New green emitting phosphors, hexagonal II-type Gd 2 O 2 CO 3 :Tb 3+ and Y 2 O 2 CO 3 :Tb 3+ , were synthesized by the simple flux method and their luminescence properties were compared with that of II-La 2 O 2 CO 3 :Tb 3+ . Bright green emission was observed in each sample and their particle sizes were in submicron scale. The excitation spectrum consisted of a broad band and some sharp peaks, which were corresponding to the 4f-5d transition of Tb 3+ and 4f-4f transition of Gd 3+ and Tb 3+ , respectively. The excitation wavelength of the 4f-5d bands depends on the distance between Tb 3+ and O 2− , which affects the crystal field effect on the 5d levels of Tb 3+ . Among lanthanum, gadolinium, and yttrium oxycarbonates, Gd 2 O 2 CO 3 is the most suitable host to obtain high emission intensity and the maximum intensity was obtained at the composition of Gd 2 O 2 CO 3 :17 at.% Tb 3+ , where it was 101% of that of a commercial LaPO 4 :Ce 3+ ,Tb 3+ phosphor.