title: A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements.
abstract: The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and a CCD spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, fast sample freezing, fast alignment of the sample, accurate and stable sample temperatures, and small size and portability of the Dewar/cryostat cryogenic unit. When coupled with the fast data acquisition rates of the CCD spectrograph, this Dewar/cryostat is capable of supporting cryogenic luminescence spectroscopic measurements on luminescent samples at a series of known, stable temperatures in the 77-300 K range. A temperature-dependent study of the oxygen quenching of luminescence in a rhodium(III) transition metal complex is presented as an example of the type of investigation possible with this Dewar/cryostat. In the context of this apparatus, a stable temperature for cryogenic spectroscopy means a luminescent sample that is thermally equilibrated with either liquid nitrogen or gaseous nitrogen at a known measureable temperature that does not vary (ΔT < 0.1 K) during the short time scale (~1-10 sec) of the spectroscopic measurement by the CCD. The Dewar/cryostat works by taking advantage of the positive thermal gradient dT/dh that develops above liquid nitrogen level in the Dewar where h is the height of the sample above the liquid nitrogen level. The slow evaporation of the liquid nitrogen results in a slow increase in h over several hours and a consequent slow increase in the sample temperature T over this time period. A quickly acquired luminescence spectrum effectively catches the sample at a constant, thermally equilibrated temperature.
authors: Chemical Physics Laboratory, Concordia University.
authors: Phoebe G
authors: PG
authors: Weaver
authors: Chemical Physics Laboratory, Concordia University.
authors: Devin M
authors: DM
authors: Jagow
authors: Chemical Physics Laboratory, Concordia University.
authors: Cameron M
authors: CM
authors: Portune
authors: Chemical Physics Laboratory, Concordia University; john.kenney@cui.edu.
authors: John W
authors: JW
authors: Kenney
mesh_terms: D003080:Cold Temperature; D005615:Freezing; D008163:Luminescent Measurements / Q000379:methods*; D009584:Nitrogen; D013057:Spectrum Analysis
chemical_list: D009584:Nitrogen