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-NaY0.8Gd0.2F4: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.