Ho3+–Yb3+ doped NaGdF4 nanothermometers emitting in BW-I and BW-II. Insight into the particle growth intermediate steps

Abstract

Here, the excellent thermal sensing capability of Ho³⁺, Yb³⁺ doped β-NaGdF₄ nanoparticles, where the system is excited into the ⁵F₅ ← ⁵I₈ transition of Ho³⁺ (640 nm), is reported. The ratio of the ²F_5/2 → ²F_7/2 transition peak of Yb³⁺ and the ⁵I₆ → ⁵I₈ transition peak of Ho³⁺ was employed for thermometry applications, resulting in a novel thermometer, which could potentially operate in BW-I and BW-II (BW – biological window). Additionally, interesting findings were made about the influence of the reaction time on the particle morphology and the presence of intermediate morphology forms.