Effects of different volume ratio of diglycol to water on the crystalline phase of β-NaYF₄:Yb³⁺, Er³⁺

NaYF₄:20%Yb³⁺, 2%Er³⁺ crystal has been prepared via a simple hydrothermal route at different volume ratio of diglycol to water. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize and analysis the samples. FE-SEM images show that the samples have a smaller size with the increase of volume ratio of diglycol to water and finally can reach nanoscale. XRD results have proven that the volume ratios of diglycol to water have an effect on crystalline phase, and α-NaYF₄ phase begins to appear in the products when volume ratio of diglycol to water reaches to 30/10 mL. The forming mechanism is proved to be correct and get a simulation diagram of the relationship between phase transition time and volume ratio of diglycol to water. TEM images indicate that the samples belong to the polycrystalline and have good crystallinity. Under the excitation of 980 nm semiconductor laser, β-NaYF₄ crystal can emit bright blue/red upconversion luminescence.