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

Uniform monoclinic monazite structure LaPO4:Eu3+ hollow spheres were s ynthesized via an attractive hydrothermal method owing to the higher yield and s implicity.Photoluminescence and Raman spectra of the sample were investigated u nder high pressure up to 26 GPa using diamond anvil cells.At ambient pressure,the sample exhibited same luminescent properties with that of bulk monazite LaPO 4: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.