Red photoluminescence and purple color of naturally irradiated fluorite

Michael Gaft1, Glen A Waychunas2, George R. Rossman3, L Nagli1, G Panczer4, D Cheskis1, Y Raichlin1

1 Ariel University, Physical Department, Ariel, Israel

2 Energy Geosciences Division, Lawrence Berkeley National Laboratory MS 74-316C, One Cyclotron Road Berkeley CA United States

3 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, United States

4 Institut Lumière Matière UMR 5306, Université Lyon 1 – CNRS, Université de Lyon, 69622 Villeurbanne, France


ABSTRACT

Natural radiation induced red fluorescence of fluorite consists of two broad bands at 750 and 635 nm with very short decay times of 16.0 and 8.0 ns, respectively. The first one is connected to a M center compensated by Na, while the second to a M+ center, possibly formed as result of the M-center destruction by UV irradiation. The optically active centers in naturally irradiated fluorite responsible for red luminescence and purple color different from one another. The most probable reason for the purple color is colloidal calcium and not MNa centers.


Purple Fluorite  Purple fluorite luminescence

Purple fluorite from Berbes, Asturias, Spain, in daylight (left) and under UV illuination (right)
Click on the images for larger images.
This type of high Na fluorite fades under LWUV but can be brought back with SWUV.

Mapimi Spectrum

Room Temperature luminescence spectrum of the red emission band 
of naturally irradiated fluorite from Mapimi, Durango, Mexico.