The Effect of Hydrostatic Pressure on Structure, Crystal-Field Strength, and Emission Properties of Neat and Ni²⁺-Activated KMgF₃

To understand excellent emission and sensitivity for hydrostatic pressure luminescent ions host material, the first principles calculations carried out within density functional theory (DFT) framework are performed to clarify the electronic structure of neat and doped with Ni²⁺ ions KMgF₃ single crystals. The results of band structure calculations show that F2p states are the principal contributors to the KMgF₃ valence band, mainly in its upper and central parts, while in the energy band gap of the KMgF₃:Ni²⁺ phosphor, new electronic states associated with the Ni²⁺ 3d-orbitals are formed. Furthermore, the zero phonon line (ZPL) spin-forbidden transition emission energies, (³A₂⇄¹E) _ZPL, (³A₂⇄³T₂) _ZPL, strength of the octahedral crystal field, 10Dq (³A₂→³T₂)_ZPL, are calculated for the KMgF₃:Ni²⁺ phosphor. Any changes of the E_m(³A₂⇄¹E)_ZPL transition energy of the KMgF₃:Ni²⁺ phosphor with pressure increasing from 0 to 20 GPa are not detected, while the crystal-field strength increases linearly with increasing pressure. Present results bring a foresight tool for predicting physicochemical properties of undoped and doped wide-gap fluorides; KMgF₃:Ni²⁺, without any toxic/harmful or expensive rare-earth can be effectively used as an optical manometer in 0–20 GPa, which covers the almost whole pressure range available at present in Diamond anvil cell experiments.