Growth and spectroscopic characterization of Pb2+:CaF2 crystals

Nicoarǎ, Irina; Paraschiva, M.; Stef, Marius; Stef, Florica

doi:10.1140/epjb/e2012-30433-3

Cited by 8 publications

(5 citation statements)

References 29 publications

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“…But a large energy separation between the lowest excited state 3 P 0 and the 3 P 1 states can also result from the strong spinorbit splitting and reduce the electron population on the radiative 3 P 1 state. 56 Many previous experiments on Pb and Bi activated phosphors and scintillators involve uoride or oxide-based largeband-gap host materials, 56,57,[59][60][61][62] which have narrow valence band width and low VBM. 63 This may lead to the electronic structure depicted in Fig.…”

Section: Discussionmentioning

confidence: 99%

Chemical trends of electronic and optical properties of ns² ions in halides

2014

J. Mater. Chem. C

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Section: Discussionmentioning

confidence: 99%

Chemical trends of electronic and optical properties of ns² ions in halides

2014

J. Mater. Chem. C

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“…For example, the temperature at which the NN type dipole (C 4v symmetry) in 0.1 mol% YbF 3 doped CaF 2 crystals can be observed is around 190 K at 100 Hz [8] with an activation energy 0.39 eV and is 223 K at 10 kHz, with an activation energy of 0.35 eV for CaF 2 :0.07 mol% YbF 3 Figure 5 Temperature dependence of the real (ε 1 ) and imaginary part (ε 2 ) of the complex dielectric constant at a fixed frequency. sample [11]. The dielectric relaxation study of Edgar and Welsh [9] of BaF 2 :Gd 3+ revealed two dielectric absorptions: one with activation energy 0.61 eV assigned to a trigonal Gd 3+ site and the second, with activation energy 0.36 eV assigned to aggregates.…”

Section: Characteristic Of Dielectric Spectramentioning

confidence: 96%

“…(ii) The temperature (T relax ) at which these peaks appear increases as the frequency increases, consequently these peaks correspond to dipole(s) relaxation [11,17,18]. (iii) The real part of the complex dielectric constant (ε 1 ) increases approximately linear in the region where the ε 2 has a peak and is approximately constant before and after this region (Fig.…”

Section: Characteristic Of Dielectric Spectramentioning

confidence: 99%

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Charge compensating defects study of YbF‐doped BaF crystals using dielectric loss

Nicoarǎ

Stef

2015

Physica Status Solidi (b)

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YbF3‐doped BaF2 crystals with various concentrations of YbF3 (0.05, 0.1, 0.17, 0.2 mol%) have been grown using the conventional Bridgman method. Dielectric relaxation is used to study the charge compensating defects in BaF2 crystals with low YbF3 concentration. The optical absorption spectra reveal the existence of both Yb2+ (in UV domain) and Yb3+ (in IR domain) ions. In the investigated temperature range (150–320 K) we have observed only one type of dielectric relaxation. This relaxation with activation energy E=0.54 eV is associated with trigonal‐type (C3v) centers. The charge compensating defects are discussed while taking also into account the optical absorption spectra and the calculated number of NNN dipoles whose relaxation is observed.

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“…But a large energy separation between the lowest excited state 3 P 0 and the 3 P 1 states can also result from the strong spin-orbit splitting and reduce the electron population on the radiative 3 P 1 state. 92 Many experiments on Pb and Bi activated phosphors and scintillators involve fluoride or oxide-based large-band-gap host materials, 92,93,[96][97][98][99] which have narrow valence band width and low VBM. 100 This may lead to the electronic structure depicted in Fig.…”

Section: Ns 2 Ions As Activatorsmentioning

confidence: 99%

Using DFT Methods to Study Activators in Optical Materials

2015

ECS J. Solid State Sci. Technol.

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Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns 2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, which can be used to search for new materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn 4+ Luminescence of materials when excited by photons or ionizing radiation is the foundation for numerous technologies, such as energy efficient lighting (fluorescent lamps and white LEDs), laser, medical imaging, and nuclear materials detection.1-3 Efficient luminescence in semiconductors and insulators usually relies on the localization of excited electrons and holes at certain impurities, which act as luminescence centers (or activators). An activator can trap electrons and holes for efficient radiative recombination and is the essential component of a phosphor or scintillator material. The commonly used activators are typically multivalent ions, which can insert multiple electronic states inside the bandgap of the host material. 45 Good examples of the multivalent ions that can act as luminescent centers are rare-earth ions (e.g., Ce 3+ , Eu 2+ ), 6-11 transition metal ions (e.g., Cr 3+ , Mn 4+ ), [12][13][14][15][16][17] and ns 2 ions (ions with outer electron configuration of ns 2 , such as Tl + , Sn 2+ ). 18-20Energy efficiency is critically important for phosphors used for lighting. To suppress the energy loss through nonradiative recombination, a phosphor is excited by directly exciting activators, not the host (see Fig. 1a). The excitation energy is less than the bandgap energy of the host but is large enough to excite the activator. Since the excitation occurs locally at the activator, the chance for the excited activator to interact with nonradiative recombination centers, such as deep defects, is small. This is important for achieving high quantum efficiencies for phosphors. In scintillators used for detecting ionizing radiation, the radiation creates charge carriers in the valence and conduction bands of the host, which are subsequently trapped by activators, leading to radiative recombination (see Fig. 1b). In scintillators, a portion of the charge carriers need to travel a certain distance before being trapped by the activators, which ...

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Growth and spectroscopic characterization of Pb2+:CaF2 crystals

Cited by 8 publications

References 29 publications

Chemical trends of electronic and optical properties of ns² ions in halides

Chemical trends of electronic and optical properties of ns² ions in halides

Charge compensating defects study of YbF‐doped BaF crystals using dielectric loss

Using DFT Methods to Study Activators in Optical Materials

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Growth and spectroscopic characterization of Pb2+:CaF2 crystals

Cited by 8 publications

References 29 publications

Chemical trends of electronic and optical properties of ns2 ions in halides

Chemical trends of electronic and optical properties of ns2 ions in halides

Charge compensating defects study of YbF‐doped BaF crystals using dielectric loss

Using DFT Methods to Study Activators in Optical Materials

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Product

Resources

About

Chemical trends of electronic and optical properties of ns² ions in halides

Chemical trends of electronic and optical properties of ns² ions in halides