Energy Transfer in (La_1-xGd_x) OBr: Tb, Ce

Gd³⁺, Ce³⁺ and Tb³⁺ in (La_1-xGd_x OBr: Tb_0.0075, Ce_y can be excited with different wavelengths in ultra-violet region. Ce³⁺ and Tb³⁺ radiate. No Gd³⁺ characteristic luminescence has been observed, yet the energy of excited Gd³⁺transfers to Ce³⁺ and Tb³⁺, thus contributes to their radiations conssque-rtly. Energy transfer may be reversible to some extent between Ce³⁺ and Tb³⁺. The existance of Gd changes the crystal field distribution makes some red shift of the Ce³⁺ excited band and causes more Tb³⁺⁵D₃→Ce³⁺→Tb³⁺⁵D₄ energy transfer. These energy transfer processes result in the strengthen of greenish luminescence to which the naked eye is most sensitive, also result in the improvements of temperature stability of both Ce³⁺ and Tb³⁺ luminescence.