Reduction, Luminescence And Microstructure Of Sm³⁺, Eu³⁺ Doped Li₂O-SrO-B₂O₃ Glasses

Sm²⁺ ion has potential application in high-density optical storage because of its property of persistent spectral hole burning (PSHB). The luminescence of Eu²⁺ strongly depends on the host, which may lie anywhere from the UV to the deep-red region of the electromagnetic spectrum. Eu²⁺ has been widely used in the field of luminescence and display. The most widely used reduction method for these two ions is to heat the samples under a highly reduced atmosphere. It needs more strict operation conditions while the request of reduction in air and reduction by X-ray radiation are easier.The main topic in this work is to realize reduction of Eu²⁺, Sm²⁺ in Li₂O-SrO-B₂O₃as-made glass and glass-ceramics by heat-treatment in air and by X-ray radiation. The luminescence spectra, delay curves were measured for the reduced Eu²⁺ and Sm²⁺ ions. The optical stability of Sm²⁺ ions was evaluated by photo-bleaching method. The PSHB at room-temperature was onserved in Sm²⁺-doped glass-ceramics. The microstructure of Li₂O-SrO-B₂O₃ as-made glass are studied.In the chapter three, Eu-doped Li₂O-SrO-B₂O₃ as-made glasses were prepared by high-temperature melting quenching; the glass-ceramics were obtained by heating the as-made glasses in air. The abnormal reduction of Eu²⁺ doped in Li₂O-SrO-B₂O₃ glass-ceramics crystallizied in air was studied. Moreover, F^- ions had a positive influence on the reduction of Eu³⁺ to Eu²⁺ ions. Reduction of the Eu³⁺ to Eu²⁺ could occur in the process of crystallization of the glass-ceramics in air. When trivalent Eu³⁺ occupied the lattice site of divalent Sr²⁺,vacancy defects of Sr were created. The negative charges could transfer to Eu³⁺ site in resulting the reduction of Eu²⁺.The rigid three-dimensional networks of BO₄ tetrahedral act as a shield partially isolate the Eu²⁺ ions from each other and resist the attack of oxygen. There were two luminescence centers of Eu²⁺ ions. In the chapter four, PSHB of Sm²⁺ ions at room temperature was realized and the burning mechanism was studied. The width and depth of the obtained spectral hole were 2.5 cm^-1 and 40 % of the total intensity, respectively. This result was better than the reported PSHB results in the reference for borates. The burning mechanism was the photoionization of electron trapped at a site other than the Sm³⁺ ions. The lifetime of Eu²⁺ ions emission decreased with increasing of temperature.In the chapter five, the photo-reduction of Sm³⁺ to Sm²⁺ ions by X-ray irradiation was observed. The microstructure of the as-made borate-glass was studied. The dependence of Sm²⁺ reducing efficiency on the X-ray irradiation time showed a linear relationship. The related defects of Sm²⁺ ions showed two different types of trap characteristics. The reducing mechanism by X-ray irradiation was explained by the trapping of the free electrons created by X-ray irradiation by the metal cations or structural defects due to Sm³⁺ ions. The radiation induced defect centers were porposed to be boron electron centers, (NBOHC), and boron oxygen hole centers (BOHC). The NBOHCs are mainly dependent on the components of the glass and the irradiation intensity. The existence of Li atoms in the glass provide non-bridging oxygen in borate groups which leads to a higher optical basicity (electron donor power). It can be suggested that the samarium ions are mainly surrounded by non-bridging oxygen and bridging oxygen of the borate groups. The negative charge is distributed on BO₄ tetrahedral and the Li⁺ ions can act as charge compensation in the near location.In the chapter five, a novel red-emitting phosphor Eu³⁺-doped Ca₃Zn₃(TeO₆)₂,a Garnet type calcium-tellurium-zinc oxide was synthesized by the general high temperature solid-state reaction in air atmosphere. Ca₃Zn₃(TeO₆)₂:Eu⁺ can be effectively excited by UV-visible light 395, 465 and 537 nm.This phosphor exhibits an intense red emission at 611 nm. The wavelengths at 395 and 465 nm can match with the widely applied output wavelengths of ultraviolet or blue LED chips. The long-wavelength excitation properties of this material have benefit as a red phosphor for application of white light-emitting diodes.The novelties of this desertation are the following: the abnormal reduction Eu³⁺, Sm³⁺ to their bivalent states were realized by crystallization of this as-made glasses in air atmosphere. The microstructure of the borate glass, photoreduction by X-ray irradiation, PSHB of Sm²⁺ ions at room-temperature in this borate glasses were first reported. These results are helpful in further research of Li₂O-SrO-B₂O₃ glasses and glass-ceramics. And this also are good references for the reduction of rare-earth ions and applications of Sm²⁺,Eu²⁺ ions.