4. Discussions
Although with the same structure, the luminescence of GTO is totally different from that of YTaO4 and LuTaO4 which exhibits characteristic CT emission of TaO3 4 group (always located around 330nmat3.76eV).ThisisascribedtoenergytransferfromTaO3 4 to Gd3þ in GTO, followed by concentration quenching [16]. For GTO, the luminescence is characterized by a super wide band composed of two Gaussian components from 8K to 300 K. The Stokes shift is very large and the excitation efficiency is almost zero below the absorption edge, indicating that both emission bands of GTO come from exciton and interband excitation. It is also likely to be intrinsic