Study On Preparation And Luminescent Properties Of γ-LiAlO₂ Based Luminescent Materials

In nature, LiAlO₂ is known to exist in three possible allotropes, namely,α-LiAlO₂,β-LiAlO₂ andγ-LiAlO₂.α-LiAlO₂ is stable andβ-LiAlO₂ is metastable phase at low temperature. They will both translate into stableγ-LiAlO₂ under certain temperature, followed by the crystal lattice volume inflation.γ-LiAlO₂ can exist stably at high temperature. In this paper,γ-LiAlO₂ is as a substrate. The rare earth luminescent materials are synthesized. Moreover, the luminescent performance is studied and improved.γ-LiAlO₂: Eu³⁺ phosphor powder was prepared by gel combustion method. The sample wasγ-LiAlO₂ phase with a single tetragonal structure whose space group was P41212. The morphology was flaky with an average particle size of about 1μm. The strongest excitation peak at 254 nm of the powder belonged to the broadband excitation, and the maximum emission peak at 613 nm corresponded to the 5D0â†'7F2 transition of Eu³⁺. The doping concentration of Eu³⁺ was closely related to the photoluminescence intensity. Within a certain range, the emission intensity increased with increasing Eu³⁺ proportion. The optimal Eu³⁺ doping mole fraction was 1%. Li⁺ was served as charge compensation agent, which can increase the luminescence intensity. The main emission peak was also located at 613 nm.The increasing range reached the maximum when the doping ratio of Eu³⁺:Li⁺ was 1:2.γ-LiAlO₂: Eu³⁺ red phosphor powder was prepared by sol-gel method using soluble nitrates as raw materials. The excitation spectrum consisted of two parts, a broad excited band and sharp peaks of Eu³⁺ ions fâ†'f transitions, of which the former was much larger than the latter. The strongest excitation peak at 254 nm belonged to the ultra excitation. The main emission peak at 613 nm corresponded to the 5D0â†'7F2 transition of Eu³⁺. Eu³⁺ ions mainly occupied non-central symmetric position in LiAlO₂ lattice. Meanwhile, we studied the relation between theγ-LiAlO₂:Eu³⁺ luminescence intensity and the flux H3BO3 doping concentration. The intensity of emission peaks first increased, then decreased with the increasing of B³⁺ doping content. The optimal content of H3BO3 was about 0.8mol%. At the same time, the crystallinity of sample was the best.Theγ-LiAlO₂: Tb³⁺ green phosphor was synthesized by citric acid sol-gel method. The emission spectrum ofγ-LiAlO₂: Tb³⁺ excited by 238 nm light showed four major emission peaks locating at 489,542,548,584 and 620nm, respectively. The main emission peak was located at 542nm corresponding to the 5D4â†'7F5 typical transitions of Tb³⁺. The doping concentration of Tb³⁺ was closely related to the luminescence intensity. Within a certain range, the emission intensity increased with increasing Tb³⁺ proportion. The optimal Tb³⁺ doping mole fraction was 1.2%. Li⁺ was served as charge compensation agent. The luminescence intensity first increased, then decreased with the increasing of Li⁺ doping content. The main emission peak was also located at 542 nm. The intensity reached the maximum value when the doping ratio of Tb³⁺:Li⁺ was 1.02:1. Meanwhile, we studied the relation between theγ-LiAlO₂: Tb³⁺ luminescence intensity and the flux H3BO3 doping concentration. The intensity of emission peaks first increased, then decreased with the increasing of B³⁺ doping concentration. The optimal content of H3BO3 was about 1.5mol%. At the same time, the crystallinity of sample was the best.