Structural-microstructural characterization and optical properties of Eu3+, Tb3+-codoped LaPO4·nH2O and LaPO4 nanorods hydrothermally synthesized with microwaves

Rhabdophane-type Eu3+,Tb3+-codoped LaPO4·nH2O single-crystal nanorods with the compositions La0.99999-xEuxTb0.00001PO4·nH2O (x=0-0.03), La0.99999-yTbyEu0.00001PO4·n?H2O (y=0-0.010), and La0.99999-zTbzEu0.000007PO4·n??H2O (z=0-0.012) were hydrothermally synthesized with microwaves. It is shown that theEu3+, Tb3+ codoping does not affect the thermal stability of these nanorods, which is due to the formation of substitutional solid solutions with both Eu3+ and Tb3+ replacing La3+ in the crystal lattice. Moreover, it is also shown that monazite-type Eu3+,Tb3+-codoped LaPO4 single-crystal nanorods can be obtained by calcining their rhabdophane-type Eu3+,Tb3+-codoped LaPO4·(n,n? or n??)H2O counterparts at moderate temperature in air, and that they are thermally stable. It is also observed that, for the same Eu3+, Tb3+-codoping content, the monazite-type Eu3+, Tb3+-codoped LaPO4 nanorods exhibit higher photoluminescent efficiency than the rhabdophane-type Eu3+,Tb3+-codoped LaPO4· (n,n? or n??) H2O nanorods. Moreover, it is found that the highest photoluminescence emission corresponds to the monazite-type La0.96999Eu0.02Tb0.00001PO4 nanorods for the La0.99999-xEuxTb0.00001PO4 system. However, for those compositions energy transfer from Tb3+ to Eu3+ does not occur. In addition, for an efficient energy transfer to occur, a content of at least 1mol% Tb3+ is needed in all the studied materials.