Color-tunable Ca4-1.5xTa2O9: xTb3+ phosphors are prepared via a convenient solid-state reaction and the cross-relaxation mechanism is investigated. The concentration of Tb3+ ions greatly affects blue-green emission in Ca4Ta2O9 samples. The cross-relaxation effect is explained with the use of Raman and emission spectra and the thermal stability of Ca4-1.5xTa2O9: xTb3+ is evaluated under excitation at 254nm. Using the theoretical fitting results, the cross-relaxation between Tb3+ ions, via energy transfer from 5D3 to 5D4, was determined to be a multipolar interaction of the dipoledipole mechanism. The critical distance was calculated to be 15.45 angstrom. The thermal quenching temperature (T50) is higher than 200 degrees C. Results show that Ca4-1.5xTa2O9: xTb3+ phosphors have good thermal stability and color tunability.