Ultra-small upconversion nanoparticles for optical fiber application

Upconversion nanoparticles are appealing to various applications due to their energy conversion capabilities. However, their potential is limited by low efficiency, reproducibility, and poor morphology control. In this work, the synthesis of NaYF₄ co-doped with Yb³⁺ and Tm³⁺ ions using both thermal decomposition (TD) and microwave irradiation heating (MW) using non-polar solvent were explored. Finding that the samples obtained by MW irradiation not only reduced reaction time but also decreased particle size from micrometers to nanometers. Also, their particle size distribution and shape control improved. The upconverted emission obtained in both cases is in consistency with the characteristic emission band of thulium located at 360, 451, 476, 645, and 802 nm corresponding with ¹D₂→³H₆, ¹D₂→³F₄, ¹G₄→³H₆, ¹G₄→³F₄, and ³H₄→³H₆ transitions, respectively.