Scintillation Process in CsI(Tl). II. Emission Spectra and the Possible Role of Self-Trapped Holes

Gwin, R.; Murray, Roger K.

doi:10.1103/physrev.131.508

Cited by 71 publications

(36 citation statements)

References 14 publications

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“…[18][19][20] The emission in CsI:Tl + appear to be related to both the hole polaron (V k center) and the electron trapped at Tl, or Tl-bound exciton. 2,84,85 The optical transitions between the ns and np states of a ns 2 ion are usually interpreted and modeled by using Seitz model. 86 The Seitz model is based on a two-electron picture, in which the ground state (ns 2 ) is a singlet 1 S 0 state and the excited states (nsnp) consist of 3 P 0 , 3 P 1 , 3 P 2 triplet states and a 1 P 1 singlet state, as shown 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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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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“…The processes that lead to nonlinearity can be classified into two major groups, based on their origin: the first is related to the transfer of g energy to charge carriers [9][10][11] and the second is due to the nonlinearity that results from the recombination of free electrons and self-trapped holes [12,13] and/or from an exciton radiative decay [14,15] resulting in ultraviolet (UV) light emission. The second group of processes is temperature dependent, whereas the first group is not.…”

Section: Nonlinearity Of the Scintillation Efficiency And Energy Calimentioning

confidence: 99%

Temperature dependence of nonlinearity and pulse shape in a doped NaI(Tl) scintillator

Ianakiev

Abhold

Alexandrov

et al. 2007

Nuclear Instruments and Methods in Physics Research Section A:

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“…03.195 of a self-trapped hole (STH), also named V k center, with an electron near a Tl + ion [10,11]. Together with this band other three components are present: a shoulder at about 480 nm which is sometimes attributed to vacancy related defects [8] but which is more likely related to the same V k À e À recombination in a different configuration [10,12], a lower band at about 400 nm which is attributed to the optical transition of a Tl + excited state [10] and, sometimes, a peak at about 300-310 nm which is related to a transition of the CsI pure crystal [5,13]. This last emission has been widely studied due to its very fast lifetime (about 10 ns) but its origin is still under debate.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, it is well known that both light output [1,2] and pulse shape [3,4] of CsI(Tl) crystals depend not only on the deposited energy but also on the atomic number and mass of the incident ion. In the past CsI(T1) had been largely studied for the detection of ionizing radiation, in particular for ions and fission products [5]. However the mismatch of the CsI(T1) scintillation emission spectrum to the spectral sensitivity of photomultipliers, together with the rising application of semiconductor detectors, prevented for a while a widespread use of this crystal as a scintillation detector.…”

Section: Introductionmentioning

confidence: 99%