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Description
Near-infrared (NIR) optical imaging is a powerful tool for cancer diagnosis, offering deep tissue penetration and minimal autofluorescence. Rare-earth tantalates (RETaO₄) are promising host materials for NIR-emitting probes due to their wide band gaps, chemical stability, and ability to accommodate diverse dopants. In this work, a complete series of undoped RETaO₄ (RE = La, Nd, Gd, Ho, Er, Yb) was synthesised via ethanol-aided solid-state reaction and characterised using XRD, UV-Vis DRS, PLE, PL, ESR, and lifetime measurements. XRD reveals a systematic structural evolution, driven by lanthanide contraction. UV-Vis DRS shows wide band gaps (4.51–5.15 eV), ensuring NIR transparency. PLE and PL reveal characteristic 4f–4f transitions and defect emissions spanning the visible to NIR, with microsecond-range lifetimes suitable for time-gated imaging. ESR confirms paramagnetic oxygen vacancies correlated with luminescence. These findings establish a comprehensive structure-property baseline for RETaO₄ hosts, providing a foundation for engineering NIR-emitting probes for cancer imaging.