The Structure And Luminescence Properties Of Eu³⁺/Tb³⁺ Doped SiO₂-B₂O₃ Phosphors For LED

Recently, white light emitting diodes as lighting source have received significant attention due to their advantages, such as environmental friendliness and good performance. Rare earth doped silicate-based phosphors become a hot research, and a lot of research have been focused on the study of choosing phosphor hosts, rare earth ions, transition metal ions and co-activator. In this research, we report our recent investigation results on the synthesis and luminescence of a full-color emitting Eu2+/Tb³⁺/Eu³⁺doped silicate-based phosphor by sol-gel method. The CIE chromaticity coordinates ?0.33,0.32? can be achieved ?the theoretical white point ?0.30,0.30??, and the prepared sample was characterized through luminescence spectra, XRD, DTA-TG, FTIR and SEM.1. Eu³⁺-doping B₂O₃-SiO₂ red phosphor were synthesized by the sol-gel method annealing at 600 ?, and the phase, morphology and luminescence properties of the phosphor were investigated. The powders exhibited orange and red emissions at 591 nm,612 nm, which were assigned to the ⁵D₀?>⁷F₁ magnetic dipole transition,⁵D₀?>⁷F₂ electric dipole transition of Eu³⁺ under 465nm and 395nm excitation respectively. The optimum ratio of B₂O₃ and SiO₂ is 1:1, and the best molar concentration is 9.00%?mol%?. Tb3-doping SiO₂ green phosphor were synthesized by the sol-gel method annealing at 600 ? ?pH=4?. The emission spectra show a strong green emission ^<sup>5D_<sub>4-⁷F₆?488 nm?,^<sup>5D_<sub>4-⁷F₅?544 nm? and ^<sup>5D_<sub>4-⁷F₄ ?585 nm? due to the transitions from ^<sup>5D_<sub>4 excited states of Tb³⁺ ions, and the excellent properties of green luminescent phosphor can be obtained by ⁷F₆-5L10 transition ?377 nm?. Luminescent properties of SiO₂-B₂O₃ composite matrix phosphor is stronger than single matrix SiO₂ and B₂O₃ phosphor, and the best molar concentration is 9.00%?mol%?.2. Eu³⁺/Tb³⁺ co-doping B₂O₃-SiO₂ phosphor were synthesized, and the excitation energy could be released not only by emitting green light but also by transferring to Eu³⁺ ions as Tb³⁺ ions absorb ultraviolet light, which finally exhibited a red emission of Eu³⁺ ions. It can be clearly seen that Eu³⁺/Tb³⁺luminescence intensity was enhanced, indicating that the symmetry of network is destroyed by B in the network under the infrared spectroscopy. The critical temperature above which the temperature quenching becomes dominant was found to be 600 ? due to clusters formed from the location migration of rare earth ions. The XRD results show that the material is amorphous. Mg2+/Tb³⁺/Eu³⁺ co-doping B₂O₃-SiO₂ phosphor exhibits three bands under 365 nm excitation:one band situated at 400-500 nm is attributed to the d-f transitions of Eu2+ ions, the second band with sharp lines peaked at 544 nm is assigned to the ^<sup>5D_<sub>4-⁷F_J transitions of Tb³⁺ ions, the third band in the orange-red region 588 nm,612 nm is originated from ⁵D_o-⁷F_J transitions of Eu³⁺ ions. The Tb³⁺?Eu³⁺ energy transfer might been blocked between Tb³⁺ and Eu³⁺ clusters due to unique crystalline of the samples annealing at 600 ? for 2 h. The Commission International de I'Eclairage ?CIE? chromaticity coordinates ?0.33,0.32? can be achieved upon 365 nm excitation. It is suggested that the Eu2+/Tb³⁺/Eu³⁺doped silicate-based phosphor can serve as a potential full-color emitting phosphor for phosphor-converted fluorescent lamps.3. Monodisperse core-shell structured SiO₂:Tb³⁺, SiO₂@B₂O₃:Tb³⁺ microspheres were synthesized in a seeded growth way. The SiO₂ spheres have been successfully coated by B₂O₃:Tb³⁺phosphors and the obtained SiO₂:Tb³⁺, SiO₂@B₂O₃:Tb³⁺particles have perfect spherical shape with narrow size distribution. Additionally, the luminensence intensity of monodisperse SiO₂@B₂O₃:Tb³⁺ microspheres after calcination at 600 ? exhibit considerably stronger than the SiO₂:Tb³⁺ after calcination at 600 ? and SiO₂@B₂O₃:Tb³⁺ after calcination at 200 ?, and the intensity is 5 times than the SiO₂@B2O³⁺:Tb³⁺ after calcinations at 200 under the excitation of 377 nm, indicating that the core-shell structure and the calcination temperature ?600 ?? are conductive to the luminenscence property of phorsphors, indicating that Tb³⁺ ions have been successfully doped into the SiO₂@B₂O₃:Tb³⁺ microspheres.