Pressure effect on optical properties and structure stability of LaPO4:Eu(3+) microspheres

Uniform monoclinic core-shell and hexagonal urchin-like LaPO4:Eu(3+) spheres are synthesized via an attractive hydrothermal method owing to the higher yield and simplicity. Photoluminescence and Raman spectra of two samples have been investigated under high pressure up to 28 GPa using diamond anvil cells. At ambient pressure, both samples exhibit same luminescent properties with that of bulk monazite LaPO4:Eu(3+). With the increase of pressure, the emission intensity of Eu(3+) decreases and the half-widths of transition lines increase for both samples, while emission peaks show a red shift toward longer wavelengths due to increase in both the crystal-field strength and the covalency. Monoclinic core-shell LaPO4:Eu(3+) becomes amorphous finally while hexagonal urchin-like one transforms to monoclinic structure at lower pressure of 3.2 GPa and turns into amorphous structure at higher pressures, which are presented based on the analysis of high pressure Raman spectra.