Tunable white light of a Ce3+,Tb3+,Mn2+ triply doped Na2Ca3Si2O8 phosphor for high colour-rendering white LED applications: tunable luminescence and energy transfer
A tunable white light emitting Na2Ca3Si2O8:Ce3+,Tb3+,Mn2+ phosphor with a high color rendering index (CRI) has been prepared. Under UV excitation, Na2Ca3Si2O8:Ce3+ phosphors present blue luminescence and exhibit a broad excitation ranging from 250 to 400 nm. When codoping Tb3+/Mn2+ ions into Na2Ca3Si2O8, energy transfer from Ce3+ to Tb3+ and Ce3+ to Mn2+ ions is observed from the spectral overlap between Ce3+ emission and Tb3+/Mn2+ excitation spectra. The energy-transfer efficiencies and corresponding mechanisms are discussed in detail. The mechanism of energy transfer from Ce3+ to Tb3+ 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 Ce3+, Tb3+ and Mn2+, respectively. The commission on illumination value of color tunable emission can be tuned by controlling the content of Ce3+, Tb3+ and Mn2+. 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 Na2Ca3Si2O8:Ce3+,Tb3+,Mn2+ phosphor. All the results suggest that Na2Ca3Si2O8:Ce3+,Tb3+,Mn2+ can act as potential color-tunable and single-phase white emission phosphors for possible applications in UV based white LEDs.