In a study published in
Inorganic Chemistry, researchers from the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences and the Chongqing University of Posts and Telecommunications reported their progress in upconversion (UC) luminescent materials. They developed an erbium-doped calcium (CaSc2O4:Er3+) that enables high-sensitivity temperature sensing in deep biological tissues and advanced anticounterfeiting under near-infrared (NIR) light.UC materials, which convert low-energy NIR light into higher-energy visible emissions, are vital for biomedical imaging and security technologies. However, conventional materials face challenges including limited tissue penetration and reliance on external sensitizers like Yb3+ or Nd3+.
In this study, the crystal was synthesized using a high-temperature solid-state method, ensuring structural stability and phase purity. X-ray diffraction confirmed that Er3+ ions successfully replaced smaller Sc3+ ions in the crystal lattice. This substitution stabilized the matrix and enhanced its luminescent efficiency. The crystal demonstrated resilience under varying temperatures and environmental conditions, critical for real-world applications.
Under 1532 nm excitation, CaSc2O4:Er3+ exhibited dual emission bands: visible red/green light and NIR signals. Researchers employed thermally coupled energy levels of Er3+ to create a multi-path optical thermometer. The system achieved a maximum temperature sensitivity of 0.44% per Kelvin, with a detection depth exceeding 6 mm in biological tissues, which is ideal for non-invasive medical diagnostics.
For anticounterfeiting, the crystal's emission color shifted from yellow to red when switching excitation wavelengths between 980 nm and 1532 nm. This tunability, invisible under normal light, allowed secure encoding on documents or products. Tests using screen-printed patterns confirmed its effectiveness, as hidden messages only appeared under specific NIR illumination.
The study highlights the dual advantages of CaSc2O4:Er3+. It reduces costs by eliminating rare-earth sensitizers, and its deep-tissue compatibility opens up avenues for minimally invasive medical tools. Compared to earlier UC materials, its excitation within the second NIR window minimizes light scattering, improving imaging resolution. For anticounterfeiting, the wavelength-dependent color shift offers a simple yet robust security solution.
