Examination on red emission of up-conversion phosphors with Bi-containing host materials

Abstract

The luminescent center Er³⁺ doped upconversion (UC) phosphors generally exhibit strong green and weak red emission, however, some UC phosphors with Bi-containing host materials exhibit an intense red emission, or the emission color can change from green to red as the Er³⁺, Yb³⁺ concentration increases. This paper examined the relationship between the red UC emission and Bi-containing host materials by comparing the UC emission colors of host materials containing or not containing Bi with different or identical crystal structures. Furthermore, novel UC phosphors Bi₂Ti₄O₁₁:xEr, yYb and Bi₂Sn₂O₇:xEr, yYb were also synthesized by solid-state reaction method to certify those facts. These UC phosphors exhibit intense red emission with increasing Er, Yb concentrations in the same way as the reported UC phosphors with Bi-containing host materials. Based on the experimental results, it can be thought that energy transfer exists between Bi³⁺ and luminescence center Er³⁺, and inferred that non-radiative relaxation (energy-loss) is more easily to occur. Therefore, Er³⁺ doped UC phosphors with Bi-containing host materials tend to exhibit lower energy red emission than green emission.