The strong coupling between the crystal lattice and excitons would lead to the generation of self-trapped excitons (STEs)[1,2], which are one type of bound state excitons. Unlike bound state excitons usually formed by binding to defects, STE can be produced even in a perfect crystal lattice, which is created by the deformation of the crystal lattice under the coupling effect due to the softness of the crystal lattice[1,3]. Once the excitation is removed, the coupling disappears, and the lattice will return to its original state, resulting in removal of STE. Therefore, STE can be regarded as one type of trapped state that exists only under an excited state. STE exhibits broadband emissions with a large Stokes shift below the bandgap, which is beneficial to the white-light emitting devices[5–10]. Identifying and investigating the basic physical properties of STE is the basis for designing optoelectronic devices and optimizing device performance.