A peculiar layered 12-fold cationic coordination compound LiInTi2O6: phase relations, crystal structure and color-tunable photoluminescence

Abstract

Developing new hosts is one of the significant and intriguing aspects in the field of luminescence materials. Herein, we report a novel LiInTi₂O₆ host for phosphors in solid state lighting. The sub-solidus phase relationships, thermal stability, crystal structure, as well as composition- and temperature-dependent luminescence were investigated and discussed by means of various analytical techniques, including powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), structure solution, photoluminescence excitation (PLE) and emission (PL) spectra, decay lifetime, high-temperature luminescence and chromaticity coordinates. LiInTi₂O₆ crystallizes in a trigonal unit cell with lattice parameters of a = b = 5.1050(1) Å, c = 28.5622(4) Å, and Z = 6 in space group Rm (No. 166), consisting of an unusual 12-fold coordination hexagonal prism structural framework. Taking LiInTi₂O₆ as the host, a series of Dy³⁺/Tm³⁺ singly-doped and co-doped phosphors was successfully synthesized. With increasing Dy³⁺ concentration, the emission colors of LiInTi₂O₆:Tm³⁺,Dy³⁺ phosphors can be appropriately tuned from blue to yellow, going through the white region, based on the principle of energy transfer. Energy transfer efficiencies were calculated and the mechanism was confirmed to follow a resonant-type electric dipole–dipole interaction. A configuration coordinate diagram was employed to explain the thermal quenching behaviour of the white lighting phosphor. Structural characteristics and evolution trends of representative titanates were summarized, providing available information for photo/electrical materials designing.