Investigation of Cu-doped Li₂B₄O₇single crystals by electron paramagnetic resonance and time-resolved optical spectroscopy

Abstract

A low-temperature study of the thermoluminescent dosimeter material, lithium tetraborate (Li 2 B 4 O 7 ) doped by Cu, has been carried out by the methods of electron paramagnetic resonance (EPR) and time-resolved polarization spectroscopy using 4-20 eV synchrotron radiation and 1 μs Xe flash lamp pulses in the region 3-6 eV. The observed EPR spectra of an unpaired hole with strong d-character and characteristic hyperfine splittings can be ascribed to Cu 2+ substituted at a Li lattice site and displaced due to relaxation. The results on the Cu + -related luminescence strongly support the conclusion about a low-symmetry position of copper impurity ions in the lithium tetraborate lattice. The temperature dependence of the decay kinetics of the Cu + -related 3.35 eV emission indicates a triplet nature for the relaxed excited state of the Cu + centres. An off-centre position of the Cu + ion in the relaxed excited state is suggested.

The Electronic Structure and Secondary Pyroelectric Properties of Lithium Tetraborate

“…Generally, electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) studies in Li 2 B 4 O 7 have focused on Cu + [15,19,46,47], Co 2+ and Mn 2+ [48,49], impurities substituting for lithium and vacancy-related defects produced by neutron irradiation at room temperature. The Cu impurity centers in the Li 2 B 4 O 7 lattice generally adopt the univalent Cu + ion state [46,47,50,51,52,53,54], independent of the valence of the initial chemical copper source additive agent used for Cu doping.…”

“…The Cu impurity centers in the Li 2 B 4 O 7 lattice generally adopt the univalent Cu + ion state [46,47,50,51,52,53,54], independent of the valence of the initial chemical copper source additive agent used for Cu doping.…”

“…Copper impurity ions substitute for lithium ions in the Li 2 B 4 O 7 lattice [19,46,47,50,51,52,53,54], with most of them being in the monovalent charge state prior to the X-ray irradiation. Heating above room temperature restores the pre-irradiation distribution of copper charge states.…”

Li2B4O7:Mn for dosimetry applications: traps and mechanisms

“…EPR and luminescence of Li 2 B 4 O 7 :Cu single crystals were studied recently [12][13][14]. Cu 2+ was observed by EPR, while Cu + was detected by luminescence.…”

Effects of synthesis, doping methods and metal content on thermoluminescence glow curves of lithium tetraborate

“…Many researchers investigated the TL properties of LTB doped materials with different activators such as: Mn, Cu, Ag, and Mg [3][4][5][6][7][8][9]. The first thermoluminescent material based on LTB activated by Mn is commercialized by Harshaw under the name TLD-800.…”