Synthesis And Luminous Properties Of Europium-doped Borate Blue Phosphors

More and more people are interest in rare earth doped borate phosphor, due to their low synthetic temperature, easy preparation, high luminescent brightness and uniform dimension. Particularly, great interest about borate phosphor has resulted in rapid developments after the emergence of GdMgB5O10: Ce3+, Tb3+ as a novel, efficient and practical green phosphor. In this paper, Rare earth metal ion activated borates luminescence materials have been successfully synthesized by a modified solid-state reaction. The synthesis conditions, the luminescent properties and simple energy transfer mechanism have been studied.This dissertation has five chapters, as follows:(1) Given an overview for the development history and current status of phosphor, reviewed the luminescence mechanism of divalent europium ion and described the current status of borate as substrate on luminescent materials and synthetic methods.(2) The blue phosphor Ca₂B₅O₉Cl:Eu²⁺ has been successfully synthesized by glycine combustion method at 750℃the first time. We have studied the different ratio of glycine and the nitric acid solution of europium ions. The crystallization of Ca₂B₅O₉Cl:Eu²⁺ have been investigated by using powder X-ray diffraction (XRD). Photoluminescence (PL) results showed that the phosphor exhibited intense blue luminescence at 434 nm when excited by 340 nm. The phosphor can be used for white light emitting diode.(3) A novel blue-emitting phosphor, Eu²⁺-doping Al4B2O9, was prepared via a modified solid-state reaction. We can obtain Al4B2O9:Eu²⁺ nanoparticles with diameters varying between 20 and 50 nm by using urea as auxiliary reagents. The crystallization and particle sizes of Al4B2O9:Eu²⁺ have been investigated by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence (PL) results showed that Al4B2O9:Eu²⁺ phosphor could be efficiently excited by ultraviolet region from 300 to 410 nm, exhibiting bright blue emission. Further investigation on concentration-dependent emission spectra indicated that Al4B2O9:0.003Eu²⁺ phosphor exhibits the strongest luminescent intensity. In addition, we also briefly studied the charge transfer mechanism of the phosphor.(4) The blue-emitting CaAl₂B₂O₇:Eu²⁺ phosphor was prepared at 800℃by a modified solid-state reaction. The results of X-ray powder diffraction (XRD) analysis confirmed the formation of CaAl₂B₂O₇:Eu²⁺. TEM images showed that the grain size of CaAl₂B₂O₇:Eu²⁺ is about 45 nm. Photoluminescence (PL) Spectroscopy showed that the phosphor could be excited efficiently by UV-visible light from 250 nm to 410 nm, and exhibit blue emission (460 nm). The mechanism of resonance-type energy transfer from Eu²⁺ to Eu²⁺ was established to be electric multipole-multipole interaction.(5) Zn²⁺ and Mg²⁺ co-doped CaAl₂B₂O₇: 0.03Eu²⁺ blue phosphors were prepared by the combustion-assisted synthesis method. The crystallization and particle sizes of synthesized optical materials were investigated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence (PL) spectroscopies were taken to investigate the luminescence characteristics. The blue luminescence of doubly doped compositions was enhanced, compared to that of the host matrix with only Eu²⁺ as an activator. The mixed composition showed the improvement in the luminescence properties compared to singly doped CaAl₂B₂O₇:Eu²⁺. A possible energy transfer from the defects created around Zn²⁺ and Mg²⁺ to the Eu²⁺ centers was studied.