Recently, the Department of Advanced Laser and Optoelectronic Functional Materials of Shanghai Institute of Optics and Precision Machinery (SIPM) of the Chinese Academy of Sciences (CAS) has investigated the mechanism of the luminescence spectral changes of Eu2+ in barium borate glass through electron paramagnetic resonance (EPR), and the related research results are summarized in the article "Electron paramagnetic resonance and luminescence properties of Eu2+ in barium borate glass". The research results were published in Ceramics?International under the title of "Electron paramagnetic resonance and luminescence properties of Eu2+ in oxyfluoride barium borate glasses".
Alkali metal borate glasses are often used as luminescent substrate glasses for rare earth ions because of their high transparency and good rare earth solubility.Eu2+ is a common rare earth luminescent ion, and it is usually doped as an activator ion in substrate materials such as glasses and phosphors.The 5d energy level of the outer layer of Eu2+ is susceptible to the influence of the external environment to produce an energy level splitting, which leads to a luminescence wavelength generation of the 5d-4f jump of Eu2+. jump of the luminescence wavelength shift. As a result, Eu2+ can emit light ranging from violet to red depending on the substrate material, which makes Eu2+ doped materials very versatile.
The electron paramagnetic resonance spectrum (EPR) of Eu2+ is characterized by a "U"-shaped spectrum, so EPR can be used to detect the presence of Eu2+ and the environment of the coordination field around Eu2+. In this study, the effect of glass components on the ligand field strength around Eu2+ was analyzed by investigating the changes of the characteristic EPR signal peaks of Eu2+ in barium borate glass samples.
The Eu2+ doped barium borate glass was prepared by under CO atmosphere and the mechanism of Eu2+ fluorescence spectral change was investigated. It is found that the increase of barium content in the glass leads to the enhancement of the intensity of the coordination field around the Eu2+ ions and the increase of the 5d energy level splitting of Eu2+, which causes the redshift of the emission spectra. The introduction of fluorine into the glass causes a decrease in the strength of the coordination field around the Eu2+ ion, which suppresses the red shift of the emission spectrum. Meanwhile, it is found that the increase of Eu2+ concentration also causes the redshift of the emission spectrum, which is attributed to the effect of the electron cloud expansion in the 5d energy level, leading to the downward shift of the center of the 5d energy level. This study systematically explains the two mechanisms that cause the wavelength change of Eu2+ luminescence, and finds that fluoride ions can provide the luminescence center with a low-field near-neighbor coordination environment, based on which the study can guide the adjustment of luminescence color of Eu2+ doped glass, phosphor and other materials.
The related research was supported by the National Natural Science Foundation of China.
Fig. 1 (a) Red-shift schematic of the emission spectra of BOxE10 and (b) BFxE10 glass samples
Fig. 2 Red-shifted schematic diagrams of the emission spectra of BO20Ey and BF20Ey glass samples
