Copper-doped lithium triborate (LiB3O5) crystals: A photoluminescence, thermoluminescence, and electron paramagnetic resonance study

Abstract When doped with copper ions, lithium borate materials are candidates for use in radiation dosimeters. Copper-doped lithium tetraborate (Li 2 B 4 O 7 ) crystals have been widely studied, but little is known thus far about copper ions in lithium triborate (LiB 3 O 5 ) crystals. In the present investigation, Cu + ions (3d 10 ) were diffused into an undoped LiB 3 O 5 crystal at high temperature. These ions occupy both Li + and interstitial positions in the crystal. A photoluminescence (PL) band peaking near 387 nm and a photoluminescence excitation (PLE) band peaking near 273 nm verify that a portion of these Cu + ions are located at regular Li + sites. After an irradiation at room temperature with x rays, electron paramagnetic resonance (EPR) spectra show that Cu + ions at Li + sites have trapped a hole and converted to Cu 2+ ions (3d 9 ) while Cu + ions at interstitial sites have trapped an electron and converted to Cu 0 atoms (3d 10 4 s 1 ). Two distinct Cu 2+ trapped-hole spectra are formed by the x rays: one due to isolated Cu 2+ ions with no nearby defects and the other due to perturbed Cu 2+ ions. When the x-ray-irradiated crystal is heated above room temperature, a thermoluminescence (TL) peak appears at 120 °C with a maximum in the emitted light near 630 nm. EPR shows that this TL peak occurs when trapped electrons are thermally released from interstitial Cu 0 atoms. Thermal quenching above room temperature prevents the electron-hole recombination at Cu 2+ ions from contributing to the TL emission.