Crystalline Tb-2(CO3)(3): Eu3+ samples were successfully synthesized by the precipitation reaction of rare-earth chloride with ammonium bicarbonate in solution directly under mild condition without further thermal treatment. The samples were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry analysis, Fourier transform infrared spectroscopy, photoluminescence, as well as lifetimes. Influences of pH, molar ratio of precipitant to rare earth ions, aging time, temperature, and surfactant on the morphology and crystal structure were investigated in detail. The obtained samples presented dumbbell-like microstructures which were assembled from nanosheets with the assistance of ethylene glycol. Under the excitation of 220-nm ultraviolet light, the Tb-2(CO3)(3) samples showed the characteristic emissions of Tb3+ corresponding to D-5(4) -> F-7(6,5,4,3) transitions, whereas the Tb-2(CO3)(3): Eu3+ samples mainly exhibited the characteristic emissions of Eu3+ corresponding to D-5(0) -> F-7(0,1,2,3,4) transitions due to an effective energy transfer from Tb3+ to Eu3+. The energy transfer efficiency from Tb3+ to Eu3+ increased with Eu3+ doping concentration. The multicolor emission of Tb-2(CO3)(3): Eu3+ samples can be tuned from green to red easily by altering the doping concentration of Eu3+. The materials are expected to apply widely in the future, and the simple method is particularly suitable for large-scale industrial production.