Enhancing luminescent and mechanical properties of carboxymethylcellulose films: The role of glycerol in lanthanide complex incorporation

Developing flexible luminescent materials through immobilizing lanthanide ion complexes in plasticized carboxymethylcellulose (CMC) films presents a significant challenge. This study focused on the synthesis of CMC films incorporating [Eu(tta)₃(H₂O)₂] and [Tb(acac)₃(H₂O)₃] complexes, with varying amounts of glycerol as a plasticizer, using casting technique deposition. The resulting films exhibited amorphous characteristics and thermal stability up to approximately 245 °C. Photoluminescence studies revealed that films containing the Eu³⁺ complex displayed intense emission in the red region (614 nm) when excited at 352 nm, attributed to the antenna effect. Notably, the CMC_Eu_20.0 GLY film, with the highest concentration of plasticizer, showed significant enhancements in experimental lifetime (0.69 ms) and quantum efficiency (39 % q (⁵D₀)) compared to the pristine complex (0.22 ms and 24 %, respectively). Films containing the Tb³⁺ complex, when excited at 300 nm, exhibited strong emission in the green region at 546 nm. An increase in excited lifetime was observed with increasing glycerol content, reaching a maximum of 1.50 ms at 15 % glycerol concentration. The mechanical properties of the films were significantly influenced by plasticizer content. The addition of 20 % glycerol resulted in a substantial increase in elongation at break from 8.9 % to 39.5 %. However, it also led to increased flexibility and reduced traction resistance, as evidenced by the decrease in Young's modulus from 3.4 to 1.5 MPa and breaking stress from 12.4 to 5.6 MPa. Interestingly, the incorporation of lanthanide complexes did not significantly affect the mechanical properties of the films. This finding suggests that luminescent properties can be tailored independently of the mechanical characteristics, offering versatility in material design for various applications.