Spectroscopic properties and location of the Tb3+ and Eu3+ energy levels in Y2O2S under high hydrostatic pressure

Abstract

In this contribution, an extensive spectroscopic study of Y₂O₂S doped with Eu³⁺ and Tb³⁺ is presented. Steady-state luminescence and luminescence excitation spectra as well as the time-resolved spectra and luminescence kinetics were obtained at high hydrostatic pressures up to 240 kbar. It was found that pressure quenches the luminescence from the ⁵D₃ excited state of Tb³⁺ and recovers additional luminescence related to transitions from the ⁵D₃ state of Eu³⁺. These effects are related to the pressure-induced increases in the energies of the ground electronic manifold 4fⁿ of Eu³⁺ and Tb³⁺ ions with respect to the band edges. Analysis of the emission and excitation spectra allowed the estimation of the energies of the ground states of all lanthanide (Ln) ions (Ln³⁺ and Ln²⁺) with respect to the valence and conduction bands edges of the Y₂O₂S host. The bandgap energy and difference between energies of the ground states of Ln²⁺ and Ln³⁺ have been calculated as functions of pressure. The experimental high-pressure spectroscopy results allow the calculation of the absolute values (calculated with respect to the vacuum level) of the energies and pressure-induced shifts of the conduction and valence band edges and the ground states of Ln³⁺ and Ln²⁺ ions in Y₂O₂S.