Bundle-shaped β-NaYF₄ microrods: Hydrothermal synthesis, Gd-mediated downconversion luminescence and ratiometric temperature sensing

In this study, bundle-shaped β-NaYF₄ microrods with uniform morphology and good monodispersity were successfully synthesized via a facile, template-free and environmentally-friendly hydrothermal route. According to the time-dependent experimental results, the formation mechanism for the crystal phase and shape evolution process has been proposed via the Ostwald-ripening process. Under single wavelength irradiation at 250 nm, intense multi-color downconversion emissions can be obtained by co-doping Ce³⁺, Gd³⁺ and X³⁺ (X = Eu, Tb and Dy) into the as-synthesized β-NaYF₄ crystals, in which Gd³⁺ plays an intermediate role in transferring the excitation energy from sensitizer Ce³⁺ to activators X³⁺. Furthermore, the temperature-dependent emission behaviors of β-NaY_0.8Gd_0.2F₄:Ce³⁺/X³⁺ dual-emitting products have been systemically investigated to explore their possible application in self-calibrated optical thermometry. Impressively, the high temperature sensitivity, good signal discriminability and excellent thermal stability of the investigated dual-emitting phosphors making them a promising candidate for temperature sensing.