A reusable and self-recoverable vitrified film of an anisometric europium(III) β-diketonate complex with UV light-responsive Eu3+ emission

We report on photophysical properties of a 20 µm thick vitrified film (fabricated from a powder of an anisometric europium(III) β-diketonate complex through a melt-processing technique and sandwiched between two quartz plates), which are highly unusual for known film-type materials based on non-mesogenic lanthanide(III) β-diketonate complexes. The film excited by light in the wavelength range of 280–425 nm exhibits a bright orange-red narrow-band emission of Eu3+ ions (due to efficient ligand-to-metal energy transfer) with 530 µs decay time. The prolonged irradiation of the film with a 337 nm nitrogen laser decreases the luminescence brightness of the Eu3+ ions without decomposition of the anisometric complexes. Then the luminescence gradually recovers during storage of the film in the dark for at least 19 h at room temperature. Interestingly, the film is capable of repeatedly reversible changing the luminescence brightness upon alternating UV laser irradiation and dark storage. The observed self-recovery phenomenon can be presented as an elastic photodeformation of local structures of the film with following changes in the Eu3+ ions emission parameters. We believe that the found film properties are promising for the design and development of novel reusable luminescent sensors or dosimeters of UV radiation.