Photoluminescence of F B centers in KF : Na +

Thermally activated processes in the relaxed excited states of aggregate color centers in KF: Na

“…At higher temperature, the shape of the spectrum is completely different: the 900 nm emission almost disappears, the intensities of the 720 and 780nm bands are reduced to about 50% and 10% of the low temperature values, and an emission band at about 2 150 nm is clearly observed. All these results are consistent with those previously reported [8] for a heavily doped crystal, confirming that the 720 and 780nm bands are due to F B and F2 centers, respectively, and that the 900 and 21 50 nm bands are both caused by F,(Na) centers, behaving as type I at low temperature and as type I1 at higher temperatures. It is easy also to deduce that, in spite of the low doping and of the proper conversion conditions, it is practically impossible to prevent formation of small amounts of other (both intrinsic and extrinsic) aggregate defects, as suspected on the basis of the absorption dichroism measurements.…”

“…Na impurities in the crystals was determined by atomic absorption spectroscopy measurements and the segregation coefficient was carefully determined as a function of the dopant level [9]. Among all crystals, the one containing 4.1 x 10-2mol% was selected for optical measurements, its dopant concentration being about 6 times smaller than that used in the previous work [8]. Samples were thin slabs (typical dimensions 5 x 5 x lmm3) cleaved from the boule in a carefully dehydrated environment.…”