Effect of host structure on the photoluminescence properties of Ln3TaO7:Eu3+ red phosphors

• Ln3TaO7:Eu3+ (Ln = La, Gd, Y, Lu) red phosphors were prepared by a solid state route.
• Phosphors show strong absorptions at near UV and emit orange–red luminescence.
• Structure changes from fluorite to weberite with increasing ordering from Lu to La.
• Eu3+ unusually occupies in VII coordination in La3TaO7 giving all 4f transitions.
• Cation ordering and coordination has great role in the luminescence properties.

Eu3+ doped Ln3TaO7 (Ln = La, Gd, Y, Lu) red phosphors were prepared using a solid state route. The Ln3+ substitution induces variation of crystalline structure from a defect fluorite to weberite types with increased ordering of the cations from Lu to La. These phosphors show strong absorptions at near UV wavelength and emit orange–red luminescence. The increased trend in luminescence lifetime further surmises uniform distribution of Eu3+ ions from Lu to La. The luminescence intensity and quantum efficiency are closely related to the degree of ordering of the cations in the lattice. The Eu3+ luminescence in La3TaO7 embodies the structural variation through intense multiband 5D0 → 7F0,1,2,4 transitions to only dominant hypersensitive electric dipole 5D0 → 7F2 transition. All the Eu3+ emission transitions (5D0 → 7F0,1,2,4) are more intense in La3TaO7 host due to increased polarizability and covalent nature of Eu3+ bonding environment with the surrounding.