Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb3+ and Bi3+could enhance emission of Eu3+ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb3+ and Bi3+ is about 2.0% and 2.0%, respectively. The co-doping Tb3+ and Bi3+ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu3+, indicating that the energy transfer occurs from Tb3+ and Bi3+ to Eu3+ ions. From further investigation it can be found that co-doping Tb3+ and Bi3+ ions can also induce excitation energy reassignment between 5D0–7F1 and 5D0–7F2 in these phosphors, and result in more energy assignment to 5D0–7F2 emission in LaPO4:Eu3+, Tb3+, Bi3+. Our research results displayed that La0.94PO4:Eu3+0.02, Tb3+0.02, Bi3+0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.