Highly -sensitive near infrared luminescent nanothermometers based on binary mixture

Abstract

We propose a simple strategy to obtain a luminescence intensity ratio nanothermometer operating in the near infrared range (1000–1700 nm) by use of binary mixtures of lanthanide doped Y2O3 selected as 1%Ho - Y2O3 + 1%Er - Y2O3 and 1%Ho - Y2O3 + 1%Nd - Y2O3. All nanoparticles were synthetized by citrate complexation method and thermally annealed at 800 °C. The temperature evolution of the emission properties was monitored in the range of 297–472 K and analyzed in terms of emission shape, intensity, dynamics, excitation wavelength, acquisition mode and weight ratio of the binary mixture. A maximum relative sensitivity of 1%K−1 at 297 K was recorded for the 3/1 weight ratio Ho – Y2O3 + Er – Y2O3 binary mixture upon excitation at 536.8 nm. For the more appropriate excitation wavelength for bioimaging applications at 649.7 nm, a relative sensitivity of 0.55–0.6% K−1 was recorded in the relevant physiological temperature range (300–320 K) for the 3/1 weight ratio Ho – Y2O3 + Er – Y2O3 binary mixture. To the best of our knowledge, our study also represents a first report on the near -infrared luminescence (around 1200 nm) lifetime thermometry for a Ho doped nanoparticle. Comparison with the literature demonstrates that our system represents a promising near-infrared thermometer, with a non-sophisticated and reproducible configuration that is open to multiple optimization routes.