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Abstract: In this paper we present results of detailed spectroscopic studies of Tb3+ luminescence from BaF2:0.075mol% Tb performed at Superlumi station of Hasylab, DESY, Hamburg and at Institute of Physics, N. Copernicus University, Torun, Poland (IF UMK Torun). We have measured UV/VUV excitation spectra of the dominant blue Tb3+ luminescence and emission spectra under excitation into various bands found from the excitation spectra. The excitation spectra are dominated by the two well known broad bands due to the parity and spin-allowed (SA) 4f8 →4f75d transitions. The higher energy triple t-band and unresolved single e-band at lower energies are widely separated (10Dq about 16,500cm−1) reflecting the single d-electron energy in the high symmetry cubic crystal field with a relatively low contribution from the low symmetry component. In addition to these bands we have also detected a number of weaker bands at lower energy sides of both dominant SA bands. While the structured band with components at 252.8, 252.3, 250.4 and 248.4nm clearly corresponds to the SF (spin-forbidden) band found earlier in LiYF4:Tb, the bands at 183, 178 and 172nm have been never, to the best of our knowledge, reported before. We present arguments that these new bands are the SF counterparts of the triple SA t-band at about 158nm. The d–f exchange energies for d(e) and d(t) electrons are different at 7779 and 8245cm−1, respectively. Although the energy levels corresponding to the identified high and low spin (HS and LS) states of the 4f75d configuration are, in BaF2, well separated, there are no SA nor SF transitions generating d–f emission in BaF2:Tb. This is because the numerous 4f8 energy levels intercept the excitation energy from 4f75d levels leading to the well known blue and green Tb3+ 4f8 emissions. [Copyright &y& Elsevier]

Abstract: Barium Fluoride (BaF2), mainly used in optical applications, has similar properties to those of CaF2 but better stability under environmental conditions. In this paper, we report measurements of loss tangent and the real part of the relative permittivity ε r of single crystal BaF2 in the temperature range from 14 to 290K at frequencies of 8, 10.4, 12.1, 17.6, 21.1 and 24.4GHz. Microwave properties of BaF2 were determined by measurements of the resonance frequency and the unloaded Q-factor of TE011 and quasi TE0mn modes cylindrical cavities containing the sample under test. Two techniques namely Hakki–Coleman Dielectric Resonator and dielectric post resonators have been used for characterizing the dielectric material. Losses due to the uncalibrated cables and adaptors inside the cryocooler are accounted in the calculation of unloaded Q-factor using the Transmission Mode Q-Factor data processing technique. The permittivity of BaF2 exhibited a 5% increase from 6.9 (14K) to 7.35 (290K). The loss tangent increased from 1×10−5 to 1.1×10−4 over the measured temperature range, 14–290K at a frequency of 10.4GHz. The measured microwave properties show that BaF2 can be used in many microwave devices. [Copyright &y& Elsevier]

Open f-shell rare-earth (RE) ions in wide bandgap host materials are usually characterized by closely spaced electronic levels due to various electron configurations and charge states. These levels provide convenient luminescent transitions that can be excited by efficient recombination of charge carriers generated in the host material by ionizing radiation. Therefore, it is the area of ionizing radiation detectors, where search for new, fast and efficient scintillator materials for high-energy physics and nuclear medicine, has yielded much of the recent advances in the understanding of radioluminescence and scintillation mechanism in some solid state, UV and VUV luminescent, RE-activated materials. In this paper we shall present selected results of basic experiments such as radioluminescence, VUV spectroscopy, time profiles and thermoluminescence, on barium fluoride (activated with Ce, Pr, Nd, Tb) and two aluminum perovskites, YAlO3 and LuAlO3, activated with Ce. We shall demonstrate that these results point to consecutive carrier capture and recombination at RE ions as the basic mechanism of radioluminescence and scintillation in these materials, despite the strong self-trapping and poor charge transport properties. Consequently, various electron and/or hole traps that intercept and retain for some time the recombining charge carriers play an active role influencing both the scintillation light yield and time profiles of scintillation pulses in these and many other wide bandgap RE-activated luminescent materials. [Copyright &y& Elsevier]