He was also known for his work in spectroscopy of rare-earth laser materials. Samples of YLF and YAG crystals doped with erbium, thulium, and holmium are being studied with selective laser excitation in the region of 780 nm, the erbium bands. These materials can be efficiently optically pumped by the AlGaAs-GaAs laser diode arrays, but dye laser excitation is used instead. He was interested in the energy transfer process: Er to Tm, to Ho, which concentrates energy emission at 2.085 μm at room temperature and at liquid nitrogen. The process is a radiationless, almost resonant transfer of energy between sites and depends on the relative concentrations of the rare earth ions. In particular his experimental interests are measuring decay rates, excited state absorption, and branching ratios and detailed theories of such processes.