User Guide

For an introduction to the application and use of Certified Reference Materials in absorption spectrophotometry


This filter is a useful tool for routinely checking the wavelength and absorbance accuracy of a visible spectrophotometer. Like its liquid counterpart, the holmium glass filter produces characteristic peaks that make it suitable for use as a wavelength reference material in the visible region of the spectrum. In this filter, the holmium glass is optically bonded a neutral density filter giving a nominal 1A background absorbance that can be used to check the absorbance accuracy of the instrument


Description and Discussion

Glass filter containing holmium oxide, bonded to a neutral density filter and mounted stress free in an anodised aluminium holder. Sliding window covers are provided to protect the surface from damage when not in use. Variations from melt to melt of the glass can cause small uncertainties in peak position, so each Starna filter is individually certified.

7 characteristic and well-defined peaks can be certified, covering the wavelength range from 360 nm to 640 nm. This spectrum is superimposed on a constant background absorbance, nominally 1A.


Typical spectra


7 peak wavelengths are certified at nominal values of 361, 419, 446, 454, 460, 537 and 638 nm.

The absorbance values, nominally 1A, are certified at wavelengths between the holmium peaks, at 431, 516, 557, 594 and 623 nm.

Note: The above values are for guidance only. TheCalibration Certificate accompanying each Starna Glass Reference gives actual values measured at a bandwidth of 1 nm and only these certified values should be used for instrument qualification. On request, Starna can provide certified values at other wavelengths and bandwidthvalues.



Catalogue Number

  Catalogue  Number

Holmium /Neutral Density glass filter