Effect of V2O5 colorant on the optical properties and crystallization behaviors of lithium disilicate glass-ceramics

To understand the coloration in glass-ceramics for dental application, the effect of V ₂O ₅ colorant on the optical properties and crystallization behaviors of lithium disilicate (LS2) glass-ceramics (GCs) has been investigated for two different systems of SiO ₂-Li ₂O-P ₂O ₅-K ₂O-ZnO and SiO ₂-Li ₂O-P ₂O ₅-K ₂O-Al ₂O ₃. For this study, the amount of V ₂O ₅, SiO ₂ + Li ₂O, and P ₂O ₅ were fixed to have 0.5, 93.5, and 1.5 mol%, respectively, while the ratios of both ZnO/K ₂O (Zn/K) and Al ₂O ₃/K ₂O (Al/K) were varied from 0.5 to 2. The GC samples were prepared by two-stage heat treatments of 500 °C for 1 h as a nucleation stage and 600, 700, and 800 °C for 2 h as a growth stage in air. The light green glass samples having only V ⁵⁺ ion continuously changed to violet, blue, green, and brown for GC samples due to its reduction into V ⁴⁺ and V ³⁺ ions with progressing crystallization. TEM-EDS analyses revealed that a small amount of V ⁵⁺ ion was incorporated into both LS2 and SiO ₂ crystalline phases, causing greenish fluorescence, while most of vanadium ions remained in a residual glassy matrix. At the growth temperature of 800 °C, while the growth rate of LS2 was increased by lowering the viscosity of the glass matrix, and thus the LS2 crystal size of the GVZ _1.5 and GVZ ₃ samples became larger (∼1 μm) compared with its size below 500 nm for the samples without V ₂O ₅ colorant. The GVAl _1.5 and GVAl ₃ samples exhibited the smaller size (<1 μm) than GVZ _1.5 and GVZ ₃ samples because of higher nucleation rate and lower growth rate, leading to undesirable high translucency for the dental application.