4f n-15d → 4f n emission of rare earth ions under high pressure
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The 4f n-15d → 4f n transitions of the rare earth ions have applications in the fields of lighting phosphors, cathode ray tube phosphors, UV and VUV laser crystals, inorganic scintillators, thin film electro-luminescent materials and plasma display panel phosphors. Understanding the properties of the 5d levels of the rare earth ions is very important. One method to study these states utilizes high pressure experiments. By applying external pressure, the inter-atom distance, the bonding angles and covalency of the materials are influenced by pressure. The relevant chemical, electrical, optical and magnetic properties of materials change with pressure. The diamond anvil cell (DAC) is a powerful tool for high-pressure optical spectroscopy. Generation of pressures by the DAC in the range 0.1-1.0 Mbar (10-100 GPa) has become a routine. The sample is placed between two opposed diamond anvils. When an external force is applied, the diamonds move together and the pressure on the sample is increased. Since the diamond anvils are transparent, the incident pumping source can be focused on the sample and the emission from the sample can be collected. In this dissertation, the DAC is used to study the 4f n-15d → 4f n emission of rare earth ions doped in different hosts under high pressure. Since the absorption edge of the diamond is at about 225 nm and the absorption of the 5d levels of most rare earth ions are at shorter wavelengths, a stepwise two-photon excitation process is utilized to populate the 5d level of the rare earth ion. Three examples utilizing high pressure are presented in this dissertation. These are the pressure dependence of electron phonon coupling of Ce3+, Pr3+ and Nd3+ in LiYF4, the 1S0 and 4f15d1 state mixing of Pr3+ in BaSO4 under high pressure and an investigation of the site distribution of Eu2+ in BaMgAl10O17 (BAM).