Enhanced luminescence of Tb 3+ by efficient energy transfer from Ce 3+ in Sr 2B 5O 9Cl host

Ce ³⁺ and Tb ³⁺ co-doped Sr ₂B ₅O ₉Cl phosphors with intense green emission were prepared by the conventional high-temperature solid-state reaction technique. A broad band centered at about 315 nm was found in phosphor Sr ₂B ₅O ₉Cl: Ce ³⁺, Tb ³⁺ excitation spectrum, which was attributed to the 4f-5d transition of Ce ³⁺. The typical sharp line emissions ranging from 450 to 650 nm were originated from the ⁵D ₄ → ⁷F _J (J = 6, 5, 4, 3) transitions of Tb ³⁺ ions. The photoluminescence (PL) intensity of green emission from Tb ³⁺ was enhanced remarkably by co-doping Ce ³⁺ in the Tb ³⁺ solely doped Sr ₂B ₅O ₉Cl phosphor because of the dipole-dipole mechanism resonant energy transfer from Ce ³⁺ to Tb ³⁺ ions. The energy transfer process was investigated in detail. In light of the energy transfer principles, the optimal composition of phosphor with the maximum green light output was established to be Sr _1.64Ce _0.08Tb _0.1Li _0.18B ₅O ₉Cl by the appropriate adjustment of dopant concentrations. The PL intensity of Tb ³⁺ in the phosphor was enhanced about 40 times than that of the Tb ³⁺ single doped phosphor under the excitation of their optimal excitation wavelengths.