Holmium Oxide Glass Filter

Wavelength accuracy is normally assessed by using either a sample containing a series of very sharp peaks such as a solution of holmium perchlorate or a holmium oxide and/or didymium doped glass filter or by measuring the emission from a lamp.

The most commonly used glass (or quartz) filter is holmium oxide. This provides a quick and easy way to check wavelength accuracy. This standard gives a series of lines in the visible region. It does not provide strong absorption peaks into the UV region and so a solution of holmium oxide in perchloric acid (holmium perchlorate) is recommended by some pharmacopoeias but for general non-pharmacopoeia instrument testing, holmium oxide glass is widely used.