High Upconversion Luminescence Research Articles

Optical thermometry using efficient upconversion luminescence in Er3+ self-sensitized NaYS2 under multi-wavelength excitation

Herein, a series of Er3+ self-sensitized NaYS2 phosphors are synthesized by the solid-gas reaction method for a novel upconversion luminescence thermometer. Er3+ possesses abundant excited state energy levels in the near-infrared region, enabling efficient upconversion luminescence by absorbing different near-infrared wavelength light. Compared to 980 nm excitation, the emission intensity is enhanced by nearly an order of magnitude under 1532 nm excitation, which can be attributed to the larger absorption cross-section of 4I13/2 and stronger absorption efficiency for Er3+. Based on the luminescence intensity ratio technique, the optical thermometry behaviors of NaYS2:Er3+ under different wavelength excitation are evaluated by employing the thermally coupled energy levels of 2H11/2/4S3/2. It can be deduced that the excitation wavelength has no significant effect on the temperature sensing parameters. Compared to other typical upconversion luminescence thermometers, NaYS2:Er3+ thermometer exhibits not only excellent sensitivity performance but also high upconversion luminescence efficiency, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing.

Upconversion luminescence and temperature sensing performance of Zn2+-doped Ba2GdAlO5: Yb3+, Er3+ phosphors

Although upconversion luminescence (UCL) materials have attracted considerable attention in biomedical, lighting, anti-counterfeiting, and solar cells due to their excellent fluorescence properties, reports of the dibarium gadolinium aluminum oxide (Ba2GdAlO5) are scarce. Herein, we synthesized the single-phase Ba2GdAlO5 material with non-stoichiometric Ba2Gd1.06Al0.94O5 (denoted as BGAO, hereafter). The X-ray Rietveld refinement reveals that the substitution of Gd for Al accounts for the non-stoichiometry. Notably, the UCL properties of BGAO are realized by doping with Yb3+ and Er3+ ion pair, and it can be further enhanced significantly by co-doping with appropriate Zn2+ ions. The SEM images show that the particle size increases as the concentration of Zn2+ ions increases. The X-ray Rietveld refinement results of the Zn-doped BGAO: 0.1 Yb3+, 0.03Er3+ phosphor indicate the substitution of Zn2+ for Ba2+ and Al3+ ions simultaneously. Grain growth and lattice distortion account for the improvement of UCL properties after Zn2+ ions doping. In addition, the temperature sensing performance of the Zn2+-doped sample has been researched based on the fluorescence intensity ratio (FIR) technique, and the maximum absolute and relative sensitivities (SA-max and SR-max) are obtained to be 4.8 × 10−3 K−1 at 498 K and 1.1% K−1 at 298 K, respectively. This work provides a candidate with high UCL intensity for potential applications in optical temperature sensors.

Nitrogen and sulfur co-doped carbon quantum dots as “on-off-on” fluorescence probes to detect Hg2+ and MnO4− and improving the photostability of Rhodamine B

BackgroundCarbon quantum dot (CQDs) are zero-dimensional carbon nanomaterials with a size of less than 10 nm CQDs are widely used in the field of ion detection by virtue of their fluorescence characteristics such as strong fluorescence intensity, good optical stability and tunable emission wavelength. Although the traditional atomic absorption method, electrochemical method and other metal ion detection methods are highly sensitive, the operation is complex, expensive and limited by the site. Therefore, we prepared the N, S-CQDs capable of detecting Hg2+ and MnO4− in water with the advantages of simple operation, low cost, and direct visual signal. ResultsN, S-CQDs with high-quantum yield (77.68%), uniform particle size (0.4 nm–2.6 nm) and green fluorescence were created utilizing a one-pot hydrothermal process with the precursors ASDA-Na4 and m-phenylenediamine. N, S-CQDs has good optical properties such as high fluorescence intensity, wavelength independence, up-conversion luminescence and fluorescence stability. We examined 27 common ions in water and found that the fluorescence of N, S-CQDs could be selectively quenched by Hg2+ and MnO4−, and the detection limits are 0.41 μM and 1.2 μM, respectively. The mechanism of quenching is further investigated. The fluorescence of N, S-CQDs-Hg2+ system can be restored by halogen ions (Cl−, Br−, I−), while the fluorescence of N, S-CQDs-MnO4- system can be partially restored by Fe2+. This forms an “on-off-on” mode of fluorescent probes. In addition, we also studied that trace amounts of N, S-CQDs can improve the photostability of RhB. SignificanceThe N, S-CQDs are fluorescent probes in an “on-off-on” mode. N, S-CQDs with green fluorescence (on) can be quenched by Hg2+ and MnO4− (off). The fluorescence quenched by Hg2+ can be restored by halogen ions again, while the fluorescence quenched by MnO4− can partially be restored (on). This ion detection method can be used to visually detect the two ions in the field, with the advantages of low cost, simple operation and visual intuition.

Polymer-coated hexagonal upconverting nanoparticles: chemical stability and cytotoxicity.

Large (120nm) hexagonal NaYF4:Yb, Er nanoparticles (UCNPs) were synthesized by high-temperature coprecipitation method and coated with poly(ethylene glycol)-alendronate (PEG-Ale), poly (N,N-dimethylacrylamide-co-2-aminoethylacrylamide)-alendronate (PDMA-Ale) or poly(methyl vinyl ether-co-maleic acid) (PMVEMA). The colloidal stability of polymer-coated UCNPs in water, PBS and DMEM medium was investigated by dynamic light scattering; UCNP@PMVEMA particles showed the best stability in PBS. Dissolution of the particles in water, PBS, DMEM and artificial lysosomal fluid (ALF) determined by potentiometric measurements showed that all particles were relatively chemically stable in DMEM. The UCNP@Ale-PEG and UCNP@Ale-PDMA particles were the least soluble in water and ALF, while the UCNP@PMVEMA particles were the most chemically stable in PBS. Green fluorescence of FITC-Ale-modified UCNPs was observed inside the cells, demonstrating successful internalization of particles into cells. The highest uptake was observed for neat UCNPs, followed by UCNP@Ale-PDMA and UCNP@PMVEMA. Viability of C6 cells and rat mesenchymal stem cells (rMSCs) growing in the presence of UCNPs was monitored by Alamar Blue assay. Culturing with UCNPs for 24h did not affect cell viability. Prolonged incubation with particles for 72h reduced cell viability to 40%-85% depending on the type of coating and nanoparticle concentration. The greatest decrease in cell viability was observed in cells cultured with neat UCNPs and UCNP@PMVEMA particles. Thanks to high upconversion luminescence, high cellular uptake and low toxicity, PDMA-coated hexagonal UCNPs may find future applications in cancer therapy.

Microwave-assisted hydrothermal synthesis of LaOF:Yb3+, Ho3+ nanorods with high thermoresponsive upconversion luminescence for thermometry

Non-contact thermometry based on upconversion luminescence from lanthanide-doped nanoparticles is the best choice when temperature probes with higher precision, accuracy, sensitivity, and spatial resolution are required. Here, LaOF:Yb3+,Ho3+ upconversion nanoparticles (UCNPs) were demonstrated to be thermometers with a high sensitivity and thermal stability within the temperature range of 303–673 K. Microwave-assisted hydrothermal synthesis was used to obtain these rod-shaped UCNPs with a trigonal crystal structure. LaOF:Yb3+,Ho3+ UCNPs displayed green emissions due to the thermally-coupled levels (5F4, 5S2) and red emissions from the Stark-split sublevels of the 5F5 energy level belonging to Ho3+ under 980 nm continuous-wave laser irradiation. The upconversion emission originating from these transitions were remarkably sensitive to the temperature variation. Their fluorescence intensity ratios were explored to evaluate their relative (SR) and absolute (SA) sensitivities. Optical heating induced by continuous laser irradiation was also examined to assess the degradation of the luminescence caused by laser exposure.

Plug-in tip sensor based on upconversion fluorescence in Er3+/Yb3+ co-doped tellurite glass for thermal monitoring of a miniature winding coil.

We demonstrate a plug-in tip sensor with a maximum cross section diameter of only 1 mm for real-time thermal monitoring of a high-density miniature winding coil, which can meet the miniaturization development needs of electromagnetic actuators. Due to the high upconversion luminescence efficiency, tellurite glass with an optimized Er3+/Yb3+ doping ratio is adhered to the end face of silica fiber for a temperature-sensitive tip. Temperature information is demodulated using the fluorescence intensity ratio technique, yielding a nonlinear response with R2 up to 0.9978. Within a wide temperature range of 253.55-442.45 K, the tip sensor exhibits good repeatability, excellent stability, high sensitivity of 52.7 × 10-4 K-1, small absolute error within ±1 K, and fast time response of 2.03 s. It has been successfully proven to be a miniaturized device with strong anti-interference ability for the health management of high-density winding coils.

High electrical properties and good upconversion luminescence in SrBi1.94-xEr0.06YbxNb2O9 lead-free piezoelectric ceramics

SrBi1.94-xEr0.06YbxNb2O9 (x = 0.000, 0.002, 0.004 and 0.006, noted as SBEN-xYb) composites were prepared using traditional solid-phase sintering technology. The influences of (Er, Yb)3+ co-doping on the electrical and luminous properties as well as energy band structure of SrBi2Nb2O9 (SBN) ceramics were systematically investigated. The outstanding comprehensive characteristics with low dielectric loss (tanδ ~ 0.073%), high remnant polarization (2Pr ~ 10.73 μC/cm2), large piezoelectric responses (d33 ~ 15 pC/N) and excellent upconversion photoluminescence (UC-PL) are simultaneously observed by Yb doping with a concentration of x = 0.004. The UC-PL spectrum excited by 980 nm laser shows double bands at 533 nm and 554 nm in the green region, and single band at 672 nm in the red region. A density functional theory (DFT) calculation was performed to reveal the physical origin of electrical conductivity and UC-PL. It is seen that the band gap consistently decreases, while the contribution from f state of (Er, Yb)3+ is intensified with increasing Yb3+, elaborating the variations of electrical conductivity and UC-PL intensity. Related mechanisms for the improvement of UC-PL and electrical properties were discussed.

Enhanced up-conversion luminescence intensity of NaY(MoO4)2: Ho3+/Yb3+ phosphor by doping with Mg2+ ions for use in high-efficiency optical temperature sensor

The sensitization of Ho3+ ions by Yb3+ ions has been widely studied in traditional up-conversion luminescence materials and has been reported in many studies. This paper aims to further improve the up-conversion luminescence intensity by doping Mg2+ ions, and this enhancement was analyzed by Judd-Ofelt theory. Using the fluorescence intensity ratio method, temperature sensing performance of the phosphor was observed when the temperature was between 323 K and 523 K. Compared with previously reported materials, this phosphor displays excellent temperature sensitivity. The NaY(MoO4)2: Ho3+/Yb3+/Mg2+ phosphor shows good color purity and high up-conversion luminescence intensity, showing broad application prospects for intense green light generation, optical devices, and temperature sensors.

High efficient upconversion luminescence of NaGdF4: Yb3+/Er3+ nanoparticle: first-principles calculation, dual-wavelength stimuli and logic gate application

ABSTRACT First-principle theory was used to design NaGdF4:Yb3+/Er3+ crystal, where the density of state, X-ray diffraction and optical coefficient had been studied through a generalised gradient approximation within density functional theory to predicate the effect of rare earth ion doping on the electronic and optical performance. Besides, NaGdF4:Yb3+/Er3+ nanoparticles were also obtained by liquid–solid–solution method and realized the enhancement of upconversion emission and the regulation of spectrum under co-excitation of the 980 nm and 1550 nm lasers. The results inspired us to establish upconversion logic gate system, where ‘INHIBIT, OR, XOR, YES, AND’ logic gate operations had been successfully developed by introducing external two excitation sources as input signals and monitoring the relative intensity signals of green and red emission bands and G/R ratio signal.

High quality upconversion luminescence and excellent thermal stability of Yb3+, Er3+ codoped Sr3NaY(PO4)3F phosphors

A series of Sr3NaY(PO4)3F (SNYPF): Yb3+, Er3+ phosphors were synthesized by high temperature solid-phase method. The green and red emission region of SNYPF: Yb3+, Er3+ in the upconversion luminescence (UCL) spectra consist of two distinctly separated peaks under 980 nm laser excitation, which can be assigned to the transition from 2H11/2, 4S3/2 and 4F9/2 to 4I15/2 of Er3+. The SNYPF: Yb3+, Er3+ phosphors possess significant optical temperature sensing feature with the maximum sensitivity value of 0.00312 K−1 (464 K) and 0.00272 K−1 (209 K), as well as 0.00242 K−1 and 0.00244 K−1 at 300 K for green and red emission, respectively. Notably, the intensity of green emission remains almost unchanged with the increasing of temperature, indicating the excellent thermal stability of the phosphors. The above results demonstrate that SNYPF: Yb3+, Er3+ is a potential UC phosphor, which is suitable for optical temperature sensing.

Controlled synthesis and upconversion luminescence properties of highly uniform and monodisperse β-NaYF4 :Yb3+ ,Tm3+ nanocrystals.

Ytterbium, thulium (Yb3+ ,Tm3+ ) co-doped β-NaYF4 upconversion nanocrystals (U-NCs) were synthesized by a convenient hydrothermal method using sodium citrate as a capping agent. X-ray diffraction (XRD) analysis revealed that NCs phase structures were dependent on reaction time. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results showed that the morphology of U-NCs could be controlled by adjusting the concentration of sodium citrate added in the hydrothermal reaction. Moreover, the emission spectra of the U-NCs were investigated to evaluate upconversion efficiency. Strong luminescence intensity of the U-NCs was observed after tuned with optimized concentration of sodium citrate. Furthermore, the U-NCs were incubated with MCF-7 cells at 37°C for 24 h. Under irradiation of a 980 nm laser, the upconversion blue emission of the NCs in MCF-7 cells can be clearly observed through a confocal microscope with an upconversion imaging system and high quality upconversion luminescence images can be acquired. Thus, prepared β-NaYF4 :Yb3+ ,Tm3+ NCs provide us with highly efficient luminescent probes which can be applied for diverse bio-applications.

Promising lanthanide-doped BiVO4 phosphors for highly efficient upconversion luminescence and temperature sensing.

The semiconductor oxide BiVO4 has been intensively studied as a highly efficient photocatalyst. Here we attempt to adopt trivalent lanthanide (Ln3+)-doped BiVO4 as a novel upconversion luminescence (UCL) material for achieving high-efficiency UCL and temperature sensing under near-infrared (NIR) irradiation. Er3+/Tm3+, Yb3+/Er3+, and Yb3+/Tm3+ ions were selected to co-dope the BiVO4 phosphors, achieving three primary colors of red, green, and blue (RGB) with high color-purity. At an optimal doping concentration, the upconversion quantum yield of the BiVO4:8%Yb3+,18%Er3+ phosphor reaches as high as 2.9%. Furthermore, we, for the first time, demonstrate the non-contact temperature sensing properties of a BiVO4:Er3+,Tm3+ phosphor via employing fluorescence intensity ratio technology. The results show that the maximum absolute thermal sensitivity is ≈70 × 10-4 K-1 at 473 K under 980 nm excitation, with high and stable sensitivity of more than 60 × 10-4 K-1 over a wide temperature range of 333-493 K. In addition, at a much safer wavelength of 1550 nm, this sample achieves maximum absolute sensitivity of 56 × 10-4 K-1 at 453 K. Moreover, the BiVO4:Er3+,Tm3+ phosphor presents high relative sensitivity of about 1.1% K-1 under both 980 and 1550 nm excitation at 293 K. These results indicate that the BiVO4 semiconductor oxide can be used as a novel host to achieve high UCL efficiency and promising thermal sensing performance, suggesting potential applications in the new fields of anti-counterfeiting, displays, and non-contact temperature sensors.

Lanthanide-semiconductor probes for precise imaging-guided phototherapy and immunotherapy

Abstract Objective: Immunotherapy is an effective tumor treatment strategy. However, its long treatment cycle limits its wide application across all cancer types. In this study, we optimized upconversion nanoparticles and manganese composite particles with a porous structure as a nanoplatform for synergistic photodynamic therapy (PDT) and photothermal therapy (PTT), and subsequent longer-term immunotherapy. Methods: The morphology, phase, and stability were first characterized to evaluate the biocompatibility of this material. The upconversion and near infrared II luminescence properties of the material and its stimuli-response effect were assessed from the absorbance and photoluminescence spectra. Phototherapy including PDT and PTT was demonstrated in vitro and in vivo, and immunotherapy was used to enhance the phototherapy. This study was approved by the School of Pharmacy's Ethics Committee of Tumor Hospital of Shaanxi Province, Xi’an Jiaotong University, China (approval No. XJTULAC2020-585) on April 2, 2020. Results: The nanoplatform showed good PDT and PTT effects with high upconversion luminescence, and exhibited a more sensitive glutathione response (detection limit: 55 μg/mL) using fluorescence recovery than that based on absorbance recovery, with the detection range extending up to 1.2 mg/mL. When the surface of the composite particles was modified with an anti-PD-L1 immune checkpoint inhibitor, it targeted A549 lung cancer cells. The resulting immune response enhanced the long-term anti-tumor effect of the therapy, especially in lung cancer patients with high PD-L1 expression. Conclusion: The designed composite can be simultaneously used to detect the glutathione concentration based on luminescence recovery in the tumor cells and as a theranostic nanoplatform for synergistic immuno-phototherapy when combined with an antibody.

Small and Bright Water-Protected Upconversion Nanoparticles with Long-Time Stability in Complex, Aqueous Media by Phospholipid Membrane Coating.

Chemical and colloidal stability in complex aqueous media are among the main challenges preventing nanoparticles from successfully entering into the biomedical field. Small core-shell upconversion nanoparticles (UCNPs) NaYF4:Yb,Er@NaYF4 of 12 nm in diameter with a high surface-to-volume ratio are utilized to demonstrate that self-assembling phospholipid bilayers (PLMs) have several benefits compared to common ligand-exchange and ligand-addition particle coatings such as poly(acrylic acid) and amphiphilic polymers. An efficient hydrophobic barrier against water quenching and toward particle disintegration is formed by PLM. Particles with this functionalization have a higher upconversion luminescence in aqueous media in contrast to common surface ligands. They attract with better colloidal stability in phosphate buffer, in a wide pH range, in high ionic solutions, and in complex cell media, as is required for biological applications. Moreover, kidney cells (NRK) are not affected by these stable PLM-coated UCNPs as first cell viability tests reveal.

Concentration dependence of upconversion luminescence of Er3+/Yb3+ in the fluorophosphate glasses with small phosphates content

Abstract Frequency upconversion into green and red luminescence in fluorophosphate glasses doped with Er3+ ions (1021 to 1016 ion/cm3) and Yb3+ ions (1021 ion/cm3) while pumped with a 970 nm diode laser is presented. The red upconversion emission results from a two-photon excitation process. The upconversion emission intensity dependence on the incident pump power shows that the green upconversion luminescence arising from 2H11/2 level is also contributed by the two-photon processes. The values of n-parameter for the 4S3/2 level change from 2.7 to 2.0 during low power excitation and continue decreasing at higher pumping energy. It has been shown that the green upconversion luminescence intensity dependence on the erbium ions content has a sharp maximum at the concentration of 2* 1019 ion/cm3. We attribute the high upconversion luminescence in case of low Er3+ and Tm3+ ions concentrations (about 1018–1016 ion/cm3) to the cooperative energy transfer from Yb–Yb* dimers. The formation of excited dimers is confirmed experimentally by cooperative luminescence band at 495 nm.

Peptide-enhanced tumor accumulation of upconversion nanoparticles for sensitive upconversion luminescence/magnetic resonance dual-mode bioimaging of colorectal tumors

Currently, it is still a great challenge to develop tumor targeting nanoparticles with high sensitivity and high resolution for improving the non-invasive detection ability of colorectal cancer (CRC) at an early stage. In this study, NaErF4:Yb@NaGdF4:Yb core@shell upconversion nanoparticles (UCNPs) were prepared with high upconversion luminescence (UCL) emission in red light region through adjusting the doping ratios of Er and Yb elements in the core. For biomedical applications, the carboxyl-terminated silica shell was introduced to transfer the as-prepared UCNPs from the organic phase to the aqueous phase, and allowed conjugation with peptide ligands derived from the l-SP5 peptide (i.e., l-SP5-H and l-SP5-C), respectively. Due to the tumor-targeting affinity of the PSP motif in the peptide ligands, the as-prepared peptide functionalized UCNPs (UCNP@SiO2-l-SP5-H and UCNP@SiO2-l-SP5-C) can be used as an active tumor targeting contrast agents for UCL/T1-weighted magnetic resonance (MR) dual-mode imaging. Both the in vitro and in vivo experimental results demonstrated that UCNP@SiO2-l-SP5-C has relatively high affinity for the HCT116 CRC subtype. Moreover, UCNP@SiO2-l-SP5-C can visualize ultra-small subcutaneous xenografted HCT116 tumors (c.a. 13 mm3 in volume) by in vivo UCL imaging. Statement of Significance1. High red emission UCNPs were synthesized for tumor-targeting dual-mode bioimaging.2. With tumor-binding affinity peptide, UCNP@SiO2-l-SP5-C shows high HCT116 tumor targeting ability.3. UCNP@SiO2-l-SP5-C successfully achieves sensitive detection of ultrasmall HCT116 tumors.

β-NaYF4:Yb,Er,Gd nanorods@1T/2H-MoS2 for 980 nm NIR-triggered photocatalytic bactericidal properties

Fabrication of β-NaYF4:Yb,Er,Gd@1T/2H-MoS2 nanocomposites for NIR-driven photocatalytic sterilization of Escherichia coli.

The construction of sublattice level energy cluster for promoting UV upconversion emission in tetragonal LiYF4

The preparation of high performance upconversion luminescence materials with stronger shortwave emissions is still a challenge. In this work, the feature of hexagon circles sublattice structure of tetragonal LiYF4 was revealed, and the sublattice level energy clusters of 4 Yb3+-1Tm3+ were constructed by the substitution of 70 mol% Yb3+ for Y3+ in tetragonal LiYF4 matrix. The sensitizing ions concentration quenching was inhibited by the hexagon circles sublattice structure, and the upconversion luminescence was dramatically enhanced, especially, the UV band emission was enhanced about 20 times and the intensity ratio of UV to blue emissions was improved about 10 folds under the excitation power density of 0.230 W/cm2. Photon numbers of upconversion emissions obviously decreased with the increasing of sublattice level energy clusters that the upconversion process of three photons was changed to two steps of two photons process. The upconversion luminescence mechanism of sublattice energy cluster construction was system investigated. The material with high performance of UV and blue UC luminescence can be a well candidate for the applications of photodynamic therapy and photocatalytic, etc. The work may be an inspiration for high efficient UC luminescence materials design and preparation.

Optical thermometry based on up-conversion luminescence behavior in BaGdF5:Er3+ glass ceramics

Er3+ ions are often used as up-conversion (UC) activators for fluorescence intensity ratio (FIR) thermometer technique, and Yb3+ ions are co-doped for improving the UC luminescence efficiency of Er3+ ions. However, Yb3+ ions will cause heating effect by absorbing 980 nm laser excitation which affects the precision of FIR technique. Challenge of FIR technique still remains to seek for superior host materials of high UC luminescence efficiency without sensitizer Yb3+ ions, in which heating effect can be reduced. Herein, glass ceramics (GC) containing Er3+-doped BaGdF5 nano-crystals (NCs) were successfully elaborated through melt-quenching method. X-ray diffraction, scanning transmission electron microscopy and element mappings are convinced the formation of BaGdF5 NCs. The UC emissions of Er3+ ions are greatly enhanced due to the Er3+ dopants incorporated into the BaGdF5 NCs with low phonon energy. The temperature dependent FIR of two thermal coupled energy levels (2H11/2/4S3/2) was carried out from 300 to 720 K, and the maximum relative sensitivity is 1.36% K−1 at 300 K. According to all the above results, the BaGdF5:Er3+ GC may have possible utilization in thermometer with high precision.

Enhanced Tumor-Accumulation of Upconversion Nanoparticles for Upconversion Luminescence/Magnetic Resonance Dual-Mode Bioimaging of Colorectal Tumor Using a Tumor Affinity Peptide with PSP Motif

Up to date, it is still a great challenge to construct tumor targeting nanoparticles with high sensitivity and resolution for improving the non-invasive detection ability of colorectal cancer (CRC) at early stage. In this study, we have prepared NaErF4:Yb@NaGdF4:Yb core@shell upconversion nanoparticles (UCNPs) with high upconversion luminescence (UCL) emission in red light region through adjusting the doping ratios of Er element and Yb element in the core. For biomedical application, the carboxyl-terminated silica shell has been introduced to transfer the as-prepared UCNPs from organic phase to aqueous phase, as well as to conjugate peptide ligands derived from L-SP5 peptide (i.e., L-SP5-H and L-SP5-C), respectively. Due to the tumor-binding affinity of PSP motif in peptide ligands, the as-prepared peptide functionalized UCNPs (UCNP@SiO2-L-SP5-H and UCNP@SiO2-L-SP5-C) can be used as active tumor targeting contrast agents for UCL/T1-weighted magnetic resonance (MR) dual-mode imaging. Both the in vitro and in vivo experimental results demonstrate that the as-prepared UCNP@SiO2-L-SP5-C has relatively high affinity with HCT116 CRC subtype. Particularly, UCNP@SiO2-L-SP5-C can even visualize ultrasmall subcutaneous xenografted HCT116 tumor (c.a. 13 mm3 in volume) by in vivo UCL imaging.