Dual-Cation Strategy Boosts Upconversion Efficiency In Stable Oxide Perovskites

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.

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.

In this study, the researchers synthesized a series of dual-cation titanate perovskites with the formula Li(1−x)NaxLaTi_₂O_₆, doped with Yb^³⁺/Er^³⁺ or Yb^³⁺/Tm^³⁺ 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, Li_₀.₁Na_₀.₉LaTi_₂O_₆:Yb^³⁺/Er^³⁺ 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.