Charge Propagation Dynamics in Temperature Quenching of Sm-Doped TiO2: Impedance Spectroscopy of Release Processes of Trapped Charges Determining Luminescence Intensity
The mechanism of the temperature quenching of luminescence in samarium-doped titanium dioxide (TiO 2 :Sm) was investigated with electrical measurement techniques. Because electrical measurements are sensitive to charge dynamics, the indirect excitation processes of the Sm dopants, i.e., trapping and...
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| Published in | Jpn J Appl Phys Vol. 52; no. 2; pp. 025601 - 025601-5 |
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| Main Authors | , , , , , |
| Format | Journal Article |
| Language | English |
| Published |
The Japan Society of Applied Physics
01.02.2013
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| Online Access | Get full text |
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| Summary: | The mechanism of the temperature quenching of luminescence in samarium-doped titanium dioxide (TiO 2 :Sm) was investigated with electrical measurement techniques. Because electrical measurements are sensitive to charge dynamics, the indirect excitation processes of the Sm dopants, i.e., trapping and recombination of injected charges into the host TiO 2 , can be clarified. Complex impedance spectroscopy between 100 and 300 K revealed a correlation between the temperature quenching of TiO 2 :Sm and the trapping and recombination processes. Analyses using equivalent circuits revealed that the main factor determining the temperature quenching properties was delocalization of the trapped charges and decoupling of free charges in TiO 2 from trapped charges. The delocalization and decoupling parameters were evaluated from the equivalent circuit constants, and a numerical model incorporating the determined values reproduced the experimentally observed temperature quenching of photoluminescence. |
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| Bibliography: | Schematic diagrams of conventional DR and PEDR. A transition in charge trapping from (a) the low-frequency region to (b) the high-frequency region indicates DR. A transition in charge recombination from (c) the low-frequency region to (d) the high-frequency region indicates PEDR. Trapping spectra of TiO 2 :Sm obtained with CIS in the dark (open circles). Solid lines are spectra calculated using Eq. ( ). Delocalization of trapped charges with increasing $T$. The strongly localized charges in (a) are represented by a capacitance, whereas the charges at high $T$ and high DOF in (c) are represented by a resistance. (b) shows the intermediate state between (a) and (c). Equivalent circuits in these representative temperature regions are also shown. Calculated $Z"$ (imaginary part of $Z^{*}$) spectra for various inclusion ratios of capacitive and resistive characteristics $p$. $\gamma$ values versus $1000/T$ for evaluation of activation energy. $\gamma$ is obtained by fitting with Fig. and calculation with Eq. ( ). Recombination spectra measured with CIS performed under UV excitation light in the same $T$ range as Fig. (open circles). Solid lines are calculated spectra for evaluating the decay time of e--h couplings, $\tau_{\text{c}}$. Evaluated $\tau_{\text{c}}$ [see Eq. ( )] with respect to $1000/T$. PL peak intensity $I_{\text{PL}}$ ($\lambda = 612$ nm) versus $1000/T$. $\gamma$ and $\tau_{\text{c}}$ illustrated in Figs. and are also replotted. Calculated $I_{\text{PL}}$ based on the numerical model of Eq. ( ). Inset indicates the expected band diagram. |
| ISSN: | 0021-4922 1347-4065 |
| DOI: | 10.7567/JJAP.52.025601 |