Nd3+-doped Ca3Ga2Ge3O12 garnet: a new optical pressure sensor

A pressure-induced shift of the emission spectrum corresponding to the near infrared F-4(3/2) -> I-4(9/2) transition of Nd3+ ions in a calcium gadolinium germanium garnet was obtained in the interval from ambient conditions up to 23 GPa in order to test its suitability as an optical pressure sensor. Although several Nd3+ non-equivalent centers are present in this garnet, which complicates the assignation of the optical transitions, the R-1, R-2 -> Z(5) transitions are unequivocally characterised and fit the requirements of an ideal optical pressure sensor. Results obtained for these emission peaks indicate large pressure coefficients of -8.8 and -10.8 cm(-1) GPa(-1); meanwhile, the rest of the R-1, R-2 -> Z(1-4) emissions remain almost unchanged under pressure. This behaviour is ascribed to the influence of the crystal-field at high pressure on the Z(5) Stark level of the ground state and can be easily reproduced exclusively by varying the cubic term of fourth rank of the crystal-field Hamiltonian, which accounts for the Nd3+ ions and is related to medium Nd3+-oxygen distances. These coefficients are larger than those found for the R-lines of Cr3+ in ruby, -7.56 cm(-1) GPa(-1), suggesting that this system may be a good candidate for a luminescence pressure sensor.

Nd3+-doped Ca3Ga2Ge3O12 garnet: a new optical pressure sensor Articles