Holmium is a rare earth element that is silvery white and malleable. Holmium reacts with oxygen to form holmium oxide. Glasses that contain holmium oxide or holmium oxide solution are useful in the calibration of spectrophotometers due to their sharp absorption peaks in the visible spectrum.
The National Institute of Technology (N.I.S.T.), formerly National Bureau of Standards (N.B.S.) uses a holmium oxide solution sealed into silica cuvettes as the standard reference material (SRM 2034) for traceability. The holmium oxide solution is prepared with holmium oxide dissolved in perchloric acid. This solution has many well-defined absorption bands. The SRM2034 was found to be stable for up to thirty years*
The HI801-11 is traceable to SRM2034 and is supplied with a certificate that identifies the peak absorbance values of the filter within 0.1 nm of uncertainty. The HI801-11 holmium oxide filter is used with the wavelength check mode found in the HI801 iris spectrophotometer. The filter is placed into the meter and the wavelength check mode is then used to verify the wavelength positioning. Once the check is complete the meter will display the wavelength peaks and they are compared to the values found on the certificate. The values should be within ±1.5 nm of the certified value.
* NIST Special Publication 260-192