Dual light-emitting Yb 3+ ,Er 3+ -doped La(IO 3 ) 3 iodate nanocrystals: up-conversion and second harmonic generation
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esearch Letter
Dual light-emitting Yb3+,Er3+-doped La(IO3)3 iodate nanocrystals: up-conversion and second harmonic generation Sylvain Regny, Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, F-38000 Grenoble, France Kévin Bredillet and Jérémy Riporto, Univ. Savoie Mont Blanc, SYMME, F-74000 Annecy, France Isabelle Gautier-Luneau, Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, F-38000 Grenoble, France Yannick Mugnier and Ronan Le Dantec, Univ. Savoie Mont Blanc, SYMME, F-74000 Annecy, France Géraldine Dantelle, Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, F-38000 Grenoble, France Address all correspondence to Géraldine Dantelle at [email protected] (Received 18 July 2019; accepted 27 September 2019)
Abstract The authors report the microwave-assisted hydrothermal synthesis of α-La(IO3)3 nanocrystals doped with Yb3+ and Er3+ ions, along with their structural and optical characterizations. 50-nm-sized α-La0.9−xYb0.1Erx(IO3)3 nanocrystals with x = 0.005, 0.01, and 0.02 were synthesized and dispersed in ethylene glycol. The as-obtained suspensions exhibit both second harmonic generation (SHG) signal and up-conversion photoluminescence (UC-PL) without interplay between the two signals under near-infrared resonant excitation. The relative intensity of SHG and UC-PL emission can be modulated according to the excitation wavelength. The most intense UC-PL signal is obtained from a 980-nm excitation, thanks to the sensitization of Er3+ by Yb3+.
Introduction With the advent of nanotechnologies and nanomedicine, numerous fluorescent optical nanoprobes have been designed for in vitro, ex vivo, and in vivo bio-imaging, such as dye-doped silica nanoparticles,[1] rare earth-doped nanocrystals,[2] and nanodiamonds[3] as recently reviewed.[4] For in vivo experiments, the penetration depth is a crucial parameter[5] and the use of emitters with excitation properties in the near-infrared (NIR) region and the so-called biologic transparency windows (BWs) is required. Based on down-conversion fluorescence, Nd3+-doped fluorescence probes[6,7] or more complex multi-doped architectures[8,9] have raised high interest with their excitation at 808 nm and their emission in the first (750–950 nm), second (1000–1350 nm), and third (1500–1800 nm) BWs, ensuring deep tissue imaging while minimizing tissue autofluorescence and photon scattering. Similarly, PbS or InP quantum dots appear as good candidates for biologic applications thanks to their tunable NIR emission.[10] Among other recent developments, the use of nanoprobes excited through a two-photon process has also been studied, allowing an excitation in the BWs and resulting in a higher spatial selectivity than the one-photon down-conversion fluorescence, as the emission only occurs at the focal point of the excitation laser. Up-conversion photoluminescence (UC-PL), two-photon excitation fluorescence, and second harmonic generation (SHG) are the different envisioned processes. The latter, characterized by transitions from virtual levels, offers the advantage
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