Mechanistic Insight into Energy-Transfer Dynamics and Color Tunability of Na4 CaSi3 O9 :Tb3+ ,Eu3+ for Warm White LEDs

Abstract

In this work, a latent energy-transfer process in traditional Eu³⁺ ,Tb³⁺ -doped phosphors is proposed and a new class of Eu³⁺ ,Tb³⁺ -doped Na₄ CaSi₃ O₉ (NCSO) phosphors is presented which is enabled by luminescence decay dynamics that optimize the electron-transfer energy process. Relative to other Eu³⁺ ,Tb³⁺ -doped phosphors, the as-synthesized Eu³⁺ ,Tb³⁺ -doped NCSO phosphors show improved large-scale tunable emission color from green to red upon UV excitation, controlled by the Tb³⁺ /Eu³⁺ doping ratio. Detailed spectroscopic measurements in the vacuum ultraviolet (VUV)/UV/Vis region were used to determine the Eu³⁺ -O^2- charge-transfer energy, 4f-5d transition energies, and the energies of 4f excited multiplets of Eu³⁺ and Tb³⁺ with different 4f^N electronic configurations. The Tb³⁺ →Eu³⁺ 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:0.03Tb³⁺ , 0.05Eu³⁺ phosphor with high thermal stability and a BaMgAl₁₀ O₁₇ :Eu²⁺ 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.

Keywords: energy transfer; luminescence; luminescence decay dynamics; phosphor; rare earths.