We present the development and performance of an optically detected magnetic resonance (ODMR) spectrometer. The spectrometer represents advances over similar instruments in three areas: (i) the exciting light is a tunable laser source which covers much of the visible light range, (ii) the optical signal is analyzed with a spectrograph, (iii) the emitted light is detected in the near-infrared domain. The need to perform ODMR experiments on single-walled carbon nanotubes motivated the present development and we demonstrate the utility of the spectrometer on this material. The performance of the spectrometer is critically compared to similar instruments. The present development opens the way to perform ODMR studies on various new materials such as molecules and luminescent quantum dots where the emission is in the near-infrared range and requires a well-defined excitation wavelength and analysis of the scattered light.

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The photophysics of single-wall carbon nanotubes (SWCNTs) is intensively studied due to their potential application in light harvesting and optoelectronics. Excited states of SWCNTs form strongly bound electron–hole pairs, excitons, of which only singlet excitons participate in application relevant optical transitions. Long-living spin-triplet states hinder applications, but they emerge as candidates for quantum information storage. Therefore, knowledge of the triplet exciton energy structure, in particular in a SWCNT chirality dependent manner, is greatly desired. We report the observation of light emission from triplet state recombination, i.e., phosphorescence, for several SWCNT chiralities using a purpose-built spectrometer. This yields the singlet–triplet gap as a function of the SWCNT diameter, and it follows predictions based on quantum confinement effects. Saturation under high microwave power (up to 10 W) irradiation allows the spin-relaxation time for triplet states to be determined. Our study sensitively discriminates whether the lowest optically active state is populated from an excited state on the same nanotube or through Förster exciton energy transfer from a neighboring nanotube.

Alkali‐intercalated graphite compounds represent a compelling modification of carbon with significant application potential and various fundamentally important phases. The intercalation of graphite with alkali atoms (Li and K) using liquid ammonia solution as a mediating agent is reported. Alkali atoms dissolve well in liquid ammonia, which simplifies and speeds up the intercalation process, and it also avoids the high temperature formation of alkali carbides. Optical microscopy, Raman, and electron spin‐resonance spectroscopy attest that the prepared samples are highly and homogeneously intercalated to a level approaching stage‐I intercalation compounds. The method and the synthesis route may serve as a starting point for the various forms of alkali‐atom‐intercalated carbon compounds (including carbon nanotubes and graphene), which can be exploited in energy storage and further chemical modifications.

Microwave reflectance probed photoconductivity (or µ-PCD) measurement represents a contactless and non-invasive method to characterize impurity content in semiconductors. Major drawbacks of the method include a difficult separation of reflectance due to dielectric and conduction effects and that the µ-PCD signal is prohibitively weak for highly conducting samples. Both of these limitations could be tackled with the use of microwave resonators due to the well-known sensitivity of resonator parameters to minute changes in the material properties combined with a null measurement. A general misconception is that time resolution of resonator measurements is limited beyond their bandwidth by the readout electronics response time. While it is true for conventional resonator measurements, such as those employing a frequency sweep, we present a time-resolved resonator parameter readout method which overcomes these limitations and allows measurement of complex material parameters and to enhance µ-PCD signals with the ultimate time resolution limit being the resonator time constant. This is achieved by detecting the transient response of microwave resonators on the timescale of a few 100 ns during the µ-PCD decay signal. The method employs a high-stability oscillator working with a fixed frequency which results in a stable and highly accurate measurement.