of UC emission thermal enhancement. [ABSTRACT FROM AUTHOR]

Extremely intense blue upconversion luminescence (UCL) is got in Tm3+/Yb3+ co-doped BiTa 7 O 19 (BTO) phosphors, which are synthesized by solid phase sintering. The doping concentration of Tm3+ is fixed at 7 mol%, and the concentration of Yb3+ is adjusted. When the concentration of Yb3+ is 80 mol%, the strongest blue UCL can be obtained under 980 nm laser excitation. The blue UCL integral intensity under 808 + 980 nm laser co-excitation is 1.54 times of the sum of intensity under 808 and 980 nm single excitation, respectively. Blue UCL thermal enhancement behavior was found for all the samples under 808 or 785 nm laser excitation, and blue UCL thermal quenching happened under 660, 660 + 808, and 359 nm excitations. It is demonstrated that UCL thermal enhancement behavior is caused by oxygen defects. The possible electron transition pathways are proposed under excitation with different laser wavelengths. Using the luminescence intensity branching ratio (LIR) technique, the maximum relative temperature sensitivity range is calculated to be from 0.00610 to 0.00732 K−1 at 303 K. The experimental results show that BTO:Tm3+/Yb3+ has excellent blue UCL with thermal enhancement, which can have some applications in the field of UCL display and temperature sensing in high temperature environment. [ABSTRACT FROM AUTHOR]

The KYb(MoO 4) 2 : Er3+, Y3+ phosphors were synthesized by high temperature solid state reaction method. By further doping Y3+ ions, the near-infrared (NIR, 804 nm, 4I 9/2 → 4I 15/2) luminescence of KYb(MoO 4) 2 : 0.1 % Er3+ phosphor is greatly enhanced. Based on the upconversion luminescence (UCL) spectra, the optimal doping concentration of Y3+ ions were 7.5 %. Its near-infrared UCL intensity is about 26.9 times that of undoped Y3+ ions. Through a series of characterization methods, we find that the enhancement of NIR upconversion emission is due to the generation of defect bands. It plays a crucial role in facilitating the transfer of energy from green light level (2H 11/2 , 4S 3/2) to red light level (4F 9/2) and near-infrared level. To explain the luminescence mechanism, the power dependence, UV-VI-NIR absorption spectra, excitation spectra at 804 nm and emission spectra at 380 nm were studied. In addition, the 804 nm single near-infrared UCL intensity of KYb (MoO 4) 2 : Er3+, Y3+ shows a linear variation with temperature in the temperature range of 298 K–673 K. The maximum sensitivity is 0.13 % K−1. This study provides a new method and theoretical support for the application of near-infrared UCL in optical temperature measurement. [ABSTRACT FROM AUTHOR]

The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO 3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO 3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO 3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO 3 :0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO 3 :0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source. [Display omitted] [ABSTRACT FROM AUTHOR]

The internal modification with rare earth ion doping proved to be a very effective strategy for improving the luminescent properties of NaYF 4 -based upconversion materials. However, greatly enhancing the luminescence efficiency of NaYF 4 :Yb3+/Er3+ remains a major challenge. Herein, the effects of Sn4+ doping on the structure and luminescent performance of such material were explored. The hydrothermal molten-salt method was applied to synthesize the Sn4+-doped NaYF 4 :Yb3+/Er3+ upconversion materials, and their crystal structures, morphologies, surface chemical composition and element states, and luminescence performance were characterized. It was found that Sn4+ doping can significantly enhance the luminescence intensity and tailor the chromaticity of NaYF 4 :Yb3+/Er3+. In particular, the green (G) and red (R) luminescence intensity levels of the 30 mol% Sn4+ doped material were increased by factors of 26.97 and 38.91, respectively. The R/G ratio was incremented from 0.34 for the undoped material to 0.83 for the 40 mol% Sn4+ doped counterpart. The Sn4+ doping led to the change of lattice distortion and crystal growth pattern of NaYF 4 :Yb3+/Er3+. The mechanism for Sn4+ doping to affect the luminescence properties of the prepared upconversion material was also explored. The changes in luminescence intensity levels and R/G ratios could be attributed to the highly asymmetric distorted lattice and crystal field resulting from Sn4+ doping. [ABSTRACT FROM AUTHOR]

Despite recent advancements in inorganic and organic phosphors, creating monodisperse afterglow nanocomposites (NCs) remains challenging due to the complexities of wet chemistry synthesis. Inspired by nanoinclusions in opal, we introduce a novel SiO2‐mediated carbon dot (CD) doping method for fabricating monodisperse, multifunctional afterglow NCs. This method involves growing a SiO2 shell matrix on monodisperse nanoparticles (NPs) and doping CDs into the SiO2 shell under hydrothermal conditions. Our approach preserves the monodispersity of the parent NP@SiO2 NCs while activating a green afterglow in the doped CDs with an impressive lifetime of 1.26 s. Additionally, this method is highly versatile, allowing for various core and dopant combinations to finely tune the afterglow through core‐to‐CD or CD‐to‐dye energy transfer. Our findings significantly enhance the potential of SiO2 coatings, transforming them from merely enhancing the biocompatibility of NCs to serving as a versatile matrix for emitters, facilitating afterglow generation and paving the way for new applications. [ABSTRACT FROM AUTHOR]

A donor/acceptor (D/A) heterojunction with an interfacial energetic offset is demonstrated to enable efficient exciton dissociation in organic photodetectors and upconversion devices (UCDs). Unfortunately, this approach usually encounters complicated optimization procedures and interfacial instability. Herein, we present an alternative strategy for achieving high-performing UCDs by utilizing an organic single-component near-infrared (NIR)-sensitive layer instead of a D/A heterojunction. The showcased UCD is constructed by vertically stacking an organic single-component Y6 NIR-detection unit and a quantum dot light-emitting unit. Due to the high dielectric constant and low exciton binding energy of the non-fullerene acceptor Y6, free carriers are directly and spontaneously generated upon NIR light excitation. As a result, the single-component UCD achieves a low light detection capability of 2.5 μW/cm2, a fast refresh rate of >3.8 × 104, and a high resolution exceeding 1100 dpi, providing a stable optical response to high-frequency NIR signals and high-quality NIR imaging. [ABSTRACT FROM AUTHOR]

Decoupling dynamic touch signals in the optical tactile sensors is highly desired for behavioral tactile applications yet challenging because typical optical sensors mostly measure only static normal force and use imprecise multi-image averaging for dynamic force sensing. Here, we report a highly sensitive upconversion nanocrystals-based behavioral biometric optical tactile sensor that instantaneously and quantitatively decomposes dynamic touch signals into individual components of vertical normal and lateral shear force from a single image in real-time. By mimicking the sensory architecture of human skin, the unique luminescence signal obtained is axisymmetric for static normal forces and non-axisymmetric for dynamic shear forces. Our sensor demonstrates high spatio-temporal screening of small objects and recognizes fingerprints for authentication with high spatial-temporal resolution. Using a dynamic force discrimination machine learning framework, we realized a Braille-to-Speech translation system and a next-generation dynamic biometric recognition system for handwriting. A sensitive upconversion nanocrystal-based biometric optical tactile sensor instantaneously and quantitatively decomposes dynamic touch signals into individual components of vertical normal and lateral shear force from a single image in real-time. [ABSTRACT FROM AUTHOR]

Ho3+-Yb3+ co-doped glass ceramics containing LiGd(WO 4) 2 were prepared by melt crystallization method. By using the methods of differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmittance, and scanning electron microscopy (SEM), the optimal heat treatment condition for the samples was identified to be 580 °C/140 min. In these conditions, the transmittance of glass ceramic is about 75 % in the 380–780 nm range. In the upconversion emission spectra, strong green emission (543 nm) and red emission (650 nm) due to 5F 4 /5S 2 , 5F 5 →5I 8 transitions are observed at 980 nm excitation. Additionally, the optimum doping concentrations of Ho3+ and Yb3+ were 0.12 % and 0.4 %. The crystal field changes around dopant ions were analyzed using J-O theory and Eu3+ probe to explain the up-conversion luminescence enhancement of glass ceramics containing LiGd(WO 4) 2. The chrominance coordinates of 0.12 % Ho3+-0.4 % Yb3+ co-doped glass ceramics are located in the green light region, and the color purity is 95.6 %. In summary, Ho3+-Yb3+ co-doped transparent glass ceramics containing LiGd(WO 4) 2 have potential applications in infrared detection and green solid-state lasers. [ABSTRACT FROM AUTHOR]

Large-area imaging techniques in the short-wave infrared spectral region remain a pressing need. Organic light-emitting diodes and infrared photodetectors can be combined to form a near-infrared (NIR) to visible upconversion device, which has great potential to replace traditional infrared imaging systems. The integration of a white organic light-emitting diode (WOLED) with infrared photodetectors has become essential to realize full-color displays for its simple preparation process and high compatibility. This work has designed and optimized a WOLED to achieve stable emission with high brightness (19 470 cd m−2) and high external quantum efficiency (EQE = 18.08%) at a wide voltage range, thereby reducing chromaticity drift caused by voltage fluctuations. Moreover, photon-generated holes in the NIR-sensitive photodetector are able to inject into the WOLED for visible light emission. Consequently, we have obtained a high-performance upconversion device with a luminance on-off ratio exceeding 5 × 103 at 850 nm NIR and a high color stability over a wide range of operating voltage. Our efforts have accomplished a high-performance upconversion device from NIR to white visible light, laying the groundwork for a preliminary exploration of full-color displays. [ABSTRACT FROM AUTHOR]

The magnetoelectric (ME) sensor is a new and promising type of magnetic field sensor with ultrahigh sensitivity. However, there are few reports on the research of real‐time measurement system which can promote its practical application. Herein, a novel real‐time measuring approach for weak AC magnetic fields at relatively low frequency is proposed using Metglas/PZT‐5B ME sensors. The system mainly consists of an oscilloscope, a signal generator, and a program developed with LabVIEW programming. Real‐time measurement of relatively low‐frequency magnetic fields has been achieved by using frequency upconversion methods, simultaneously displaying the frequency and magnitude of the magnetic field. As a result, the real‐time measurement system is able to detect a weak AC magnetic field as low as 0.1 nT@1 Hz, which is promising to push the ME sensor to practical application. [ABSTRACT FROM AUTHOR]

Upconversion nanoparticles (UCNPs) are well-reported for bioimaging. However, their applications are limited by low luminescence intensity. To enhance the intensity, often the UCNPs are coated with macromolecules or excited with high laser power, which is detrimental to their long-term biological applications. Herein, we report a novel approach to prepare co-doped CaF2:Yb3+ (20%), Er3+ with varying concentrations of Er (2%, 2.5%, 3%, and 5%) at ambient temperature with minimal surfactant and high-pressure homogenization. Strong luminescence and effective red emission of the UCNPs were seen even at low power and without functionalization. X-ray diffraction (XRD) of UCNPs revealed the formation of highly crystalline, single-phase cubic fluorite-type nanostructures, and transmission electron microscopy (TEM) showed co-doped UCNPs are of ~ 12 nm. The successful doping of Yb and Er was evident from TEM–energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy (XPS) studies. Photoluminescence studies of UCNPs revealed the effect of phonon coupling between host lattice (CaF2), sensitizer (Yb3+), and activator (Er3+). They exhibited tunable upconversion luminescence (UCL) under irradiation of near-infrared (NIR) light (980 nm) at low laser powers (0.28–0.7 W). The UCL properties increased until 3% doping of Er3+ ions, after which quenching of UCL was observed with higher Er3+ ion concentration, probably due to non-radiative energy transfer and cross-relaxation between Yb3+-Er3+ and Er3+-Er3+ ions. The decay studies aligned with the above observation and showed the dependence of UCL on Er3+ concentration. Further, the UCNPs exhibited strong red emission under irradiation of 980 nm light and retained their red luminescence upon internalization into cancer cell lines, as evident from confocal microscopic imaging. The present study demonstrated an effective approach to designing UCNPs with tunable luminescence properties and their capability for cellular imaging under low laser power. [ABSTRACT FROM AUTHOR]

Femtosecond fluorescence upconversion experiments were combined with CASPT2 and time dependent DFT calculations to characterize the excited state dynamics of the mutagenic etheno adduct 1,N2‐etheno‐2'‐deoxyguanosine (ϵdG). This endogenously formed lesion is attracting great interest because of its ubiquity in human tissues and its highly mutagenic properties. The ϵdG fluorescence is strongly modified with respect to that of the canonical nucleoside dG, notably by an about 6‐fold increase in fluorescence lifetime and quantum yield at neutral pH. In addition, femtosecond fluorescence upconversion experiments reveal the presence of two emission bands with maxima at 335 nm for the shorter‐lived and 425 nm for the longer‐lived. Quantum mechanical calculations rationalize these findings and provide absorption and fluorescence spectral shapes similar to the experimental ones. Two different bright minima are located on the potential energy surface of the lowest energy singlet excited state. One planar minimum, slightly more stable, is associated with the emission at 335 nm, whereas the other one, with a bent etheno ring, is associated with the red‐shifted emission. [ABSTRACT FROM AUTHOR]