Bright blue upconversion emission of LaF₃: Yb³⁺, Tm³⁺ nanoparticles

In this paper, discrete Yb³⁺-Tm³⁺ co-doped LaF₃ nanoparticles with controlled chemical composition, and size distribution were readily synthesized using reverse micelles with microemulsions as confined reaction media. The morphology of the final product was characterized by the FESEM and HRTEM images. When the solid sample disperses in the ethanol without ultrasonic treatment, it is maize cob-like aggregator. The average diameter and length of the maize cob are about 110 and 575 nm, respectively. We suggested that the nanoparticles assemble into well-defined superstructures arising from the solvent evaporation, molecular cross-linking or interaction from surfactant molecules attached to specific nanoparticles crystal faces. After ultrasonic treatment for 30 min, the maize cob-like aggregator turns into a lot of nanoparticles owing to ultrasonic breach above a series of factors. The HRTEM image taken from individual nanoparticles indicates the crystalline nature, and the interplanar spacing of ∼ 0.366 mn corresponding to the [002] planes of pure hexagonal phase LaF., The TEM image of the samples annealed at 300 °C for 30 minutes displays the average diameter of NCs increased to about 35 nm and is in good agreement with XRD result. In addition, the NCs exhibit nearly monodisperse property, which is in favor of optimizing luminescence of the sample. 0The nanoparticles present a bright blue upconversion luminescence under the 978 nm excitation from a laser diode, which provides a promising upconversion phosphor for optoelectronic or biological applications.