New green-emitting Gd2O2CO3:xTb(3+) fine particles were synthesized by a flux method using the 0.476Li(2)CO(3)-0.270Na(2)CO(3)-0.254K(2)CO(3) eutectic mixture. The emission intensity of the Gd2O2CO3:16.9 atom %Tb3+ phosphor was equivalent to that of the commercial LaPO4:Ce3+Tb3+, in spite that the size was apparently smaller (ca. 1/10) than the commercial one.