Pressure effect on optical properties and structure stability of LaPO4:Eu3+ hollow spheres

Uniform monoclinic monazite structure LaPO4:Eu3+ hollow spheres were synthesized via an attractive hydrothermal method owing to the higher yield and simplicity. Photoluminescence and Raman spectra of the sample were investigated under high pressure up to 26 GPa using diamond anvil cells. At ambient pressure, the sample exhibited same luminescent properties with that of bulk monazite LaPO4:Eu3+. With the increase of pressure, the emission intensity of Eu3+ decreased and the half-widths of transition lines increased, while emission peaks showed a red shift toward longer wavelengths due to increase in crystal-field strength. No phase transformation appeared before amorphization for monoclinic LaPO4:Eu3+ hollow spheres, which was confirmed based on the analysis of high pressure Raman spectra. The large surface energy of hollow spheres was proposed to prevent the occurrence of phase transformation.