Ce-doped Crystals Research Articles

Scintillation and dosimetric properties of Ce-doped MgAl2O4 single crystals

The undoped and Ce-doped MgAl2O4 single crystals were synthesized by the floating zone method equipped with four xenon arc lamps, and the photoluminescence (PL), scintillation, and dosimetric properties were investigated. The Ce-doped crystals showed PL emission peaks at around 420 and 720 nm. The former was ascribed to the 5 d-4f transition of Ce3+ ion, and the latter was ascribed Mg deficiency. The PL decay time profiles of the Ce-doped crystals exhibited the fast decay, and the decay time constants were the typical value of others Ce-doped materials. Thus, the decay time constants were attributed to the 5 d-4f transitions of Ce3+ ion. In addition, optically-stimulated luminescence (OSL) signals could be detected in all the crystals when the stimulation wavelength was 470 nm. The OSL dose response functions showed linearly proportional relationship from 10 to 1000 mGy in all the Ce-doped crystals. The thermally-stimulated luminescence (TSL) glow curves exhibit three peaks due to antisite of Al3+ ion, V center and antisite of Mg2+ ion. All the Ce-doped crystals showed improved TSL intensity and dose response sensitivity compared the undoped crystal. The 0.2 and 1% Ce-doped crystals showed linearly response at the dose range of the 0.1–1000 mGy.

Tailoring the scintillation properties of β-Ga2O3 by doping with Ce and codoping with Si

Measurements of pulse height spectra and scintillation time profiles performed on Czochralski-grown β-Ga2O3, β-Ga2O3:Ce, and β-Ga2O3:Ce,Si crystals are reported. The highest value of scintillation yield, 7040 ph/MeV, was achieved for pure β-Ga2O3 at a low free electron concentration, nevertheless Ce-doped crystals could also approach high values thereof. Si-codoping, however, decreases the scintillation yield. The presence of Ce, and the more of Ce and Si, in β-Ga2O3 significantly increases the contribution of the fastest components in scintillation time profiles, which makes β-Ga2O3 a very fast scintillator under γ-excitation.

Luminescence and scintillation properties of rare-earth-doped LaAlO3 single crystals

LaAlO3 perovskite single crystals doped with Ce, Eu or Tb have been grown by micro-pulling-down method. X-ray diffraction analysis confirmed low-temperature rhombohedric phase. Energy-dispersive Laue mapping revealed sub-grains in the grown crystals. For the Ce-doped crystals, very low radioluminescence efficiency was found and the observed emission was ascribed to defects. Photoluminescence spectra were significantly different from the radioluminescence ones. They were significantly quenched at room temperature and the related luminescence showed also unusually high Stokes shift. High radioluminescence efficiency was found for the Tb-doped samples and especially for the Eu-doped ones, which would point to the fact that in LaAlO3 the scintillation process is more favorable for the luminescence ions which tend to capture an electron first.

Development and measurement of luminescence properties of Ce-doped Cs2LiGdBr6 crystals irradiated with X-ray, γ-ray and proton beam

The effect of higher Ce-concentration on the luminescence and scintillation properties of Cs2LiGdBr6 single crystals are studied. We used the Bridgman method for the growth of Ce-doped Cs2LiGdBr6 single crystals. Luminescence properties of the grown crystals are measured by X-ray and proton excitations. We measured the pulse height and fluorescence decay time spectra of Cs2LiGdBr6:Ce3+ with a bi-alkali photo multiplier tube (PMT) under γ-ray excitation from 137Cs source. Improvements in the scintillation properties are observed with the increase of Ce-concentration in the lattice. Detailed procedure of the crystal growth is also discussed.

Temperature dependence spectroscopic study of Ce-doped Cs3LaCl6 and Cs3LaBr6 scintillators

Single crystals of Ce-doped Cs3LaCl6 and Cs3LaBr6 show promising scintillation properties in gamma-ray detection. Their thermal response in the range from 40K to 500K is discussed in this work. The steady state photoluminescence spectra, photoluminescence decay time, and X-ray excited radioluminescence of Ce-doped and undoped Cs3LaCl6 and Cs3LaBr6 were studied. The photoluminescence and radioluminescence emission intensity of the Ce-doped crystals decreases less than 25% from 40K to 500K. The photoluminescence decay time of Ce3+ increases with increasing temperature.

Growth of 4H-SiC Crystals on the 8° Off-Axis 6H-SiC Seed by PVT Method

In this work we present the growth of 4H-SiC crystals (2 inch in diameter) on the 8° off- axis C-face 6H-SiC seeds, inclined toward [11-20] direction. The growth of crystals by physical vapour transport method (PVT) was realized with the open seed backside in the experimental setup with graphite resistive heater. Some of the crystals were doped with cerium in the purpose of the 4H polytype growth stabilization. For Ce-doped crystals the seed backside carbonization process was decreased in comparison with such effect observed in the undoped SiC crystals.

Cerium Activated Scintillation in Yttrium Halides: First Principles Theory and Prediction

Recently, scintillation has been observed in Ce-doped YI3, YBr3, and YCl3 crystals. In particular, YI3 has been reported to be among the scintillators with the highest luminosity. In this work, we present a systematic study of scintillation in any of the four YHa3:Ce materials where Ha = F, Cl, Br, I, using ab initio calculations. Last year, our group demonstrated successful application of a method of gauging scintillation properties of Ce-doped crystals based on first-principle calculations using density functional theory. This method has been developed as an integral component of a High Throughput Scintillator Discovery facility based at the Lawrence Berkeley National Lab. By analyzing the energies and spatial localization of the highest occupied band in the ground state and in the lowest excited state, we are able to make qualitative predictions about the possibility of scintillation in Ce-doped compounds. In this paper we present the details of our theoretical approach in application to yttrium halides and compare them with the available experiments. Our results yield a prediction of Ce-based scintillation for all four materials: YF3, YCl3, YBr3 and YI3 and are in correspondence with the available experimental data. We believe that our method is the first use of first-principles calculations to predict some of the factors necessary for the activation of Ce3+ ions in crystals.

Shallow Traps in ${\rm YAlO}_{3}:{\rm Ce}$ Single Crystal Perovskites

The aim of this work is to investigate the influence of shallow traps on scintillating properties of YAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :Ce. Wavelength-resolved thermally stimulated luminescence measurements following X-ray irradiation at 10 K have been performed on both undoped and Ce-doped crystals. Different and composite glow curves and emission spectra were obtained. Following glow peaks analysis of YAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :Ce, their room temperature decay time was evaluated to be of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> s. The presence of an athermal tunneling recombination process between traps and Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions below 100 K has been evidenced by phosphorescence decays.

Electron paramagnetic resonance study of centres involved in storage processes in K 2YF 5: RE thermoluminescent phosphors

Ce 3+- and Tb 3+-activated K 2YF 5 crystals, which have been shown to exhibit thermoluminescence (TL) response to α, β, γ and X-rays, are investigated using electron paramagnetic resonance (EPR). X-ray irradiation at room temperature of Ce-doped crystals produces at least four distinct paramagnetic centres in the g ≈ 2 range. Irradiation at 77 K leads to the predominant production of only one of these centres, which appears to be a V- or H-type intrinsic trapped hole centre. Most of these centres can also be created in the Tb-doped crystals. In addition, the appearance of strongly angular dependent EPR signals in a wide magnetic field range, suggest that the Tb activator ions may act as electron or hole traps. We show that both Ce- and Tb-doped crystals exhibit, next to their well-studied TL above room temperature, very strong TL in the 100–300 K range. The possible involvement of the centres observed with EPR in the TL processes is discussed.

Perspectives for high resolution and high light output LuAP:Ce crystals

After its introduction in 1994, LuAlO/sub 3/:Ce (LuAP:Ce) encountered problems of 1) low light output, 2) self-absorption of scintillation light, 3) nonproportionality of light output versus energy, and 4) poor energy resolution, and 5) small non-uniform crystals. Studying newly available LuAP:Ce-doped and undoped crystals (from Photonic Materials), we have found that self-absorption is chiefly dependent on the host crystal structure and not on Ce doping. We examined the scintillation properties of these crystals and found 6.8/spl plusmn/0.3% energy resolution for 662 keV for 2 mm/spl times/2 mm /spl times/10 mm pixels. The intrinsic resolution is equal to 2.8/spl plusmn/0.4% at 2360/spl plusmn/120phe/MeV (9800/spl plusmn/500 ph/MeV) light yield. These crystals have nonproportionality of 93/spl plusmn/4% at 16 keV and intrinsic energy resolution close to that of YAP:Ce. Fast components of the scintillation comprise only about half of the light that is emitted in 100 microseconds.

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.

Study on the absorption characteristics and birefringence of Ce-doped SBN

Cerium-doped Sr 0.60 Ba 0.40 Nb 2 O 6 (SBN:60) crystals were obtained by Czochralski method. Optical transmission spectra were measured and the absorption coefficients were calculated in the visible range. The results showed that Ce-doped crystals were transparent for wavelengths more than 650 nm and the fundamental absorption edge shifted towards the longer wavelength direction with increasing Ce concentrations. In addition, the birefringence of crystals were investigated based on the theory of interference between extraordinarily and ordinarily polarized light, and the birefringence values were determined in the long wavelength region. As a result, the birefringence becomes larger by doping of SBN crystals with cerium.

Scintillation response of Ce-doped or intrinsic scintillating crystals in the range up to [formula omitted

A hybrid photomultiplier (HPMT) was used to study the scintillation response {Nphels(E) photoelectron and L.Y.(E) light yields and energy resolutions} of various known or newly developed scintillators—namely, Ce-doped crystals (perovskites or garnets), CsI(Tl) and the intrinsic BGO crystal—at different energies in the range 8keV–1.33MeV. Detailed comparative studies of the scintillation properties of these crystals are presented. A newly developed fast and heavy LuAG:Ce scintillator is characterized by about a 50% higher L.Y. compared to that of well-known and popular BGO (roughly 12500ph/MeV against 8080ph/MeV, respectively).

LiCaAlF 6:Ce crystal: a new scintillator

Scintillation properties of LiCaAlF 6:Ce crystal, well known as the effective UV laser material, is reported. Ce 3+ emission at 286–305 nm with a single exponential decay time of 35 ns provides a scintillation pulse. Radiation damage in pure and Ce-doped crystals is studied. In contrast to the majority of fluoride crystals, cerium is responsible for the ultradeep traps formation revealing thermostimulated luminescence. Overlapping of color center absorption and Ce 3+ ion emission bands limits the scintillation efficiency of LiCaAlF 6:Ce at high radiation doses.

CHARACTERISTICS AND RESPONSE RATE OF STIMULATED PHOTOREFRACTIVE SCATTERING SELF-PUMPED PHASE CONJUGATOR IN RARE-EARTH DOPED BaTiO3

Characteristics and response times of the stimulated photorefractive scattering self-pumped phase conjugator(SPS-SPPC) in the series of Rh-doped and Ce-doped BaTiO3 crystals are investigated.The experimental results show that the SPS-SPPC has higher reflectivity and faster response rate at greater incident angle.The phenomenon was properly analysed using characteristics of two-wave mixing.By the way,the phase conjugation reflectivity of Ce:BaTiO3 is higher than that of Rh:BaTiO3 crystals'.

Light-induced absorption and properties of shallow impurity levels in undoped and Ce-doped BaTiO 3

Spectral and temporal characteristics of light-induced absorption for BaTiO3 crystals undoped and doped with various amounts of Ce were investigated and compared. Dark decay of light-induced absorption with two time constants corresponding to two shallow levels was observed in all crystals investigated. Light-induced absorption spectra were then resolved into two components, slow and fast, according to the dark-decay time constants. The resolved spectra reveal that in all the undoped and Ce-doped crystals the two shallow levels have the same defect origins, independently of doping. The thermal activation energies of the two shallow levels were deduced to be ∼0.7 and ∼0.5 eV in all crystals, and the 0.7-eV shallow level is attributed to Fe4+/5+. Some other important parameters for the two shallow levels were also determined.

Radiation damage in pure and rare earth doped LiBaF/sub 3/ crystals

Absorption, emission, excitation and thermoluminescence for pure, Eu- and Ce-doped LiBaF/sub 3/ crystals, both as grown and irradiated, were investigated. High purity of initial crystal was shown to be necessary to reduce the afterglow and decrease the radiation damage level. Doping by Ce or Eu ions could be used to change the spectral and kinetic characteristics. The exciton luminescence and blue afterglow were suppressed in Eu- or Ce-doped crystals. Radiation-induced absorption spectrum was a complex and included more than six overlapping bands. Emission of these color centers appears in the luminescence spectrum.

Absolute light output of scintillators

The absolute light outputs of BGO, CsI(Tl) and some new Ce-doped crystals have been measured to an accuracy of about /spl plusmn/5% using calibrated XP2020Q photomultipliers and standard S3590.03 and S2740.03 photodiodes. The use of small crystals, 9 mm in diameter and 1 mm thick, reduces the corrections for imperfections in the light collection process and in the photoelectron collection by the photomultipliers. The measured light-output of 8500/spl plusmn/350 ph/MeV (photons/MeV) for the BGO crystals agree well with the earlier measurement done by Holl et al. (1988). The carried out study highlighted the importances of the spread in the published emission spectra of the crystals which seems to limit measurement accuracy. Finally, a simple comparative method of measuring light output to an accuracy of /spl plusmn/10%, is proposed using an uncalibrated XP2020 photomultiplier and a 1 mm thick BGO crystal as a standard.

Temporal characteristics of decay of light-induced absorption in photorefractive BaTiO 3 crystals

We report the observations of the decay processes of light-induced absorption in one undoped and two Ce-doped BaTiO3 crystals. Two decay times were found, they had not a strong dependence on intensity in our experiment. We present a model with two different shallow trap centers to explain the experimental results. The theoretical and experimental results agree well with each other. The light-induced absorption coefficients and decay times corresponding to the two shallow levels are also given.