title: Studies of terbium bridge: saturation phenomenon, significance of sensitizer and mechanisms of energy transfer, and luminescence quenching.
abstract: Terbium chain in the form of S → (Tb(3+))n → A (S = Ce(3+) or Eu(2+), A = Eu(3+)), as a promising energy transfer (ET) approach, has been proposed to enhance Eu(3+) emission for solid-state lighting. However, the viewpoint of ET from S to A via the terbium chain (Tb(3+)-Tb(3+)-Tb(3+)-...) is very doubtful. Here, hosts of Ba3Ln(PO4)3, LnPO4, LnBO3, and Na2Ln2B2O7 doped with Ce(3+) → (Tb(3+))n → Eu(3+) or (Tb(3+))n → Eu(3+) are synthesized to prove the universality of S → (Tb(3+))n → A in inorganic hosts and to study the unsolved issues. Saturation distance of Tb(3+)-Eu(3+), estimated with the empirical data of different hosts, is proposed to be a criterion for determining whether a spectral chromaticity coordinate keeps constant. A branch model is put forward to replace the chain model to explain the role of (Tb(3+))n in ET from Ce(3+) to Eu(3+) and the necessity of high content of Tb(3+); the term "terbium bridge" is used to replace "terbium chain", and the value of n is determined to be two or three. The intensity quenching of Eu(3+) emission is attributed to the surface defects ascribed to the smaller particles and larger specific surface area rather than the concentration quenching of Tb(3+). Based on the saturation distance and the mechanism of luminescence quenching, the necessary concentration of Tb(3+) for (Tb(3+))n can be estimated as long as the cell parameters are already known and the luminescent efficiency of Eu(3+) can be further improved by optimizing the synthesis method to decrease the quantity of surface defects.
authors.affiliation: MOE Key Laboratory of Bioinorganic and Synthetic Chemistry/State Key Laboratory of Optoelectronic Materials and Technology, Key Laboratory of Environment and Energy Chemistry of Guangdong Higher Education Institutes, School of Chemistry and Chemical Engineering, Sun Yat-Sen University , No. 135, Xingang Xi Road, Guangzhou 510275, P.R. China.
authors.forename: Dawei
authors.initials: D
authors.lastname: Wen
authors.forename: Jianxin
authors.initials: J
authors.lastname: Shi
authors.forename: Mingmei
authors.initials: M
authors.lastname: Wu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Su