Upconversion Research Articles

Synthesis of Highly Luminescent Silica-Coated Upconversion Nanoparticles from Lanthanide Oxides or Nitrates Using Co-Precipitation and Sol-Gel Methods.

Upconversion nanoparticles (UCNPs) are under consideration for their use as bioimaging probes with enhanced optical performance for real time follow-up under non-invasive conditions. Photostable and core-shell NaYF4:Yb3+, Er3+-SiO2 UCNPs obtained by a novel and simple co-precipitation method from lanthanide nitrates or oxides were herein synthesized for the first time. The sol-gel Stöber method followed by oven or supercritical gel drying was used to confer biocompatible surface properties to UCNPs by the formation of an ultrathin silica coating. Upconversion (UC) spectra were studied to evaluate the fluorescence of UCNPs upon red/near infrared (NIR) irradiation. ζ-potential measurements, TEM analyses, XRD patterns and long-term physicochemical stability were also assessed and confirmed that the UCNPs co-precipitation synthesis is a shape- and phase-controlling approach. The bio- and hemocompatibility of the UCNPs formulation with the highest fluorescence intensity was evaluated with murine fibroblasts and human blood, respectively, and provided excellent results that endorse the efficacy of the silica gel coating. The herein synthesized UCNPs can be regarded as efficient fluorescent probes for bioimaging purposes with the high luminescence, physicochemical stability and biocompatibility required for biomedical applications.

Combustion synthesized La2O3: Er3+/Yb3+ phosphor for simultaneous upconversion emission and photo-thermal signal generation

The Er3+/Yb3+ doped La2O3 phosphor is prepared through combustion synthesis route and then studied using frequency upconversion (UC) and photoacoustic spectroscopic techniques. Prepared phosphor sample was annealed at high temperature ∼2100°C for short time and then structural and optical characterizations were performed. A photoacoustic cell was fabricated to record photoacoustic signal generation. Samples have shown strong upconversion emission at 409 nm, 523 nm, 548 nm, and 672 nm due to the 2H9/2 →4I15/2, 2H11/2 →4I15/2, 4S3/2 → 4I15/2 and 4F9/2→ 4I15/2 transitions, respectively. The photoacoustic measurement has revealed that heat generation in the sample increases in line with the increase in upconversion emission although both properties are opponent to each other. Studies show that prepared phosphor is efficient for generating strong upconversion emission as well as strong photoacoustic signal (also photo-thermal signal) and hence present dual functional sample seems useful for upconversion imaging as well as photo-thermal therapy.

Impact of nitridation on the up-conversion luminescence property of Yb3Al5O12: Er3+ phosphors upon 980 nm excitation

In this work, the nitriding method was used to improve the up-conversion (UC) luminescence intensity and temperature sensing sensitivity of phosphor materials. Yb3Al5O12: Er3+ and partially nitrided Yb3Al5O12-1.50xNx: Er3+ phosphors by using AlN as nitrogen source were prepared via solid-state reaction method. The influence of nitridation on the UC luminescence and temperature sensing properties of Yb3Al5O12: Er3+ phosphors upon 980 nm excitation were discussed. Almost pure red UC emission was obtained, and the intensity of the red UC emission of the samples was enhanced by 25 % after nitridation. Meanwhile, the absolute temperature sensitivity respectively derived from the intensity ratios of the green and red emissions increased by 5 % and 50 % after nitridation. Judd-Ofelt theory was utilized to analyze the change of the crystal field environment around Er3+ and confirmed that the introduction of N3– reduced the symmetry around Er3+ and strengthened the covalence between Er3+ and ligands, which may result in the enhancement of UC emission intensity and temperature sensing sensitivity. The experiment proved that Yb3Al5O12: Er3+ red UC phosphors had potential application in luminescence imaging and temperature sensors.

Optical temperature sensing characteristics of Yb3+/Nd3+ co-doped YAG single crystal fiber based on up-conversion luminescence

YAG: 5 mol%Yb3+/x mol%Nd3+(x = 0, 0.5, 1, 2, 4, 7) and YAG: 2 mol%Nd3+ single crystal (SC) fluorescent materials were prepared using laser heated pedestal growth (LHPG) method. The up-conversion (UC) spectra of YAG: Yb3+/Nd3+ were recorded under 980 nm laser excitation, the results show that the optimal material was obtained at 5 mol%Yb3+/2 mol%Nd3+. An integrated YAG single crystal fiber (SCF) with end 5 mol%Yb3+/2 mol%Nd3+ co-doped was prepared by the LHPG method, the temperature-dependent characteristics were measured in the range from 348 K to 1448 K. It shows that the fluorescence intensity increases and then decreases with the increase of temperature. Fluorescence intensity ratios (FIR) in Nd3+ UC spectra, including FIR1 (4F7/2/4F5/2 → 4I9/2), FIR2 (4F9/2/4F5/2 → 4I9/2) and FIR3 (4G5/2/4F9/2 → 4I9/2), vary monotonically in temperature ranges of 348–1273 K, 523–1273 K, and 673–1273 K, respectively. The maximally absolute and relative sensitivities for FIR1 were, respectively, achieved to be 2.34 × 10−3 K−1 at 738 K and 4.61 × 10−1 %K−1 at 390 K, and these values for FIR2 were accordingly achieved to be 1.19 × 10−3 K−1 at 1273 K and 4.59 × 10−1 %K−1 at 735 K, and for FIR3 they were 4.66 × 10−3 K−1 at 1273 K and 4.09 × 10−1 %K−1 at 760 K. Therefore, we believe that the fabricated YAG: Yb3+/Nd3+ fluorescent materials have favorable application potential for optical thermometer.

Self-ratiometric fluorescent platform based on upconversion nanoparticles for on-site detection of chlorpyrifos

Monitoring organophosphorus pesticides is significant for food safety assessment. Herein, we developed upconversion nanoparticles (UCNPs)-based self-ratiometric fluorescent platform for the detection of chlorpyrifos. The UCNPs have the ability to confine the detection and reference functions in one nanoparticle. Specifically, the blue upconversion (UC) emission (448 nm) in the shell layer of UCNPs is quenched by the product of the acetylcholinesterase-mediated reaction, while the red UC emission (652 nm) from the core remains constant as a self-calibrated reference signal. Employing the inhibition property of chlorpyrifos, self-proportional fluorescence is employed to detect chlorpyrifos. As proof-of-concept, test strips are fabricated by loading the UCNPs onto filter paper. Combined with the smartphone and image-processing algorithm, chlorpyrifos quantitative testing is achieved with a detection limit of 14.4843 ng mL−1. This portable platform displays anti-interference capability and high stability in the complicated matrix, making it an effective candidate for on-site application.

Th4+ Co‐doped YF3 : Yb3+, Er3+ Nanostructures for Enhanced Visible and NIR‐II Emissions and Potential Application as Cryogenic Thermometer

AbstractRemarkable enhancement in green and red upconversion (UC) emissions by 124 and 88 %, respectively was achieved whereas down‐conversion (DC) luminescence in NIR‐II region (~1540 nm) was improved by 20 % in Th4+ co‐doped YF3 : Yb3+,Er3+ nanocrystalline particles. The same is ascribed to lowering of symmetry via formation of asymmetric Er−F bonds and less symmetric Y3+ sites due to distortions on Th4+ co‐doping. Benefiting from the distinct temperature response of stark sublevels of the 4S3/2 and 4F9/2 states, we have proposed a strategy for luminescence intensity ratios (LIR) based thermometry involving thermally coupled (TCL) stark sub‐levels. This can be promising in more accurate temperature read‐out at cryogenic temperatures (~ −193 °C). Using the same, high Sa and Sr values of 0.0139 K−1 (80 K) and 0.682 % K−1(80 K) were obtained for 4S3/2 (1)/4S3/2 (2)→4I15/2 transitions. Higher Sa and Sr values of 0.226 K−1 (80 K) and 2.627 %K−1(80 K) were obtained for 4F9/2 (1)/4F9/2 (2)→4I15/2 transitions. The high sensitivity values were obtained than that reported for the YF3 host. We believe this work with improved UC luminescence on Th4+ addition will be boon to cryogenic temperature‐sensing.

A multi-mode optical thermometry based on the up-conversion La2MgGeO6: Er3+, Yb3+ phosphor

The up-conversion (UC) La2MgGeO6: Er3+, Yb3+ phosphors were prepared by a high-temperature solid-phase method. The structural phase and luminescence characteristics of the samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence spectra. The research systematically investigated a multi-mode optical thermometry based on fluorescence intensity ratios (FIR) of the thermal-coupled energy levels 2H11/2/4S3/2, non-thermal-coupled energy levels 4S3/2/4F9/2, and the fluorescence lifetime of the 4S3/2 state. Based on these methods, the maximum relative sensitivity reached 1.130%K−1, 0.623%K−1, and 2.914%K−1, respectively. According to the results, the manufactured samples have remarkable temperature measuring performance, which is characterized by a broad temperature measurement range, high sensitivity, and superior stability.

Highly stable multi-responsive yellow-emissive fluoride RbCdF3:Mn2+,Yb3+ for advanced optical anti-counterfeiting

Multi-responsive luminescent materials have significant advantages in optical anti-counterfeiting owing to the diversity of their luminescence modes. However, the development of multi-responsive luminescent materials that simultaneously exhibit more than three types of luminescence modes remains challenging. Herein, RbCdF3:Mn2+,Yb3+, a novel multi-responsive fluoride that exhibits all luminescence modes of Stokes, upconversion (UC), radioluminescence (RL), persistent luminescence (PersL), photostimulated luminescence (PSL), and thermoluminescence luminescence (TL) is developed. All modes produce bright-yellow emission (∼565 nm). Moreover, the PersL of RbCdF3:Mn2+,Yb3+ can be charged by both the high-energy X-rays and commercial 254 nm UV lamp, which is rarely observed for fluorides. Furthermore, RbCdF3:Mn2+,Yb3+ also exhibits superior luminescence stability at high temperatures and high humidity. Specifically, the emission intensity at 498 K is 141.14 % of that at room temperature, and retains 76.47 % after being dispersed in water for 50 days when excited by 254 nm light. The unique multi-responsive luminescent features and excellent environmental stability endow RbCdF3:Mn2+,Yb3+ with great potential for practical applications in advanced optical anti-counterfeiting.

Effective BPA degradation via atom-sharing Bi/Bi4O5Br2:Yb3+, Tm3+ plasma heterojunctions with enhanced charge transfer and light absorption

To achieve efficient degradation of organic pollutants, two critical objectives are enhancing photogenerated carrier separation and expanding the spectral response range. In this study, we synthesized atom-sharing Bi/Bi4O5Br2:Yb3+,Tm3+ (Bi/BYT) heterojunctions with surface plasmon resonance (SPR) effects and upconversion (UC) by employing self-sacrificial Bi4O5Br2:Yb3+,Tm3+ (BYT) fractions as a source of metallic Bi. Results revealed that the optimal Bi/BYT-2 catalyst exhibited the highest BPA degradation efficiency within 120 min, representing a significant 1.3-fold improvement over BYT alone. This outstanding catalytic performance can be attributed to the synergistic interplay between UC fluorescence, the unique SPR effect of Bi metal, and the atom-sharing heterojunction. These factors effectively broaden the spectral absorption range and significantly enhance the separation and utilization efficiency of photoinduced carriers. This study lays the groundwork for the development and design of novel atomic-level contact heterojunctions, offering insights into enhancing photocatalytic efficiency through plasmon resonance and UC fluorescence on non-precious metal surfaces.

Volumetric Temperature Mapping Using Light-Sheet Microscopy and Upconversion Fluorescence from Micro- and Nano-Rare Earth Composites.

We present a combination of light-sheet excitation and two-dimensional fluorescence intensity ratio (FIR) measurements as a simple and promising technique for three-dimensional temperature mapping. The feasibility of this approach is demonstrated with samples fabricated with sodium yttrium fluoride nanoparticles co-doped with rare-earth ytterbium and erbium ions (NaYF4:Yb3+/Er3+) incorporated into polydimethylsiloxane (PDMS) as a host material. In addition, we also evaluate the technique using lipid-coated NaYF4:Yb3+/Er3+ nanoparticles immersed in agar. The composite materials show upconverted (UC) fluorescence bands when excited by a 980 nm near-infrared laser light-sheet. Using a single CMOS camera and a pair of interferometric optical filters to specifically image the two thermally-coupled bands (at 525 and 550 nm), the two-dimensional FIR and, hence, the temperature map can be readily obtained. The proposed method can take optically sectioned (confocal-like) images with good optical resolution over relatively large samples (up to the millimetric scale) for further 3D temperature reconstruction.

Realizing Superior Luminescence in Oxyfluoride Glass‐Ceramics by Enhancing Nano‐Micro Phase Separation

AbstractIn this work, a novel series of oxyfluoride glasses‐ceramics (GCs) is developed by enhancing the phase separation through the substitution of LaF3 for La2O3. The thus‐derived GCs exhibit a remarkable 2700‐fold increase in up‐conversion (UC) luminescence of Er3+ ions compared to the precursor glass. From the 19F Nuclear Magnetic Resonance analysis, this enhancement is attributed to the structural disorder‐to‐order transition in the fluoride‐rich phase. Upon isothermal heat treatment, the translucent GCs transform into transparent ones, making UC luminescence even stronger. The enhanced UC luminescence leads to strong temperature‐sensing ability of the studied glasses. The nano‐micro phase separation is clarified by atomistic simulations and scanning electron microscopy. This study implies that phase separation engineering is a powerful way to achieve superior photonic performances.

Green upconversion luminescence of ZnO:Yb3+/Ho3+ nanophosphors prepared by various synthesis methods: Sol-gel and co-precipitation

ZnO: Yb3+/Ho3+ nanophosphors were synthesized using sol-gel and co-precipitation methods. The effects of co-doping and synthesis methods were investigated on the nanopowder's crystal structure, morphology, and optical properties. X-ray diffraction (XRD) confirmed the hexagonal wurtzite structure of the ZnO powder. The calculated crystallite sizes of the nanopowders are 30.4 nm and 21.3 nm for sol-gel and co-precipitation methods, respectively. Scanning electron microscopy (SEM) revealed that different synthesis methods and doping influence the morphology of the prepared nanophosphors. Energy dispersive X-ray spectrometer (EDS) confirmed the elemental composition and phase purity. Diffuse reflectance spectra (DRS) exhibited several absorption bands at 448 and 541 nm from sol-gel synthesized nanopowders and 453, 483, 536, and 641 nm from co-precipitation synthesized nanopowders. The energy band gap (Eg) was affected by the various methods and doping. DRS with the aid of Kubelka-Munk demonstrated that Eg ranges from 3.23 to 3.27 eV and 3.28–3.33 eV for samples prepared with sol-gel and co-precipitation method, respectively. The upconversion (UC) photoluminescence (PL) emission spectra upon excitation wavelength of 980 nm revealed two emission peaks located at 545 and 661 nm from ZnO:Yb3+/Ho3+ nanophosphors prepared by sol-gel method. These emission peaks can be attributed to 5S2/5F4 → 4I8 and 5F5 → 5I8 transitions of Ho3+ ions. The power dependence of the UC emission intensity of ZnO:Yb3+/Ho3+ was also examined. Power dependence revealed that a two-photon process was involved in the UC emissions and the possible UC mechanisms were discussed in detail. To investigate possible degradation, the stability of the UC was examined. In fact, there was no indication of phosphor UC degradation. Green emission, on the other hand, increased by about 10 % during the first 8 h of the experiment before stabilizing.

Color tunable upconversion luminescence of Er3+ -Yb3+ codoped KY3F10 prepared by a hydrothermal treatment

The KY3F10: Er3+, Yb3+ upconversion (UC) phosphor was prepared using a hydrothermal technique. The study investigated the impact of sample structure, morphology, Er3+ doping concentration, and annealing time on the UC emission properties. The results revealed that the synthesized samples had cubic KYb3F10 structures, with a block size of approximately 200–500 nm for the 12-hour annealed sample, which reduced to a grain size of 50–100 nm for the 5-hour annealed sample. Intense UC light emission was observed in the sample at 1.0%Er3+, and 10%Yb3+ doping concentration for an annealing time of 12 h. Their respective peak emissions were measured at 551 and 665 nm, with green light visible to naked eye. The color purity of the green light was estimated to be 96.7%, while the decay time for the green emission light was 557.6 ms and 716.2 ms for red emission light. When the annealing time of the 1.0% Er3+, 10% Yb3+ doping sample was shortened to 5 h, the light color changed to bluish-white. The correspounding peak emissions were measured at 479 nm, 547 nm and 654 nm. These findings suggest that the annealing time has a substantial impact on both the sample size and UC luminescence. The study also discusses the UC luminous mechanism in detail.

Improvement of upconversion and temperature sensing properties in Ho3+/Yb3+ co-doped Ca0.5Gd(WO4)2 phosphor via incorporation of Bi3+

A series of Ca0.5Gd(WO4)2: Ho3+/Yb3+/Bi3+ phosphors prepared by solid-state reaction method were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), elemental mapping, upconversion (UC) spectroscopy and decay time analysis. Under 980 nm excitation, four up-converted emission bands of Ho3+ were observed in all samples. The concentration quenching effect of the UC emission appears by changing the concentration of Ho3+ in Ca0.5Gd(WO4)2: x mol% Ho3+, 40 mol% Yb3+ and Yb3+ in Ca0.5Gd(WO4)2: 1 mol% Ho3+, y mol% Yb3+, and the optimal concentration of Ho3+ and Yb3+ were determined to be 1 and 40 mol%, respectively. Compared to Bi3+-absent sample, the upconversion luminescence (UCL) intensities of green emission (540 nm) and red emission (644 nm) in Ca0.5Gd(WO4)2: 1 mol% Ho3+, 40 mol% Yb3+ via 15 mol% Bi3+ doping were increased by 2.5 and 3.6 times, respectively. The involved UCL mechanism based on the power dependent UC emission spectra were analyzed in detail. Additionally, the temperature sensing performances based on non-thermally coupled levels (NTCLs) 5F4(5S2) → 5I8, and 5F5 → 5I8 of Ho3+ ions and thermal quenching properties of the samples were also investigated in the range of 298–573 K. The maximum relative sensitivity (SR) of Ca0.5Gd(WO4)2: 1 mol% Ho3+, 40 mol% Yb3+ and Ca0.5Gd(WO4)2: 1 mol% Ho3+, 40 mol% Yb3+, 15mol% Bi3+ reached 0.0094 K-1 and 0.0112 K−1 at 298 K, respectively. The results indicated that doping Bi3+ ions can enhance the UCL intensity and optical temperature sensing of Ca0.5Gd(WO4)2: Ho3+/Yb3+.

Multimode Luminescent Properties from Tb3+-Yb3+ Codoped CaMoO4 for Solar Cell Spectral Conversion

NIR and visible emitting CaMoO4:Tb3+/Tb3+-Yb3+ phosphors were synthesized to harness the energy losses attribute to wavelength mismatch between response spectrum of incident solar photons and solar cells. The X-ray diffraction (XRD), field emission scanning microscopy (FE-SEM), fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy, photoluminescence (PL), up-conversion and life time measurements were used to characterized the prepared phosphors. XRD study followed by Rietveld refinement confirms the tetragonal crystal structure with space group I41a(88). The phosphors exhibit strong green emission (5D4→7F4) in visible region after an excitation wavelengths 378 nm and 980 nm, respectively through down-shifting (DS) and up-conversion (UC) processes. The UV photons (378 nm) are also split it into two NIR photons (2F7/2→2F5/2) through down-conversion process. Fluorescence quenching was observed by increasing concentration of Tb3+ and Yb3+ ions. Lifetime measurements clearly illustrates the energy transfer from Tb3+ to Yb3+ ions and mechanism involved is co-operative energy transfer. The estimated values of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are achieved as 69% and 169% respectively.

Upconversion luminescence and optical thermometry behaviors of Yb3+ and Ho3+ co-doped GYTO crystal

Optical thermometry based on the upconversion (UC) luminescence intensity ratio (LIR) has attracted considerable attention because of its feasibility for achievement of accurate non-contact temperature measurement. Compared with traditional UC phosphors, optical thermometry based on UC single crystals can achieve faster response and higher sensitivity due to the stability and high thermal conductivity of the single crystals. In this study, a high-quality 5 at% Yb3+ and 1 at% Ho3+ co-doped Gd0.74Y0.2TaO4 single crystal was grown by the Czochralski (Cz) method, and the structure of the as-grown crystal was characterized. Importantly, the UC luminescent properties and optical thermometry behaviors of this crystal were revealed. Under 980 nm wavelength excitation, green and red UC luminescence lines at 550 and 650 nm and corresponding to the 5F4/5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+, respectively, were observed. The green and red UC emissions involved a two-photon mechanism, as evidenced by the analysis of power-dependent UC emission spectra. The temperature-dependent UC emission spectra were measured in the temperature range of 330–660 K to assess the optical temperature sensing behavior. At 660 K, the maximum relative sensing sensitivity (Sr) was determined to be 0.0037 K−1. These results highlight the significant potential of Yb,Ho:GYTO single crystal for optical temperature sensors.Graphical abstract

Rectangular cross-sectional Nd3+/Yb3+ co-doped AlN nanorods with strong up-conversion emission for high-sensitivity optical thermometry

Due to the characteristics of non-contact, high sensitivity and spatial resolution, nanoscale optical thermometry is necessary in many applications such as micro/nano electronics, integrated optics and biomedicine. Herein, we report the synthesis of Nd3+/Yb3+ co-doped AlN (AlN:Nd3+/Yb3+) nanorods using an arc discharge method and investigate their phase, composition and morphology using XRD, Raman, XPS, EDS, ICP, SEM and TEM. The nanorods with rectangular cross-section are highly single crystalline and have a uniform smooth surface. Upon excitation at 980 nm, AlN:Nd3+/Yb3+ nanorods exhibit up-conversion (UC) visible emission bands (around 544, 595 and 667 nm) and near-infrared emission bands (around 755 and 806 nm), which correspond to intra-4f electron transitions of the Nd3+ ions. Later, the temperature dependence of UC luminescence behavior was systemically studied using luminescence intensity ratio (LIR) technique. It was verified that LIRs with non-thermally coupled levels (4G7/2/4F5/2 or 4G7/2/4F7/2) are suitable for temperature sensing. The maximum relative sensitivity based on 4G7/2/4F7/2 is 4.63% K−1 at 298 K, which is one of the highest values reported for optical thermometers. This work provides an efficient method for synthesizing wide-band gap semiconductors with doped size-mismatched functional atoms that can be used for high-sensitivity optical thermometry.

High-temperature dynamic luminescence of MgGa2O4: Tb3+, Er3+ phosphors for advanced anti-counterfeiting and information encryption

Long persistent luminescence (LPL) anti-counterfeiting technology is widely used in optical information storage, information security, and anti-counterfeiting fields due to the advantages of non-interference with background light and high imaging resolution. However, the performance of most LPL materials is greatly compromised in harsh environments such as high temperature, which seriously affects the effectiveness of anti-counterfeiting measures due to the accelerated decay rate of LPL luminescence. In this work, we synthesized a series of MgGa2O4: Tb3+ (MGO: Tb3+), which possess stable crystal structure with obvious LPL properties above room temperature, and the optimum temperature is determined to be 423 K. Moreover, the additional introduction of Er3+ ions enhances the security of anti-counterfeiting, and the combination of photo-stimulated luminescence (PSL) and upconversion (UC) phenomena enables color tuning from red to orange to green by extending the 980 nm laser irradiation time. Finally, the anti-counterfeiting strategy utilizing MGO: Tb3+ and MGO: Tb3+, Er3+ possesses an extremely high level of security, making it an attractive performance for designing advanced anti-counterfeiting technology.

Understanding and Effective Tuning of Red‐to‐Green Upconversion Emission in Ho‐Based Halide Double Perovskite Microcrystals

AbstractHo‐based lead‐free double perovskite microcrystals (MCs), Cs2NaHo1‐xYbxCl6, are synthesized and demonstrated to be promising optical temperature sensing materials by understanding the concentration‐dependent upconversion (UC) luminescence mechanisms. By optimizing the dopant concentration, a dominant emission shifting from red to green is successfully achieved in an activator‐rich system. During this process, the red to green emission intensity ratio (R/G) can be changed from 12.5 (pure red light) to 0.14 (pure green light). It is clarified that the cross‐relaxation (CR) process between activator and the energy transfer process between Yb3+ and Ho3+ are the key mechanisms of UC luminescence intensity and R/G ratio variation. Moreover, the intensity of red and green UC emission shows strong dependence on temperature, resulting from the competition between CR and energy transfer in the emission levels. The high‐sensitivity Ho‐based thermometer can be obtained by Cs2NaHo0.99Yb0.01Cl6 MCs with bright red UC luminescence, whose fluorescence intensity ratio thermometer gains maximum relative sensitivities reaching 0.68% K−1 at 400 K. The multicolor UC luminescence quantitative modeling mentioned here is crucial for understanding the concentration‐dependence UC luminescence characteristics and to optimize the design of the Ho‐based thermometer. This study can be an extension of the application range for perovskite UC materials.

Excited-Multimer Mediated Supramolecular Upconversion on Multicomponent Lanthanide-Organic Assemblies.

Upconversion (UC) is a fascinating anti-Stokes-like optical process with promising applications in diverse fields. However, known UC mechanisms are mainly based on direct energy transfer between metal ions, which constrains the designability and tunability of the structures and properties. Here, we synthesize two types of Ln8L12-type (Ln for lanthanide ion; L for organic ligand L1 or L2R/S) lanthanide-organic complexes with assembly induced excited-multimer states. The Yb8(L2R/S)12 assembly exhibits upconverted multimer green fluorescence under 980 nm excitation through a cooperative sensitization process. Furthermore, upconverted red emission from Eu3+ on the heterometallic (Yb/Eu)8L12 assemblies is also realized via excited-multimer mediated energy relay. Our findings demonstrate a new strategy for designing UC materials, which is crucial for exploiting photofunctions of multicomponent lanthanide-organic complexes.