Expanding near-infrared emission bandwidth in K2NaCrF6:Fe3+ phosphors through dipole-dipole energy transfer

Currently, the application potential of Cr3+ doped near-infrared (NIR) fluoride phosphors excited by blue light is promising. However, the development of near-infrared fluoride phosphors with wider emission bandwidth remains a challenge. Herein, we employed the hydrothermal method to prepare K2NaCrF6:Fe3+ phosphors. Upon excitation at 432 nm, the K2NaCrF6:xFe3+ phosphors exhibited broad near-infrared emission, with the main peak ranging from 752 nm to 780 nm. As the Fe3+ ion concentration increased, the luminescence intensity of the K2NaCrF6:xFe3+ phosphor decreased, accompanied by a redshift in the emission band and an increase in the full width of the emission spectrum half-peak. These changes can be attributed to the dipole-dipole interaction, specifically the energy transfer from Fe3+ to Cr3+, leading to the 4T2(4F) → 4A2(Cr3+) and 4T1(4G) → 6A1(6S) (Fe3+) transitions.