Dual-mode Emission Research Articles

Endogenetic Carbon Dot Strategy within Melamine-Formaldehyde Microspheres for Multifunctional Hybrid Fluorescence/Room-Temperature Phosphorescence Applications in Dry States and Aqueous Environments.

Developing hybrid fluorescence (FL)/room-temperature phosphorescent (RTP) materials in dry-state, aqueous, and organic solvents holds paramount importance in broadening their applications. However, it is extremely challenging due to dissolved oxygen and solvent-assisted relaxation causing RTP quenching in an aqueous environment and great dependence on SiO2-based materials. Herein, an efficient endogenetic carbon dot (CD) strategy within melamine-formaldehyde (MF) microspheres to activate RTP of CDs has been proposed through the pyrolysis of isophthalic acid (IPA) molecules and branched-chain intra-microspheres. The formation mechanism of CDs@MF from molecules to CDs with a branched chain of microspheres has been systematically studied. Detailed investigations revealed that endogenetic CDs within MF microspheres strongly construct covalent and hydrogen-bonded interfacial connections, coupled with the protection provided by the microsphere shell, greatly suppressing nonradiative decay of CDs, resulting in a yellow or orange RTP duration of about 7 s that is visible to the naked eye, even in aqueous or organic environments. Three samples glowed bright white and orange light stemming from hybrid FL/RTP dual-mode emission with a quantum yield of 29%-36% and were successfully applied to single CD-based white and orange LEDs with tunable color temperature. Additionally, the CDs@MF microspheres for water-resistant advanced anticounterfeiting and time-dependent information encryption were also successfully demonstrated. It provided an effective strategy for multifunctional solvent-resistant FL/RTP microspheres by an endogenetic CD strategy.

Dual-Mode Emission and Solvent-Desorption Dependent Kinetic Properties of Crystalline-State Chemiluminescence Reaction of 9-Phenyl-10-(2-phenylethynyl)anthracene Endoperoxide.

The chemiluminescence (CL) feature and reactivity of the aromatic endoperoxide 9-phenyl-10-(2-phenylethynyl)anthracene endoperoxide (PPEA-O2) were investigated in the crystalline state. For this, PPEA-O2 crystals were prepared using dichloromethane and n-hexane. These crystals exhibited an α-phase structure containing n-hexane as a crystal solvent. The crystal structure of nonperoxidic anthracene (i.e., PPEA) was also confirmed. After optimizing heating conditions to 120 °C for the thermolytic reaction of PPEA-O2 in crystals while maintaining the solid state, its CL characteristic and reactivity were investigated. Two key findings were derived: (1) dual-mode emission with maxima at 510 and 1275 nm and (2) distinct observation of CL emission at the first 2-3 min after the start of heating owing to the rapid thermolytic reaction coupled with n-hexane desorption. The 510 and 1275 nm emissions were attributed to the PPEA excimer and 1O2 (1Δg), respectively. We proposed a mechanism involving the triplet-triplet annihilation of the excited triplet states of PPEA to explain excimer production with postulated pathways for generating these triplet states from PPEA-O2. The rapid thermolytic reaction of PPEA-O2 in α-phase crystals with simultaneous n-hexane desorption was attributed to the formation of transient vacant spaces, which increased the molecular freedom necessary for the reaction ("transient vacant space effect"). Thus, the CL of PPEA-O2 proved useful for identifying characteristic reactivity and analyzing the luminescence mechanism of aromatic endoperoxides in the crystalline state.

Unveiling the Antithermal Quenching Behavior in 0D Inorganic Metal Halide Cs2InCl5(H2O) Mediated by Upconversion Emission.

Inorganic metal halides (IMHs) often suffer from severe fluorescence thermal quenching, limiting their application at elevated temperatures. Therefore, the exploration of IMHs exhibiting antithermal quenching (ATQ) behavior is of great importance. In this study, we developed a green synthetic route using a solvent evaporation method to successfully synthesize the 0D IMHs Cs2InCl5(H2O). By precise control over the doping ratios of Sb3+, Yb3+, and Er3+, unique dual-mode emission properties are obtained. As the temperature increases, the compound exhibited downconversion and upconversion luminescence, with relative sensitivity SR-max values of 7.11% K-1 and 1.21% K-1, respectively. Particularly anomalous is the compound's manifestation of an unconventional ATQ behavior during the upconversion process. In situ structural analysis confirmed that under high-temperature conditions, the 0D Cs2InCl5(H2O) metal halide undergoes structural evolution, transitioning through a Cs3In2Cl9 phase, which is responsible for the ATQ. This study provides experimental evidence for the abnormal ATQ of 0D metal halides, offering new inspiration for the multifunctionalization of 0D metal halides in high-temperature temperature sensing and dual-mode luminescence.

Dual-mode emission optical temperature sensor and white light-emitting diodes using Ca2Mg0.01Y7.73Si6O26:0.24Bi3+, 0.02Eu3+ phosphors regulated by cation-controlled crystal fields

Efficient luminescent materials with dual functionalities for WLEDs and non-contact temperature sensing remain a challenge due to limitations in luminescence efficiency and tunability. This study addresses these challenges by engineering Ca2Y8Si6O26:Bi3+ phosphors through strategic cation substitution (Ba2+, Mg2+, Lu3+, and Sc3+) and Eu3+ co-doping. The results reveal that cation substitution improves the crystal structure and enhances Bi3+ ion luminescence intensity, while Eu3+ doping introduces a red emission component, enabling single-component warm white light emission.The optimized phosphor composition, Ca2Y7.76Si6O26:0.24Bi3+, exhibits strong excitation at 332 nm and an emission peak at 499 nm. With Mg2+ and Eu3+ co-doping, Ca2Mg0.01Y7.73Si6O26:0.24Bi3+, 0.02Eu3+ achieves dual-mode temperature sensing with high sensitivity values of 0.006 % (499 nm/422 nm) and 0.029 % (618 nm/422 nm). Additionally, colorimetric analysis demonstrates a tunable shift towards warm white light emission with increasing Eu3+ concentrations.These findings underscore the potential of Ca2Mg0.01Y7.73Si6O26:0.24Bi3+, 0.02Eu3+ phosphors as a scalable solution for advancing high-performance single-component WLEDs and dual-mode temperature sensors. This research provides a practical pathway to overcoming current limitations in solid-state lighting and temperature monitoring technologies.

Hierarchical Dual-Mode Efficient Tunable Afterglow via J-Aggregates in Single-Phosphor-Doped Polymer.

The development of polymer-based persistent luminescence materials with color-tunable organic afterglow and multiple responses is highly desirable for applications in anti-counterfeiting, flexible displays, and data-storage. However, achieving efficient persistent luminescence from a single-phosphor system with multiple responses remains a challenging task. Herein, by doping 9H-pyrido[3,4-b]indole (PI2) into an amorphous polyacrylamide matrix, a hierarchical dual-mode emission system is developed, which exhibits color-tunable afterglow due to excitation-, temperature-, and humidity-dependence. Notably, the coexistence of the isolated state and J-aggregate state of the guest molecule not only provides an excitation-dependent afterglow color, but also leads to a hierarchical temperature-dependent afterglow color resulting from different thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) behaviors of the isolated and aggregated states. The complex responsiveness based on the hierarchical dual-mode emission can serve for security features through inkjet printing and ink-writing. These findings may provide further insight into the regulated persistent luminescence by isolated and aggregated phosphors in doped polymer systems and expand the scope of stimuli-responsive organic afterglow materials for broader applications.

ZBS glass synthesized containing both Eu3+-Eu2+ CsPbBr3 quantum dots with multi-color luminescence for white LEDs

In this article, zinc-borosilicate silicon（ZBS） glass containing europium (Eu) ions and CsPbBr3 quantum dots (QDs) (ZEQ) was synthesized via melting crystallization route. The composition and luminescent properties are investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD and XPS results imply that Eu 3+, Eu 2+ ions and CsPbBr3 QDs are coexisted in ZBS glass. The dual-mode emission from cyan to orange-red can be achieved by adjusting the melting temperature. Besides, the ZEQ has good water resistance, outstanding light irradiation and excellent heating-cooling cycle stability. Moreover, based on the ZEQ, the light-emitting diodes (LEDs) are designed to obtain the white light with the correlated color temperature (CCT) of 5255 K, the Coherent Infrared Energy (CIE) color coordinate of (0.337 0.313), the NSCT color gamut of 116 % and 87 % of Rec.2020. Thus, this article provides a novel material ZEQ, which is tunable luminescence and ultra-stable. The strategy provides the route that the luminescence of Eu ions and QDs can be observed at the same time, solving the difficulty of the rare earth ions entering into the QDs lattice. Moreover, the ZEQ is expected to be used as the light source for solid-state lighting and also provides valuable research results for future exploration of functional glass containing both rare-earth ions and QDs materials.

Multi-effective nanoplatform with down/upconversion dual-mode emissions for NIR-II imaging and PDT/PTT synergistic therapy of early atherosclerosis.

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.

Visible-excitable long-afterglow material with dual-mode emission of delayed fluorescence and room temperature phosphorescence

The BA@Fluo can achieve dual-mode emission of RTP and TADF, and colorful afterglow can be achieved under temperature regulation. Particularly, BA@Fluo was characterized by fluorescence discoloration, and increased quantum yield caused by grinding.

Development and standalone testing of the Air-breathing Microwave Plasma CAThode (AMPCAT)

Air-breathing electric propulsion (ABEP) refers to a spacecraft in very-low Earth orbit (VLEO) harnessing upper atmospheric air as propellant for an electric thruster. This allows the orbital altitude to be maintained via drag-compensation, removing the need for on-board propellant storage and allowing a mission lifetime which is not limited by propellant capacity. A cathode (or neutraliser) is required for the high-specific impulse electrostatic thruster designs proposed for an ABEP application. One such study is the AETHER EU H2020 project, which aims to design an ABEP system that can be tested on-ground in a VLEO-representative environment. There is therefore a need to develop a cathode for ABEP as conventional thermionic hollow cathodes are susceptible to oxygen poisoning. The Air-breathing Microwave Plasma CAThode (AMPCAT) presented here is based on a plasma electron source, using a 2.45 GHz microwave antenna directly-inserted into the plasma volume to ionise neutral air particles. This study details the cathode design and the results of iterative standalone testing, with a particular focus on: (a) the identification of a dual-mode current emission, with transition from lower- to higher-current mode with air at bias values around 70 V between the extracting anode and internal cathode surfaces, (b) a comparison of performance relative to xenon, for which the peak extracted current is 30–40% higher than air at equivalent inputs, and (c) the effect of antenna electrical isolation, using alumina shielding thicknesses in the 0.1–0.7 mm range. Standalone cathode tests demonstrate 0.8 A of stable extracted current with 0.1 mg/s mass flow rate of a 0.48O2 + 0.52N2 mixture, relative bias of 80 V and input microwave power of 70 W. To the authors’ knowledge, the demonstration of an extracted current in the 1 A order using air, without visible material degradation after several hours of operation, is a novel development in the cathode literature.

Pb2+/Mn2+ co-doped Cs2ZnBr4 microcrystals with dual-band tunable white light emission

The photoelectric properties of lead halide perovskite have been extensively investigated. However, its application in the field is greatly limited due to its poor instability and high lead content. With the aim of addressing these problems, in this study, Cs2ZnBr4:Pb2+/Mn2+ microcrystals were initially synthesized using a simple precipitation method. By manipulating the lead concentration, the emission ranging from cyan to green could be adjusted in Cs2ZnBr4:Pb2+. Co-doped Cs2ZnBr4:Pb2+/Mn2+ microcrystals with the precise regulation of the doping concentration of Pb2+ and Mn2+ were obtained through precipitation. The dual-mode emission of cyan and orange-red is successfully obtained. It is important that single white light emission is achieved in Cs2ZnBr4:Pb2+/Mn2+ microcrystals, exhibiting tunability from cold white to warm white. Moreover, Cs2ZnBr4:Pb2+/Mn2+ microcrystals are demonstrated remarkable air stability: it retains 86.27 % of the initial fluorescence intensity after 45 days in ambient conditions; it exhibits excellent UV stability, with 88.3 % of the initial fluorescence intensity maintained even after nearly 30 h of ultraviolet irradiation. Therefore, this research is anticipated to have broad applications not only in the field of solid-state lighting as UV-excited white LEDs but also in serving as a valuable reference for the exploration of low-lead halide luminescent materials.

Color-Tunable Dual-Mode Organic Afterglow for White-Light Emission and Information Encryption Based on Carbazole Doping.

Dual-mode emission materials, combining phosphorescence and delayed fluorescence, offer promising opportunities for white-light afterglow. However, the delayed fluorescence lifetime is usually significantly shorter than that of phosphorescence, limiting the duration of white-light emission. In this study, a carbazole-based host-guest system that can be activated by both ultraviolet (UV) and visible light is reported to achieve balanced phosphorescence and delayed fluorescence, resulting in a long-lived white-light afterglow. Our study demonstrated the critical role of a charge transfer state in the afterglow mechanism, where the charge separation and recombination process directly determined the lifetime of afterglow. Simultaneously, an efficient reversed intersystem crossing process was obtained between the singlet and triplet charge transfer states, which further boosted the delayed fluorescence properties of the doping system. As a result, delayed fluorescence lifetime was successfully prolonged to approach that of phosphorescence. This work presents a delayed fluorescence lifetime improvement strategy via doping method to realize durable white-light afterglow.

PH-controlled construction of 2D and 3D micro-nano hybrid carbon architectures with fluorescence/phosphorescence dual-mode emission for white-emitting diodes

Developing nanocarbon-based white-emitting diodes (WLEDs) with high energy conversion efficiency is still extremely challenging due to the issue of Kasha's rule and serious self-aggregation caused luminescent quenching of nanocarbon in a solid-state. Herein, the synergistic strategy of framework and intercalator between nanosheets and carbon dots (CDs) was adopted. Three novel 2D nanosheets, 3D nanoflowers and 3D parasa consocia-like micro-nano carbon architectures decorated with dispersive CDs were successfully fabricated through one-step hydrothermal reaction at different pH medium. The pH-regulated mechanisms of morphology and structure, via degree modulation of condensation and carbonization, were further proposed. All samples exhibited bright white emission, derived from fluorescence/phosphorescence dual-mode emission. The hybrid emission made sufficient utilization of single and triplet excitons with the quantum yield of 16%–30%. The superior white light with CIE coordinates of (0.331,0.334) was recorded for neutral sample (p-CNDs-N), ascribed to the multiple energy level transitions from polydisperse luminescence centers. The luminous efficiency was remarkably improved in HCl (p-CNDs-H) and NaOH treated samples (p-CNDs-OH), resulting from inner carbonization, external cross-linked network and the passivation of surface defect sites. This is the first example for pH-controlled fabrication of multi-dimension hybrid nanocarbon structures and pH-controlled fluorescence/phosphorescence dual-mode emission for highly efficient carbon-based WLEDs.

Synthesis of matrix-free carbon dots for information encryption, fingerprinting, and antibacterial activity

Matrix-free room-temperature phosphorescent nanomaterials have received great attention because of their applications in information encryption, optoelectronics, fingerprinting, bioimaging, and sensing. Therefore, we report matrix-free room-temperature phosphorescent carbon dots via controlled growth techniques followed by hydrothermal treatment using pyromellitic acid and urea. Two forms of carbon dots have obtained in single reaction vessels, one in aggregated and the other in solution state. The aggregated state green-phosphorescence carbon dots (GP-CDs) showed fluorescence and phosphorescence emissions at 452 nm and 511 nm, respectively. However, the remaining liquid-state carbon dots (L-CDs) displayed fluorescence only. The result illustrated that an ordered and self-protective structure has formed in GP-CDs, and this type of order has not achieved in L-CDs. The compacted and more ordered structures stabilize and induce the efficient generation of a triplet state, which is responsible for a room-temperature phosphorescent generation. Further, GP-CDs have been applied in fingerprint detection and data authentication as they showed dual mode emissions. Interestingly, the L-CDs possess − 17 mV zeta potential and exhibited potential antibacterial activity against Gram-positive and Gram-negative bacteria.

Improving quantification of renal fibrosis using Deep-DUET.

Accurate quantification of renal fibrosis has profound importance in the assessment of chronic kidney disease (CKD). Visual analysis of a biopsy stained with trichrome under the microscope by a pathologist is the gold standard for evaluation of fibrosis. Trichrome helps to highlight collagen and ultimately interstitial fibrosis. However, trichrome stains are not always reproducible, can underestimate collagen content and are not sensitive to subtle fibrotic patterns. Using the Dual-mode emission and transmission (DUET) microscopy approach, it is possible to capture both brightfield and fluorescence images from the same area of a tissue stained with hematoxylin and eosin (H&E) enabling reproducible extraction of collagen with high sensitivity and specificity. Manual extraction of spectrally overlapping collagen signals from tubular epithelial cells and red blood cells is still an intensive task. We employed a UNet++ architecture for pixel-level segmentation and quantification of collagen using 760 whole slide image (WSI) patches from six cases of varying stages of fibrosis. Our trained model (Deep-DUET) used the supervised extracted collagen mask as ground truth and was able to predict the extent of collagen signal with a MSE of 0.05 in a holdout testing set while achieving an average AUC of 0.94 for predicting regions of collagen deposits. Expanding this work to the level of the WSI can greatly improve the ability of pathologists and machine learning (ML) tools to quantify the extent of renal fibrosis reproducibly and reliably.

Structural and optical properties of composite phosphor Thx(MoO4)2/Bi2(1-x)Mo2O9; [formula omitted] doped with Ho3+/Yb3+ as a multifunctional materials

Composite phosphor’s, Thx(MoO4)2/Bi2(1-x)Mo2O9:2Ho3+/5Yb3+ have been synthesized cumulatively by facile co-precipitation process in ethylene glycol (EG) medium and subsequently placed for calcinations. Rietveld refinement of XRD patterns and FTIR analysis confirms the phase formation with a systematic variation of individual phases in dual-phase composite system [Th(MoO4)2-Orthorhombic; β-Bi2Mo2O9-Mononclinic]. Phase-dependent UV-Vis absorption of REs ions (Ho3+/Yb3+) has been observed and the difference between the optical bandgap of both phases leads to show the different aspect of the efficacy of optical properties. PL emission spectra of these phosphors show a strong green, relatively weak red and NIR emissions under λexci= 450 nm. The Yb3+ ions in the phosphor act as sensitizer and responsible for commencing the efficient UC emission, which shows nearly identical emission behavior under 980 nm excitation. Drastic changes in emission intensity (UC/DC) are observed with a relative dual-phase variation. Basically, the different crystal field scenarios around REs ions pertaining to both phases are responsible for the changes in emission intensity. The properties like dual-mode emission, phase dependent emission, color tuning properties, make them multifarious, that can be used for biological cell imaging, phototherapy, optical switching, display devices, solar cells, LEDs, etc.

NIR-II Luminescent and Multi-Responsive Rare Earth Nanocrystals for Improved Chemodynamic Therapy.

Chemodynamic therapy (CDT) based on the Fe2+-mediated Fenton reaction can amplify intracellular oxidative stress by producing toxic •OH. However, the high-dose need for Fe2+ delivery in tumors and its significant cytotoxicity to normal tissues set a challenge. Therefore, a controllable delivery to activate the Fenton reaction and enhance Fe2+ tumor accumulation has become an approach to solve this conflict. Herein, we report a rare-earth-nanocrystal (RENC)-based Fe2+ delivery system using light-control techniques and DNA nanotechnology to realize programmable Fe2+ delivery. Ferrocenes, the source of Fe2+, are modified on the surface of RENCs through pH-responsive DNAs, which are further shielded by a PEG layer to elongate blood circulation and "turn off" the cytotoxicity of ferrocene. The up-/down-conversion dual-mode emissions of RENCs endow the delivery system with both capabilities of diagnosis and delivery control. The down-conversion NIR-II fluorescence can locate tumors. Consequently, up-conversion UV light spatiotemporally activates the catalytic activity of Fe2+ by shedding off the protective PEG layer. The exposed ferrocene-DNAs not only can "turn on" Fenton catalytic activity but also respond to tumor acidity, driving cross-linking and enhanced Fe2+ enrichment in tumors by 4.5-fold. Accordingly, this novel design concept will be inspiring for developing CDT nanomedicines in the future.

Cancer bioimaging using dual mode luminescence of graphene/FA-ZnO nanocomposite based on novel green technique

Graphene based nanomaterials are explored in the field of cancer bioimaging and biomedical science and engineering. The luminescent nanostructures with a low toxicity and high photostability can be used as probes in bioimaging applications. This work is aimed to prepare graphene/folic acid-zinc oxide (GN/FA-ZnO) nanocomposite with dual-mode emissions (down-conversion and up-conversion) to be used in cancer bioimaging. The dual mode emissions offer long luminescence lifetime, multicolor emissions detected by the naked eyes after excitation and narrow band absorption and emission spectra. ZnO nanospheres and nanorods structures were prepared using co-precipitation technique and were conjugated with FA to separate the bulk graphite layers electrostatically into GN. The optical, morphological, surface charge and structural properties of the prepared nanostructures were investigated and discussed using different characterization techniques such as UV–visible spectroscopy, photoluminescence (PL) spectroscopy, scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), Zeta potential, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), and Fourier transform infrared (FTIR). GN/FA-ZnO nanocomposites were injected into Swiss albino mice implanted with Ehrlich Tumor and the bioimaging was investigated using photon imager and digital camera. The results showed clear fluorescence and confirmed that the green design of GN/FA-ZnO nanocomposite with targeting behavior was capable of selective bioimaging of the tumor. This study presented a novel dual mode emission nanocomposite for tumor targeting and is a promising strategy for the fabrication of a new design of spectral encoding.

Multifunctional optical thermometry using dual-mode green emission of CaZrO3:Er/Yb/Mo perovskite phosphors.

The weak emission intensity of rare-earth element-doped dual-mode materials leads to low-sensor sensitivity, which is a challenge in optical sensor applications. The present work achieved high-sensor sensitivity and high green color purity based on the intense green dual-mode emission of Er/Yb/Mo-doped CaZrO3 perovskite phosphors. Their structure, morphology, luminescent properties, and optical temperature sensing properties have been investigated in detail. Phosphor shows a uniform cubic morphology with an average size of approximately 1 μm. Rietveld refinement confirms the formation of single-phase orthorhombic CaZrO3. Under the excitation of 975 and 379 nm, the phosphor emits pure green up and down-conversion (UC and DC) emission at 525/546 nm corresponding to 2H11/2/4S3/2-4I15/2 transitions of Er3+ ions, respectively. Intense green UC emissions were achieved because of energy transfer (ET) from the high-energy excited state of Yb3+-MoO42- dimer to the 4F7/2 level of Er3+ ion. Furthermore, the decay kinetics of all obtained phosphors confirmed ET efficiency from Yb3+-MoO42- dimer to Er3+ ions, leading to strong green DC emission. Moreover, the DC of the obtained phosphor shows that a sensor sensitivity value of 0.697% K-1 at 303 K is higher than the UC (0.667% K-1 at 313 K) because the thermal effect generated by the DC excitation source light is ignored compared with UC luminescence. CaZrO3:Er-Yb-Mo phosphor shows intense green dual-mode emission with high green color purity, 96.50% of DC and 98% of UC emissions, and high sensitivity, making it suitable for optoelectronic devices and thermal sensor applications.

Improvement in the dual-mode multicolor luminescence of the NaAlSiO4:Er3+, Yb3+ phosphors and the mechanistic investigations

Na0.90-yAlSiO4:0.1Er3+,yYb3+ (0 ≤ y ≤ 0.007) phosphors were prepared by the solid state reaction method and their dual mode multicolor luminescence properties were systematically investigated. The phosphors were crystallized into the carnegieite polymorph of NaAlSiO4 at 1300 °C. The synthesized phosphors were characterized by using powder XRD technique, FT-IR and UV-VIS-NIR diffuse reflectance spectra. Upon 380 nm excitation, the phosphors emitted visible and NIR downconversion emission, which follows the quantum cutting process. The upconversion emission spectra, irrespective of the laser excitation wavelength (980 nm, 808 nm, or 1550 nm), show characteristics sharp green, and red emissions, from 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 transitions of Er3+, respectively. Intense green (552 nm), red (664 nm) and NIR (809 nm) emissions were observed at 980, 808 and 1550 nm laser excitation, respectively. The dual mode emission of the Na0.90-yAlSiO4:0.1Er3+,yYb3+ (0 ≤ y ≤ 0.007) phosphors is enhanced upon Yb3+ co-doping. By analyzing the dependence of upconversion emission intensities on the laser excitation power, a possible upconversion emission mechanism is proposed.

Fe/Mn Bimetal-Doped ZIF-8-Coated Luminescent Nanoparticles with Up/Downconversion Dual-Mode Emission for Tumor Self-Enhanced NIR-II Imaging and Catalytic Therapy.

ZIF-8, as an important photoresponsive metal-organic framework (MOF), holds great promise in the field of cancer theranostics owing to its versatile physiochemical properties. However, its photocatalytic anticancer application is still restricted because of the wide bandgap and specific response to ultraviolet light. Herein, we developed lanthanide-doped nanoparticles (LDNPs) coated with Fe/Mn bimetal-doped ZIF-8 (LDNPs@Fe/Mn-ZIF-8) for second near-infrared (NIR-II) imaging-guided synergistic photodynamic/chemodynamic therapy (PDT/CDT). The LDNPs were synthesized by encapsulating an optimal Yb3+/Ce3+-doped active shell on the NaErF4:Tm core to achieve dual-mode red upconversion (UC) and NIR-II downconversion (DC) emission upon NIR laser irradiation. At the optimal doping concentration, the UC and DC NIR-II emission intensities of LDNPs were increased 30.2- and 13.2-fold above those of core nanoparticles, which endowed LDNPs@Fe/Mn-ZIF-8 with an outstanding capability to carry out UC-mediated PDT and NIR-II optical imaging. In addition, the dual doping of Fe2+/Mn2+ markedly decreased the bandgap of the ZIF-8 photosensitizer from 5.1 to 1.7 eV, expanding the excitation threshold of ZIF-8 to the visible light region (∼650 nm), which enabled Fe/Mn-ZIF-8 to be efficiently excited by UC photons to achieve photocatalytic-driven PDT. Furthermore, Fe2+/Mn2+ ions could be responsively released in the tumor microenvironment through degradation of Fe/Mn-ZIF-8, thereby producing hydroxyl radicals (·OH) by Fenton/Fenton-like reactions to realize CDT. Meanwhile, the degradation of Fe/Mn-ZIF-8 endowed the nanosystems with tumor self-enhanced NIR-II imaging function, providing precise guidance for CDT/PDT.