Time-resolved microwave Conductivity (TRMC) measurements were conducted as previously described, with the modification that a novel set of simulations and sensitivityfactor calculations were employed to allow measurement of both dark-and photo-conductivity of semiconductor powder samples packed into 3 mm EPR tubes to keep samples air free during transfer and measurement. We recently described this methodology in detail for the exact cavity used here,, and the approach is closely related to our methods for measuring the dielectric loss of molecules in solution. Briefly, the data acquisition, and processing are as follows: (1) resonance curves (microwave power reflection vs. frequency) are acquired for the empty cavity, the cavity with an empty tube inserted, and one con-taining the sample. The empty cavity data provides the background power reflectance, from which the relative power reflection coefficient is calculated for the empty tube and sample measurements. (2) TRMC transients are gathered for each sample in the series at varying laser pulse intensities to ensure a linear correlation in the response. (3) The resonance characteristic of each sample is used to calculate a unique sensitivity factor (K) by which the raw transient data is transformed into the yield-mobility product. Transients are then fit using a bi-exponential function convoluted with the 7 ns cavity response (exponentially-modified-gaussian). The resulting peak value (sum of pre-exponential factors) and amplitude-weighted average lifetime are typical figures of merit we report. For all experiments, a Nd:YAG laser system equipped with a 355 nm pumped optical parametric oscillator (OPO) was employed for sample excitation (Spectra-Physics PremiScan ULD/500 OPO, pumped by a Spectra-Physics Quanta-Ray, or Continuum Panther OPO pumped by a Continuum Powerlite). TRMC transients with fits for all samples are depicted in Figure . Variations in EPR tube geometry dominate measurement errors in dark conductivity and dielectric constant. In contrast, systematic errors in TRMC transients are usually dominated by the uncertainty in the fraction of incident light absorbed by the sample. Random error estimation was performed by calculating the average yield for samples and subsequently determining the standard deviation of the mean.