Color-tunable luminescence and temperature sensing properties of Bi/Sm or Bi/Eu codoped BaGdGeO phosphors.

Novel temperature-sensitive luminescent materials, BaGdGeO doped with Bi, Bi/Sm or Bi/Eu 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 2/, = 4). The crystal lattice of the compounds consists of zigzag chains of edge-sharing MeO (Me = Bi, Eu or Sm) dimers, [GeO] units, and ten-coordinated Ba atoms. Under UV excitation the powders exhibit the luminescence corresponding to the P → S (310-550 nm) transition in Bi and G → H (550-730 nm) in Sm or D → F (570-720 nm) transitions in Eu ions. Heating of BaGdBiSmGeO and BaGdBiEuGeO 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 BaGdBiSmGeO and BaGdBiEuGeO germanates reach 0.19% K/0.80% K and 2.21% K/0.58% K, respectively. The above parameters indicate that BaGdGeO:Bi/Sm or Bi/Eu samples can be used as potential luminescent materials for non-contact temperature measurement.