Study of the luminescence of Eu2+ and Eu3+ states in Ca3Ga2Ge3O12:Eu garnet using synchrotron radiation excitation

Abstract

The work is dedicated to the investigation of Eu 2þ and Eu 3þ luminescence centers in the Ca 3 Ga 2 Ge 3 O 12 garnet using synchrotron radiation excitation. The luminescence of Eu 2þ and Eu 3þ states was observed in the emission spectra of Ca 3 Ga 2 Ge 3 O 12 :Eu ceramics under excitation with energies in the exciton range and the range above band gap of this garnet. The luminescence of Eu 2þ ions Ca 3 Ga 2 Ge 3 O 12 host is observed in the band peaked at 450-460 nm with decay time in the ten ns range and excited in the two wide bands peaked at 5.04 and 6.05 eV, related to the allowed 4f-5d transitions of Eu 2þ ions. The Eu 3þ luminescence can be excited via the Eu 2þ luminescence. We have also found the energies of formation of excitons bound with Eu 2þ and Eu 3þ ions in Ca 3 Ga 2 Ge 3 O 12 , being equal to 7.64 and 6.95 eV, respectively, and the onset of interband transitions in this garnet which is equal to 7.83 eV at 8 K. Strong increase of the luminescence intensity of Eu 2þ and Eu 3þ centers is observed under excitation above 21 eV due to multiplication of electronic excitation in Ca 3 Ga 2 Ge 3 O 12 host.

Site construction of Eu2+ and sensitized luminescence of Eu3+ in LaF3:Eu nanophosphor

“…An emission of 5 D 0 -7 F 0 around 586 nm also is observed, indicating that some Eu 3+ occupy no strict crystallographic symmetry site due to the existence of many surface defects in the nanophosphor. 5 D 0 − 7 F 0 emission is only observed in a host crystal with a relatively low site symmetry such as C s , C n, and C nv , and its intensity is usually weaker compared with that of the other 5 D 0 emissions. However, LaF 3 only provides a D 3h site.…”

“…This partial reduction has inspired some researchers to intentionally prepare Eu 2+ and Eu 3+ coactivated phosphor via the controlling reduction of Eu 3+ to Eu 2+ . [1][2][3][4][5][6][7] These phosphors show tunable luminescence and potential application in the lighting or display field. For example, Ca 2 Al 2 SiO 7 :Eu 2+ , Eu 3+ shows adjustable luminescence in the spectral range from red light to yellow light, 8 and CaYAlO 4 :Eu 2+ , Eu 3+ shows a tunable luminescence color in the range from green to yellow, and then to red.…”