Solvent effect in monoclinic to hexagonal phase transformation in LaPO4:RE (RE=Dy3+, Sm3+) nanoparticles: Photoluminescence study

Nanosized phosphor materials, LaPO4:RE (RE=Dy3+, Sm3+) have been synthesized using water, dimethyl sulfoxide (DMSO), ethylene glycol (EG) and mixed solvents at a relatively low temperature of 150 °C. X-ray diffraction (XRD) study reveals that as-prepared nanoparticles prepared in DMSO and EG are well crystalline and correspond to monoclinic phase. In the mixed water-DMSO or water-EG solvents, XRD patterns are in good agreement with hexagonal phase, but transformed to monoclinic phase at higher temperature of 900 °C. TEM images show well-dispersed and rice-shaped nanoparticles of diameter 5-10 nm, length of 13-37 nm for Dy3+-doped LaPO4 and diameter of 25-35 nm, length of 73-82 nm for Sm3+-doped LaPO4. Dy3+-doped LaPO4 shows two prominent emission peaks at 480 and 572 nm corresponding to 4F9/2→6H15/2 (magnetic dipole) and 4F9/2→6H13/2 (electric dipole) transitions, respectively. Similarly, for Sm3+-doped LaPO4, three prominent emission peaks at 561, 597 and 641 nm were observed corresponding to 4G5/2→6H5/2, 4G5/2→6H7/2 (magnetic dipole) and 4G5/2→6H9/2 (electric dipole) transitions, respectively. The luminescence intensity of the sample prepared in EG is more than that of DMSO or mixed solvents. Enhancement of luminescence is also observed after heat-treatment at 900 °C due to removal of quencher such as water, organic moiety and surface defects/dangling bonds. The samples are re-dispersible in polar solvent and can be incorporated in polymer film.

Research highlights► Nanomaterials. ► Optical properties. ► Luminescence materials.