Single crystals doped with rare earth (RE) ions are excellent candidates as basic materials for single photon sources due to the presence unusual types of energy transfer processes. In a cooperative absorption process, two neighboring RE ions are simultaneously excited by absorbing each a single photon, whereas in cooperative luminescence two excited neighboring RE ions relax at the same time emitting a single photon. Another important process is energy transfer upconversion, where nearby excited RE ions pass their energies to a single RE ion. To understand these processes, the incorporation of RE ions in the crystal lattice must also be investigated in detail. For practical reasons nanocrystals in the diameter range below 100 nm have to be used as single photon sources. The effect of particle size on the spectroscopic properties of RE ions is expected to be of great interest. Accordingly, the candidate will examine the energy transfer and incorporation processes by classical and laser spectroscopic methods in RE doped bulk and nano-sized oxide crystals, e.g. LiNbO3 and Li6Y(BO3)3. Theoretical work using quantum chemical programs (e.g. SIESTA and GULP) are also planned for the interpretation of the experimental results and defining future scientific plans.
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