Synthesis and luminescence properties of Eu³⁺ and Sm³⁺ doped and co-doped BiPO₄ powders by a hydrothermal route

BiPO₄:Eu³⁺, BiPO₄:Sm³⁺, and BiPO₄:(Eu³⁺, Sm³⁺) powders were synthesized by a hydrothermal route. The X-ray diffraction and Fourier-transform infrared spectroscopy results show that the samples are pure hexagonal phases. The excitation spectrum of BiPO₄:Eu³⁺ sample shows the characteristic absorption peaks of Eu³⁺ corresponding to the direct excitation from the ground state to the higher excited states of the europium f-electrons. The excitation spectrum of BiPO₄:Sm³⁺ sample consists of several narrow excitation lines due to the characteristic f–f transition of Sm³⁺. The emission spectrum of BiPO₄:Eu³⁺ specimen excited by 395 nm consists of lines mainly locating in the red area. The emission spectrum of BiPO₄:Sm³⁺ sample is composed of four emission bands, which are attributed to transitions from ⁴G_5/2 excited state to ⁶H_J/2 (J = 5, 7, 9, and 11) ground states of Sm³⁺. The excitation and emission spectra of BiPO₄:(Eu³⁺, Sm³⁺) samples are different from single doped BiPO₄ samples. The introduction of Sm³⁺ can broaden and enhance the excitation intensity of Eu³⁺ and improve the emission dominance of Eu³⁺ at 617 nm.