Synthesis And Upconversion Luminescence Properties Of Tm³⁺-Yb³⁺ Codoped3CaO·Al₂O₃Powders

With the technology development of semiconductor laser, the manufacturing compact solid-state laser has attracted more interesting in the applications of information processing, data storage, medical diagnosis and underwater optical communication. Therefore, the exploration of the rare earth doped upconversion matrix materials and the research of the upconversion luminous mechanism are particularly important. Compared with the most used upconversion fluoride matrix materials, oxide matrix materials exhibit excellent thermal and chemical resistance properties, especially the aluminate matrix materials have very big advantage in these respect. On the other hand, the blue emission from the1G4â†'3H6and1D2â†'3F4transitions of Tm3+makes it an important activation center for the manufacture of blue/green laser.The Tm3+/Yb3+co-doped nCaO·mAlO3of aluminate oxide upconversion matrix materials were synthesized by combustion method using metal nitrates, urea and β-alanine as raw material and incendiary agent respectively, then igniting at500℃. The experimental results show that,3CaO·AlO3(C3A) has superior upconversion luminescence properties compared with12CaO·7Al2O3(C12A7) and CaO·AlO3(CA). The X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were conducted to investigate the microstructure and the composition of the C3A powders; Up-conversion emission spectra, power dependence of the emission intensity, energy level rate equations, down-conversion emission spectra, fluorescence decay curve and the Up-conversion emission spectrum of Au nano-rod composited C3A were analyzed to study their optical properties.The XRD and SEM investigations revealed that the pure phase3CaO·Al2O3(C3A) microcrystalline powders were obtained with the grain size of2-5μm. Up-conversion emission bands at291,363/369,451/459,476/481,647/653and789nm corresponding, respectively, to the transitions1I6â†'3H6,1D2â†'3H6,1D2â†'3F4,1G4â†'3H6,1G4â†'3F4and1G4â†'3H5were observed under excitation at980nm. The power dependences of the1G4and1D2emissions intensity show that, in low pump power range (2.15-2.55mW), the1G4level of Tm3+was pumped by two photons absorption process through Yb3+cooperative sensitization. The1D2level was pumped by three photons absorption process. In higher pump power range (2.55-3.55mW), the1G4level of Tm3+was pumped by three photons absorption process of continuous energy transfer. The1D2 level was pumped by four photons absorption process. The calculating result of energy level rate equations was in agreement with that experimental ones.Under362nm excitation,451and459nm emission bands corresponding to the transition of1D2â†'3F4were observed in C3A:Tm3+/Yb3+. The lifetime curves of451and459nm emission bands were measured under the excitation of355nm laser light. Fitting results showed that these two emission bands were both including a fast decay component and a slow decay component. The decay times of the two fast decay components and the two slow decay components were11μs and52μs, respectively. The broad double emission peaks of Tm3+those belong to the same energy level transition was due to the stark energy level splitting which affected by the crystal field. According to the metal surface plasma resonance theory, after the coupling of luminescent material and metal nanoparticles, the sueface local electric field of the metal nanoparticles would be enhanced by the resonance with the incident light and causing the change of crystal field. The Au-nanorod was synthesized by the Seed-Mediated method. The absorption spectrum of the Au-nanorod shows two absorption bands centred at550and890nm which belong to the end face and side face, respectively. The up-conversion emission spectra of C3A:Tm3+/Yb3+and Au-nanorod coupled C3A:Tm3+/Yb3+under980nm excitation was measured and normalized by480nm emission bond. The emission intensity ratio of the two bands corresponding to the transition of1G4â†'3H6and1D2â†'3F4changed significantly validating the broad double emission peaks of Tm3+was due to the stark energy level splitting which affected by the crystal field.