A universal J–O calculation method for phosphors was proposed and used for NaYF₄:Er³⁺/Yb³⁺.

Three dimensional (3D) flower-shaped microarchitectures of NaY(WO₄)₂ were synthesized via a microwave-assisted hydrothermal process in the presence of trisodium citrate (Na₃Cit) and a post-calcination process. The effects of reaction conditions on the morphology of precursor microstructures were studied. It was found that Na₃Cit, as the chelating agent and shape modifier, plays a key role in the microstructure growth. A possible growth mechanism for the flower-shaped microarchitectures was proposed. The as-formed precursor can completely transform into NaY(WO₄)₂ with its original flower-shaped morphology via a heat treatment process. The concentration and temperature quenching behaviors of Eu³⁺ fluorescence in the flower-shaped NaY(WO₄)₂ were studied, and the optimal doping concentration was confirmed, meanwhile the activation energy was obtained. Judd-Ofelt parameters Ω_λ (λ = 2, 4 and 6) of Eu³⁺ in the flower-shaped NaY(WO₄)₂ phosphor were obtained by using the emission spectrum of Eu³⁺, moreover the radiative transition properties were analyzed.

To realize photothermal therapy (PTT) of cancer/tumor both the photothermal conversion and temperature detection are required. Usually, the temperature detection in PTT needs complicated instruments, and the therapy process is out of temperature control in the present investigations. In this work, we attempt to develop a novel material for achieving both the photothermal conversion and temperature sensing and control at the same time. To this end, a core-shell structure with NaYF₄:Er³⁺/Yb³⁺ core for temperature detection and NaYF₄:Tm³⁺/Yb³⁺ shell for photothermal conversion was designed and prepared. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the temperature sensing properties for the NaYF₄:Er³⁺/Yb³⁺ and core-shell NaYF₄:Er³⁺/Yb³⁺@NaYF₄:Tm³⁺/Yb³⁺ nanoparticles were studied. It was found that the temperature sensing performance of the core-shell nanoparticles did not become worse due to coating of NaYF₄:Tm³⁺/Yb³⁺ shell. The photothermal conversion behaviors were examined in cyclohexane solution based on the temperature response, the NaYF₄:Er³⁺/Yb³⁺@NaYF₄:Tm³⁺/Yb³⁺ core-shell nanoparticles exhibited more effective photothermal conversion than that of NaYF₄:Er³⁺/Yb³⁺ nanoparticles, and a net temperature increment of about 7 °C was achieved by using the core-shell nanoparticles.

GdF3:Eu3+ nanocrystals (NCs) and nanorods were synthesized by a microemulsion-mediated hydrothermal process. The structure, shape and particle size were characterized by means of x-ray diffraction (XRD) and transmission electron microscopy (TEM). The vacuum ultraviolet (VUV) spectrum of GdF3:Eu3+ NCs shows that the Gd3+ ion can absorb one VUV photon excited in the 6GJ levels and relaxes through two-step energy transfer to Eu3+, yielding two visible photons at room temperature. The visible quantum efficiency of GdF3:Eu3+ NCs was calculated to be close to 170% by the peak intensity ratio of correlative transition emission under VUV excitation at 160 nm.

A novel strategy is proposed to prepare hexagonal EuF₃ nanocrystals by doping lanthanide ions (Ln³⁺) with large ionic radius (such as La³⁺, Ce³⁺, Pr³⁺, Nd³⁺ and Sm³⁺). Complete phase transition from orthorhombic to hexagonal phase can be achieved with the increase of ionic radius or doping concentration of Ln³⁺ ions. Meanwhile, the size and self-assembly degree of the product can be reduced dramatically. The possible growth and phase transformation mechanism of EuF₃ nanocrystals was proposed. Finally, Eu³⁺ ion was used as the structural probe to investigate the effect of phase transition on the luminescence. It was found that the emissions of the ⁵D₀ level of Eu³⁺ are greatly enhanced with the phase transition from orthorhombic to hexagonal phase. The luminescent enhancement is attributed to the larger radiative transition rate of the ⁵D₀ level in the environment with lower symmetry, which can be confirmed by Judd–Ofelt (J–O) theory.