"Phonon energy" is typically used to describe the resonance energy of lattice vibrations. As the host phonon energy decreases , we need more number of phonons to bridge the energy gap between excited state and ground state. Consequently, in host materials with low phonon energy, chance of radiative relaxation (upconversion efficiency) increases by lowering probability of non-radiative relaxation.
In order to decide the best host for upconversion measurements among several candidates, lattice phonon energy of the material should be measured (or calculated). So the question is that whether it's value should be calculate theoretically or is there any experimental technique to directly/indirectly measure this value ?
The best method is neutron diffraction but if you know the speed sound for your material and the lattice period, you can have a crude estimate of the largest frequency by s* \pi/a. Actual largest frequency would be a bit smaller.
Thank you dear Laura
I already have the data for Raman measurement but the point is that I don't know whether should I choose the phonon energy of the host based on the maximum energy that I see in the graph or not ? I've added the one of the graphs here. For instance in this material phonon energy of the host (or let's say maximum phonon energy of the host) is 815 cm-1 ?
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