Impurity-Related Excitonic Processes in CaF2 : Sr (original) (raw)
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4 Growth and Characterization of Doped CaF 2 Crystals
2017
The alkaline-earth fluorides crystallize in the cubic structure and constitute an important class of relatively simple ionic crystals whose optical and lattice-dynamical properties have theoretical and experimental interest. The CaF2 crystals have been used for long time in many optical components due to its exceptional transparency in the UV as well as in the IR spectral domain. CaF2, SrF3 and BaF2 have been among the first solid-state laser hosts and they were lased at the beginning of the 1960s doped with RE3+ ions; these rare-earth doped crystals, however, have been abandoned as laser systems during a long time. The reason resides in the charge compensation which is required to maintain the electrical neutrality of crystals. This process gives rise to a rich multisite structure including so-called isolated centers and more or less complex centers [Petit et al., 2008], which leads to broad absorption and emission bands comparable with those of glasses. Rare earth doped CaF2 recen...
Two types of additional absorption spectra in CaF2 crystals
Soviet Physics Journal, 1969
A study of two types of additional absorption spectra observed in colored CaF 2 crystals is reported. The spectral shape for the additively colored crystal is governed by the experimental conditions; during photochemical coloring, it depends on the thermal prehistory of the sample. In all cases, a spectrum consisting of bands at 370 and 560 nm appears in crystals having a band near 200 nm. An additional band appears at 560 nm in the Smakula spectrum at high-irradiation doses; there are three stages in the increase of this band with increasing dose. A similar dependence on the radiation dose is observed for the 560-nmband in synthesized CaF 2 crystals. It is suggested that this band is due to defects produced in the lattice during the irradiation.
Luminescence of defect clusters in the disordered anion sublattice of CaF2 crystals
Solid State Ionics, 2018
The fast quenching of CaF 2 crystals preheated up to 1000°C allows to stabilize the high-temperature disordering of anion sublattice typical for the superionic state of the crystal. Such procedure results in the formation of structured ultraviolet to vacuum ultraviolet (UV-VUV) absorption with a lengthy long-wavelength tail stretching into the visible spectral range. Such absorption in the quenched crystals cannot be related to any local center and testifies to the presence of nano-sized complexes of displaced anions, the electron structure of which is drastically changed as compared with a regular lattice. Possibly, these clusters are frozen dynamic clusters that were discovered earlier in the superionic state with quasi-elastic diffuse neutron-scattering technique. Four luminescence bands in near UV and visible spectral range correspond to four low-energy absorption bands. Unlike absorption bands that are of zone nature, the luminescence occurs from the localized state that arises due to strong electron-vibration coupling in the clusters. Absorption and luminescence states are divided by a potential barrier that is responsible for the spacing between corresponding excitation and emission bands as well as the temperature quenching of luminescence. The luminescence study reveals the features of the electronic structure of clusters within preheated/quenched CaF 2 crystals. The quenching method allows to study the high-temperature superionic state of crystals with fluorite structure using a wide set of experimental techniques.
Effect of Ca colloids on in-situ ionoluminescence of CaF2 single crystals
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2020
This work reports in-situ ion beam induced luminescence (IBIL) of CaF 2 crystals using 2-MeV proton excitation. The in-situ IBIL experiments were carried out at pelletron Tandem accelerator at the National Center for Physics, Islamabad, Pakistan. The spectrophotometry UV-Visible analysis revealed that proton beam induced Ca colloids. Their concentration increases with fluence, and the mean size reaches about 10 nm. The IBIL results showed a wide luminescence band extended from 230 to 450 nm and a new band at about 210 nm, attributed to the selftrapped exciton (STE) decay. It was found that the luminescence intensity increases linearly with dose. From the absorption measurements, indicating the colloid formation in CaF 2 by proton irradiation, we believe that the latter colloids are responsible for the luminescence improvement during proton beam irradiation.
Synthesis, Fabrication, and Photoluminescence of CaF 2 Doped with Rare Earth Ions
Journal of Fluorescence, 1998
Ambient condition wet synthetic techniques were used to synthesize CaF2 doped with europium and erbium. Photoluminescence spectroscopy and energy-dispersive x-ray analyses were used to study the electronic states of rare earth (RE) ions and the degree of heterogeneity/homogeneity in the matrix. Raman spectroscopy was used to study the degree of crystallinity of CaF2. Effects on the photoluminescence spectra were studied
Cathodoluminescence emission spectra of Nd-Doped CaF2
Physica Status Solidi (a), 1994
N. CAN (a), N. KAZANCI (b), P. D. TOWNSEND (a), and A. V. CHADWICK (c) Rare-earth doping of CaF, results in material which exhibits significant cathodoluminescence (CL) signals. Therefore CL measurements made on CaF,:Nd are reported for the temperature range 50 to 300 K with different excitation modulation frequencies. Since annealing treatment can be used to modify the spectra, the effects of annealing treatments of CaF, : Nd have been examined. Dopant levels used in the present study are 1.0, 0.1, and 0.01% Nd. All dopant levels exhibited different CL spectra with a combination of broad emission bands from the CaF, host and lines from the Nd dopants. Broad bands are centred near 340 and 645 nm. The intense emission lines at 360, 389, and 419 are assigned to Nd transitions from 4D3i2 to 41j (j = 9/2 and 11/2) and 2P112 to 419i2, respectively. Other transitions from 4D,,,, 4G9,2, 4G7i2 and 4G,i,. 'G7/, to 41, (j = 9/2 to 15/2) are found. The 340 nm band is associated with the intrinsic emission, self-trapped exciton (STE) emission, of CaF,. The temperature dependence of the intensity of the emission band is discussed The intrinsic emission band intensities decrease with increasing Nd content.
Japanese Journal of Applied Physics, 2010
Present work describes the first detailed -ray light yield of Ce 3þ perturbed emission in CaF 2 host. (1-, 3-, 5-, 10-, and 20-mol %-) Ce 3þ -doped single crystalline CaF 2 scintillator crystals were grown by the micro-pulling-down method. Their transmittances were measured to be approximately 80% at UV to visible wavelengths. All the crystals exhibited emission peaks at approximately 330 nm, which were identified as the Ce 3þ perturbed emission, when they were irradiated by 1 GBq 137 Cs. The photoluminescence decay kinetics was measured to be about 40 ns for all the crystals. Scintillation light yield in unit of photons/MeV (ph/MeV) was measured, and the 5% sample showed the highest light yield of around 900 ph/MeV with 2 ms shaping time. #