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This work presents a novel paradigm for upconversion‐assisted ferroelectric photovoltaic devices. The system comprises a ferroelectric active layer (BiFeO3), an upconverter layer (Yb; Er‐doped ZnO), a conductive ITO‐coated glass substrate, and a reflective coating (Al) at the rear end of the glass substrate. The photovoltaic efficiency of the single‐layer BFO was found to be 0.71%. With the prescribed device model, the total solar efficiency of BiFeO3 improved significantly and touched solar conversion efficiency of 2.21%. This model's projection widens the future perspectives of device performance in emerging photovoltaic technology, mainly perovskite‐based solar cells. [ABSTRACT FROM AUTHOR]

In this study, TiO2-ZnO:Yb3+/Ho3+ upconversion phosphors are synthesized by a solid-phase reaction method and their Yb3+ concentration dependence is analyzed. The crystal structure of the phosphors is analyzed by X-ray diffractometry, where each sample is composed of Zn2TiO4 and Yb2Ti2O7. Photoluminescence characteristics are analyzed and peaks are observed at wavelengths of 539 nm (5F4, 5S2 → 5I8) and 669 nm (5F5 → 5I8). High intensity luminescence is obtained for samples with Yb = 7–8 mol%. Analysis of temperature characteristics shows absolute and relative sensitivities of 0.0052 K−1 and 0.40% K−1, respectively. The samples are found to be chemically stable, indicating that TiO2-ZnO:Yb3+/Ho3+ could be used as a temperature sensor. [ABSTRACT FROM AUTHOR]

Recent reports of upconversion and white light emission from graphitic particles warrant an explanation of the physics behind the process. A model is offered, wherein the upconversion is facilitated by photoinduced electronic structure modification allowing for multiphoton processes. As per the prediction of the model, it is experimentally shown that graphite upconverts infrared light centered around 1.31 μm (0.95 eV) to broadband white light centered around 0.85 μm (1.46 eV). The results suggest that upconversion from shortwave infrared (≈3 μm, 0.45 eV) to visible region may be possible. The experiments show that the population dynamics of the electronic states involved in this upconversion process occur in the timescale of milliseconds. [ABSTRACT FROM AUTHOR]

Fluoride-upconversion transparent ceramic materials doped with Er ions have attracted extensive interest due to their higher stability, lower phonon energy, and higher upconversion efficiency. xEr:Sr 5 (PO 4) 3 F (S-FAP) (x=0.5–5 at%) transparent ceramics have been synthesized by hot pressing sintering in this work, and the maximum optical transmittance of the sample reached 74.52 and 82.45% at 500 and 1000 nm, respectively. The XRD results of the powder and ceramic samples were consistent with the diffraction characteristics of the hexagonal S-FAP crystal structure. The SEM and TEM images of powder revealed that the morphology of the sample was composed of mostly rice grains with a diameter of around 20 nm. The XPS and EDS results confirmed the presence of Er3+ and the uniform distribution of Er elements. The thermally etched surface and cross section of ceramics revealed residual pores as the most important scattering source, and the SEM images of the ceramics show that Er doping can obviously promote the growth of the average grain size of S-FAP transparent ceramics. Furthermore, the upconversion luminescence characteristics and fluorescence lifespan of S-FAP transparent ceramics with varied Er doping concentrations were examined, as well as the upconversion luminescence process. The findings in this work indicate that Er:S-FAP transparent ceramics can be employed as a potential upconversion fluorescent material in display technology, biomedicine, temperature sensing, and other applications. • The xEr:S-FAP (x=0–0.05) transparent nanostructured ceramics with highly optical quality were prepared by hot-pressed sintering for the first time. • The microstructural characteristics, upconversion luminescence property, and mechanism of as-synthesized xEr:S-FAP transparent ceramics were investigated for the first time. • The wide visible light spectrum from red light to green light was achieved by changing the doping amount of Er3+ from 0.5 to 5 at%. [ABSTRACT FROM AUTHOR]

Photocatalytic technology exhibits promising prospects in environmental remediation owing to its sustainable and environmentally friendly advantages. Among the bismuth-rich halide oxides, Bi4O5I2 has demonstrated remarkable efficacy in dye degradation due to its favorable valence band and conduction band positions. In this study, we successfully synthesized Bi4O5I2/NaYF4:Yb,Tm composites through a solvothermal method. When exposed to visible light, the Bi4O5I2/NaYF4:Yb,Tm composite achieved an impressive degradation rate of 86.7% for RhB solution after 60min of light-induced reaction. Moreover, the incorporation of NaYF4:Yb,Tm into Bi4O5I2 extended the utilization of near-infrared (NIR) spectroscopy. Under 980nm NIR light irradiation, the degradation rate of Rhodamine B (RhB) solution by the Bi4O5I2/NaYF4:Yb,Tm composite reached 43.0% after 240min of light reaction. Free radical capture experiments confirmed that h+ and • O2− played a significant role as the primary active species in the degradation process of RhB by the Bi4O5I2/NaYF4:Yb,Tm composites. Furthermore, we explored the mechanism behind the photocatalytic degradation of RhB solution using the Bi4O5I2/NaYF4:Yb,Tm composites. Bi4O5I2/NaYF4:Yb,Tm holds great potential as a promising candidate for utilization of NIR light for photocatalytic reactions. [ABSTRACT FROM AUTHOR]

Circularly polarized luminescence (CPL)‐active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high‐energy (HE) photons for excitation to emit low‐energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion‐downshifting‐synergistic systems offers avenues for dual‐excitation or dual‐emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their synergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are promising biomarkers especially for early‐stage cancer diagnostics, but the implementation of miRNA‐based diagnostic tests is still hindered by the limitations of current analytical methods. The small size, low concentrations in biofluids and high sequence homology of miRNAs are challenges for assay development. Currently, most of the sensitive detection methods rely on enzymatic amplification steps, which complicate the analysis and can lead to biases in quantitation. Therefore, there is an increasing need to develop enzyme‐free detection methods that are sensitive, specific and user‐friendly. In this study, a simple direct hybridization assay for the DNA analogue of miR‐20a was developed. The assay is based on upconverting nanoparticle labels, which enable ultrasensitive detection, and hairpin structured probes, which provide additional hybridization stability due to base stacking. The limit of detection was 0.73 fM with plasma recoveries between 76 % and 111 %, demonstrating that the assay could be used for direct detection of miRNAs from complex sample matrices without isolation of RNA. Due to the simplicity and the excellent sensitivity for an amplification‐free method, the assay has a great potential for miRNA‐based clinical applications. [ABSTRACT FROM AUTHOR]

In this work, Yb3+ and Er3+-co-doped Sr 9 In(PO 4) 7 upconversion fluorescent materials with dual functionality were synthesized though simple high-temperature solid state method. Based on International Commission on Illumination (CIE) color coordinates, the calculation of color purity at different temperatures demonstrates the attainment of highly pure green luminescence (color purity >90 %) for the synthesized materials. The analysis of activation energy proves that synthesized materials are stable. Utilizing the fluorescence intensity ratio (FIR) of the thermally coupled energy levels (2H 11/2 , 4S 3/2) as a metric for optical sensing performance, absolute sensitivity and relative sensitivity are determined, and their maximum values are 0.44 % and 1.13 %, respectively. Inspired by the variation in CIE coordinates with temperature, thermally responsive two-dimensional barcode image was developed, demonstrating the practical application of Sr 9 In(PO 4) 7 :Yb/Er materials in the field of information security and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Photon avalanching nanoparticles (ANPs) exhibit extremely nonlinear upconverted emission valuable for subdiffraction imaging, nanoscale sensing, and optical computing. Avalanching has been demonstrated with Tm3+-, Pr3+-, or Nd3+-doped nanocrystals, but their emission is limited to a few wavelengths and materials. Here, we utilize Gd3+-assisted energy migration to tune the emission wavelengths of Tm3+-sensitized ANPs and generate highly nonlinear emission from Eu3+, Tb3+, Ho3+, and Er3+ ions. The upconversion intensities of these spectrally discrete ANPs scale with nonlinearity factor s = 10-17 under 1064 nm excitation at power densities as low as 7 kW cm-2. This strategy for imprinting avalanche behavior on remote emitters can be extended to fluorophores adjacent to ANPs, as we demonstrate with CdS/CdSe/CdS core/shell/shell quantum dots. ANPs with rationally designed energy transfer networks provide the means to transform conventional linear emitters into a highly nonlinear ones, expanding the use of photon avalanching in biological, chemical, and photonic applications.

The optical spectroscopy and the decay kinetics of samples with composition Sr3Yb(PO4)3, Sr3Y0.98Yb0.02(PO4)3, Sr3Y0.98Er0.02(PO4)3 and Sr3Yb0.98Er0.02(PO4)3 have been studied at room temperature. The presence of efficient energy transfer and migration processes has been clearly evidenced in the Sr3Yb(PO4)3 and Sr3Yb0.98Er0.02(PO4)3 materials, giving rise to strong visible upconversion upon excitation in the spectral region around 1 μm in the latter material. The strong anti-Stokes emission is connected to fast migration in the 2F5/2 level of Yb3+, due to the inefficient concentration quenching for this ion. In this class of materials, the upconversion processes could be optimized even in the presence of high concentrations of the Yb3+ sensitizer.

The pyrochlore-structured (A2B2O7) compounds have emerged as a focal point in contemporary research and materials science, captivating attention for their intriguing properties such as photoluminescence, superconductivity, ionic mobility, and potential applications in high-temperature barrier coatings. Their potential application in up- or down-conversion photoluminescence further positions them for integration into a myriad of optoelectronic and sensing devices. Building on extensive prior research, this review delves into the upconversion (UC) luminescence properties of numerous pyrochlore-structured host materials (titanates, zirconates, hafnates, and ytterbium pyrochlores), specifically those doped with rare earth ions. While these materials may share similar chemical and structural characteristics, their luminescent capabilities exhibit significant variation upon rare earth ion doping. The phase transitions of various pyrochlore-structured compounds with respect to cation ratio, the relationship between crystal structure, doping concentrations, and UC luminescent properties in pyrochlore-structured compounds are summarized in detail. Through controlled doping strategies and structural adjustments, researchers have been able to tailor the luminescence properties of pyrochlore structured compounds to meet specific application requirements. The intricate exploration of the UC luminescence properties of pyrochlore-structured compounds, especially when doped with rare earth ions, showcases the rich potential for these materials in a wide array of applications across various fields, from advanced sensing technologies to innovative optoelectronic devices, paving the way for exciting advancements in materials science and beyond.

For the first time, the preparation of 3D biophotonic scaffolds is reported. Scaffolds are prepared using the porogen burn-off technique and are capable of converting NIR to green emission, used to release nitric oxide from S-Nitroso-N-Acetylpenicillamine. NIR to green conversion is obtained by mixing CaWO4 crystals (codoped with Yb3+ and Er3+) with bioactive borosilicate glass prior to the sintering process. The scaffold fabrication process has a detrimental impact on the upconversion properties of the crystals embedded in the porous scaffold due to the formation of internal/surface crystalline defects and surface chemical bonds in the crystals. Nonetheless, we demonstrate that the brightness of the green emission, under 980 nm pumping, is sufficient to release nitric oxide from the scaffold covered with S-Nitroso-N-Acetylpenicillamine. Addition of upconverter crystals, in the bioactive scaffold, has no impact on porosity, mechanical properties, reactivity in simulated body fluid nor cytocompatibility. The progressive dissolution of the scaffold, associated with the precipitation of a reactive layer (HA), has no noticeable influence on the green emission under 980 nm pumping, showing that the development of such biophotonic scaffolds opens the path to light actuated drug release in a spatial–temporal manner, in vivo. Degradation of the up-converter particles does not lead to differences in cells viability.

High-sensitivity optical temperature measurement has attracted extensive attention in both fundamental studies and practical applications. In this study, a series of upconversion (UC) luminescence phosphors composed of NaGd(PO3)4 (NGP) doped with 20 at% Yb3+ and various concentrations of Er3+ (0.5 at% as the optimal concentration) was synthesized by high-temperature solid-state method. And their crystal structure and the distribution of lanthanide dopants were analyzed using X-ray diffraction with Rietveld refinement verifies. Under 980 nm laser excitation, the obtained phosphors show the characteristic Er3+ upconversion green and red emission bands through two-photon processes. The fluorescence intensity ratio (FIR) based on the thermal coupled states demonstrates the thermal sensing ability in a wide temperature range of 200–573 K. The thermal sensitivity is relatively high with the maximum absolute thermal sensitivity Sa of 0.53 % K−1 (523 K) and the maximum relative thermal sensitivity Sr of 2.60 % K−1. The phosphor NGP:Yb/Er also exhibits high repeatability as the thermal sensors reach 97 %. These findings postulate the potential of NGP:Yb/Er as a promising candidate in optical thermal sensing applications.

Pressure‐induced performance enhancement of a given material is an emerging phenomenon, however, among the various known examples very few enhanced properties can retain to ambient conditions. Both new structural mechanism and new material systems are the key challenge to achieve recoverable properties via pressure treatment. Herein, an "Er‐rich" erbium oxyfluoride ErOF is reported with retainable enhanced upconversion (UC) emission by high pressure treatment. The UC emission increases to more than twice the intensity of its pristine state, and followed by additional improvement to 5.1‐fold increase by heat treatment at 100 °C. The site symmetry breaking of Er3+ ions along with the crystal phase transition from R3¯$\bar{3}$m to Pnma, revealed by X‐ray diffraction, is believed to be the underlying reasons for the enhanced UC emission after release. Further, high‐resolution transmission electron microscopy (HRTEM) study reveals that the defects relieved with heat treatment might account for the UC emission enhancement in the released sample. Time‐resolved spectra and I‐P curves are measured comparatively to further illustrate the intrinsic mechanism of UC processes. The findings open up a window to advance UC performance through structure optimization by pressure engineering, thus facilitating its potential applications under ambient conditions. [ABSTRACT FROM AUTHOR]

Alkaline zirconium fluorides (AxZryFx+y, A = Li, Na, and K), featuring unique crystallographic structures, have recently emerged as a class of attractive hosts for fabricating lanthanide (Ln3+)‐doped upconversion nanocrystals (UCNCs) that exhibited distinct morphology, upconversion luminescence (UCL) performance, and physicochemical property. In this paper, for the first time the controlled preparation of Yb3+/Er3+‐doped UCNCs is reported based on the trigonal Cs2ZrF6 host, leading to tunable morphology and size of the resulting UCNCs by varying the reaction temperature and time. By further incorporating Na+ ions into the Cs2ZrF6 crystal lattice, sub‐10 nm Yb3+/Er3+/Na+ tridoped UCNCs with highly improved crystallinity and thus greatly enhanced UCL intensity are obtained. Moreover, these resulting UCNCs display abnormal thermal enhancement of UCL over a temperature range from 333 to 493 K, enabling the fabrication of supersensitive luminescent nanothermometers for temperature sensing. Based on the luminescence intensity ratio of two nonthermally coupled levels (i.e., 4F9/2 and 2H11/2) of Er3+, the as‐prepared Cs2ZrF6:Yb/Er/Na UCNCs exhibit an extremely large absolute sensitivity of 177.3% K−1 and a considerably high relative sensitivity of 1.52% K−1 at 333 K. These results unambiguously demonstrate that Cs2ZrF6 is a suitable host material for preparing small‐sized Ln3+‐doped UCNCs as nanothermometer for high‐performance ratiometric temperature sensing. [ABSTRACT FROM AUTHOR]

Photodynamic therapy (PDT) is a minimally invasive treatment for several diseases. It combines light energy with a photosensitizer (PS) to destroy the targeted cells or tissues. A PS itself is a non-toxic substance, but it becomes toxic to the target cells through the activation of light at a specific wavelength. There are some limitations of PDT, although it has been used in clinical studies for a long time. Two-photon excitation (TPE) and upconversion (UC) for PDT have been recently developed. A TPE nanoparticle-based PS combines the advantages of TPE and nanotechnology that has emerged as an attractive therapeutic agent for near-infrared red (NIR) light-excited PDT, whilst UC is also used for the NIR light-triggered drug release, activation of 'caged' imaging, or therapeutic molecules during PDT process for the diagnosis, imaging, and treatment of cancers. Methods: Nine electronic databases were searched, including WanFang Data, PubMed, Science Direct, Scopus, Web of Science, Springer Link, SciFinder, and China National Knowledge Infrastructure (CNKI), without any language constraints. TPE and UCNP were evaluated to determine if they had different effects from PDT on cancers. All eligible studies were analyzed and summarized in this review. Results: TPE-PDT and UCNP-PDT have a high cell or tissue penetration ability through the excitation of NIR light to activate PS molecules. This is much better than the conventional PDT induced by visible or ultraviolet (UV) light. These studies showed a greater PDT efficacy, which was determined by enhanced generation of reactive oxygen species (ROS) and reduced cell viability, as well as inhibited abnormal cell growth for the treatment of cancers. Conclusions: Conventional PDT involves Type I and Type II reactions for the generation of ROS in the treatment of cancer cells, but there are some limitations. Recently, TPE-PDT and UCNP-PDT have been developed to overcome these problems with the help of nanotechnology in in vitro and in vivo studies. [ABSTRACT FROM AUTHOR]

Highly transparent inorganic photochromic materials have several promising applications, especially for anti‐counterfeiting application. Enriching and enhancing the luminescent properties of perovskite by doping transition metals and rare earth elements into the host is a feasible and attractive route. Codoping of Mn2+ and Er3+ can realize novel anti‐counterfeiting properties with upconversion emission and photochromic ability within a double perovskite structure of Cs2AgInCl6.The Cs2AgInCl6: Mn2+, Er3+ single crystal can be observed in a reversible color variation from yellow to dark violet by implementing under 365, 520 nm illumination or thermal treatment. In addition, the crystal emits red and green light under the excitation of 365 nm ultraviolet and 980 nm laser, respectively. The introduction of Mn2+ endowed Cs2AgInCl6 with photochromic ability, and Mn2+ acted as a bridge for energy transfer from host excitons to Er3+, facilitating emission in the visible region. Er3+ achieve upconversion luminescence in the material through its abundant energy levels and acting synergistically with Mn2+. Herein, the Cs2AgInCl6:Mn2+, Er3+ combines various optical properties and has applications for specific anti‐counterfeiting demands. [ABSTRACT FROM AUTHOR]

The ZnS: Ho3+, Yb3+, Mn2+ nanomaterials fabricated by the co-precipitation method have the zinc-blende structure with the crystallite size about 90 ∼ 100 nm. The X-ray diffraction (XRD), the scanning electron microscope (SEM) and the transmission electron microscope (TEM) characterizations confirm that the doping of the Mn2+ has less effect on the structure of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials. With the excitation of a 978 nm laser, the upconversion (UC) emissions of the ZnS: Ho3+, Yb3+, Mn2+ nanomaterials include two emission bands located at 551 and 664 nm, which correspond to the transitions 5F4 (5S2)→5I8 and 5F5→5I8 of the Ho3+ ions. The UC emission characterization confirms that the UC emission of the ZnS: Ho3+, Yb3+ nanomaterials can be modulated by the doping of the Mn2+ ions, the increase of the incident laser power and the change of the laser pulse-width. The red emission of the ZnS: Ho3+, Yb3+ nanomaterials particle will increase significantly with the incorporation of the Mn2+ ions. The incident laser power and the laser pulse-width also can modulate the intensity ratio G/R of the green to the red. With the increase of the incident laser power, the emission intensity ratio G/R will also increase. With the increase of laser pulse-width from 0.2 to 0.8 ms, the above intensity ratio G/R will decrease significantly. The modulation between the green and red emission is due to the energy transfer from the 5F4 (5S2) state to the 5F5 state of the Ho3+ ions through the state 4T1 of the Mn2+ ions. [ABSTRACT FROM AUTHOR]

A series of BiTa7O19(BTO):Ho3+/Yb3+ phosphors were prepared by high-temperature solid state sintering, which exhibited outstanding pure green upconversion luminescence (UCL) under 980 nm laser excitation. When Ho3+ doping 10 mol%, Yb3+ has almost no concentration quenching point. By optimizing the preparation process, the phase purity of the sample can be improved. Under 980 nm laser excitation power density of 124.99 W/cm2, the UCL intensity of the optimized sample is 1.79 times that of the non-optimized sample. The maximum relative temperature sensitivity SR of 0.384% K−1 at 557 K and 0.40% K−1 at 723 K can be obtained by using luminescence intensity ratio (LIR) technique. All experiments show that BTO is an excellent UCL host, and BTO:Ho3+/Yb3+ can be used in UCL display and temperature sensing. [ABSTRACT FROM AUTHOR]

[Display omitted] Antibacterial photodynamic therapy (aPDT) is highly effective in killing bacteria, while the problem of hypoxia and limited light penetration in deep tissue has not been properly solved. In addition, few aPDT works take into account the regulation of inflammation, which is an important regulatory process after antimicrobial therapy and the final purpose of treatment. In this work, to address the above isssues, we have designed a multi-functional composite UCNPs-Ce6-Mn(CO) 5 Br@Silane (referred to as UCM@Si), which consists of several key components: Up-conversion nanoparticles (UCNPs: NaErF 4 :Tm3+@NaYF 4 :Yb3+), Chlorin e6 (Ce6) and Manganese pentacarbonyl bromide (Mn(CO) 5 Br). When exposed to near-infrared (NIR) light (980 nm), the UCNPs can emit strong red light at 655 nm which further trigger the aPDT of Ce6. The generated reactive oxygen (ROS) subsequently break the metal carbonyl bond of Mn(CO) 5 Br, leading to the production of carbon monoxide (CO) molecules as well as manganese ions (Mn2+), which further decomposes hydrogen peroxide (H 2 O 2) in the microenvironment to oxygen (O 2). Therefore, this simple nanocomposite not only provides substantial self-oxygen replenishment for enhanced aPDT, but also facilitates effective inflammation regulation via CO across a wide range of deep infections. This approach leverages the unique properties of these materials to combat bacterial infections by simultaneously killing bacteria, regulating inflammation, and enhancing the oxygen levels in the affected microenvironment. This O 2 and CO gas based aPDT treatment system offers a promising approach to comprehensively address microbial-induced infectious diseases, particularly deep infections, holding the potential clinical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Phototherapy has garnered increasing attention as it allows for precise treatment of tumor sites with its accurate spatiotemporal control. In this study, we have successfully synthesized degradable bifunctional phototherapy agents (UCNPs@mSiO 2 @MPN-MC540/DOX) based on upconversion nanoparticle (UCNPs) and metal phenolic network (MPN), serving as a novel nanoplatform for multimodal tumor treatment in the near-infrared (NIR) biological window. To address the issue of low light penetration depth, the UCNPs we synthesized exhibited efficient light conversion ability under 808 nm laser irradiation to activate the photosensitizer Merocyanine 540 (MC540) for photodynamic therapy. Simultaneously, the 808 nm NIR light can also excite the MPN layer to achieve photothermal therapy for tumors. Additionally, the MPN layer possesses the capability of self-degradation under weakly acidic conditions. Within the tumor microenvironment, the MPN layer gradually degrades, facilitating the controlled release of the chemotherapy drug doxorubicin (DOX), thus achieving pH-responsive drug release and reducing the side effects of chemotherapy. This study provides an example of NIR-excited multimodal tumor treatment and pH-responsive drug release, offering a therapy model for precise tumor therapy. [ABSTRACT FROM AUTHOR]

We report upconversion emission multicolor tuning based on mixing two kinds of lanthanide-doped NaYF4 nanoparticles. The upconversion emission can be continuously and precisely modulated by adjusting the ratio of the nanoparticles with Tm3+ and Er3+. The chromaticity coordinates of the mixed solution are calculated by upconversion fluorescence spectra, which presents linear variation under different mixing ratio. Moreover, the corresponding relational equations of chromaticity coordinate and concentration ratio are established. In this way, it is easier to achieve the desired chromaticity and provides a quantificational method to realize chrominance adjustment. [ABSTRACT FROM AUTHOR]

Cyclometalated iridium (Ir) complexes demonstrate impressive capabilities across a range of fields, including biology and photocatalysis, due to their tunable optical characteristics and structure flexibility. However, generating upconversion luminescence of Ir complexes under near‐infrared light excitation is challenging. Herein, by employing lanthanide‐doped upconversion nanoparticles (UCNPs) as the sensitizer, a new strategy is demonstrated to gain upconversion luminescence of Ir complexes via triplet energy transfer. This design relies on a rationally designed hybrid of core‐shell structured NaYbF4:Tb@NaTbF4 UCNPs and new Ir phosphonate complexes, in which UCNPs can migrate upconverted energy to the surface of nanoparticles through Tb3+‐mediated energy migration and then sensitize the upconversion luminescence of Ir complexes upon 980 nm excitation. Both experimental and theoretical investigations highlight the significance of triplet energy transfer from excited Tb3+ ions to the triplet state of Ir complexes in the sensitization of upconversion luminescence of Ir complexes. These findings may open exciting avenues for fabricating hybrid Ir materials with new functions and driving the development of UCNP‐based nanomaterials. [ABSTRACT FROM AUTHOR]

High-phase purity yttrium aluminum garnet (YAG) nanoparticles (NPs), which account for more than half of the market share in solid-state lasers, are crucial luminescent ceramic matrixes used in upconversion luminescence (UCL) applications. As is well known, the optical performance of YAG NPs is greatly influenced by their phase purity, necessitating a long-duration, high-temperature annealing process to eliminate intermediate impurity phases and subsequent inspection of the crystal phases using traditional methods such as XRD. Here, we report a convenient direct method to evaluate the phase state of YAG NPs by correlating the macroscopic UCL properties with the phase evolution process of YAG NPs, given the strong dependence of UCL on the host phase structure. Yb3+/Er3+-codoped YAG NPs were fabricated using flame spray pyrolysis (FSP), an efficient industrial mass production method. The UCL intensity ratios of 556 and 546 nm (I556/I546) for Er3+ ions are used as a key parameter to assess the YAG phase states. When the I556/I546 ratio is larger than 1.80, FSP-prepared YAG:Yb3+/Er3+ NPs undergo a complete phase transformation from amorphous to hexagonal YAlO3 (YAH) and ultimately to cubic YAG, resulting in pure cubic YAG NPs with orange-to-green UCL color modulation. Our results offer an efficient optical crystal-phase probe applied for YAG and can enable the exploration of industrial phase monitoring for other optical materials. [ABSTRACT FROM AUTHOR]

Reversible optical regulation has potential applications in optical anti-counterfeiting, storage, and catalysis. Compared to common power materials, the reverse opal structure has a larger specific surface area and an increased contact area for optical regulation, which is expected to achieve higher regulation rates. However, it is difficult to achieve reversible and repeatable regulation of the luminescent properties of photonic crystals, especially with the current research on the structural collapse of photonic crystals. In this work, WO3: Yb3+, Er3+ inverse photonic crystals were prepared by the template approach, and reversible multi-mode optical modification was investigated. Upon heat treatment in a reducing atmosphere or air, the color of the photonic crystals can reversibly change from light yellow to dark green, accompanied by changes in absorption and upconversion of luminescence intensity. The stability and fatigue resistance of this reversible optical modification ability were explored through cyclic experiments, providing potential practical applications for photocatalysis, optical information storage, and electrochromism. [ABSTRACT FROM AUTHOR]

The triplet annihilator is a critical component for triplet–triplet annihilation upconversion (TTA-UC); both the photophysical properties of the annihilator and the intermolecular orientation have pivotal effects on the overall efficiency of TTA-UC. Herein, we synthesized two supramolecular annihilators A-1 and A-2 by grafting 9,10-diphenylanthracene (DPA) fragments, which have been widely used as triplet annihilators for TTA-UC, on a macrocyclic host—pillar[5]arenes. In A-1, the orientation of the two DPA units was random, while, in A-2, the two DPA units were pushed to a parallel arrangement by intramolecular hydrogen-bonding interactions. The two compounds showed very similar photophysical properties and host–guest binding affinities toward electron-deficient guests, but showed totally different TTA-UC emissions. The UC quantum yield of A-2 could be optimized to 13.7% when an alkyl ammonia chain-attaching sensitizer S-2 was used, while, for A-1, only 5.1% was achieved. Destroying the hydrogen-bonding interactions by adding MeOH to A-2 significantly decreased the UC emissions, demonstrating that the parallel orientations of the two DPA units contributed greatly to the TTA-UC emissions. These results should be beneficial for annihilator designs and provide a new promising strategy for enhancing TTA-UC emissions. [ABSTRACT FROM AUTHOR]

Integrated photonics (IP) is an emerging technology in photonics in which optical waveguides (WGs) and devices are fabricated as an integrated structure onto the surface of a flat substrate. IP technology has the great potential for reshaping the high-speed optical communication, sensing, and imaging exploiting the benefits of miniaturization, low cost, and high efficiency. Erbium-doped waveguide technology has become a popular area of research as it is compatible with CMOS technology. This is largely due to the success of erbium-doped fiber amplifiers (EDFAs) in achieving high gain, high saturation power, and low noise figure (NF) in high-speed long-haul optical fiber links. In this paper, we report the performance enhancement of Er–Yb: co-doped waveguide amplifier (EYCDWA) for C-band (1530–1565 nm) employing backward pumping with a standard 980-nm pump in the presence of energy transfer upconversion (UC). The performance of EYCDWA is evaluated in terms of signal enhancement (relative gain), net internal gain (NIG), and NF using numerical simulations. The length of WG, ion densities of Er 3 + and Yb 3 , and excess losses are adjusted to achieve record high NIG of 11 dB/cm and signal enhancement of 15.5 dB/cm at signal wavelength of 1530 nm. Also, NF values in the range of 4.9–5.1 dB are observed for C-band wavelengths for input signal power of − 15 dBm. [ABSTRACT FROM AUTHOR]

Visible and near-infrared (NIR) upconversion luminescence (UCL) emissions originating from the BaY2F8: Yb3+, Tm3+ systems were investigated under a laser excitation at 980 nm. The BaY2F8:20 mol% Yb3+, x mol% Tm3+ and BaY2F8: y mol% Yb3+, 0.5 mol% Tm3+ phosphors showed prominent UCL at 800 and 810 nm. The optimized doping concentrations of Yb3+ and Tm3+ in the BaY2F8 host matrix were evaluated, their spectroscopic properties were determined, and studies on their temperature-dependent behaviour were carried out. The temperature-sensing properties were studied by generating the fluorescence intensity ratio (FIR) of the UCL peaks originating from the thermally-coupled energy levels of the Tm3+ ions. The Stark sublevels of 1G4 level of Tm3+ ions were utilized to estimate the temperature-sensing abilities of the phosphor. [ABSTRACT FROM AUTHOR]

The upconversion fluorescence thermometry has been recognized as one of the most promising techniques for the temperature measurement and multi-mode fluorescence temperature sensing can improve the accuracy and widen the temperature range. Herein, a fluorescence thermometry was developed based on the MgAlON: Er3+ transparent ceramic. It was demonstrated that the enrichment of Er3+ in grain boundaries increased susceptibility to temperature variations of the cross-relaxation rate, which endowed the non-thermally coupled energy levels with temperature sensing properties and led to the multi-mode thermometric capability. A novel four-mode temperature sensor based on fluorescence intensity ratios (2H 11/2 /4S 3/2 and 4F 9/2 /4S 3/2) and fluorescent lifetimes (4F 9/2 and 4S 3/2) was realized in the temperature range of 180–500 K, which brought about the maximum absolute and relative sensitivities reached 0.0258 K−1 and 2.95% K−1, respectively. This work reveals that the MgAlON: Er3+ and the grain boundary functionalization of transparent ceramics could have potential applications for fluorescence thermometry. • A novel four-mode MgAlON: Er3+ fluorescent temperature sensor was prepared. • The maximum absolute and relative sensitivities of MgAlON: Er3+ reached 0.0258 K−1 and 2.95% K−1, respectively. • The grain boundary enrichment of Er3+ makes the cross-relaxation rate temperature-sensitive, forming a multi-mode fluorescence thermometry. [ABSTRACT FROM AUTHOR]

Upconversion (UC) nanomaterials are of interest to researchers because of their excellent photostability, effective quantum efficiency and optical temperature dependence. However, most UC nanomaterials are thermally quenched, which causes optical nanothermometers to be susceptible to their own thermal effects, reducing the accuracy of temperature measurements. In this paper, NaYF4:Yb3+/Ho3+/Tm3+/Gd3+ nanorods with UC luminescence and resistance to thermal quenching are prepared through a simple hydrothermal method. The UC luminescence intensity of NaYF4:Yb3+/Ho3+/Tm3+/Gd3+ nanorods is adjusted by doping with Tm3+ ions. The luminescence intensity at each location shows different temperature dependence as the temperature increases. When the temperature reaches 573 K, the integrated luminescence intensity is three times that at 293 K. At the same time, the intensity at all temperature points in the range of 293–573 K is greater than the intensity at 293 K, which shows that the nanorods have excellent resistance to thermal quenching. In addition, the relative sensitivity (Sr) of LIR(I696/I476), LIR(I696/I541), LIR(I696/I646), LIR(I696/I802), and LIR(I541/I476) is investigated based on the luminescence intensity ratio (LIR) technique. The Sr of LIR(I696/I802) is found to have larger values in the low-temperature range, while Sr of LIR(I696/I476) has larger values in the high-temperature range. The use of LIR(I696/I802) and LIR(I696/I476) in separate temperature bands allows Sr to reach 0.93–1.67 %K−1 in the range of 293–573 K, confirming that the nanorods have high Sr over a wide temperature interval. This study indicates that the NaYF4:Yb3+/Ho3+/Tm3+/Gd3+ nanorods are promising candidates for optical thermometers with high sensitivity, wide temperature range, and resistance to thermal quenching. [ABSTRACT FROM AUTHOR]

Upconversion (UC) phosphors exhibiting luminescence color tuning (LCT) through variations in infrared excitation intensity offer great potential for high‐security anti‐counterfeiting applications. However, the current LCT capability is limited to high excitation intensities, hindering developments of non‐invasive counterfeit detection. In this study, two orders of magnitude reduction are achieved in excitation intensities for LCT in YF3:Yb/Er, accomplished by attaining an unprecedentedly efficient three‐photon excited red emission for mixing with the two‐photon excited green emission. To enable this breakthrough, deoxygenation techniques are employed during sample preparations, which surprisingly prevent concentration quenching of Yb3+ ions, facilitating efficient three‐photon excitation of the red emission for Yb3+ concentrations ≥ 30% even at excitation intensities as low as 10 mW cm−2. At excitation intensities of 100 mW cm−2, the three‐photon excitation contributes to 91–94% of the red emission, resulting in an 11–17‐fold increase in the red‐to‐green intensity ratio. This low‐excitation‐induced LCT, shifting from green to orange, showcases its potential for anti‐counterfeiting. Furthermore, present YF3:Yb/Er phosphors demonstrate an impressive UC quantum yield of 7.8%, surpassing the popular NaYF4:Yb/Er phosphor (5.6%) under the same excitation intensity of 31.8 W cm−2. These findings represent a significant advancement in highly efficient UC fluoride phosphors, promising diverse applications across various fields. [ABSTRACT FROM AUTHOR]

The development of blue/green/red tricolor upconversion (UC) phosphors under invisible light irradiation has attracted significant interest in emerging applications such as anti‐counterfeiting, three‐dimensional (3D) optical data storage, and solid‐state 3D displays. In this study, a series of LiYO2:RE3+,Yb3+ (RE = Tm, Ho, Eu) phosphors are successfully prepared via first precipitation process followed by calcination, and completely optimized for efficient tricolor UC luminescence with 980 nm laser excitation. Mechanisms involving two‐ or three‐photon absorption processes and low‐phonon‐energy‐suppressed multi‐phonon relaxation have been proposed for Ho3+(Eu3+)/Yb3+ and Tm3+/Yb3+ codoping, respectively. In addition, the RE3+ (Yb3+) concentration‐induced phase transition of the LiYO2 host is discussed for interesting possibilities in spectral regulation. Based on the broad color gamut achieved by the tricolor UC phosphor mixture, homochromatic and polychromatic metamerisms are experimentally fabricated via screen printing for high‐level anti‐counterfeiting and information security. Moreover, for a proof‐of‐concept demonstration, prototypes of 3D optical data storage and volumetric displays are constructed by embedding tricolor UC mixtures and their 3D printed patterns in polydimethylsiloxane. It is believed that the continuous exploration of tricolor UC under invisible light excitation for metamerism anti‐counterfeiting and 3D displays can promote the development of high‐level information security and advanced volumetric display technologies. [ABSTRACT FROM AUTHOR]

The lead-free ceramics K0.5Na0.5NbO3: x wt% Er3+ (x = 0, 1, 2, 3 and 4) were produced via solid-state method. The ceramic was sintered at 1100 °C to produce a pure-phase perovskite with an orthorhombic structure. No extra phases in the XRD spectra demonstrate that all the Er3+ ions have dispersed into the host lattice. At room temperature, PL emission spectra were examined under the wavelengths 488 and 980 nm. In both emission spectra, green emission bands (528 and 549 nm) and slightly faint red emission bands (662 nm) were found. Observing the effect of pump power revealed that two photons are involved in the emission process. The time decay profile indicates an average lifetime of Er3+ ions is 25.05 μs. The ferroelectric hysteresis loop at room temperature showed decent shapes with good remnant. Thus, by combining the optical and ferroelectric properties, KNN may have potential applications to be employed in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Presented is an infrared-induced sensor constructed of upconversion nanoparticles and DNAzyme for ultra-sensitive, and rapid detection of uranyl ions. The detection method eliminates the use of chemically labeled nucleic acid probes, possesses high selectivity, and a uranyl detection limit of 39 nM. The technique is successfully applied to the detection of uranyl in various water samples as well as human serum, illustrating the excellent sensitivity and specificity of the quantification platform. [ABSTRACT FROM AUTHOR]

Obtaining non-contact optical temperature sensing materials with good thermal stability and luminescent properties is one of the current research hotspots. In this work, Er3+/Yb3+ co doped CaGdAlO4:Erx,Yb0.10 (x = 0.006, 0.008, 0.010, 0.012, 0.014) single-phase phosphors were prepared by high-temperature solid-state method. For CaGdAlO4 : Erx, Yb0.10 powders with different Er3+ doping concentrations, the particle sizes range from 0.6 μm to 4.2 μm. When the samples are under 980 nm laser excitation, there exists two emission bands in the 500 * 575 nm range and one emission band in the 630 * 690 nm. The two stronger green emission bands located at 528 and 550 nm, and they could be attributed to ² H11/2→4 I15/2 and 4S3/2 →4 I15/2 transitions, while the weaker red emission band at 663 nm could be attributed to 4F9/2 →4 I15/2 transition of Er3+. The optimal upconversion luminescence intensity was obtained from CaGdAlO4 :Er0.010,Yb0.0. In the temperature range of 300 * 573 K, based on fluorescence intensity ratio FIR528/550 parameters, the absolute sensitivity SA increases from 44.4 x10-4 K-1 (@300 K) to 52.0 x 10-4 K-1 (@ 445 K), and then decreases to 49.0 x 10-4 K-1 (@ 573 K). The relative sensitivity SR decreases monotonically from 0.95 x 10-2 K-1 (@ 300 K) to 0.27 x 10-2 K-1 (@ 573 K). Furthermore, the heating-cooling cycling experiment shows that the thermal repeatability of temperature sensing for the phosphor is better than 98%. The results demonstrate that CaGdAlO4 :Er0. 010, Yb0.10 phosphors have potential applications in the field of optical temperature sensing. [ABSTRACT FROM AUTHOR]

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The luminescence properties of erbium and yttrium co‐doped cadmium difluoride with three different concentrations of yttrium were investigated. First, we synthesized single crystal samples with good optical quality using the Bridgman technique. From the optical absorption spectra, recorded at room temperature, both in the ultraviolet–visible and infrared spectral ranges, Judd–Ofelt analysis was performed based on yttrium concentrations to predict the radiative properties of Er3+ luminescent ions. For the 10% optimum concentration of yttrium, a detailed photoluminescence investigation was carried out. We mainly explored green, red, and near‐infrared fluorescence under different excitation wavelengths and presented their highlight spectroscopic characteristics. The desired transitions had relatively high emission cross‐sections both under visible and near‐infrared excitation. Optical gain followed a similar trend. Furthermore, the dynamic fluorescence study showed a significant increase in the measured lifetime under an 800 nm infrared excitation. The upconversion process under an 800 nm excitation produced quantum efficiency greater than 100% due to the contribution of more than one energy transfer mechanism. [ABSTRACT FROM AUTHOR]

The enhancement in the efficiency of triplet-triplet annihilation upconversion (TTA-UC) is mainly determined by the triplet energy transfer (TET) and triplet-triplet annihilation (TTA) between the sensitizers and annihilators. The TET process works efficiently by adjusting the concentration ratio of the sensitizers and annihilators. The efficiency of TTA is determined by the properties of the annihilator. Because TTA is a Dexter-type energy transfer and is affected by the diffusion rate, the energy levels of the excited states and the molecular size are both crucial in TTA. In this study, four isomerized dimers of 9,10-diphenlanthracene (DPA) and anthracene (An) were designed and prepared as annihilators for TTA-UC. The singlet and triplet energy levels could be adjusted by altering the connection position while maintaining the molecular weight and size. When PtOEP was used as the sensitizer, the maximum upconversion efficiency of 9-[4-(9-anthracenyl)phenyl]-10-phenylanthracene (9DPA-9An) was ∼11.18%. This is four times higher than that of 9,10-diphenyl-2,9 ' -bianthracene (2DPA-9An, 2.63%). The calculation of the energies of T1 and the higher triplet state (T3, because E (T2) is similar to the E (T1) of these dimers) for these dimers has provided insights into the underlying reasons. These indicated that the energy gap value of 2 × E (T1) - E (T3) is the determining factor for TTA efficiency. This work may provide a better understanding of the excited-state energy levels, which is crucial for designing novel annihilators to enhance the TTA-UC efficiency. [ABSTRACT FROM AUTHOR]

The goals of this work are to design and develop a technology for fabrication and study of multifunctional properties of core/shell nanoparticles (NPs) as magnetic/luminescent markers. The new hybrid core/shell Fe3O4/Gd2O3:1% Er3+, 18% Yb3+, 2.5% Mg2+, x% Nd3+ NPs doped with different concentrations of neodymium ions, where x = 0%, 0.5%, 0.75%, 1%, 2%, 4%, were synthesized by the co-precipitation method. The NPs were characterised using XRD, TEM, SEM, EDX, confocal microscopy and photoluminescence. Fe3O4 (core) consists of several 13 nm NPs. The core/shell NPs have sizes from 220 nm to 641 nm. In this latter case, the shell thicknesses were 72, 80, and 121 nm. The upconversion efficiency properties and magnetic properties of the hybrid NPs were investigated. In the core/shell NPs, the addition of Nd3+ quenches the luminescence. The magnetic response of core/shell samples is rather paramagnetic and does not differ significantly from that registered for the shell material alone. For Gd2O³:1% Er3+, 18% Yb3+ and Fe3O4/Gd2O3:1% Er3+, 18% Yb3+, 2.5% Mg2+, 0.5% Nd3+, at 300 K, the values of the magnetization registered at ~ 40 kOe are similar and equal to ~ 5.3 emu·g-1. The survivability of the HeLa tumor cells with the presence of the core/shell NPs was investigated for 24 h. The NPs are non-toxic up to a concentration of 1000 µg·ml-1 and penetrate cells in the process of endocytosis which has been confirmed by confocal microscope studies. [ABSTRACT FROM AUTHOR]

Recent reports of upconversion and white light emission from graphitic particles warrant an explanation of the physics behind the process. A model is offered, wherein the upconversion is facilitated by photoinduced electronic structure modification allowing for multiphoton processes. As per the prediction of the model, it is experimentally shown that graphite upconverts infrared light centered around 1.31 μm (0.95 eV) to broadband white light centered around 0.85 μm (1.46 eV). The results suggest that upconversion from shortwave infrared (≈3 μm, 0.45 eV) to visible region may be possible. The experiments show that the population dynamics of the electronic states involved in this upconversion process occur in the timescale of milliseconds.

The performance optimization of photoluminescent (PL) materials is a hot topic in the field of applied materials research. There are many different crystal defects in photoluminescent materials, which can have a significant impact on their optical properties. The luminescent properties and chemical stability of materials can be effectively improved by adjusting lattice defects in crystals. We systematically studied the effect of doping ions on the energy transfer upconversion mechanism in different defect crystals by changing the matrix alkali metal ions. Meanwhile, the influence mechanism of crystal defect distribution on luminescence performance is explored by adjusting the ratio of Na–Li. The PL spectra indicate that changing the alkaline ions significantly affects the luminescence performance and efficiency of UCNPs. The change in ion radius leads to substitution or gap changes in the main lattice, which may alter the symmetry and strength of the crystal field around doped RE ions, thereby altering the UCL performance. Additionally, we demonstrated the imaging capabilities of the synthesized upconversion nanoparticles (UCNPs) in cellular environments using fluorescence microscopy. The results revealed that Na0.9Li0.1LuF4–Yb, Er nanoparticles exhibited significantly enhanced fluorescence intensity in cell imaging compared to other compositions. We further investigated the mechanism by which structural defects formed by doping ions in UCNPs with different alkali metals affect energy transfer upconversion (ETU). This work emphasizes the importance of defect regulation in the ETU mechanism to improve the limitations of crystal structure on the luminescence performance and promote the future application of upconversion nanomaterials, which will provide important theoretical references for the exploration of high-performance luminescent materials in the future.