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 didymium 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 didymium is optically bonded to 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 didymium (a mixture of neodymium & praseodymium) oxide, optically 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.

9 characteristic and well-defined peaks can be certified, covering the wavelength range from 430 nm to 890 nm. This spectrum is superimposed on a constant background absorbance, nominally 1A.

Typical spectra


9 peak wavelengths are certified at nominal values of 473, 514, 530, 572, 586, 739, 748, 807 and 879 nm.

Note: The above values are for guidance only. TheCalibration Certificate accompanying each Starna Didymium 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 wavelengthsand bandwidth values.

The absorbance values, nominally 1A, are certified at wavelengths between the didymium peaks, at 410, 455, 550, 637 and 773 nm.


Catalogue Number

  Catalogue  Number

Didymium /Neutral Density glass filter