NIR I‐to‐NIR I Time‐Gated Luminescence Detection From Tm 3+ ‐Doped Gd 3 TaO 7 for Deep Tissue Imaging

ABSTRACT Bioimaging has been employed as a contactless diagnostic technique, with optical imaging (OI) standing out for its high sensitivity and resolution. OI faces challenges, particularly related to the excitation wavelengths that allow deeper tissue penetration. Here, we present a system with temporal resolution that combines time‐gated luminescence (TGL) with both excitation and emission operating within the near‐infrared (NIR) biological transparency window (BW). Using Tm 3+ as a dopant, excitation at 808 nm is performed, a wavelength that benefits from a minimum of water absorption and reduces photodamage to biological tissues. Spherical Tm 3+ ‐doped and Tm 3+ /Yb 3+ co‐doped Gd 3 TaO 7 particles are synthesized with controlled morphology and size. Under 808 nm excitation, Tm 3+ ‐singly doped samples exhibit strong TGL, whereas Yb 3+ co‐doping leads to significantly weaker luminescence. Confocal spectroscopy enables spectra acquisition near the excitation wavelength, shedding light on the emission mechanisms of Tm 3+ . Excitation at 808 nm directly populates the 4 H 6 level of Tm 3+ , followed by a phonon‐assisted one‐photon process. In co‐doped samples, energy transfer from Tm 3+ to Yb 3+ occurs, but inefficient back transfer results in quenching of Tm 3+ emission at 800 nm. These results highlight the feasibility of TGL systems operating within NIR biological windows and underscore their potential for advancing OI applications.