Key Takeaways & Executive Findings
- •• • 42-fold thermal enhancement of green upconversion luminescence from 300 to 560 K in Sc2Mo3O12:Yb/Er thin film, enabling reliable operation in high-temperature environments where conventional sensors fail due to thermal quenching. • • 11.3 Å3 reduction in cell volume via anisotropic NTE along a- and c-axes amplifies Yb3+→Er3+ energy transfer (kET ∝ R−6), directly countering thermal quenching and boosting signal intensity for high-sensitivity thermometry. • • 358% extension of Er3+ lifetimes due to symmetry-breaking distortions that suppress nonradiative 2H11/2 → 4F9/2 relaxations, providing a lifetime-based sensing modality with maximum relative sensitivity (Sr) of 1.28% K−1, surpassing Boltzmann-limited approaches. • • Record relative sensitivity (Sr) of 4.33% K−1 at 300 K achieved through multi-modal thermometry, with sub-200 nm thickness and SiO2/Si compatibility, enabling on-chip integration for high-resolution thermal mapping in quantum devices, aerospace diagnostics, and wearable sensors.
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Abstract
Thermal quenching in lanthanide-based optical sensors severely limits performance at elevated temperatures. Negative thermal expansion (NTE) hosts have shown promise in bulk systems, but their potential in thin-film architectures for integrated photonics remains unexplored. This work demonstrates a Yb3+/Er3+ co-doped Sc2Mo3O12 thin film that leverages anisotropic NTE dynamics to achieve a 42-fold thermal enhancement in green upconversion luminescence from 300 to 560 K. In situ thermodiffraction and time-resolved spectroscopy reveal a dual mechanism: lattice contraction along the a- and c-axes reduces the cell volume by 11.3 Å3, amplifying Förster-type energy transfer (kET ∝ R−6) from Yb3+ to Er3+, and symmetry-breaking distortions suppress nonradiative 2H11/2 → 4F9/2 relaxations, extending Er3+ lifetimes by 358%. The strain-engineered crystal field enables multi-modal thermometry with record sensitivities: a relative sensitivity (Sr) of 4.33% K−1 at 300 K, and maximum Sr = 1.28% K−1 through lifetime-based sensing, outperforming conventional Boltzmann-limited approaches. The sub-200 nm thickness and SiO2/Si compatibility position this platform for on-chip integration, addressing unmet needs in high-resolution thermal mapping for quantum devices, aerospace diagnostics, and wearable sensors. This work deciphers the interplay between NTE and luminescence at the atomic scale and establishes a universal strategy to design anti-thermal-quenching thin films for extreme-environment photonics.
1. Introduction
Lanthanide-doped upconversion luminescent materials have revolutionized photonic technologies, from sub-diffraction-limited bioimaging to non-contact nanothermometry, owing to their narrow emission bands, long-lived excited states, and exceptional photostability. However, a fundamental limitation persists: thermal quenching, where elevated temperatures amplify nonradiative relaxations, eroding emission intensity and undermining device functionality. While strategies like phonon-assisted energy transfer and surface/defect engineering offer partial mitigation, they often lack the robustness or tunability required for extreme environments. The emergence of negative thermal expansion (NTE) materials presents a paradigm shift, as NTE matrices contract upon heating, compressing the lattice and shortening sensitizer-activator distances, which acts as a geometric lever to amplify energy transfer efficiency. This counterintuitive behavior not only suppresses thermal quenching but can even enhance luminescence, as demonstrated in bulk crystals like Sc2Mo3O12. Yet, the physics governing NTE-driven luminescence remains under-explored in thin films, a critical gap given their dominance in integrated photonics and microsensor technologies.
Thin films introduce interfacial strain and altered phonon spectra that can either exacerbate or mitigate thermal quenching, necessitating precise control over NTE dynamics at the nanoscale. Existing commercial approaches for luminescent temperature sensing, such as those based on Boltzmann-limited intensity ratios, suffer from low sensitivity and poor performance at elevated temperatures, stalling their adoption in high-precision applications like quantum device thermal management and aerospace diagnostics. This experimental protocol specifically addresses the bottleneck by engineering a Yb3+/Er3+ co-doped Sc2Mo3O12 thin film that leverages anisotropic NTE to achieve a 42-fold thermal enhancement in green upconversion luminescence from 300 to 560 K. Through in situ thermodiffraction and time-resolved spectroscopy, we decipher a dual mechanism: lattice contraction along the a- and c-axes reduces the cell volume by 11.3 Å3, amplifying Förster-type energy transfer (kET ∝ R−6) from Yb3+ to Er3+, while symmetry-breaking distortions suppress nonradiative 2H11/2 → 4F9/2 relaxations, extending Er3+ lifetimes by 358%. This strain-engineered crystal field enables multi-modal thermometry with record sensitivities: a relative sensitivity (Sr) of 4.33% K−1 at 300 K and maximum Sr = 1.28% K−1 through lifetime-based sensing, outperforming conventional Boltzmann-limited approaches. The sub-200 nm thickness and SiO2/Si compatibility further position this platform for on-chip integration, addressing unmet needs in high-resolution thermal mapping for quantum devices, aerospace diagnostics, and wearable sensors.
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CHEN Haisheng, AN Yu, WANG Yinghan, DU Xiaona, HU Minghao, BAI Gongxun, YE Shi, LIU Weiwei, ZHANG Yang (2025). Thermally Enhanced Upconversion Luminescence in Sc2Mo3O12:Yb/Er Thin Film Toward Versatile and High-Sensitivity Luminescent Temperature Sensing. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3378-6
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Frequently Asked Questions
What is the primary failure mechanism under prolonged high-temperature operation, and how does the Sc2Mo3O12:Yb/Er thin film mitigate it?
The primary failure mechanism is thermal quenching, where elevated temperatures amplify nonradiative relaxations, reducing emission intensity. The film mitigates this via anisotropic negative thermal expansion (NTE): lattice contraction along the a- and c-axes reduces cell volume by 11.3 Å3, which amplifies Förster-type energy transfer (kET ∝ R−6) from Yb3+ to Er3+ and suppresses nonradiative 2H11/2 → 4F9/2 relaxations, extending Er3+ lifetimes by 358%. This results in a 42-fold thermal enhancement of green upconversion luminescence from 300 to 560 K, ensuring stable performance at elevated temperatures.
How does the cost and scalability of this thin-film platform compare to conventional bulk NTE-based sensors?
The thin-film architecture is compatible with standard SiO2/Si substrates and has a sub-200 nm thickness, enabling on-chip integration using established semiconductor fabrication processes. This reduces material consumption and allows for wafer-scale production, potentially lowering costs compared to bulk single crystals that require complex growth and polishing. However, precise control of strain and NTE dynamics during deposition may introduce additional process complexity, necessitating optimization for high-yield manufacturing.
What are the operational thresholds and sensitivity metrics that make this sensor suitable for quantum device thermal mapping?
The sensor achieves a relative sensitivity (Sr) of 4.33% K−1 at 300 K and a maximum Sr of 1.28% K−1 through lifetime-based sensing, outperforming conventional Boltzmann-limited approaches. It operates effectively from 300 to 560 K with a 42-fold thermal enhancement of green upconversion luminescence. These metrics, combined with sub-200 nm thickness and SiO2/Si compatibility, enable high-resolution thermal mapping with minimal thermal mass and high spatial resolution, critical for quantum devices where precise temperature control is essential.
What are the potential degradation pathways for the Sc2Mo3O12:Yb/Er thin film under repeated thermal cycling, and what is the expected lifetime?
Repeated thermal cycling may induce microcracking or delamination due to strain mismatch between the film and substrate, as well as gradual oxygen vacancy formation that could alter NTE behavior. However, the film's strain-engineered crystal field and SiO2/Si compatibility suggest robust integration. While the paper does not report accelerated aging data, the 358% lifetime extension of Er3+ and stable NTE dynamics up to 560 K indicate reliable operation. Long-term stability tests under cyclic thermal loading are recommended to quantify degradation rates.
How does the multi-modal thermometry approach (intensity ratio and lifetime) enhance reliability compared to single-mode sensing?
Multi-modal thermometry combines luminescent intensity ratio (LIR) and lifetime-based sensing, providing cross-validation to mitigate errors from fluctuations in excitation power, detector drift, or environmental perturbations. The LIR mode yields Sr = 4.33% K−1 at 300 K, while lifetime-based sensing offers maximum Sr = 1.28% K−1, extending the dynamic range and self-calibration capability. This redundancy is critical for applications requiring high precision, such as aerospace diagnostics and wearable sensors, where single-mode sensors may fail under variable conditions.
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