Optical temperature sensing based on phonon-assisted population of Dy3+ sensitized by Gd3+ in Gd2Ge2O7 nanophosphors

Abstract Herein, we propose a series of unprecedented Dy3+-doped triclinic Gd2Ge2O7 nanophosphors by solid-state reaction method. As the doping concentration arises, the XRD peaks shift to large angle and absorption edge energy increases from 5.42 to 5.45 eV. Under 275 nm excitation, Dy3+ ions are sensitized by Gd3+ and exhibits two strong emission peaks at 484 and 575 nm as well as two weak emission peaks at 455 and 663 nm. The interaction between Gd3+ and Dy3+ is dipole-dipole interaction and the critical distance is estimated to be 16.58 A. For sample with optimal doping concentration, along with temperature increases from 300 to 570 K, PL intensity of 484 nm and 575 nm slightly decreases, while that of 455 nm sharply increased about 4 times. The interval of thermally coupled levels Dy3+: 4F9/2 and 4I15/2 is estimated to be 1317 cm−1. Population at Dy3+: 4I15/2, 4F9/2 energy levels in GGO lattice can be attributed to thermally-coupled levels of Dy3+ and phonon-assisted absorption transition of Gd3+. The temperature sensitivity of 1.5 at% Dy3+ ions in GGO is calculated to be as high as 2029.5/T2. This work paves a new way to search for high performance optical thermometric materials based on phonon-assisted transition and energy-transfer mechanism.