Fluorimeter cell and its calibration

A fluorimeter reference cell which comprises a first material which emits an absorption spectrum when an excitation light is incident upon the first material. The absorption spectrum has a defined characteristic enabling wavelength calibration of the fluorimeter. The reference cell further comprises a second material which has dispersive properties such that the absorption spectrum is scattered or reflected at an angle to the angle of incidence of the excitation light incident on the reference cell. The reference cell may comprise a quartz cell containing the first material which may comprise a rare earth salt solution or another optically transparent solution with a well-defined absorbance pattern. The second material may comprise a light scattering colloid such as colloidal silica. The reference cell may have a triangular cross-section with a surface ground to a diffuse finish and/or is coated with a reflective coating. The scattering may be provided only by the surface coating.