Upconversion properties of Tm3+-Er3+ co-doped layered perovskites and in-vitro cytotoxicity of their exfoliated nanomaterials

Abstract

The upconversion behavior of Er3+/Tm3+ co-doped Ruddlesden-Popper type K2Ln2Ti3O10 layered perovskites was investigated. The lanthanide pair was selected for achieving 980 nm-driven green, red, and NIR emission. The perovskites having different dopant compositions were synthesized by a conventional solid-state procedure by substitution of La3+ ions in the host lattice. Moreover, the single nanosheets having approximately 1.8 nm thickness and 2 μm lateral size were obtained via chemical exfoliation. The non-doped and co-doped layered materials and the nanosheets derived from these materials were characterized by X-ray diffraction, Scanning Electron Microscopy, Atomic Force Microscopy and custom-made experimental set-up of upconversion emission spectroscopy. According to the XRD profiles, the perovskites had the layered orientation and water molecules in the interlayer domain because of their hygroscopic nature. The co-doped layered perovskites presented two-photon excited green and red emissions, identified as 4S3/2→4I15/2 with 2H11/2→4I15/2 and 4F9/2→4I15/2 of the Er3+ transitions with a NIR emission. The intensity of red to green ratio emission of the materials increased with respect to the co-dopant concentration. The nanosheets' upconversion emission was weak in the visible region compared to their layered morphology. On the other hand, the NIR emission based on 3H4→ 3H6 transition of the Tm3+ ions was preserved despite the acid and solvent treatments to break apart the layered orientation. MTT assay and Calcein/PI staining were conducted to evaluate cytotoxicity of non-doped and Er3+/Tm3+ co-doped K2Ln2Ti3O10 perovskites and their exfoliated nanosheets on HEK 293 and HepG2 cell lines. Both assays indicated that although cell viability decreases with increasing concentration, good cell viability was observed at even 100 μg/mL. In addition to their excellent luminescent and optical features, the nanomaterials also demonstrated low cytotoxicity increasing the potential for their use in laser-based biological applications.