Synthesis And Luminescence Performances Of Rare Earth Doped Ca₉R(VO₄ )₇ (R=RE, Y, Bi)

Rare-earth (RE) doped materials have been widely applied in luminescence and display, laser devices, bio-medicine and many other fields. Vanadate materials, an important branch of RE doped inorganic materials, have represented excellent application value in PDP, FED and LED areas because of their stable luminescence efficiency. Vanadates are commonly used as host of luminescence due to the outstanding chemical and temperature stability.In this work, RE doped Ca9R(VO4)7 (R= La3+-Lu3+, Bi3+, Y3+), with the same structure as Ca3(VO4)2, was selected to be the host material. The luminescence powder of Ca9R(VO4)7 was prepared by the high temperature solid-state reaction. Their structures were characterized, and the excitation spectra, emission spectra, luminescence decay curves, the temperature stability of luminescence and their potential applications were also systematically investigated. Through the site-selective excitation and emission spectrum technique by using Eu3+ as the spectroscopic probe ion, the surrounding environment of the RE ions doped in the host was analyzed.In Chapter 3, the detailed structures of Ca9R(VO4)7 (R=Y, Bi, La–Lu), including space group and structural feature, were investigated by XRD, DTA, FT-IR and Raman measurements. The results indicated that Ca9R(VO4)7 had the pure Ca3(VO4)2 sturcture with space group R3c and Z=21. R3+ replaced the position of Ca2+ after being doped into the crystal lattice to form substitutional solid solution. The changes of cell volume followed the rule of shrinkage of lanthanide series, which is to say, as the increasing radius of RE3+ ions, the relative cell volume increased. In addition, the vibration modes of both V-O and R-O in the lattice were compared and analyzed by FT-IR and Raman spectra.In Chapter 4, Eu-based vanadate Ca9Eu(VO4)7 phosphors were synthesized and the photoluminescence properties were investigated. The excitation spectra showed very wide absorption band in the region of 200-450 nm, which is due to the absorption of VO43? and f–f transition from Eu3+ ions. The excitation band matched well with the radiation of near UV-excited InGaN based LED chips. The phosphor can be efficiently excited to realize an intense red luminescence (614 nm) corresponding to the electric dipole transition 5D0â†'7F2 of Eu3+ ions. Ca9Eu(VO4)7 phosphor also showed high quenching temperature and stable color purity with the elevated temperature. The emission decreased slowly with increasing temperature to 150°C (decreases by about 18 % of the initial value at room temperature) and the CIE values keep the value of about (x=0.65, y=0.35). These results indicated that Ca9Eu(VO4)7 phosphor was a promising red luminescence material. The crystallographic site-occupations of the Eu3+ ions in Ca9Eu(VO4)7 were investigated by the site-selective excitation and emission spectra. Three sites of"Eu"present in Ca9Eu(VO4)7 and the Eu3+ ions are distributed in the stoichiometric host with a highly similar environment.In Chapter 5, the luminescence performances of Ca9Dy(VO4)7 were systematically studied, together with the doping effect of Eu3+ and Bi3+ ions. The emission spectra consisted of spectral peaks at 483 nm (blue color), 573 nm (yellow color) and a weak band at 669 nm (red color) corresponding to 4F9/2–6H15/2, 4F9/2–6H13/2 and 4F9/2–6H11/2 emission transitions of Dy3+ ions, respectively. The ratio between yellow and blue luminescence (Y/B) could be tunned to achieve white luminescence with excellent CIE color coordinates (x=0.38, y=0.40) near to the centre of white color. This indicated that Ca9Dy(VO4)7 phosphor was superior to YVO4:Dy3+ for the white LED application. Furthermore, after doping with Eu3+ in Ca9Dy(VO4)7, Dy3+ and Eu3+ could show luminescence together; while after doping with Eu3+, there was a quenching effect on the lifetime of Dy3+ ions luminescence.In Chapter 6, the luminescence properties of Eu3+ doped Ca9R(VO4)7 (R = Bi, La, Sm, Gd, Y, Lu) were analyzed. In Ca9Bi(VO4)7:Eu3+, Bi3+ ions were sensitive to the luminescence of Eu3+ ions. In Ca9Lu(VO4)7:Eu3+, neither energy transition between Lu3+ and Eu3+ ions nor energy loss from nonradiative transition could be found. In Ca9(Gd,Y)(VO4)7:Eu3+, the transition of Gd3+/Y3+â†'[VO4]3-â†'Eu3+ took place. In Ca9Sm(VO4)7:Eu3+, Sm 3+ and Eu3+ ions showed luminescence together.The novelties of this dissertation are as follows: the structure characteristics, photoluminescence performances and luminescence decays of RE doped vanadates Ca9R(VO4)7 (R=La3+-Lu3+, Bi3+, Y3+) were systematically studied. The features about microstructure of Ca9R(VO4)7 and crystallographic site-occupations of RE ions were firstly investigated by the site-selective excitation and emission spectra. The doping effect on luminescence properties with two kinds of RE ions were discussed for the first time, such as the RE3+ ions'effect on Eu3+ luminescence. Overall, it provided a useful reference for further development and application of rare earth doped Ca9R(VO4)7 phosphor.