Ce-doped LiCaAlF6 Research Articles

Effects of chemical composition control of colquiriite-type neutron scintillator single crystals

In this study, charge compensation was performed by co-doping Na + ions at the Ca2+ sites of Ce-doped LiCaAlF6 single crystals to prevent the generation of cation vacancies owing to Ce3+-doping at the Ca2+ sites. Consequently, an improved radiation resistance and increased light yield under neutron irradiation was achieved. In contrast, the Al metal of the starting material used as a substitute for AlF3 significantly increased the effective segregation coefficient keff of the Eu2+ ions in Eu-doped LiCaAlF6 and Eu-doped LiSrAlF6 single crystals. The Al metal and EuF3 in the starting materials produced EuF2 via a chemical reaction, and the Eu2+ ions in EuF2 could be substituted at the Ca2+ and Sr2+ sites. In addition, the Ca/Sr ratio control of the Li(Ca,Sr)AlF6:Eu solid-solution scintillator single crystals improved the light yield through band-gap control, and the Li(Ca,Sr)AlF6:Eu single crystal with a 25% Sr concentration exhibited the highest light yield.

LET dependence of TSL properties in Ce:LiCaAlF6 crystals

We have investigated thermally-stimulated luminescence (TSL) properties of Ce-doped LiCaAlF6 crystals irradiated with ionizing radiations of different linear energy transfers (LET) – X-rays and He ion beams. It was found that the TSL glow peaks mainly appeared around 120 and 250–400°C, and the ratio of the former peak intensity to the latter was found to decrease with increasing the LET. Furthermore, together with the TSL properties measured with X-rays, diffusion length of electron-hole pairs was estimated to lie in a range of 30–120nm depending on the LET and concentration of Ce.

Linear energy transfer effects on time profiles of scintillation of Ce-doped LiCaAlF6 crystals

We measured temporal profiles of the scintillation of Ce-doped LiCaAlF6 scintillator crystals at different linear energy transfers (LETs). Based on the comparison of high-LET temporal profiles with those at low LET, a fast component was observed only at low LET. The disappearance of the fast component at high LET is tentatively ascribed to the quenching of excited states at crystal defects owing to the interaction between excited states via the Auger process. In addition, the rise and the initial decay behavior were dependent on the LET. This LET-dependent behavior is explained by an acceleration process and a deceleration process in energy transfer at high LET. The LET-dependent temporal profiles provide the basis for a discrimination technique of gamma-ray and neutron detection events using these scintillators based on the nuclear reaction, 6Li(n,α)t.

Ionizing radiation induced emission: Scintillation and storage-type luminescence

In solid state ionizing radiation detectors, mainly two types of luminescent materials, scintillators and dosimeter materials, have been investigated for a long time. The former one transduces the energy of high energy ionizing radiation (keV–GeV) to thousands of UV-visible photons immediately and the latter storages energies under radiation exposure. After the excitation by visible photons (OSL) or thermal energies (TSL), dosimeter materials release the storage energies by UV-visible emission. In this work, Ce-doped CaF2, Eu-doped LiCaAlF6, Ce-doped LiCaAlF6, and Pr-doped LuAG were evaluated on their scintillation, OSL, and TSL properties. In Ce-doped CaF2, Eu-doped LiCaAlF6, and Pr-doped LuAG, scintillation and dosimeter properties showed a complementally relation while Ce-doped LiCaAlF6 exhibited different properties.

Crystal Growth of Na-Co-Doped Ce:LiCaAlF6 Single Crystals and Their Optical, Scintillation, and Physical Properties

We have grown Ce- and Na-co-doped LiCaAlF6 (Ce,Na:LiCAF) single crystals with various Ce and Na concentrations by the micro-pulling-down (μ-PD) method. Physical properties such as crystallinity, transmittance, photoluminescence, scintillation, and radiation resistance were investigated to evaluate the effects of charge compensation by Na co-doping in the Ce-doped LiCaAlF6 (Ce:LiCAF) crystal. Ce2%:LiCAF, Ce1%Na1%:LiCAF, Ce1.5%Na1.5%:LiCAF, and Ce2%Na2%:LiCAF crystals with no visible cracks and inclusions were prepared. The Ce1%Na1%:LiCAF crystal showed high crystallinity comparable to the crystal grown by the Czochralski method. In the transmittance and photoluminescence spectra of all crystals, an absorption peak around 270 nm and emission peaks around 285 and 310 nm originating from Ce3+ ions were observed, respectively. With increasing Ce and Na concentrations, the light yield systematically increased, and scintillation decay times decreased. Improvement of radiation resistance accomplished by charge co...

Thermoluminescence and color center peculiarities of Ce doped LiCaAlF 6 and LiSrAlF 6 crystals

Energy storage in pure and Ce-doped LiCaAlF6 and LiSrAlF6 crystals has been investigated. X-ray irradiated samples were treated thermally to determine the number of color centers. The absorption spectra and thermostimulated luminescence were studied to establish a relation between coloration and glow curve peaks. The similarity of the induced absorption band positions in both crystals in contrast to energy storage efficiency was observed. The coloration of LiSrAlF6:Ce is much higher than of LiCaAlF6:Ce. The color center nature is discussed starting from intrinsic and activator defect structure. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Energy transfer in pure and Ce-doped LiCaAlF6 and LiSrAlF6 crystals

Intrinsic ultra-fast scintillations at pulsed X-ray excitation were found in LiCaAlF6 and LiSrAlF6. Radiative recombination features of Ce-doped crystals are explained by differences of lattice properties, defect structure and Ce3+ ion environment in these crystals. The role of exciton formation, electron and hole traps, and energy transfer to the activator centers are discussed.

Energy storage in Ce-doped LiCaAlF6 and LiSrAlF6 crystals

Absorption, emission and thermoluminescence (TL) of as-grown and X-irradiated pure and Ce-doped LiCaAlF6 (LiCAF) and LiSrAlF6 (LiSAF) crystals have been analyzed. It is shown that the energy storage is defined by the dissimilarity of basic matrix properties, intrinsic defect structure, preferred Ce3+ ion disposition and charge compensation defect type. This is the reason of higher colorability and TL efficiency of as-grown Ce:LiSAF compared to Ce:LiCAF. Pre-filling of ultra-deep traps leads to enormous increases in the TL response. Due to these properties Ce:LiSAF and Ce:LiCAF are promising thermoluminescent dosimetric materials.

Energy transfer in LiCaAlF6:Ce3+

Time-resolved X-ray excited luminescence, induced absorption and thermostimulated luminescence in pure and Ce-doped LiCaAlF6 crystals have been investigated. It was found that the Ce-doped samples have a fast rise time and a 25ns decay time following pulsed photoexcitation and a 6ns rise time and a 50ns decay time following pulsed X-ray excitation. This may be connected with the transport and sequential capture of charge carriers at or near the Ce3+ ion. The overlapping self-trapped exciton emission (280nm) and Ce3+ ion absorption (270nm) bands also makes excitonic energy transfer possible. Shallow and deep traps were found in the LiCaAlF6:Ce3+ crystals.

A new effective thermoluminescent material: LiCaAlF6:Ce.

Absorption, emission and thermostimulated luminescence (TSL) of as-grown and X ray irradiated pure and Ce-doped LiCaAlF6 crystals were investigated. Ce-containing samples demonstrate intensive TSL in the UV region (280-310 nm) with a main peak at 350 degrees C. It is found that the well known UV laser crystal LiCaAlF6:Ce is a promising thermoluminescent dosemetric material.