Photoluminescence of Eu3+-activated GdTaO4 with both M type and M′ type structures

A series of Eu3+ doped M and M′ type gadolinium orthotantalate Gd1− xEuxTaO4 (x = 0–0.20) have been synthesized by high temperature solid state reaction. The emission and excitation spectra for M and M′ type gadolinium orthotantalate are studied in detail. The structural difference between M and M′ type structure obviously influences their luminescence properties. The main excitation bands in M′ type Gd1− xEuxTaO4 shift to shorter wavelength because of a shorter distance of Ta-O in comparison with M type. The strong evidence from excitation spectra, emission spectra and diffusive reflection spectra of these two system show Gd3+ can play an intermediate role of energy transfer in the process of luminescence. There is energy transfer from TaO43− to Gd3+ and finally to Eu3+ via the charge transfer states and spectral overlap.