Mechanistic Insight into Energy-Transfer Dynamics and Color Tunability of Na CaSi O :Tb ,Eu for Warm White LEDs.

In this work, a latent energy-transfer process in traditional Eu ,Tb -doped phosphors is proposed and a new class of Eu ,Tb -doped Na CaSi O (NCSO) phosphors is presented which is enabled by luminescence decay dynamics that optimize the electron-transfer energy process. Relative to other Eu ,Tb -doped phosphors, the as-synthesized Eu ,Tb -doped NCSO phosphors show improved large-scale tunable emission color from green to red upon UV excitation, controlled by the Tb /Eu doping ratio. Detailed spectroscopic measurements in the vacuum ultraviolet (VUV)/UV/Vis region were used to determine the Eu -O charge-transfer energy, 4f-5d transition energies, and the energies of 4f excited multiplets of Eu and Tb with different 4f electronic configurations. The Tb →Eu energy-transfer pathway in the co-doped sample was systematically investigated, by employing luminescence decay dynamics analysis to elucidate the relevant energy-transfer mechanism in combination with the appropriate model simulation. To demonstrate their application potential, a prototype white-light-emitting diode (WLED) device was successfully fabricated by using the yellow luminescence NCSO:0.03Tb , 0.05Eu phosphor with high thermal stability and a BaMgAl O :Eu phosphor in combination with a near-UV chip. These findings open up a new avenue to realize and develop multifunctional high-performance phosphors by manipulating the energy-transfer process for practical applications.