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The spectral responsivity can be obtained with a source that emits a known and broad spectrum in the UV/vis/NIR region. In general, different types of light sources can be used:
- Lamps (e.g. tungsten ribbon lamps)
- Sphere-type spectral radiators
- Chromophore standards
Tungsten ribbon lamps and integrating sphere-type spectral radiance transfer-standards
are traceable, but are tedious to align, can impose restrictions on measurement geometry, need regular and expensive recalibrations, and often do not fit into compact fluorescence instruments. Moreover, their spectral radiances/emission intensities exceed those of typical fluorescent samples by ca. four (tungsten ribbon lamp) to two (integrating sphere radiator; not shown) orders of magnitude, see Figure 2. Accordingly, their use requires special attenuation procedures that do not introduce additional spectral effects.
Chromophore-based spectral fluorescence standards
are easy to operate and offer a unique flexibility with respect to measurement geometry and type of instrument to be calibrated. They can be measured under routine conditions. Thus, many sources of systematic error can be elegantly avoided. Aside from proper choice and combination of candidate materials to cover the UV/vis/NIR region prerequisites for the reliability of spectral fluorescence standards are the traceable and accurate measurement of their corrected emission spectra with a reported uncertainty and the characterization of their calibration-relevant properties according to EN ISO/IEC 17025 and ISO Guides 34 and 35.
Comparison of the typical spectral radiance of a tungsten ribbon lamp (top) and typical fluorophores (bottom).
Certified Fluorescence Standard
Instrument Effects on Fluorescence Signals
Kit Spectral Fluorescence Standards: Principle and Properties
Tracability, Certification, and Proviniency Testing
References
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