Designing Er3+/Ho3+-Doped Near-Infrared (NIR-II) Fluorescent Ceramic Particles for Avoiding Optical Absorption by Water

Rare-earth-doped ceramics, which are near-infrared (NIR) fluorescent materials, have applications as photonic materials in various fields, including medical biology. The NIR wavelength range in which these rare-earth-based materials function is highly transparent in biological tissues and is suitable for deep-tissue imaging. However, the most commonly used 980-nm excitation light is partially absorbed by the water involved in the observation system. In the present study, we focused on the wavelength bands of 800-nm excitation and 1150-nm emission, where no water absorption exists, and investigated the rare-earth doping composition to obtain a ceramic material, NaYF4, with the above excitation and emission wavelengths. NaYF4 particles co-doped with rare-earth ions Er3+ (sensitizer to 800 nm) and Ho3+ (emitter at 1150 nm) were designed for over-1000 nm NIR fluorescent probes. The fluorescence intensity at 1150 nm was maximum at a rare-earth composition of Y3+: Er3+: Ho3+ = 82:14:4 (mol%). The obtained fluorescent Er3+/Ho3+-doped NaYF4 particles exhibited a long fluorescence lifetime (3300 +/- 120 mu s at 25 degrees C), which is characteristic of rare-earth elements. Er3+/Ho3+-doped NaYF4 is expected to have applications as a long-lifetime NIR-II fluorescent material with the highest transparency in biological tissues.

Automated summary

Rare-earth-doped ceramics are NIR fluorescent materials with various potential applications. In this study, NaYF4 ceramic material with specific excitation and emission wavelengths was synthesized by controlling the doping composition of rare-earth ions. The obtained Er3+/Ho3+-doped NaYF4 particles showed long fluorescence lifetime and are expected to have wide applications in biological tissues.