Survey and research on up-conversion emission character and energy transition of Yb/Er/Tm co-doped phosphate glass and glass ceramic

By conventional high-temperature melting method, Yb³⁺/Er³⁺/Tm³⁺ co-doped phosphate glass was synthesized. After annealing the precursor glass, the phosphate glass ceramic (GC) was obtained. By measuring the X-ray diffraction (XRD) spectrum, it is proved that the LiYbP₄O₁₂ and Li₆P₆O₁₈ nano-crystals have existed in the phosphate GC. The up-conversion (UC) emission intensity of the GC is obvious stronger compared to that of the glass. The reason is that the shorter distance between rare earth ions in the glass ceramic increases the energy transitions from the sensitized ions (Yb³⁺) to the luminous ions (Er³⁺ and Tm³⁺). By studying the dependence of UC emissions on the pump power, the 523 and 546 nm green emissions of Er³⁺ ions in the glass are two-photon processes. But in the glass ceramic, they are two/three-photon processes. The phenomenon implies that a three-photon process has participated in the population of the two green emissions. Using Dexter theory, we discuss the energy transitions of Er³⁺ and Tm³⁺. The results indicate the energy transition of Tm³⁺ to Er³⁺ is very strong in the GC, which changes the population mechanism of UC emissions of Er³⁺.