Energy Transfer Behavior and Color-Tunable Properties of Ca2Al2SiO7:RE3+ (RE3+ = Tm3+, Dy3+, Tm3+/Dy3+) 
for White-Emitting Phosphors
Tm3+/Dy3+-codoped Ca2Al2SiO7 phosphors have been synthesized using a high-temperature solid-state reaction method. The crystal structure, x-ray diffraction patterns, and photoluminescence (PL) properties of the rare-earth (RE) ions, and energy transfer (ET) processes between RE ions, were investigated in detail. The quenching concentration of Tm3+ and Dy3+ singly doped in Ca2Al2SiO7 was determined to be 0.006 mol and 0.02 mol, respectively. Under excitation at 357 nm, Ca2Al2SiO7:Tm3+ phosphors showed emission lines of Tm3+ corresponding to 1D2 → 3F4 and 1G4 → 3H6 transitions. Efficient ET from Tm3+ to Dy3+ ions was observed, leading to color-tunable emissions of Ca2Al2SiO7:0.006Tm3+,xDy3+ (x = 0 mol to 0.02 mol) phosphors. Theoretical calculations revealed that the efficiency of the ET gradually increased with increase in the Dy3+ ion concentration, reaching a maximum of ∼ 42.1% at Tm3+ ion concentration of 0.006 mol. Furthermore, at 473 K, the quantum efficiency was calculated to be 79.8% at room temperature, confirming the good thermal stability of the Ca2Al2SiO7:0.006Tm3+,xDy3+ phosphors.