Influence of Chemical and Mechanical Pressure on the Luminescence Properties of Near-Infrared Phosphors

Abstract

In this study, we aim to compare the changes in the luminescence properties of Ga2O3:Cr3+ modified by Al or Sc ion substitution (chemical pressure) and hydrostatic pressure. We find the same behavior for Ga2-xAlxO3:Cr3+ and different behavior for Ga2-xScxO3:Cr3+ in terms of the optical properties under chemical and mechanical pressure. We consider Al substitution, which does not affect the chemical bond angles in the Cr3+ local environment and changes the crystal volume, like mechanical pressure does. As confirmed by Raman spectroscopy, the Sc ions cause lattice distortion and influence the chemical bond lengths and angles in the Cr3+ local environment. The energy structure diagrams of all levels of the d3 configuration of the Cr3+ ion as a function of pressure are calculated by considering the pressure dependence of the Racah parameters. The energy structure diagrams presented in the paper show a decrease in the energy of the 2E, 2T1, and 2T2 excited levels with an increase in Dq. This does not align with the behavior predicted for these excited levels by the standard Tanabe-Sugano diagram. It seems correct that a high-pressure experiment involving Cr3+ and other transition metals should be interpreted using the method and diagrams presented herein.