Optical Transition Properties Of Eu³⁺ In Eu(DBM)₃phen Mono-dispersed Microspheres And Eu(DBM)₃phen/PS Fluorescent Microfibers

Amongst all lanthanide complexes, europiumβ-diketone complexes exhibit illustrious luminescence properties thanks to the antenna effect of ligands and f-f electron transitions of Eu3+, resulting in important applications in laser, phosphor or optical data storage devices based on photoluminescent, electroluminescent and hole-burning spectroscopies. However, the disadvantages of the pureβ-diketones complexes, low processing ability, poor thermal stability, and low mechanical strength, limited the use of them. Adding the complexes into the organic, inorganic, or organic/inorganic hybrid matrixes my be an viable approach to improve the performance of the (3-diketones complexes. Electrospinning, a spinning technique, is a unique approach using electrostatic forces to produce fine fibers from polymer solutions or melts.Rare earth complexes Eu(DBM)3phen (DBM=dibenzoylmethide;Phen= 1,10-phenanthroline) and fluorescent fiber Eu(DBM)3phen/PS (PS=polystyrene) were studied in this thesis. Mono-dispersed microspheres of ternary complex Eu(DBM)3Phen were prepared through a facile process. Eu(DBM)3phen/PS, a novel fluorescent fiber, was synthesized through electrospinning technology furtherly. The obtained sample was characterized by means of X-ray powder diffraction (XRD) and Scanning Electron Microscope (SEM). In addition, the luminescence properties of the samples were investigated by spectroscopy and the fluorescence decay. According to J-O theory, the optical transition intensity parameters Q(=2,4 and 6) were obtained. The radiative transition properties of 5D0 level, including transition rates, branch ratios and radiative transition lifetime were calculated. As a potential material for microsphere lasers, the optical gain performance for 5D0→7F2 transition was also evaluated.From the FE-SEM image, it can be seen that the prepared sample consists of mono-dispersed microspheres. It should be mentioned that the broad band in the near ultraviolet region is extremely stronger than the f-f transitions of Eu3+. This fact means that the energy transfer from Phen and DBM to Eu3+ is very efficient. According to J-O theory, the optical transition intensity parametersΩ(=2,4 and 6) were obtained to be 20.99×10-20,0.98×10-20 and 1.79×10-20 cm2, respectively. The obtained internal quantum efficiency is around 70%, which is relatively high. The optical gain parameter g(λ)/N depends on the P value. P changes from 0 to 1.0 with a step size of 0.1. It can be seen that the positive gain appears when P gets such a small value around 0.1, thus implying that the pumping threshold for achieving the lasing operation upon 5D0→7F2 transition would be low. This may make the Eu(DBM)3phen a promising material for realizing microsphere lasers.The excitation spectrum of novel fluorescent fiber Eu(DBM)3phen/PS was different from the spectrum of the rare earth complex Eu(DBM)3phen. The optical transition intensity parameters of the Eu(DBM)3phen/PS were compared with Eu(TTA)3phen/PS and Eu(DBM)3phen/PMMA system.