Preparation, characterization, and photoluminescence properties of Tb ³⁺-, Ce³⁺-, and Ce³⁺/Tb³⁺-activated RE₂Si₄N₆C (RE = Lu, Y, and Gd) phosphors

Photoluminescence properties of Tb³⁺ and Ce³⁺ singly doped and Ce³⁺/Tb³⁺-codoped RE₂Si ₄N₆C (RE = Lu, Y, and Gd) phosphors were investigated. Tb³⁺ shows similar luminescence properties in RE₂Si ₄N₆C (RE = Lu, Y, and Gd) host lattices and emits bright green light under UV excitation around 300 nm. The luminescence properties of Ce³⁺ in RE₂Si₄N₆C host lattices are influenced by the size of the RE³⁺ ions (Lu₂Si ₄N₆C and Y₂Si₄N₆C vs Gd₂Si₄N₆C). Both Ce³⁺-activated Lu₂Si₄N₆C and Y₂Si₄N ₆C phosphors exhibit a broad band emission in the wavelength range of 450-750 nm with peak center at about 540 nm, while Ce³⁺-activated Gd₂Si₄N₆C shows a broad emission band in the wavelength range of 500-800 nm with peak center at about 610 nm. This difference is ascribed to the different site occupations of Ce³⁺ on the two crystallographic sites in Gd₂Si₄N₆C as compared to the Y and Lu compounds. In Ce³⁺/Tb³⁺-codoped RE ₂Si₄N₆C (RE = Lu, Y, and Gd) phosphors, it is observed that energy transfer takes place from Ce³⁺ to Tb ³⁺ in Ce³⁺/Tb³⁺-codoped Lu₂Si ₄N₆C and Y₂Si₄N₆C but in the reversed direction from Tb³⁺ to Ce³⁺ in Ce ³⁺/Tb³⁺-codoped Gd₂Si₄N ₆C, depending on the position of the 5d level of Ce³⁺ versus the ⁵D₄ level of Tb³⁺. The potential applications of these phosphors are pointed out.