In the ever-evolving landscape of luminescent materials, mechanoluminescence (ML) has emerged as a uniquely intriguing phenomenon. Unlike its better-understood counterparts, photoluminescence and electroluminescence, mechanoluminescence generates light triggered purely by mechanical stimuli such as pressure, friction, or deformation. This direct conversion of mechanical energy into optical emission offers a new frontier in passive, energy-efficient light emission technologies, promising transformative implications across varied scientific and industrial domains.
Historically, mechanoluminescent materials have been primarily investigated as single-matrix systems where the emitted light intensity often suffers from inconsistency and limited brightness. These limitations have stymied efforts to harness ML for practical applications where reliability and intensity are critical. As research deepens, the pivotal challenge remains: how can the intrinsic ML performance — especially emission intensity and stability — be systematically enhanced? This question drives ongoing investigations into complex material architectures rather than isolated phosphors.
A pioneering study by Dengfeng Peng and Tianlong Liang, alongside their team at Shenzhen University, confronts these challenges through an innovative heterojunction design. By fabricating a composite heterostructure combining calcium fluoride (CaF₂) with calcium zinc oxysulfide (CaZnOS), they have revealed a new paradigm for enhancing mechanoluminescent output. This CaF₂/CaZnOS heterojunction, doped with carefully selected lanthanide ions, exemplifies a deliberate approach to leverage interfacial effects and energy transfer dynamics in ML materials.
The heterojunction structure is critical for two reasons: it stabilizes the composite physically and optically, and it modulates the energy pathways that result in efficient light emission. Importantly, CaF₂ inclusion increases the optical transparency within polydimethylsiloxane (PDMS) films formed from the mixture, facilitating improved light extraction. When doped with terbium ions (Tb³⁺), the heterojunction exhibits mechanoluminescent intensities approximately twice as intense as a reference single matrix CaZnOS doped solely with Tb³⁺, marking a significant leap in performance.
Diving deeper, the researchers have demonstrated that codoping with ytterbium ions (Yb³⁺) in conjunction with terbium creates a complex energy transfer mechanism within the heterojunction. Contrary to initial expectations, visible light emission intensity decreases relative to samples doped only with Tb³⁺; however, near-infrared (NIR) emission substantially exceeds that of materials doped only with Yb³⁺. This tradeoff underscores the nuanced interplay of energy states and cooperative transfer processes when multiple lanthanide ions coexist within the lattice.
Through precise photophysical measurements, the team observed a progressive reduction in luminescence lifetime upon increasing Yb³⁺ concentrations. This phenomenon directly corresponds to cooperative energy transfer from donor Tb³⁺ ions to acceptor Yb³⁺ ions, resulting in quenching of Tb³⁺ visible emissions while enhancing Yb³⁺ NIR output. The efficiency of this energy transfer, denoted η_ET, reaches an impressive 66.9%, a remarkable figure in downconversion research that translates into a calculated quantum efficiency (η_QE) of 166.9%. These numbers highlight the capability of the heterojunction system to surpass unity quantum yields typically limited by single-ion emission.
Expanding this methodology, the researchers integrated a praseodymium (Pr³⁺)-ytterbium ion pair into the heterojunction environment. This pairing resulted in even higher energy transfer efficiency, measured at 85.1%, and a commensurate quantum efficiency reaching 185.1%. The impressive efficacy of these lanthanide codoped heterojunctions not only validates the cooperative energy transfer mechanism but also illuminates a versatile framework for designing advanced ML materials with tailored emission spectra spanning visible to near-infrared wavelengths.
The implications of such a mechanism are profound for future ML research and applications. By demonstrating that lanthanide codoping in heterojunctions enhances downconversion pathways, this work challenges the prevailing focus on monolithic phosphor systems and opens the door for engineered multi-ion architectures. The cooperative energy transfer pathways provide a tunable parameter to optimize emission wavelengths, lifetimes, and intensities—parameters essential for integrating ML materials into smart sensing platforms, wearable devices, and optical communication systems.
Looking ahead, the interdisciplinary trajectory of ML research will harness advances across materials science, semiconductor physics, chemistry, and information technology. The integration of artificial intelligence in the design phase promises to expedite the discovery and optimization of ML heterostructures. Combining atomic layer deposition, chemical vapor deposition, and soft chemical synthesis techniques will enable fabrication of epitaxial single-crystal heterojunctions possessing superior uniformity and tailored interfacial properties. Alongside, one-dimensional whisker and fiber heterojunctions present outstanding opportunities to couple mechanoluminescence with mechanical reinforcement, thus enhancing the material’s multifunctional capabilities.
The development of these next-generation ML materials is projected to expand the operational pressure range, increase sensing sensitivity, and shorten response times pivotal in real-world applications. Furthermore, the complementary exploitation of both downconversion and upconversion luminescence processes could yield devices capable of more efficient mechanical-to-optical energy conversion, thereby establishing a new class of passive optical sensors and lighting elements.
Mechanoluminescent materials engineered via these heterojunction strategies hold transformative potential for industries such as smart manufacturing and structural health monitoring. Their passive, self-powered nature suits deployment in environments where electrical power is constrained or unwanted, enabling continuous, real-time detection of stress or damage. Subsequently, advances in healthcare devices leveraging ML-based sensors may allow novel modalities for monitoring physiological parameters or therapeutic mechanical stimuli without cumbersome power sources.
As the field moves toward commercialization and standardization, the CaF₂/CaZnOS heterojunction system stands as a landmark achievement. It signifies not only a leap in ML industry feasibility but also a conceptual shift that favors heterostructured, codoped systems designed at the atomic and mesoscale for enhanced performance. The findings published in the journal Materials Futures resonate throughout the interdisciplinary materials science community, igniting enthusiasm for further exploration of downconversion mechanoluminescence mechanisms.
The research led by Tianlong Liang, Yuantian Zheng, Qi’an Zhang, and colleagues represents a collaborative breakthrough in engineering passive ML materials with unprecedented efficiency. Their combined expertise offers a blueprint for future material design that strategically manipulates ion-ion interactions within tailored heterostructures. As such, this work pushes mechanoluminescence beyond a laboratory curiosity toward a practical technological platform poised to revolutionize light-emitting sensing devices and beyond.
In summary, the novel concept of utilizing lanthanide-codoped heterojunctions—specifically CaF₂/CaZnOS composites—has ushered in a new era of mechanoluminescence research centered on downconversion efficiencies and cooperative energy transfer phenomena. This approach unlocks enhanced brightness, spectral control across visible and near-infrared regimes, and improved device integration prospects. The horizon of ML science appears broadened not just by the light it emits but by the avenues of innovation it illuminates for the future.
Subject of Research: Mechanoluminescence enhancement via lanthanide-codoped CaF₂/CaZnOS heterojunctions and cooperative downconversion energy transfer mechanisms.
Article Title: Downconversion mechanoluminescence from lanthanide codoped heterojunctions.
News Publication Date: 2025.
Web References: http://dx.doi.org/10.1088/2752-5724/add7f3
References:
Tianlong Liang, Yuantian Zheng, Qi’an Zhang, Ziyi Fang, Mingzhi Wu, Yang Liu, Qidong Ma, Jiazhen Zhou, Maryam Zulfiqar, Biyun Ren, Yanze Wang, Jingnan Zhang, Xiaoyu Weng, Dengfeng Peng. Downconversion mechanoluminescence from lanthanide codoped heterojunctions. Materials Futures, 2025, 4(2): 025701. DOI: 10.1088/2752-5724/add7f3
Image Credits: Dengfeng Peng and Tianlong Liang from Shenzhen University.
Keywords
Lanthanides, Heterojunctions, Mechanoluminescence, Downconversion, Energy Transfer, Lanthanide Codoping, CaF₂, CaZnOS, Terbium, Ytterbium, Praseodymium, Quantum Efficiency
