Impact of synthesis methods and coordination agents on the structure, morphology, and luminescent efficiency of triple-doped Nd3+, Yb3+ and Tm3+ yttrium orthovanadate

Abstract

The research and study of novel fluorescent nanomaterials based on lanthanide ions that can be excited by infrared radiation is essential for the development of new technologies in the biomedicine, photonics, and optoelectronics fields. The present work focuses on the structural and morphological study of new orthovanadate Y0.9Nd0.02Tm0.03Yb0.05VO4 and Y0.9Nd0.02Tm0.05Yb0.03VO4 samples. Their optical properties were also analyzed, including the evaluation of up-conversion (UC) and down-conversion (DS) mechanisms under infrared excitation at 980 nm and 808 nm. The samples were synthesized using both the sol-gel method and hydrothermal synthesis with urea and citric acid (CA) or maleic acid (MA) addition. These samples were reacted with tetraethyl orthosilicate (TEOS) to obtain silica-coated samples. X-ray diffraction (XRD) analysis confirmed the tetragonal symmetry compatible with a zircon-type structure of the diffraction pattern. FTIR spectra revealed bands corresponding to the several vibrational modes of VO4 3− groups and the presence of silica in the TEOS-treated samples. The synthesis method and the addition of CA or MA influenced the agglomeration, shape and morphology of the particles, as evidenced by transmission electron microscopy images. Photoluminescence (PL) studies of investigated samples after being excited with infrared radiation provided a detailed description of the energy transfer mechanisms involved in the DS and UC processes. These processes are related to the synthesis method used to obtain them and to the chelating agents added. Excitation of the samples at 808 nm generates DS processes and PL spectra with bright emission bands corresponding to electronic transitions of the Nd3+ and Yb3+ ions, while excitation at 808 and 980 nm gives rise to UC processes and PL spectra showing intense blue, red and NIR-I emission bands of Tm3+ ions, along with green and red emissions of Nd3+ ions.