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

In this study, weaim to compare the changes in the luminescenceproperties of Ga2O3:Cr3+ modifiedby Al or Sc ion substitution (chemical pressure) and hydrostatic pressure.We find the same behavior for Ga2-x Al x O3:Cr3+ anddifferent behavior for Ga2-x Sc x O3:Cr3+ in terms ofthe optical properties under chemical and mechanical pressure. Weconsider Al substitution, which does not affect the chemical bondangles in the Cr3+ local environment and changes the crystalvolume, like mechanical pressure does. As confirmed by Raman spectroscopy,the Sc ions cause lattice distortion and influence the chemical bondlengths and angles in the Cr3+ local environment. The energystructure diagrams of all levels of the d(3) configurationof the Cr3+ ion as a function of pressure are calculatedby considering the pressure dependence of the Racah parameters. Theenergy structure diagrams presented in the paper show a decrease inthe energy of the E-2, T-2(1), and T-2(2) excited levels with an increase in Dq. Thisdoes not align with the behavior predicted for these excited levelsby the standard Tanabe-Sugano diagram. It seems correct thata high-pressure experiment involving Cr3+ and other transitionmetals should be interpreted using the method and diagrams presentedherein.