It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)₃(H₂O)₂] and [Tb(acac)₃(H₂O)₃] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln³⁺–β-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand–Ln³⁺ intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the ⁵D₄ emitting level of the Tb³⁺ ion to the excited triplet state T₁ of the tta ligand coordinated to the Eu³⁺ ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.

Thermally excited state absorption in Eu ³⁺ is used to propose a new ratiometric luminescent thermometer with a predicted calibration factor.