Effect of heat treatment temperature on the morphology and upconversion properties of LaF3:Yb,Er nanoparticles

Tegze, Borbála Ágnes and Tolnai, Gyula and Hessz, Dóra and Kubinyi, Miklós and Madarász, János and Sáfrán, György and Hórvölgyi, Zoltán (2023) Effect of heat treatment temperature on the morphology and upconversion properties of LaF3:Yb,Er nanoparticles. JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 148 (20). pp. 10795-10802. ISSN 1388-6150

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Abstract

LaF 3 :5%Yb 3+ ,0.5%Er 3+ upconverting nanoparticles were synthesized with co-precipitation method and heat treated at temperatures 300–600 °C. The morphology of the particles was characterized by high-resolution transmission electron microscopy coupled with energy-dispersive spectrometry and dynamic light scattering. Crystal structure was studied by X-ray diffraction (XRD), and thermal behaviour was investigated by simultaneous thermogravimetry and differential thermal analysis (TG/DTA). Upconversion behaviour was studied in detail by fluorescence spectroscopy, with 980 nm excitation. Particle sizes increased with increasing heat treatment temperature, and samples showed significant aggregation above 500 °C. Hexagonal LaF 3 crystal structure was identified for all samples, with increased crystallinity after heat treatment at 400 °C, which was corroborated with TG/DTA results. XRD and energy-dispersive spectrometry results revealed that at higher temperatures new crystal phases formed, as some Yb 3+ and Er 3+ dopant ions segregated into new nanocrystals, made of, for example, YbOF and YbOOH, which caused a significant decrease in the upconversion emission of the samples. The highest upconversion emission was achieved after heat treatment at 400 °C.

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