Ultraviolet-blue ionic luminescence of alkali feldspars from bulk and interfaces

Laboratory driven ionic thermal exchange of alkali feldspars from K to Na p roduces samples which are strongly luminescent in the ultraviolet region ne ar 320 nm. The sites providing this luminescence are suggested as being cor related with the motion of Na atoms along interface-interphases of the mate rial (i.e. with NaO bond fracture). The thermoluminescence peaks show multi -order kinetics. Thermal preheatings of low albite sensitize the feldspar l attice with respect to thermoluminescence generated by exposure to UV irrad iation and heating produces a strong blue luminescence spread over the rang e 350 nm to 500 nm band in feldspars. The upper temperature for thermolumin escence in feldspars is similar to 300 degrees C, which is also the point w here ionic conductivity of albite (010) begins, but the 300 degrees C regio n is also the starting point of a large second glow peak in adularia. Whils t it seems appropriate to link the Na motion to the 350-500 nm emission, it is unclear whether these changes are the result of the large anisotropic t hermal vibration of Na atoms or the massive Na jumps that occur when the la ttice reaches 300 degrees C. A speculative model is considered in which the UV TL emissions of natural minerals are linkedto different interface-inter phases (grain boundaries, exsolution limits, twinning planes, antiphase dom ains). Increased interface coherency energies are related to the kinetic or der and the spectral position of luminescence emission peaks.