Microwave Synthesis and Up-Conversion Properties of SHG-Active α-(La, Er)(IO₃)₃ Nanocrystals

Abstract

Pure α-La(IO 3 ) 3 and α-La 0.85 Er 0.15 (IO 3 ) 3 nanocrystals were synthesized by a microwave-assisted hydrothermal method leading to a reaction yield of 87 ± 4%. Electron microscopy and dynamic light scattering characterizations provide evidence for the formation of nanocrystals with an average size of 45 ± 10 nm for α-La(IO 3 ) 3 and 55 ± 10 nm for α-La 0.85 Er 0.15 (IO 3 ) 3 . When dispersed in ethylene glycol, the nanocrystal suspensions exhibit second-harmonic generation under near-infrared excitations at 800 and 980 nm whereas additional photoluminescence by up-conversion is simultaneously observed in the case of α-La 0.85 Er 0.15 (IO 3 ) 3 nanocrystals. Quantitative assessments of the second-harmonic generation efficiency from second-harmonic scattering experiments at 1064 nm result in relatively high ⟨d⟩ coefficients measured at 8.2 ± 2.0 and 8.0 ± 2.0 pm V −1 for α-La(IO 3 ) 3 and α-La 0.85 Er 0.15 (IO 3 ) 3 , respectively. The relative intensity between second-harmonic generation and photoluminescence is discussed following the excitation wavelength.

Dual light-emitting Yb3+,Er3+-doped La(IO3)3 iodate nanocrystals: up-conversion and second harmonic generation

“…Acentric α-La(IO3)3 is known for its SHG activity as initially demonstrated from comparative micron-sized powder experiments. 17,18 Recently, we reported the synthesis of α-La(IO3)3 nanocrystals and the quantitative assessment of its orientation-averaged SHG efficiency 19 that was found comparable to the other HNPs of interest (KTP, BaTiO3, LiNbO3, etc). 20,21 We also evidenced the possibility of doping α-La(IO3)3 nanocrystals with Er 3+ ions by La 3+ substitution and showed that Er 3+ -doped α-La(IO3)3 nanocrystals emit both UC-PL and SHG signals under 800-nm and 980-nm excitations.…”

“…α-La1-y-xYbyErx(IO3)3 nanocrystals, with y = 0.1 and x = 0.005, 0.01 and 0.02, were synthesized using a microwave-assisted hydrothermal method, as reported in [19]. In the following, the nanocrystals will be referred to as α-La0.9-xYb0.1Erx(IO3)3.…”

“…MHz, 100-120 fs) as the excitation source. 19,21 Emitted signals were collected perpendicularly to the laser beam through a spectrometer (Andor Shamrock 193) coupled to a CCD camera (Andor iDus 401). The power-law dependences were obtained by adjusting the excitation power from 250 to 800 mW thanks to a half-wave plate associated with a polarizer cube.…”

Evidence of reaction intermediates in microwave-assisted synthesis of SHG active α-La(IO3)3nanocrystals

“…Note that, with such a synthesis method, the α-La(IO 3 ) 3 phase crystallizes as nanocrystals (Figure S5), which could be used as nanoprobes in bio-imaging. 28 Hereafter we explore phase transformation in solid state or in hydrothermal conditions, with the goal of obtaining α-La(IO 3 ) 3 from other lanthanum iodate compounds.…”

“…20,21 This is particularly the case for lanthanum iodates: according to the synthesis conditions (temperature, pH, concentration, :IO 3 molar ratio of 1:3 and heated at 250°C. 28 In the latter case, microwave heating was selected for its rapid heating rates, 29,30,31 with the idea of decoupling the nucleation and growth stages, an essential procedure to obtain homogeneous and size-controlled nanocrystals for bio-imaging applications. Indeed, acentric α-La(IO 3 ) 3 nanocrystals, also called harmonic nanoparticles (HNP), could be used as bio-labelling nanoprobes like BaTiO 3 32 or KTiOPO 4 33 nanocrystals as they can be excited in the three biological transparency windows, circumventing the limitations (low penetration depth, photobleaching, blinking, optically resonant conditions, …) encountered with most fluorescent probes.…”