Search

Preparation from the aqueous alkoxide route of doped and co-doped lithium niobate nanocrystals with Er 3+ and Yb 3+ ions, and detailed investigations of their optical properties are presented in this comprehensive work. Simultaneous emission under femtosecond laser excitation of second harmonic generation (SHG) and up-conversion photoluminescence (UC-PL) is studied from colloidal suspensions according to the lanthanide ion contents. Special attention has been paid to produce phase pure nanocrystals of constant size (∼20 nm) thus allowing a straightforward comparison and optimization of the Er content for increasing the green UC-PL signals under 800 nm excitation. An optimal molar concentration at about 4 molar% in erbium ions is demonstrated, that is well above the concentration usually achieved in bulk crystals. Similarly, for co-doped LiNbO 3 nanocrystals, different lanthanide concentrations and Yb/Er content ratios are tested allowing optimization of the green and red up-conversion excited at 980 nm, and analysis of the underlying mechanisms from excitation spectra. All together, these findings provide valuable insights into the wet-chemical synthesis and potential of doped and co-doped LiNbO 3 nanocrystals for advanced applications, combining both SHG and UC-PL emissions from the particle core.

Here we report on the non-hydrothermal aqueous synthesis and characterization of nanocrystalline lithium aluminum iodate, LiAl(IO 3 ) 4 . Morphological and compositional analyses were carried out by using scanning electron microscopy (SEM) and energy-dispersive X-ray measurements (EDX). The optical and vibrational properties of LiAl(IO 3 ) 4 have been studied by UV-Vis and IR spectroscopy. LiAl(IO 3 ) 4 is found to crystallize in the non-centrosymmetric, monoclinic P 2 1 space group, contrary to what was reported previously. Theoretical simulations and Rietveld refinements of crystal structure support this finding, together with the relatively high Second Harmonic Generation (SGH) response that was observed. Electronic band structure calculations show that LiAl(IO 3 ) 4 crystal has an indirect band gap Egap=3.68 eV, in agreement with the experimental optical band gap Egap=3.433 eV. The complex relative permittivity and the refraction index of LiAl(IO 3 ) 4 have also been calculated as a function of energy, as well as its elastic constants and mechanical parameters. LiAl(IO 3 ) 4 is found to be a very compressible and ductile material. Our findings imply that LiAl(IO 3 ) 4 is a promising material for optoelectronic and non -linear optical applications.