Fabrication of novel Li+ and Sm3+ doped CeO2@PVP orangish-red luminescent hybrid nanofiber for investigation of structural, optical and antibacterial activity: Unusual electronic transition modification by Li+ doping

Abstract

Sm3+-doped and Sm3+/Li+ co-doped CeO2 nanofibers were synthesized via a co-precipitation-assisted electrospining method. Li+ co-doping led to an improvement in both crystallinity and luminescence efficiency. XRD with W-H and Scherer showed single-phase CeO2 with lattice modifications due to doping. In Sm3+ and Li + doped NFs, it is observed that the aggregation size gradually increases and becomes localizes at different regions within the NFs, favoring the formation of a random aggregation distribution. The porous nature of the fibers with large gaps between NFs makes them potential candidates for moisture sensors. PL measurements revealed an intense yellow emission at 574 nm ( 4 G5/2 → 6 H5/2) instead of the hypersensitive electric dipole transition at 669 nm ( 4 G5/2 → 6 H9/2) in Sm3+-doped NFs, supporting the magnetic dipole transitions of the CeO2 host and revealing that Sm3+ ions are located in a position of high symmetry with an inversion center in the local medium, which underlines the efficient luminescence mechanisms within the CeO2 host. The calculated critical distance (Rc = 19.66 Å) indicated that energy migration occurs predominantly through electric multipolar interactions facilitated by the structural features of the NF matrix. When cryogenic temperatures were reached for CeO2:0.02Sm3+0.05Li+@PVP NF, the partially magnetic and partially electric dipole character attributed to the 4 G5/2 → 6 H7/2 transition became dominant, as Li + doping reduced the possibility of Sm3+ ions occupying asymmetric sites in the CeO2 lattice. The analyzed correlated color temperature (CCT) values suggest that the prepared Sm3+-doped nanofibers are promising “cold” candidates with commercial potential for solid-state applications, exhibiting a high color purity of 72.7 %. Moreover, under the tested conditions, CeO2 and Sm3+ iondoped nanofibers exhibited no measurable antibacterial activity. However, Li+ incorporation significantly enhanced antimicrobial performance without inducing cytotoxic effects, thereby supporting cell viability.