Rare Earth Ions Naln (wo <sub> 4 </ Sub>) <sub> 2 </ Sub> (ln = Y, La) Preparation And Luminescent Properties Of Nanocrystals Study

In this paper, the rare earth doped NaY(WO₄)₂ and NaLa(WO₄)₂ nanocrystals have been prepared by a hydrothermal synthesis procedure. X-Ray diffraction, transmission electron microscope, fluorescence spectra and upconversion luminescence spectra were used to study the preparation process and luminescence properties of the rare earth doped NaY(WO₄)₂ and NaLa(WO₄)₂ nanocrystals.The temperature of hydrothermal treatment has great affect on the formation of NaY(WC>4)2 nanocrystals. The pure NaY(WO4>2 nanocrystals can be obtained only when the temperature reached 260℃. The Eu³⁺ ion has been used as a probe for the structural environment of rare earth ion. It has been found that the Eu³⁺ ions are lack inversion symmetry in the NaY(WO₄)₂ nanocrystals. The dependence of the luminescence intensity of the Eu³⁺ doped NaY(WO₄)₂ nanoparticles on doping concentration of Eu³⁺ ions were discussed. The luminescence intensity increased with the increase of doping concentration and reached a maximum at 20 mol% Eu³⁺ doping concentration. The luminescence concentration quenching of Eu³⁺ in the NaY(WO₄)₂ nanocrystals was found to be similar to that in the NaY(WO₄)₂ bulk crystals. The upconversion luminescence intensity of the Yb³⁺-Er³⁺ codoped NaY(WO₄)₂ nanocrystals was found to be much stronger than that of the Er³⁺ doped NaY(WO₄)₂ nanocrystals.The XRD patterns and TEM images shows that the Eu³⁺ doped NaLa(WO₄)₂ nanocrystals with an average size of 10-30 nm can be obtained via hydrothermal treatment for different time at 180-℃. The luminescence intensity of Eu³⁺ doped NaLa(WO₄)₂ nanocrystals depended on the size of the nanocrystals. The bright upconversion luminescence of the 2 mol% Er³⁺ and 20 mol% Yb³⁺ codoped NaLa(WO₄)₂ nanocrystals under 980 nm excitation could also be observed. The Yb³⁺-Er³⁺ codoped NaLa(WO₄)₂ nanocrystals prepared by the hydrothermal treatment at 180°C and then heated at 600℃ shows a 20 times stronger upconversion luminescence than those prepared by hydrothermal treatment at 180°C or by hydrothermal treatment at 180℃ and then heated at 400℃.