First-principles calculations of the structural, electronic, optical and elastic properties of the new phosphors, Na₂ZrF₆ and K₂ZrF₆

Two recently reported phosphor materials, Na₂ZrF₆ and K₂ZrF₆ (J. Appl. Phys. 112 (2012) 013506) are characterized using the plane-wave based first-principles calculations. The optimized crystal structure, electronic, elastic and optical properties at the ambient and elevated hydrostatic pressure are calculated. The calculated band gaps are 6.61 (5.87) eV for Na₂ZrF₆ (K₂ZrF ₆), respectively. Peculiarities in the chemical bonding between the constituting elements are evaluated by calculating the effective Mulliken charges. These materials are characterized by high covalence of the Zr ⁴⁺-F^- bonding, as confirmed by the cross-sections of the electron density difference for both materials.