References designed for the visible region only are available from Starna. These references can be manufactured from optical glass rather than the UV grade quartz required for UV references.
Many other Starna wavelength references, designed principally for use in the UV, can be used in the visible region, and are also listed below

Holmium Oxide Solution (240 - 650 nm)

The most widely used liquid wavelength reference, recognised by  most Pharmacopoeias and standardisation bodies, including:

• European Pharmacopoeia
• Deutsches Arzneibuch (German Pharmacopoeia).
• United States Pharmacopoeia
• American Society for Testing and Materials
• Therapeutic Goods Administration (Australia)
• British Pharmacopoeia

When prepared in dilute perchloric acid, holmium oxide gives a spectral scan containing 14 characteristic and well - defined peaks covering the wavelength range from  240 nm to  650 nm.

Approximate peak wavelength values (in nm) are: 241, 250, 278, 288, 334, 346, 361, 385, 417, 451, 468, 485, 537, 641

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Didymium Oxide Solution  (290 – 870 nm)  

The spectrum of didymium in perchloric acid contains 14 peaks that can be certified for wavelength, covering the range from 290 nm to 870 nm. This reference is useful for its NIR coverage, but has few peaks in the UV and is not accepted by the Pharmacopoeias for wavelength qualification in this region.

Approximate peak wavelength values (in nm) are: 298, 329, 354, 444, 469, 482, 512, 522, 576, 732, 740, 794,799, 864

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Holmium Oxide Glass (240 - 640 nm)

This solid material is physically more robust than Its liquid equivalent and can therefore be used in a more demanding  environment, so is useful as a routine wavelength calibration check. It is, however, not accepted  by all the Pharmacopoeias for  wavelength qualification.

Approximate peak wavelength values (in nm) are:242, 279, 288, 334,  361, 419, 446, 454, 460, 537, 638

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Didymium Glass Filter (430 – 890 nm) 

The didymium (neodymium & praseodymium) Glass  filter  produces characteristic peaks in the  visible region of the spectrum, with 11 well-defined peaks  from  430 nm to 890 nm.

Approximate peak wavelength values (in nm) are: 431, 473, 513, 529, 573, 585, 685, 741, 749, 807, 879.

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Combined Holmium/Neutral Density Glass

With this combined filter, the holmium spectrum is superimposed on an approximately constant 1A background, useful as an absorbance accuracy check. 7 peak wavelengths are certified at nominal values of 361, 419, 446, 454, 460, 537 and 638 nm.

Absorbance values, nominally 1A, are certified at wavelengths between the holmium peaks at 431, 516, 557, 594 and 623 nm.

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Combined Didymium/Neutral Density Glass

With this combined filter, the holmium spectrum is superimposed on an approximately constant 1A background, useful as an absorbance accuracy check. 9 peak wavelengths are certified at nominal values of 473, 514, 530, 572, 586, 739, 748, 807 and 879 nm.

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

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Starna Green Broadband References (250 - 650 nm)

Specially developed for instruments with wider Spectral Band Widths (up to 20 nm), but a good general purpose reference, Starna Green has broad peaks at  258 nm, 416 nm and 630 nm. This reference material may also be used to qualify the absorbance scale, and four different concentrations cover an absorbance range from approximately 0.25 A to 1.A. The references are available singly or in any combination.

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Samarium Oxide Solution (230 – 560 nm) 

Samarium perchlorate is a particularly useful reference material for checking the wavelength scale over the commonly  used region from 200 nm to 500 nm.

Approximate peak wavelength values (in nm) are: 235, 279, 290, 305, 318, 332, 344, 362, 374, 391, 401, 415,464, 479

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Starna wide-range wavelength references (335 – 1945 nm)

This exceptionally wide-range filter contains a mixture of rare earth oxides and provides 20 peaks for wavelength calibration between in the NIR. It is equivalent to NIST SRM 2065. Nominal peak wavelength values (in nm) are: 335, 345, 361, 375, 386, 402, 418, 485, 538, 583, 642, 748, 804, 976, 1076, 1151, 1222, 1366, 1469, 1945

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