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What is Fluorescence ?

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Fluorescence is the property of some substances to re-emit (in most cases at longer wavelength so at lower energy) the received electromagnetic radiation, in particular they absorb the ultraviolet radiation and re-emit it in the visible.

Examples of this process are the materials that contain fluorescent pigments, such as the ink of a highlighter and fluorescent paints.

The fluorescent properties of an object often become evident with the use of a Wood’s lamp which produces radiation in the ultraviolet band, but depending on the materials, lower wavelengths may be necessary.

The mechanism of fluorescence is the following : an incident radiation (in the example of the Wood lamp is ultraviolet radiation) excites the atoms of the fluorescent substance, promoting an electron to an energy level (orbital) less bound, with more energy and therefore more “external”. Within a few tens of nanoseconds, the excited electron returns to the previous level in two or more steps, that is, passing for one or more excited states at intermediate energy.

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All decays except one are, usually, non radiative, while the last emits light at a longer wavelength than the incident radiation (not necessarily in the visible spectrum): this light is called “fluorescence”.

 The Fluorescence spectrometer

For the study of the fluorescence we used the grating spectrometer already described in one of the previous posts, supplemented by a cell sample holder and by a source of excitation. The spectra has been acquired with the software Theremino Spectrometer.

Fluorimetro
Fluorescence Spectrometer Scheme
fluo_setup
Cuvette sample holder and excitation laser source
oliveOilFluo
Olive Oil fluorescence excited by UV laser

Fluorescence Spectra

Chlorophyll

FluoClorofilla
Chlorophyll fluorescence excited by UV laser (I), by 532nm green laser (II) and by 650nm red laser (III)

Fluorescein

fluoresceina
Fluorescence Spectrum of Fluorescein excited by UV laser and by green laser

Olive Oil

OLIOBUONO_FLUO_UV
Olive Oil fluorescence excited by UV laser, emission peak due to Chlorophyll A

Heated Olive Oil

OLIO_OLIVA_HEATED_FLUO_UV
Olive Oil Fluorescence after heating cycle, emission peaks due to peroxides

Quinine

CHININO_FLUO
Quinine Fluorescence Spectrum excited by UV laser

Cumarine

ALLURE_FLUO_UV
Perfume Fluorescence Spectrum excited by UV laser, peak due to cumarine content

Pdf document with the description of the fluorescence experiments : Fluorescenza_ENG

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