Synthesis, structural and spectroscopic investigation of Nd3+,Y3+ codoped CaF2 nanoparticles as water colloids: Exploiting emission in the near infrared region for nanothermometry

Nd3+,Y3+ codoped CaF2 nanoparticles (NPs) have been synthesized by a microwave-assisted hydrothermal method, using citrate moiety as capping agent. Y3+ ions have been introduced in the crystal structure to declusterize the Nd3+ ions and improve the emission properties. After a structural and morphological characterization of the obtained NPs, the optical properties of colloidal dispersions have been analyzed in the near infrared (NIR) range. The emission spectra reveal several transitions associated with different sites where the Nd3+ions are accommodated in the crystal structure. Some bands show a marked dependence on the temperature, and a thermometric investigation reveals good thermal relative sensitivities in the physiological temperature range (20–60 ◦C), proving the applicability of the investigated colloidal NPs as optical nanothermometers.