Non-concentration quenching and energy transfer enhanced green emission in Ca8SrGd(PO4)7:Eu2+,Tb3+ for near-UV white LEDs with a high color rendering index

Abstract

Compared with the well-studied energy transfer from Ce³⁺ to Tb³⁺, the energy transfer from Eu²⁺ to Tb³⁺ has the advantage of high doping concentration of Tb³⁺, because Eu²⁺ and Tb³⁺ tend to occupy different lattice sites. Herein, the energy transfer from Eu²⁺ to Tb³⁺ is achieved in the Ca₈SrGd(PO₄)₇ host for an efficient Tb³⁺ doped green phosphor. The decrease in the lifetime of Eu²⁺ emission with the increasing Tb³⁺ concentration reveals the energy transfer from the Eu²⁺ to Tb³⁺ ions. Notably, the Tb³⁺ emission of Ca₈SrGd(PO₄)₇:Eu²⁺,Tb³⁺ has the strongest intensity at the unity doping ratio of Tb³⁺, indicating a non-concentration quenching effect. The absorption efficiency in the near-ultraviolet region was increased from 6% to 75% after Eu²⁺ was doped into Ca₈SrTb(PO₄)₇, and the emission was enhanced by approximately six times. Consequently, a high quantum efficiency (internal: 63% and external: 51%) was achieved in Ca₈SrTb(PO₄)₇:Eu²⁺. Finally, a near-ultraviolet chip excited white LED was fabricated by applying the as-prepared Ca₈SrTb(PO₄)₇:Eu²⁺ as the green phosphor, with a high color rendering index of 93, and a low correlated color temperature of 3728 K. These results indicate that the presented phosphor has potential in lighting applications, providing a new perspective for developing efficient Tb³⁺ activated phosphors through energy transfer and high doping concentration.