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.