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 degrees 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 degrees 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 E-4(9/2)-> H-6(15/2) (magnetic dipole) and E-4(9/2)-> H-6(13/2) (electric dipole) transitions, respectively. Similarly, for Sm3+-doped LaPO4, three prominent emission peaks at 561,597 and 641 nm were observed corresponding to (4)G(5/2)-> H-6(5/2), (4)G(5/2)-> H-6(7/2) (magnetic dipole) and (4)G(5/2)-> H-6(9/2) (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 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.