Douglas S. Hamilton - Summary of Research Activity

The emphasis of our research program is the investigation of the optical properties of solid state materials, specially those incorporating substitutional lanthanide (rare-earth) and transitional metal ions in an insulating crystalline or amorphous host. The research is conducted primarily using laser-based spectroscopic techniques with picosecond, nanosecond and CW lasers.

Currently we are completing a study of upconversion and energy transfer in Tm³⁺:Ce³⁺:YAG crystals. It is the first measurement of energy transfer rates from a narrow-band system (Tm³⁺ 4f levels) to a broad-band system (Ce³⁺ 5d levels) which overcomes the unwanted problems associated with initial optical excitation of the broad-band system by the laser pulse. This is accomplished by two-laser-pulse upconversion pumping of the Tm³⁺ ions at wavelengths far removed from the absorption bands of the Ce³⁺ ions. Investigations of the kinetics of the Tm³⁺ and Ce³⁺ fluorescence as a function of temperature and dopant concentration have revealed information on the nature of the Tm³⁺-Tm³⁺ and Tm³⁺-Ce³⁺ interactions. Such interactions are important in assessing these materials and excitation processes for potential diode-laser-pumped solid state lasers in the blue and near UV.

We have recently begun a study of Gd³⁺ to Cr³⁺ energy transfer in Cr³⁺:Gd₃Al₅O₁₂. In this case, the Gd³⁺ donor ions are stoichiometric constituents of the host lattice instead of being a substitutional dopant. Initial results indicate a rapid and coherent migration of the excitation on the Gd sublattice followed by a phonon-mediated single transfer step to the Cr³⁺ ion. These studies will provide some useful information on the behavior of scintillator materials utilizing a host-to-impurity energy transfer for the luminescence conversion process.

With the difficulty in obtaining unique solid-state materials with specialized optical properties being a key stumbling block to our research progress, we have recently obtained funding to develop a laser-heated pedestal growth facility to synthesize our own optical materials. We currently have our 200W CO₂ operational and completed the design of the reflective optics for the growth chamber and we anticipate growing our first materials early in the summer of 2004. This will put our laboratory in a more favorable position for grant funding once the facility becomes operational.