Nanocomposites and nanomaterials

Spectroscopic study of luminescent biphasic                          Lа1-xYbxVO4 nanoparticles 
Chukova O.1, 2, Nedilko S.A.1, Nedilko S.G.1, 2, Voitenko T.1, Rahimi Mosafer H.S.2, Paszkowicz W.2, Stasiv V.2, Zhydachevskyy Y.2, Suchocki A.2
1 Taras Shevchenko National University of Kyiv, Volodymyrska Str., 64/13, Kyiv-01601, Ukraine. 
E-mail: chukova@univ.kiev.ua
2 Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, Warsaw 02-668, Poland.

The LaVO4 compound is widely used as a matrix for luminescent RE3+ ions and one of their various advantages is an opportunity to get crystal phases of different structure of lattice dependently on synthesis conditions and amount of dopants. The samples of biphasic crystal composition can also be formed. 
The studied Lа1-xYbxVO4 (x ≤ 2) nanoparticles were prepared by aqueous nitrate-citrate sol-gel synthesis. Phase compositions and crystal lattice parameters were determined using a Philips X’Pert Pro Alpha1 diffractometer operating with CuKα1 radiation. The XRD analysis has shown that all the synthesized samples are biphasic and they compose of monazite and zircon crystalline nanoparticles. The microstructure of the samples and chemical elements distributions were studied using SEM INCA X-max System from Oxford Instruments. Morphology of the nanoparticles depends on dopant concentration. Increase of the Yb3+ ions content leads to decrease of average sizes of nanoparticles from ~100 nm to 40 - 60 nm. 
Luminescence properties of the synthesized samples were studied. They consist of spectral lines appeared in the 970 – 1040 nm range which are caused by the f-f electron transitions in the Yb3+ ions. Structure of the spectra depends on the Yb3+ concentration. The carried out analysis has revealed that Yb3+ ions form at least two different types of emission centers in the studied materials. Correlations between crystalline structure, morphology of the nanoparticles, reflection spectra and luminescence properties of the samples were analyzed and discussed. The assumption was made that changes of the samples morphology are caused by changes of nanoparticles crystal structure, as well as appearance of two types of emission centers are related with the Yb3+ ions located in the nanoparticles of different crystal structure. 
This work has received funding from Ministry of Education and Science of Ukraine and Polish Academy of Sciences.