Researchers at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences have developed a new way to significantly enhance upconversion luminescence in oxide perovskites, a class of materials known for their thermal and chemical stability but limited optical efficiency.
Led by Professor JIANG Changlong, the team introduced a dual-cation substitution strategy in titanate perovskites by precisely adjusting the sodium-to-lithium ratio at the crystal’s A-site. This controlled substitution triggers a structural transition that improves energy transfer between rare-earth ions, resulting in a marked increase in luminescence intensity and quantum yield.
The findings were published in Journal of Alloys and Compounds.
Efficient and stable luminescent materials are in growing demand for applications such as solid-state lighting, full-color displays and secure anti-counterfeiting. While fluoride-based upconversion materials can deliver high efficiency, they often suffer from poor long-term stability. Oxide perovskites offer greater robustness, but their use has been restricted by low efficiency and thermal quenching.
To overcome these limitations, the researchers synthesized a series of dual-cation titanate perovskites with the formula Li(1−x)NaxLaTi₂O₆, doped with Yb³⁺/Er³⁺ or Yb³⁺/Tm³⁺ ion pairs. Replacing Li⁺ with Na⁺ induces a phase transition from a tetragonal to a rhombohedral structure, which alters the local crystal field around the luminescent ions and enables more efficient energy transfer.
Among the tested materials, Li₀.₁Na₀.₉LaTi₂O₆:Yb³⁺/Er³⁺ showed the best performance. Compared with the baseline compositions, the optimized phosphor achieved up to 32-fold enhancement in upconversion intensity and more than 70-fold improvement in quantum yield, while maintaining excellent thermal stability.
Under 980 nm laser excitation, the phosphors emit bright and tunable green and blue light across a wide temperature range, highlighting their potential for use in high-performance lighting devices and durable anti-counterfeiting labels.
Schematic overview of structure-guided Na+/Li+ substitution strategy in titanate perovskites for enhanced upconversion emission and applications in NIR-triggered light-emitting diodes (LED) and anti-counterfeiting. (Image by JIANG Changlong)