Ultrasensitive quadrature photopyroelectric quantum yield spectroscopy of Ti3+:Al2O3. Evidence for domination of de-excitation mechanism by inter-configurational nonradiative transitions in an unthermalized manifold

The lock-in quadrature channel of photopyroelectric spectroscopy (PPES) was used in a novel ultrasensitive non-contact configuration to measure Ti3+:Al2O3 crystal nonradiative quantum yield bulk spectra, η(b)NR(λ), which were analyzed allowing for both inter- and intra-configurational decay pathways of the Ti3+ ion in a two-dimensional harmonic oscillator adiabatic model. They were found to be dominated by inter-configurational de-excitation of the highly vibronically excited Ti3+ ion above cross-over, in clear break with current theoretical practices in unthermalized systems.