Pt(( n Bu) 3 P) 2 (ethynylbenzene) 2 ] and [Pt(( n Bu) 3 P) 2 (1,4-diethynylbenzene) 2 ], which possess D 2h micro-symmetry in their ground states, were studied at 77 K by time-resolved infrared (TRIR), FTIR, steady-state emission, and time-resolved photoluminescence spectroscopies. The primary luminescence peaks are at 22 573 cm -1 and 20 408 cm -1 , respectively, with additional resolved structure from both phenyl ring and ethynyl vibrations. A quantum chemical modeling study showed that the HOMO is composed of conjugated π-obitials, which include contribution from the d xy orbital on the platinum metal, while the LUMO consists of only the ligand π* antibonding orbitals, thus the excitation is a mixture of ππ* and MLCT. From the results of the TRIR study and from group theoretical requirements, it has been concluded that the excitation in the lowest triplet manifold is confined to one ligand, resulting in a reduction of symmetry to C 2V . For the ethynylbenzene compound, the lowest energy grow-in in the TRIR spectrum is in the range of a stretching vibration for a carbon-carbon double bond. In the 1,4-diethynylbenzene compound, the low-energy grow-in in the TRIR spectrum is intermediate between a doubly and triply bound carbon stretch. An explanation of the localization is presented through a coupling of the lowest energy 3 B 3u electronic manifold to a B 3u anti-symmetric ethynyl stretch on the peripheral ligands.

Hafnium oxide thin films with varying oxygen content were investigated with the goal of finding the optical signature of oxygen vacancies in the film structure. It was found that a reduction of oxygen content in the film leads to changes in both, structural and optical characteristics. Optical absorption spectroscopy, using nanoKelvin calorimetry, revealed an enhanced absorption in the near-ultraviolet (near-UV) and visible wavelength ranges for films with reduced oxygen content, which was attributed to mid-gap electronic states of oxygen vacancies. Absorption in the near-infrared was found to originate from structural defects other than oxygen vacancy. Luminescence generated by continuous-wave 355-nm laser excitation in e-beam films showed significant changes in the spectral profile with oxygen reduction and new band formation linked to oxygen vacancies. The luminescence from oxygen-vacancy states was found to have microsecond-scale lifetimes when compared with nanosecond-scale lifetimes of luminescence attributed to other structural film defects. Laser-damage testing using ultraviolet nanosecond and infrared femtosecond pulses showed a reduction of the damage threshold with increasing number of oxygen vacancies in hafnium oxide films.

A model for the multiple-pulse laser-induced breakdown behavior of dielectrics is presented. It is based on a critical conduction band (CB) electron density leading to dielectric breakdown. The evolution of the CB electron density during the pulse train is calculated using rate equations involving transitions between band and mid-gap states (native and laser-induced). Using realistic estimations for the trap density and ionization cross-section, the model is able to reproduce the experimentally observed drop in the multiple-pulse damage threshold relative to the single-pulse value, as long as the CB electron density is controlled primarily by avalanche ionization seeded by multiphoton ionization of the traps and the valence band. The model shows that at long pulse duration, the breakdown threshold becomes more sensitive to presence of traps close (within one photon energy) to the CB. The effect of native and laser-induced defects can be distinguished by their saturation behavior. Finally, measurements of the multiple-pulse damage threshold of hafnium oxide films are used to illustrate the application of the model.

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