Which material is best suited for verifying the wavelength calibration of a spectrophotometer?

The best material for verifying the wavelength calibration of a spectrophotometer is holmium oxide glass. Holmium oxide has well-defined and sharp absorption peaks across a range of wavelengths, particularly in the ultraviolet and visible regions of the spectrum. These distinct peaks serve as reliable reference points for calibration.

When using holmium oxide glass for wavelength calibration, each peak corresponds to a specific wavelength, allowing for precise adjustment and verification of the spectrophotometer's readings. This ensures that the instrument provides accurate measurements at those specific wavelengths, which is critical for any quantitative analysis performed using the spectrophotometer.

In contrast, while other materials such as potassium dichromate solutions may also be used for calibration purposes, they do not provide as sharp or well-defined spectral lines as holmium oxide glass. Neutral density filters and Wratten filters serve different purposes that are not primarily focused on wavelength accuracy; they are used more for attenuation of light rather than for establishing precise wavelength references. Therefore, holmium oxide glass is the preferred choice for this specific calibration task.