Studies On Spectroscopy Of Rare Earth Oxides And Minerals

The spectra of the rare earth are complicated, confused and variable. The study on spectra of the rare earth can not only enrich the knowledge of the rare earth, but also provide the theoretical basis for researching the rare earth materials. This work is to study the spectra of the rare earth oxides and some typical rare earth minerals found in China. The aim is to determine their characteristics and mechanisms, and further to clarify the relationship among various spectra. This PhD thesis is divided into two parts: (1) the study on vibrational Raman and infrared spectra, (2) the study on electronic spectra, including the photoluminescence, visible absorption, electronic Raman spectra and the electronic infrared spectroscopy.1. Three kinds of laser Raman spectrometers and six wavelengths of exciting source, including 325.0nm, 457.9nm, 488.0nm, 514.5nm, 632.8nm and 785.0nm laser lines, are used to obtain the Raman spectra. The vibrational characteristics of the specimens have been analyzed systematically by Raman and infrared spectra. The main results are as follows:(1) The infrared spectra from 400~800cm-1 and Raman spectra from 80~ 800cm-1 of nine cubic rare earth oxides are first reported completely. It is evident from these data that the crystal structure determines the frequency position, and clearly shows the effect of the lanthanide contraction in this series of compounds. An abnormal phenomenon in the Raman spectrum of Yb2O3 is found. It is supposed that the special Raman spectrum may be the mixed or coupled spectra of the electronic Raman spectrum of Yb3+ and the vibrational Raman spectra of Yb2O3. The special Raman effect of Yb2O3 may be related to some key questions about the theory of the electronic Raman spectra.(2) The light rare earth sesquioxides are easy to be hydrated and carbonated in air. It is determined from the Raman and infrared spectra and X-ray diffraction patterns of RE2O3(RE=La,Pr,Nd,Sm) specimens that the major hydrated and carbonated products are RE(OH)3, hexagonal RE2O2CO3, tetragonal RE2O2CO3 and RE2O(CO3)2. The crystal structure of Pr(OH)3 has been measured in detail. Pr(OH)3 is hexagonal with 2 molecules per unit cell (a=0.6465, c=0.3759), spacegroup P63/m, and density Dx=4.684g/cm3. Some omitted data of Pr(OH)3 in the JCPDS file 45-86 are supplemented and the two errors of indices have been corrected.(3) The Raman spectra of the metamict minerals are very weak, but strong and sharp notably after heating. The characteristic frequencies of the Raman and infrared spectra of the fergusonite and aeschynite group minerals, monazites and the rare earth fluoro-carbonate minerals have been determined and assigned. The influence of the minerals' compositions and crystal structures on vibrational peaks has been discussed.2. As to the study on the electronic spectra of the rare earth, the main results are as follows.(1) Based on a reconstructed Raman microprobe, a new method of obtaining high-resolution visible region absorption spectra is designed. The method makes it possible to establish a relationship among four kinds of spectra of the rare earth specimen, including visible region absorption spectra, photoluminescence spectra, infrared spectra and Raman spectra. The method plays an important role in distinguishing and studying the complicated and confused spectral characteristics and mechanisms of the rare earth.(2) It is found and explained that due to the Boltzmann distribution law at room temperature, the positions of the fine peaks of the photoluminescence band stemming from the transitions between an excited state and the ground state of a RE3+, match these of the absorption bands from the transitions between the ground state and the excited state. The Stark split energy levels of the ground state 4I15/2 and two excited states 2S3/2 and 4F9/2 of the Er3+ in Er203 have been determined. And the transmitting form of the Stark split energy levels between the ground state and the two excited states has been clarified.(3) A concept of the electronic infr...