Review—Photoluminescence Properties of Cr3+-Activated Fluoride Phosphors

The Cr 3+ -activated phosphor properties are discussed in detail from an aspect of spectroscopic point of view. The host materials considered here are a various kind of fluoride compounds. The photoluminescence (PL) and PL excitation spectra of such Cr 3+ -activated fluoride phosphors are analyzed based on Franck−Condon analysis within the configurational-coordinate model. A method is proposed for obtaining reliable crystal-field ( Dq ) and Racah parameters ( B and C ) based on a general ligand field theory with paying an attention to difficulty in the exact estimation of such important ligand field parameters. The intra- d -shell Cr 3+ states, such as 2 E g ( 2 G ), T 2 g 4 ( 4 F ), and T 1 g 4 ( 4 F ), in various fluoride hosts are determined and plotted against Dq in the Tanabe−Sugano energy-level diagram. A comparative discussion of Cr 3+ and Mn 4+ as efficient activator ions for near-IR and red-emitting phosphors is given. Key properties of the Cr 3+ -activated fluoride phosphors are also presented for use of such near-IR or red-emitting fluoride phosphors in future light-emitting and related device applications.