Evaluation of Triboluminescent Rare Earth Complexes by the Drop-Tower System

Abstract

Rare earth ions exhibit very high color purity from their own electronic configuration localized on f-orbitals. In general, it is known that the ff-emission of rare-earth ions by photoexcitation is promoted by the antenna effect due to the molecular energy transfer using organic ligands having high absorption coefficients. Recently, rare earth complexes exhibiting triboluminescence have been frequently discovered. However, there are several hypotheses for this principle, and there are many unclear points in triboluminescence compared to photoluminescence by the ligand-excitation. In order to understand easily and qualitatively the degree of stimulation to the emission intensity of the system which shows the phenomenon of light emission from rare earth when the crystal is crushed, an evaluation method using a Drop-Tower system is explained. A europium complex EuL^val coordinating a chiral moiety introduced into the ligand was used as the rare earth complex.