Synthesis and characterization of well-dispersed amorphous LnBO3·3H2O (Ln: Dy, Tb) nanoparticles

Abstract

Lanthanide nanoborates (LnBO3·3H2O (Ln: Dy, Tb)) were prepared in the presence of polyethylene glycol (PEG) using a buffered-precipitation method. The same procedure was performed without adding PEG to expose the chemical formulations of the samples. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectrum (FTIR) strongly supported amorphous lanthanide orthoborates having LnBO3·3H2O structure. From TEM images, the mean particle size and standard deviation for Dy and Tb were calculated as 15.2 ± 6.3 nm and 15.4 ± 6.1 nm, respectively. The percentages of PEG molecules in the samples were determined as 7.5% for Dy and 4.31% for Tb by TGA. The average hydrodynamic sizes and surface charges of DyBO3·3H2O and TbBO3·3H2O nanoparticles in the distilled water were measured as 150.7 nm (PDI 0.152) + 40.9 ± 8.8 mV and 151.3 nm (PDI 0.105) + 41.9 ± 6.8 mV, respectively. The energy band gaps of both lanthanide nanoborates were determined as 5.3 eV by applying the Kubelka–Munk function to the measured UV–Vis diffuse reflectance spectra. The amorphous DyBO3·3H2O and TbBO3·3H2O nanoparticles exhibited strong paramagnetic behavior with μeff/μB values of 8.57 for Dy and 8.73 for Tb, respectively, at room temperature. The characteristic photoluminescence emission corresponding to the transition from 5D4, 5D4 and 5D4 excited states to 7Fj (j = 6, 5, 4, 3, 2, 1, 0) of the Tb+3 ions was observed in the wavelength range of 370–700 nm. Similarly, the emission spectrum of Dy+3 ions composed of peaks of different strength extends in the wavelength range of 370–850 nm. Although the emission peaks were found to be nearly temperature independent for both samples, the normalized integrated intensity of full spectrum corresponding to TbBO3·3H2O sample decreased by %25, and increased by %10 for DyBO3·3H2O over the temperature range of 10–300 K.