Near-Infrared Luminescence and Color Tunable Chromophores Based on Cr3+-Doped Mullite-Type Bi2(Ga,AI)4O9 Solid Solutions

Cr3+-activated mullite-type Bi2Ga(4-x)AlxO9 (x = 0, 1, 2, 3, and 4) solid solutions were prepared by the solid state reaction, and their spectroscopic properties were investigated in conjunction with the structural evolution. Under excitation at 610 nm, Bi-2[Ga((4-y))Aly](3).97O9:0.03Cr(3+) (y = 0, 1, 2, 3, and 4) phosphors exhibited broad-band near-infrared (NIR) emission peaking at similar to 710 nm in the range 650850 nm, and the optimum Cr3+ concentrations and concentration quenching mechanism were determined. Except for the interesting NIR emission, the body color changed from white (at x = 0) to green (at x = 0.08) for Bi2Ga4xO9:xCr3+, and from light yellow (at x = 0) to deep brown (at x = 0.08) for Bi2Al4xO9:xCr3+, respectively. Moreover, as a result of variable Al/Ga ratio, the observed body color for Bi-2[Ga(4-y)Aly](3).97O9:0.03Cr(3+) (y = 0, 1, 2, 3, and 4) varied from deep brown to green. The relationship between the observed colors and their diffuse reflectance spectra were also studied for the understanding of the different absorption bands. The results indicated that Cr3+-doped Bi2Ga(4-x)AlxO9 solid solutions appeared as the bifunctional materials with NIR phosphors and color-tunable pigments.