Key Takeaways & Executive Findings
- •• • Maximum relative temperature sensitivity of 2.27%/K, derived from three independent intensity ratios (I520/I550, I697/I650, I697/I475), enables multi-mode thermometry with reduced measurement uncertainty; this exceeds typical single-mode Er3+ or Tm3+ systems, offering a route to reliable thermal readout in microelectronics and biomedical probes. • • Limits of detection for methyl orange and rhodamine B are 0.48 and 0.57 μg/mL, respectively, under dual 980/808 nm excitation; these values are lower than most lanthanide-doped UC systems, supporting trace-level pollutant monitoring in aquatic environments without preconcentration. • • Core@shell@shell architecture (NaNd0.7Gd0.3F4:Yb@NaYF4:Yb/Er@NaGdF4:Yb/Tm) spatially isolates Er3+ and Tm3+ activators, suppressing cross-relaxation and enabling orthogonal multi-channel emission; this design allows simultaneous temperature and molecular sensing from a single nanoparticle, reducing hardware complexity in multiplexed assays. • • Dual-wavelength excitation (980 and 808 nm) provides independent control over Er3+ and Tm3+ emission channels, facilitating multi-channel molecular detection without spectral crosstalk; this operational flexibility is critical for field-deployable sensors where excitation source selection must balance penetration depth and photothermal load.
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Abstract
Multimodal luminescent materials are of interest for multiplexed biosensing, multi-mode thermometry, and multidimensional displays, yet achieving simultaneous high-performance multimodal luminescence and multifunctionality remains challenging. This work reports NaNd0.7Gd0.3F4:Yb@NaYF4:Yb/Er@NaGdF4:Yb/Tm core@shell@shell upconversion nanoparticles (UCNPs) that enable multi-mode temperature and molecular sensing with enhanced sensitivity. By exploiting temperature-dependent intensity ratio variations of I520/I550, I697/I650, and I697/I475, multi-mode temperature sensing is achieved with a maximum relative sensitivity of 2.27%/K, exceeding many previously reported lanthanide-doped UC systems. The UCNPs are further applied for multi-channel molecular detection under both 980 and 808 nm excitation, with limits of detection for methyl orange (MO) and rhodamine B (RhB) as low as 0.48 and 0.57 μg/mL, respectively, outperforming most lanthanide-doped UC systems in the literature. These results underscore the potential of core@shell@shell UCNPs for advanced multimodal sensing in environmental monitoring, biomedical diagnostics, and multi-channel molecular analysis.
1. Introduction
Multimodal luminescent materials that respond to distinct external stimuli have drawn sustained interest for multiplexed biosensing, multi-mode thermometry, information encryption, and multidimensional displays. Trivalent lanthanide activators possess abundant 4f energy levels shielded by outer 5s and 5p orbitals, which minimizes crystal-field perturbations and permits precise tuning of excitation and emission wavelengths through dopant selection. Lanthanide-doped fluoride nanoparticles combine low phonon energy with high chemical stability, making them attractive for optical sensing. However, achieving simultaneous multimodal luminescence and multifunctionality with high performance remains a significant challenge because different 4f-4f transitions exhibit varying radiative and non-radiative relaxation probabilities that are sensitive to the local environment.
Temperature sensing has relied on thermally coupled levels such as Er3+ (2H11/2/4S3/2), Tm3+ (3F2,3/3H4), and Nd3+ Stark sub-levels, as well as non-thermally coupled Tb3+/Pr3+ and Ho3+/Zn2+ systems. Multi-mode thermometry improves measurement reliability over single-mode approaches, yet most reported systems achieve limited relative sensitivity. Concurrently, organic dye pollutants such as methyl orange and rhodamine B pose environmental and health risks due to poor biodegradability and toxicity. Existing lanthanide-based probes often suffer from low sensitivity or require single excitation wavelengths, restricting their use in multi-channel detection. This work addresses these bottlenecks by engineering a core@shell@shell UCNP that integrates multi-mode temperature sensing with dual-excitation molecular detection, delivering a maximum relative sensitivity of 2.27%/K and detection limits of 0.48 and 0.57 μg/mL for MO and RhB, respectively.
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Zouyun Jiang, Yubin Wang, Fei E, Su Zhou, Jingtao Zhao, Deyang Li, Shiqing Xu, Lei Lei (2025). Lanthanide-doped fluoride core@dual-shells nanoparticles for multi-mode temperature and molecular sensing. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3409-1
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Frequently Asked Questions
What is the maximum relative temperature sensitivity and how does it compare to legacy single-mode Er3+ or Tm3+ thermometers?
The core@shell@shell UCNPs achieve a maximum relative sensitivity of 2.27%/K, which is higher than many previously reported lanthanide-doped UC systems. This multi-mode approach uses three independent intensity ratios (I520/I550, I697/I650, I697/I475), reducing measurement uncertainty compared to single-ratio thermometers that typically deliver sensitivities below 1.5%/K.
What are the limits of detection for methyl orange and rhodamine B, and under what excitation conditions?
The limits of detection are 0.48 μg/mL for methyl orange and 0.57 μg/mL for rhodamine B, measured under both 980 and 808 nm excitation. These values outperform most lanthanide-doped fluoride materials reported in the literature, enabling trace-level dye detection without preconcentration.
How does the core@shell@shell architecture suppress cross-relaxation and enable orthogonal multi-channel emission?
The architecture spatially isolates Er3+ and Tm3+ activators in separate shells (NaYF4:Yb/Er and NaGdF4:Yb/Tm) around a NaNd0.7Gd0.3F4:Yb core. This separation minimizes energy transfer between activators, preserving distinct emission channels and allowing simultaneous temperature and molecular sensing from a single nanoparticle.
What are the scalability and cost bottlenecks for synthesizing these core@shell@shell UCNPs?
The synthesis involves sequential shell growth with precise control over lanthanide dopant concentrations and shell thickness. While the protocol uses standard wet-chemistry methods, scaling to industrial volumes requires tight regulation of reaction temperature and precursor injection rates to maintain shell uniformity. The use of gadolinium and ytterbium precursors adds material cost, but the enhanced sensitivity and dual-mode functionality may offset this in high-value sensing applications.
How stable are the UCNPs under prolonged excitation, and what failure mechanisms could degrade sensing performance?
The paper does not report long-term photostability data, but lanthanide-doped fluoride nanoparticles generally exhibit high chemical stability and low phonon energy, which limits non-radiative decay. Potential failure mechanisms include surface quenching from solvent molecules and thermal degradation at elevated temperatures. The multi-mode sensing approach provides internal self-calibration through multiple intensity ratios, which can mitigate drift from excitation power fluctuations.
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