| dc.description.abstract | The amount of thermal energy that a system possesses, otherwise known as its temperature, is a property whose measurement has been utilized in experiments since Galileo constructed his first thermoscope. Over the centuries succeeding Galileo, scientific advancements lead to improved measurement methodologies and apparatuses. This allowed measurements with increased accuracy and sensitivity, coupled with decreased sensor size and acquisition time. A recent advancement in
this field is optical thermometry, which utilizes fluorescing color centers in diamonds. The stalwart of optical thermometry is the utilization of optical detection of magnetic resonance (ODMR) of nitrogen–vacancy (NV) color centers. This method’s main drawback is its use of microwave fields to measure the electron spin resonance (ESR) of the color center, which is detrimental to in vivo measurements. An alternative method is to use heavier Group-IV elements to create a split vacancy color center. These color centers have spectra whose zero phonon lines (ZPL’s) and phonon sidebands (PSB’s) have a high enough contrast ratios to perform all-optical fluorescence thermometry. By quantifying the temperature dependence of various properties (peak width, central wavelength, amplitude, and Debye–Waller factor (DWF)) of their photoluminescence (PL) spectral peaks, these color centers have been used as thermometers with high spatial resolution, precision, and sensitivity without the drawbacks of NV based thermometers. One such color center, germanium–vacancy (GeV), has been found to have a precision of 0.008 nm/K, sensitivities in the range of a few mK/√Hz, and a spatial resolution on the micron scale; although, better sensitivities and higher spatial resolutions are possible. While these color centers avoid the damages incurred by the ODMR measurements, they are still hindered by a heating penalty induced by linear laser radiation absorption from the pump laser. The relationship between pump power and fluorescence brightness, coupled with the relationship between fluorescence brightness and sensitivity, leads to the incurring of a substantial heating penalty for increased sensitivity in measurements. Another split-vacancy color center, nickel–vacancy (NiV), operates in the near-infrared (near-IR), which can penetrate farther through biological materials than the optical PL of Group-IV color centers. | |
