Search

The temperature dependence of the photoluminescence (PhL) spectral distributions has been reported for the lithium tetraborate Li 2 B 4 O 7 (LTB) and Li 2 B 4 O 7 :Cu (LTB:Cu) single crystals and for glassy LTB:Cu. It was found that the emission peaks of the LTB and LTB:Cu single crystals are non-elementary and splittable by temperature increase into several elementary peaks. By the sample heating the temperature quenching of PhL as well as the redistribution of the PhL intensity among elementary peaks was observed. Heating of the LTB:Cu single crystal samples caused no shift of the spectral maxima of the individual PhL peaks. The curve describing the temperature dependency of individual PhL peaks for the LTB:Cu single crystal is characterized by maxima resulting from combination of PhL and thermostimulated luminescence (TSL). The PhL intensity for glassy LTB:Cu is significantly lower than that for LTB:Cu single crystal with the equivalent copper dopant content. As compared to the LTB:Cu single crystal, the PhL spectral maximum for glassy LTB:Cu is wider and shifted to the lower energy range. Heating of the glassy LTB:Cu sample results in the PhL temperature quenching without any shift of the spectral maximum.

We have studied the thermoluminescence (TL) and roentgenoluminescence (RL) of glassy and crystallized (Li2B4O7)0.999(MnO2)0.001-(Li4B10O17)0.999(MnO2)0.001 samples. The results demonstrate that annealing influences the relative TL and RL intensities in the samples owing to crystallization processes. The TL and RL intensities of the crystalline materials are several times higher than those of the thermoluminescent material (Li2B4O7)0.999(MnO2)0.001 and have a maximum at B2O3 excesses of 7–11 mol %.

Li2B4O7:Cu single-crystal annealing in the reducing environment results in a sharp drop of intensity of thermoluminescence (TSL) and X-ray luminescence (XL) peaks. It was suggested that during annealing in the reducing environment, an oxygen vacancy is produced in the LTB structure at the bridging oxygen atom site. Oxygen vacancy charge compensation takes place at the expense of reduction of the doping Cu+ ion to the Cu0 state. In this case the A0-type thermoluminescence center formation mechanism due to irradiation becomes impossible.

The influence of reducing annealing and repeated oxidizing annealing of the Li2B4O7:Mn single crystals on their thermostimulated luminescence (TSL) and X-ray luminescence (XL) has been studied. Because of the oxygen vacancies formation and the dopant ions reduction, the reducing annealing results in a drastic decrease of the luminescence intensity along with the simultaneous shift of a part of the maxima and redistribution of the peak intensities. The repeated annealing in the oxidizing environment leads only to the partial reduction of the luminescent properties of the Li2B4O7:Mn crystals.

TheX-rayluminescencespectraofdopedlithiumtetraboratehavebeenanalyzedonthebasisofaccountingthe set of spectral transitions for different atomic charge states. It has been shown that the X-ray luminescencepeculiarities are to a great extent due to the transitions between the energy levels of dopant atoms and ions, aswellastothelevels,whichformthelithiumtetraboratematrix.PACSnumbers:78.55.Qr,71.55.Ak