Tunable white light of a Ce,Tb,Mn triply doped NaCaSiO phosphor for high colour-rendering white LED applications: tunable luminescence and energy transfer.

A tunable white light emitting NaCaSiO:Ce,Tb,Mn phosphor with a high color rendering index (CRI) has been prepared. Under UV excitation, NaCaSiO:Ce phosphors present blue luminescence and exhibit a broad excitation ranging from 250 to 400 nm. When codoping Tb/Mn ions into NaCaSiO, energy transfer from Ce to Tb and Ce to Mn ions is observed from the spectral overlap between Ce emission and Tb/Mn excitation spectra. The energy-transfer efficiencies and corresponding mechanisms are discussed in detail. The mechanism of energy transfer from Ce to Tb is demonstrated to be a dipole-quadrupole mechanism by the Inokuti-Hirayama model. The wavelength-tunable white light can be realized by coupling the emission bands centered at 440, 550 and 590 nm ascribed to the contribution from Ce, Tb and Mn, respectively. The commission on illumination value of color tunable emission can be tuned by controlling the content of Ce, Tb and Mn. Temperature-dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. White LEDs with CRI = 93.5 are finally fabricated using a 365 nm UV chip and the as-prepared NaCaSiO:Ce,Tb,Mn phosphor. All the results suggest that NaCaSiO:Ce,Tb,Mn can act as potential color-tunable and single-phase white emission phosphors for possible applications in UV based white LEDs.