Ce^(3+) sensitized Tb^(3+) and Dy^(3+) photoluminescence in β-LaB_(5)O_(9) prepared by sol-gel method

Rare earth(RE) pentaborates,both α-and β-polymorphs,are good candidates for photoluminescent hosts suitable for various RE activators,Ce^(3+) acts not only as an activator itself,but also as a sensitizer to other rare earth activators,like in the case of commercial green phosphor CeMgAl_(11)O_(19):Tb^(3+).In this work,two solid solutions of β-La_(0.9-x)Ce_(0.1)Tb_(x)B_(5)O_(9)(0≤x≤0.15) and β-La_(0.9-y)Ce_(0.1)Dy_(y)B_(5)O_(9)(0≤y≤0.07)were prepared by sol-gel method with high crystallinity,and the phase purity was confirmed with careful analyses on powder X-ray diffraction patterns.Energy transfers are expected due to the overlapping of Ce^(3+)emission with the Tb^(3+)/Dy^(3+)excitation.Indeed,the steady photoluminescence spectra indicate the decrease of the Ce^(3+)emission and the increase of the Tb^(3+)/Dy^(3+) emission,and the fluorescence decay curves exhibit the decrease of the average lifetime of Ce^(3+).The energy transfer efficiency is estimated to be 60% at χ=0.15 and 55% at y=0.07,respectively.The mechanism is likely through the dipole-dipole electric interactions for both cases.With this rationale,the Tb^(3+)and Dy^(3+)emissions are greatly enhanced,in particular,the white emission of Dy^(3+)in β-La_(0.85)Ce_(0.1)Dy_(0.05)B_(5)O_(9) is enhanced by 20 times.