Color-tunable luminescence and temperature sensing properties of Bi 3+ /Sm 3+ or Bi 3+ /Eu 3+ codoped Ba 2 Gd 2 Ge 4 O 13 phosphors.

Novel temperature-sensitive luminescent materials, Ba ₂ Gd ₂ Ge ₄ O ₁₃ doped with Bi ³⁺ , Bi ³⁺ /Sm ³⁺ or Bi ³⁺ /Eu ³⁺ ions, have been prepared using a conventional solid-state reaction technique. The XRPD study has verified that all the synthesized germanates crystallize in the monoclinic system (space group C 2/ c , Z = 4). The crystal lattice of the compounds consists of zigzag chains of edge-sharing Me ₂ O ₇ (Me = Bi ³⁺ , Eu ³⁺ or Sm ³⁺ ) dimers, [Ge ₄ O ₁₃ ] units, and ten-coordinated Ba atoms. Under UV excitation the powders exhibit the luminescence corresponding to the ³ P ₁ → ¹ S ₀ (310-550 nm) transition in Bi ³⁺ and ⁴ G _5/2 → ⁶ H _J (550-730 nm) in Sm ³⁺ or ⁵ D ₀ → ⁷ F _J (570-720 nm) transitions in Eu ³⁺ ions. Heating of Ba ₂ Gd _1.94 Bi _0.01 Sm _0.05 Ge ₄ O ₁₃ and Ba ₂ Gd _1.89 Bi _0.01 Eu _0.1 Ge ₄ O ₁₃ phosphors leads to an irregular decrease in the intensity of the main emission lines. It has been found that the fluorescence intensity ratio between a wide band in the 310-530 nm region and peaks at longer wavelengths may be successfully used as a temperature-dependent characteristic. Absolute/relative sensitivity values for Ba ₂ Gd _1.94 Bi _0.01 Sm _0.05 Ge ₄ O ₁₃ and Ba ₂ Gd _1.89 Bi _0.01 Eu _0.1 Ge ₄ O ₁₃ germanates reach 0.19% K ^-1 /0.80% K ^-1 and 2.21% K ^-1 /0.58% K ^-1 , respectively. The above parameters indicate that Ba ₂ Gd ₂ Ge ₄ O ₁₃ :Bi ³⁺ /Sm ³⁺ or Bi ³⁺ /Eu ³⁺ samples can be used as potential luminescent materials for non-contact temperature measurement.