The light induced valence change of europium in Sr2SiO4∶ Eu involving transient crystal structure

摘要: Sr2SiO4 ∶ Eu3+ shows orange-red emission of substitutively present in two different Sr sites. The light-induced spectral changes from sharp line to yellow-white broad band are observed Eu at room temperature under irradiation with short UV or X-rays. attributed the optically assisted reduction Eu3+ → Eu2+. photoreduced containing contributions both Eu2+ and comparison chemically reduced samples. This is explained on basis preferential Sr(1) sites due unsatisfied EuSr–O–Si bonds. absence photoactivity for Ba2SiO4 ∶ Eu3+ (space group = Pnam) as well Ca2SiO4 ∶ = P21/n) indicates that crystal structure plays an important role photoreduction because prevailing orientational positional disorder latter. Further, orientationally disordered monoclinic random domains persist within orthorhombic lattice Sr2SiO4, resulting positionally atoms SiO4 tetrahedra. Electron paramagnetic resonance studies confirm electron trapping by dynamically (SiO4)4− high energy photon illumination formation radical anion (SiO4)5−. substitutional indicate [Eu3+ ← O2−] charge-transfer (CT) state directly involved process. excitation produces CT which relaxes transfers electrons groups rearrangement local environment mediates transfer process cause yellow stable reverts red annealing elevated Ar atmosphere thermally activated detrapping charge carriers defect centers which, turn, convert Eu3+. conversion Eu2+ → Sr2SiO4 reversible, thereby a highly efficient material application optical storage medium.