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The SPECTRA is optimized for the most common fluors and fluorescent proteins used in bioanalysis today. Bright outputs cover the visible spectrum and beyond, with particularly impressive performance in the typically underserved visible spectral regions- green, yellow and red. The optically independent outputs are well suited for both live and fixed cell analysis. Bandwidths for any SPECTRA light engine may be tailored for specific spectral needs.

This page titled 11.1: Absorption of Light is shared under a not declared license and was authored, remixed, and/or curated by Kathryn Haas.

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All outputs are optimized for high performance in terms of stable, durable, powerful, switchable light. Output power is independently selectable for each color band. Micro-second switching among color bands (5-10 kHz) is enabled electronically- eliminating all mechanical shuttering. SPECTRA light engines are the ideal choice for customers who wish to address unique spectral bands with independent electronic control in systems critically synchronized with camera exposure times.

SPECTRA light engines may be used with any major brand microscope, connecting via direct couple, liquid light guide or optical fiber. SPECTRA light engines are pre-aligned, require no maintenance, and need no bulb replacements.

The absorption spectrum shown above in Figure \(\PageIndex{1}\) is a simple case in which only one absorption band is observed in the visible region of the spectrum. In a simple case like this, the color of a complex can be predicted as the complementary color of the light absorbed by the solution. When a solution or object absorbs a certain wavelength, we see the complementary color; or the color opposite to the absorbed wavelength on the color wheel in Figure \(\PageIndex{2}\). In the case of the Cu(II) complex spectrum shown in Figure \(\PageIndex{1}\), the color of the light absorbed at 530 nm is green, and the predicted color observed is pink.

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The table below lists the approximate colors of absorption corresponding to wavelengths of light absorbed, and gives similar information to that deduced from Figure \(\PageIndex{2}\).

Lumencor’s light engines are unique, solid state illuminators, ideally suited for use with fluorescence microscopes and bioanalytical instruments. SPECTRA light engines enhance overall microscope performance and reduce cost. Flexible designs provide as few as two and as many as seven color bands with a variety of delivery optics.

The d-orbital splitting in coordination complexes results in a gap (\(\Delta\)) that happens to be just the right magnitude to absorb visible light. Because metal complexes can absorb visible light, they display an array of colors. Not only is the color attractive to the eye, it is an indication of the chemical and physical properties of the metal complex. The color (like the magnitude of \(\Delta\)) depends on the identity of the metal ion, the coordination geometry, and the ligand identity. Chemists don't just "look" at color, though - we measure it using electronic absorption spectroscopy. This is usually done in a lab using a UV-visible spectrophotometer.

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The absorption spectrum of a metal complex can be used to calculate the splitting energy, \(\Delta\), when the absorption corresponds to a \(d \rightarrow d \) transition. Let's use the \(d^9\) Cu(II) complex (discussed above) as an example. A \(d^9\) metal ion has only one visible-light \(d \rightarrow d\) transition. Let's assume that the coordination geometry is approximately octahedral (although it is actually a Jahn-Teller distorted octahedron, and more like a square plane). If we assume it's octahedral, then the \(d\)-orbital splitting diagram (see Figure \(\PageIndex{1}\)) leads us to expect one electronic transition: an electron is excited from the \(t_{2g}\) to \(e_g\). The energy absorbed is equal to the energy of the \(\Delta\).

Many cases are not as simple as a \(d^9\) octahedral case because there are multiple possible electronic transitions, and also multiple absorption bands in the UV-vis spectrum. In these more complex cases, the actual energy of the transition are affected by differences in electron-electron repulsion energies in the ground state and the excited states. We will learn how to account for multiple possible excited states and electron-electron repulsions using Tanabe-Sugano diagrams later in this chapter.

An example of such a measurement is shown below in Figure \(\PageIndex{1}\) for a Cu(II) complex. The sample appears a pink color to the eye, and when it is measured using a UV-visible spectrometer, it is shown to absorb visible light at approximately 530 nm. The absorption spectrum can indicate the oxidation state of Cu, the ligands bound to the Cu(II) ion, and the coordination geometry. The color of the solution in Figure \(\PageIndex{1}\) is a shade of pink.