Therefore, except the oxygen vacancies, we speculated that there is still a small mount of Tb3+ oxided to Tb4+ in green sample in order to maintain the valence balance. At least up to 1300 °C, a few percent of V4+, relatively few Tb4+ and oxygen vacancies can exist stably in green sample. Under 80% N2 + 20% CO2 growth atmosphere, V5+ in TV is uneasy to be reduced to the lower oxidation state, whereas the whole V5+ also keep the most Tb3+ ions stably in the TbO8 dodecahedron lattices. The addition of Ca3(VO4)2 could diminish the green coloration of TV crystal, because oxide ions can readily diffuse via oxygen vacancies which are produced by the addition of Ca2+