Ultraviolet- and Near-Infrared-Excitable LaPO<sub>4</sub>:Yb<sup>3+</sup>/Tm<sup>3+</sup>/Ln<sup>3+</sup> (Ln = Eu, Tb) Nanoparticles for Luminescent Fibers and Optical Thermometers
Artur Tymiński, Emilia Śmiechowicz, Inocencio R. Martín, Tomasz Grzyb
Abstract
High Resolution Image Download MS PowerPoint Slide The widespread demand for multifunctional materials that can be used for anticounterfeiting purposes, as dual-mode phosphors, or as optical nanothermometers has inspired us to synthesize Yb 3+ /Tm 3+ /Ln 3+ (Ln = Eu, Tb)-doped LaPO 4 nanoparticles (NPs) and, based on these, luminescent fibers that utilize and extend the properties of the NPs. They show intense dual-mode color-tunable emission and temperature-dependent up-conversion (UC) luminescence, which makes them multifunctional and of a high potential applicability. The nanomaterials were obtained by a simple and fast coprecipitation method, yielding pure-phase monoclinic products. The products were used as luminescence activators in cellulose fibers, showing their potential applications for security purposes. They can emit strong UC and down-conversion luminescence within one particle, under excitation of commercially available near-infrared (NIR) and ultraviolet (UV) excitation sources. The pure red and green emissions under UV irradiation resulted from the presence of Eu 3+ or Tb 3+ ions in the structure of the products, whereas violet-blue emission was obtained under NIR excitation because of Yb 3+ and Tm 3+ codopants. After simultaneous UV/NIR double-laser excitation, they obtained NPs that show a complex luminescence resulting from Tm 3+ (after energy transfer from Yb 3+ ), Tb 3+, or Eu 3+ . The obtained UC emission can be tuned, giving a huge color shift (from orange or green to blue). What is more, thanks to the presence of thermalized levels of Tm 3+ ions, these materials can act as promising temperature nanosensors in a wide range of temperatures from 293 to 679 K. Using the fluorescence intensity ratio technique, relatively high thermal sensitivity ( S r ) was obtained, 0.024 and 0.022 K –1 for 293 K for the Yb 3+ /Tm 3+ /Eu 3+ and Yb 3+ /Tm 3+ /Tb 3+ samples, respectively.