Color‐Tunable Blue to Green Ca 4‐1.5 x Ta 2 O 9 : x Tb 3+ Phosphor: Cross‐Relaxation Mechanism and Thermal Stability

Color‐tunable Ca 4‐1.5 x Ta 2 O 9 : x Tb 3+ phosphors are prepared via a convenient solid‐state reaction and the cross‐relaxation mechanism is investigated. The concentration of Tb 3+ ions greatly affects blue‐green emission in Ca 4 Ta 2 O 9 samples. The cross‐relaxation effect is explained with the use of Raman and emission spectra and the thermal stability of Ca 4‐1.5 x Ta 2 O 9 : x Tb 3+ is evaluated under excitation at 254 nm. Using the theoretical fitting results, the cross‐relaxation between Tb 3+ ions, via energy transfer from 5 D 3 to 5 D 4 , was determined to be a multipolar interaction of the dipole–dipole mechanism. The critical distance was calculated to be 15.45 Å. The thermal quenching temperature ( T 50 ) is higher than 200°C. Results show that Ca 4‐1.5 x Ta 2 O 9 : x Tb 3+ phosphors have good thermal stability and color tunability.