Synthesis, properties and application of intense blue/green pigments based on Co/Cr doped Mg2TiO4 with excess MgO

Mg 2.2- x Co x TiO 4 (0 ≤  x  ≤ 0.6) and Mg 2.2- x Cr x TiO 4 (0 ≤  x  ≤ 0.6) solid solutions with spinel structure were successfully synthesized by solid-phase reaction. Excess MgO was added to achieve the single phase of the compounds. The transition metal ions Co/Cr tune the colors of Mg 2 TiO 4 to intense blue and green, respectively. The root of the observed intense blue color of Mg 2.2- x Co x TiO 4 is attributed to the 4 A 2 (F) → 4 T 1 (P) transition of Co 2+ in tetrahedral coordination. In Cr doped Mg 2 TiO 4 , Cr exists in a mixed oxidation states of +3 and + 6. The green color of the as-synthesized Mg 2.2- x Cr x TiO 4 is attributed to 4 A 2 (F) → 4 T 1 (F) at 410 nm–500 nm and 4 A 2 (F) → 4 T 2 (F) at 610 nm transitions of Cr 3+ . Besides, the Cr 3+ - Ti 4+ charge-transfer transition at 410 nm–500 nm is also the reason why it shows green. The as-synthesized pigments were dispersed into PMMA to prepare blue/green plastics.