Multiple Intersystem Crossing Processes in Ge-Doped Silica Glass

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Multiple Intersystem Crossing Processes in Ge-Doped Silica Glass: Emission Mechanism of Twofold Coordinated Ge Atoms Yu Nagayoshi, Ryosuke Matsuzaki, and Takashi Uchino J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b08162 • Publication Date (Web): 26 Sep 2018 Downloaded from http://pubs.acs.org on October 2, 2018

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The Journal of Physical Chemistry

Multiple Intersystem Crossing Processes in Ge-doped Silica Glass: Emission Mechanism of Twofold Coordinated Ge atoms

Yu Nagayoshi, Ryosuke Matsuzaki and Takashi Uchino* Department of Chemistry, Kobe University, Nada, Kobe 657-8501, Japan

*Corresponding author Email: [email protected] Phone: +81-78-803-5681 Fax: +81-78-803-5681

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The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract It has been well documented that ~5 eV optical excitation of a twofold coordinated Ge atom in Ge-doped silica glass results in a singlet-singlet emission at ~4.2 eV and a triplet-singlet emission at ~3.1 eV, which are connected by thermally activated intersystem crossing (ISC). However, the true mechanism of the ISC, whose rate shows an apparent non-Arrhenius temperature dependence, has not been well understood and appreciated. In this work, we perform detailed photoluminescence measurements on highly luminescent Ge-doped silica glass with an internal quantum yield of ~40 % in a wide temperature range from 3 to 500 K. It has been found that there exist at least three triplet excited states of the twofold coordinated Ge atom, contributing respectively to three different ISC channels. One is a temperature independent ISC process and the others are temperature dependent ones with activation energies of ~40 and ~170 meV. We have also found that non-radiative transitions, which have often been neglected in previous studies, need to be considered for a full description of the entire emission characteristics. Our conclusion is that the non-Arrhenius characteristics of the ISC rate is not due to a wide and continuous distribution of activation energies of the ISC process, as is often proposed, but instead results from multiple ISC pathways consisting of higher order triplet states.


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1. INTRODUCTION Molecular triplet states play a crucial and fundamental role in excited state dynamics of a variety of molecular systems, including transition metal complexes and aromatic chromophores.1,2 In particular, the population of a triplet state through intersystem crossing (ISC) is a key factor in molecular photoreactivity.3−5 In the simplest case, ISC is induced by direct spin-orbit coupling (SOC) between singlet and triplet states. It has generally been presumed that the spin-forbidden ISC process is much slower than the spin-allowed internal conversion (IC), and hence that the electronic spin-orbit coupling matrix elements are treated independently from the vibrational degrees of freedom, according to the Condon approximation.4 However, recent time-resolved experiments and state-of-the-art theoretical calculations on transition metal complexes6−9 and thiobases10,11 have demonstrated that these assumptions do not necessarily hold; rather, a spin-vibronic mechanism, which takes into account the interplay amongst spin, electronic and nuclear dynamics, is often responsible for the observed ISC processes. Accordingly, it has been increasingly recognized that ISC consists of a variety of deactivation pathways, including direct and indirect ISC channels, depending on the energy level, vibrational modes, and the orbital feature of the triplet states.5,12 It should be noted that some defect-related color centers in solid state systems also 3 ACS Paragon Plus Environment


exhibit singlet and triplet levels and the related ISC relaxation process, as in the case of the molecular systems mentioned above. In this regard, a twofold coordinated Ge atom in Ge-doped silica glass is one of the well-studied defects in solids.13,14 This Ge-related defect center is also referred to as a germanium lone pair center (GLPC) that shows absorption at ~5 eV and two emissions at ~3.1 and ~4.2 eV.15−17 These two emission bands at higher (~4.2 eV) and lower (~3.1 eV) energies are attributed to the S1→S0 and T1→S0 transitions, respectively, which are interconnected by ISC.15 During the past decades, numerous investigations have been conducted for the GLPC18−31 due to the central role of its photosensitivity,24 which enables various applications such as fiber Bragg grating25 and second harmonic generations.26 Previous works30,32−34 have demonstrated that the ISC rate (kISC) of GLPC shows a strong non-Arrhenius temperature dependence, which is believed to result from a wide distribution of the activation energies of the ISC process34 owing to local structural inhomogeneity around the GLPC in the glass matrix.35−38 It should be noted here that in the previous literature, the ISC process of GLPC has been analyzed in terms only of one direct S1→T1 channel. Recent studies on metal complex systems,8,9 however, have revealed that a non-Arrhenius dependence of kISC is a natural consequence of multiple ISC pathways consisting of temperature-dependent and independent ones.


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Hence, in this work, we reinvestigate the temperature dependence of the singlet and triplet emissions of GLPC from a view point of multiple ISC channels. We carried out steady-state and time-resolved Photoluminescence (PL) measurements of a highly luminescent (quantum yield ~ 40% at room temperature) Ge-doped silica glass in a wide temperature range from 3 to 500 K. From the low-temperature (T < ~50 K) PL excitation (PLE) measurements, it has been found that in addition to the well-recognized first triplet state (T1), there exist second (T2) and third (T3) excited triplet states, whose energy levels are almost comparable to the first singlet excited state (S1). Also, the present PL measurements have unveiled the importance of non-radiative recombination in the T1→S0 relaxation process, which has not been fully taken into account in previous investigations.15,30−39 On the basis of these observations and the steady state approximation approach, we present a recombination scheme for the GLPC in terms of the multiple ISC scheme, thereby shedding light on the detailed emission mechanism in Ge-doped silica glass.

2. EXPERIMENTAL PROCEDURES High-purity silica glass powder (Kojundo Kagaku Co., 99.999 % in purity) and α−GeO2 crystal powder (Wako Chemical, 99.999 % in purity) were used as stating



materials. Ge-doped silica glass samples were prepared by heating the SiO2/GeO2 (molar ratio SiO2:GeO2=1:1) mixture powder with a weight of ~0.2 g at ~1900 °C under a flowing inert gas (N2 or Ar) atmosphere. The heating was carried out in a graphite crucible by using a high-frequency induction heating (IH) unit, which is rated at 4 kW at a maximum frequency of 420 kHz. The heating temperature was raised up to ~1900 °C at a rate of ~500 °C/min and maintained at the same temperature for 2−3 min. The temperature of the system was monitored with a radiation thermometer. After the heating process, the system is naturally cooled to room temperature. As a result, a disk-shaped sample with a diameter of ~10 mm and a thickness of ~1 mm was obtained. Recently, we40 have demonstrated that the IH method is useful to prepare highly oxygen-deficient and hence highly luminescent silica glass because the rapid heating and quenching during IH will create and freeze the relevant defect structures in the lattice. The thus obtained samples were crushed into powder of several micrometers for subsequent measurements. In this work, we also employed a commercial fused quartz (silica) glass (HERALUX-E-LA, Shin-Etsu Quartz Products Co., Ltd.) and measured its optical properties for comparison. X-ray photoelectron spectroscopy (XPS) was carried out with XPS spectrometer (Ulvac-Phi, PHI X-tool) utilizing Al Kα X-rays. Steady-state PL spectra were recorded


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on a spectrofluorometer (JASCO, FP 6600) with a monochromated xenon lamp (150 W). The absolute internal PL quantum yield, which is defined as the ratio of the number of photons emitted by the sample to the number of photons absorbed by the sample, was obtained at room temperature with an integrated sphere system. Diffuse reflectance spectra were measured using a UV/VIS spectrophotometer (JASCO, V-570) equipped with an integrating sphere to collect scattered light. Time-dependent PL measurements were carried out with a gated image-intensified charge-coupled device (Princeton Instruments PI-MAX:1024RB) and 300 lines/mm grating by using the third harmonic (355 nm) of a Q-switched Nd:YAG laser (Spectra Physics, INDI 40, pulse width ~10 ns, repetition rate 10 Hz) as an excitation source. During the PL measurements, the sample temperature was controlled in a closed-cycle N2 cryostat in the temperature region from 80 to 500 K or a closed cycle He refrigerator cryostat in the temperature region from 3 to 300 K.

3. RESULTS 3.1. Steady-State PL Measurements. From the quantitative XPS analysis, the Si/Ge atomic ratio of the resulting sample was estimated typically to be 86:14, implying that a part of GeO2 was evaporated during the heating process. Figure 1(a) shows



Figure 1. (a) Typical temperature dependent PL spectra of the Ge-doped silica glass prepared by IH method. The PL measurements were carried out under S0→S1 excitation at 5 eV. Individual spectra are displaced by 200 with respect to each other. The inset shows a simplified energy scheme of the electronic levels for the GLPC. (b) Room-temperature PLE spectra measured at different emission energies at 3.2 and 4.2 eV. The inset shows the diffuse absorbance spectrum measured at room temperature.

typical temperature dependent PL spectra of the Ge-doped silica measured under the S0→S1

(~5 eV) excitation, showing two PL bands peaking at ~4.2 and ~3.2 eV

attributed to the S1→S0 and T1→S0 transitions, respectively (see also the simplified energy levels shown in the inset of Fig. (a)).15 In agreement with previous reports,30,32−34 the intensity of the ~4.2-eV (~3.1-eV) band shows a marked decrease (increase) with increasing temperature, hence showing a thermally activated ISC behavior. The corresponding room-temperature PL excitation (PLE) spectra measured at two emission


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energies at 3.2 and 4.2 eV are shown in Fig. 1(b). The room-temperature diffuse absorbance spectrum is also shown in the inset of Fig. 1(b). Although one sees a slight increase in absorption in the energy region above ~4 eV, a possible effect of reabsorption will not be so large as to influence the shape of the PL/PLE spectra. Figure 1(b) demonstrates that when monitoring the PL intensity at 3.2 eV, the intensity of the ~4.8-eV PLE band is more than three times larger than that of the 3.8 eV PLE band. Note also that the intensity of the 4.8-eV PLE band measured at an emission energy at 3.2 eV is much stronger than that measured at an emission energy at 4.2 eV. In other words, the S0→S1 excitation at ~5 eV results preferentially in the T1→S0 emission at 3.2 eV rather than in the S1→S0 emission at 4.2 eV at room temperature owing to the thermally activated ISC channels. The internal emission quantum yields for the 3.1 and 4.2 eV PL bands were 39 and 4 %, respectively, at room temperature under the S0→S1 (~5 eV) excitation. For comparison, we measured the PL spectra of a commercial fused quartz sample under similar conditions. As shown in Fig. S1 in Supporting Information, the T1→S0 emission at 3.2 eV for the fused quartz sample is about ninety times less than that for the sample prepared by IH method. Thus, the present IH-treated sample includes a larger number of GLPCs than the fused quartz sample, and is suitable for the detailed analysis of the



Figure 2. Temperature dependence of the PL signals obtained under 5-eV excitation. (a) Integrated PL intensity of the S1→S0 (IS(T)) and the T1→S0 (IT(T)) emission bands peaking at ~4.2 and ~3.1 eV, respectively, as a function of temperature T. The solid lines given for IS(T) and IT(T) are fits of the data to Eqs. (7) and (8), respectively. The fitted values of the parameters are also shown. (b) Temperature dependence of the ratio of IS(T) to IT(T). The solid line is the result of calculation with Eq. (9) using the fitted values of the parameters shown in (a).

emission characteristics. In what follows, we show the results for the IH-treated sample unless otherwise noted. Figure 2 (a) shows the temperature dependence of the integrated PL intensity of the S1→S0 ( ) and T1→S0 ( ) emission bands in the temperature range from 3 to 500 K. Figure 2(a) shows that the S1→S0 (T1→S0) emission shows an almost monotonous decrease (increasing) in intensity with increasing temperature, as mentioned earlier. However, Fig. 2(a) reveals that when the temperature of the system goes beyond ~350 K, the T1→S0 emission decreases in intensity (observation #1). This indicates that at such high temperatures (T > ~350 K), a non-radiative recombination 10 ACS Paragon Plus Environment

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process begins to dominate in the T1→S0 recombination process. As shown in Fig. S2 in Supporting Information, a similar temperature-induced decrease in the T1→S0 emission intensity was also observed from the fused quartz sample, implying that the observed temperature dependent behavior is not specific only to the highly defective and emissive sample but to any Ge-doped silica samples. We should note, however, that this high-temperature-induced decrease in intensity of the T1→S0 emission band has not been reported and recognized. This is most likely because the temperature range employed in the previous PL measurements has been limited from cryogenic temperatures to ~300 K.30−38 We next investigated the PL characteristics of the T1→S0 emission band at ~3.1 eV in more detail. For this purpose, great attention is paid to the low-temperature (3−150 K) PL spectra of the ~3.1-eV band measured under the S0→T1 (~3.8-eV) excitation, which enables the T1→S0 emission without ISC. Figure 3(b) demonstrates the corresponding PL excitation (PLE) spectra monitored at the peak position of the PL spectra shown in Fig. 3(a). The intensity of both the ~3.1-eV PL and the ~3.8-eV PLE bands shows an appreciable decrease with increasing temperature (observation #2, see also the insets in Fig.3(a) and Fig.3(b)). This result is noteworthy in that the thermally activated non-radiative recombination process cannot be neglected in the T1→S0



Figure 3. Low-temperature (T < 150 K) (a) PL and (b) PLE spectra. The PL spectra in (a) were recorded with excitation at 3.78 eV and the PLE spectra in (b) with emission at 3.15 eV. The inset in (a) illustrates the temperature dependence of the PL peak intensity, whereas the inset in (b) shows that of the PLE intensities at the designated energy. The solids lines in the insets are guides to the eye.

relaxation process even in the low temperature region (T ~350 K) temperature regions, even without performing any further fitting procedure. It is hence most likely that the above analysis captures the underlying emission mechanism related to the ISC process. As mentioned earlier, we assert that three ISC channels exist: one is a temperature independent S1→T1 process, and the others are



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temperature dependent S1→Tn processes (n=2, 3) with activation energies of !$% 840 &

and !$% 8170 meV [see the fitted values shown in Fig. 2(a)]. Similar multiple ISC pathways, consisting of temperature independent and dependent ones, have also been reported in some transition metal complexes,9,42 aromatic compounds43−45 and chlorophyll binding proteins.46 On the basis of the recent studies of ISC on small molecular systems,5 we propose the configuration coordinate diagram for the emission scheme of the GPLC, as shown in Fig. 5. First, we will explain the temperature independent S1→T1 process. We can treat

Figure 5. Schematic configuration coordinate diagram of the relative positions of the potential surfaces for the singlet (S0 and S1) and triplet (T1, T2 and T3) states. The inset shows the corresponding energy level scheme. 22 ACS Paragon Plus Environment

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this ISC as a case of a weak coupling limit between the initial and final states.47 In the weak coupling limit, the displacement of the final state (T1) minima with respect to the initial state (S1) is small, resulting in a small reorganization energy. In other words, the potential energy surfaces of the S1 and T1 states are nearly nested, as predicted from previous quantum chemical calculations on Ge(OH)2.37 This can be viewed as an ISC process with a small Huang-Rhys displacement parameter. In this weak coupling limit, the transition probability depends exponentially on the adiabatic energy difference, and the resulting recombination process will not show temperature dependent kinetics, since an intersection of their potential energy surfaces cannot be expected.9,47 Note, however, that this process will hardly occur in reality and is hence evident only at very low temperatures (T < ~50 K) where the thermally activated ISC processes are suppressed. On the other hand, the temperature dependence of ISC can be interpreted in terms of an ISC channel with a strong coupling limit,47 which corresponds to a substantial horizontal displacement of the potential energy surfaces of the two electronic states. In the strong coupling limit the transition probability exhibits a generalized Arrhenius type temperature behavior whereupon the transition probability depends exponentially on the energy barrier for the intersection of the two potential surfaces.47 That is, as the temperature of the system increases, the vibrational modes in S1 are thermally excited,



and, accordingly, the photoexcited electrons have enough kinetic energy to overcome their local potential energy barriers. This leads to thermally activated ISC processes, as denoted as ISC(2) and ISC(3) in Fig. 5, making a major contribution to the entire ISC-related emission process in the moderate temperature range (~100 < T < ~300 K). The present investigations have also demonstrated that at least two non-radiative recombination processes must be considered in the T1→S0 process to fully reproduce the temperature dependence of [see Fig. 2(a)]. One of the activation energies is extremely small (~5 meV), and the other is very high (~350 meV). Thus, the effect of the former process will be overwhelmed by the thermally activated ISC with increasing temperature, whereas the effect of the latter process will not be explicitly observed until the temperature exceeds ~350 K. This explains the reason why, irrespective of their underlying contributions to the whole emission process, these non-radiative processes have been overlooked and unnoticed in previous works.15,30−38 Finally, we will comment on the validity of the previous model concerning the ISC of the GLPC,

15,30−38

which assumes that the apparent non-Arrhenius temperature

dependence of kISC is attributed to inhomogeneous distribution of the activation barriers derived from conformational disorder of the defect centers in a glassy matrix. If the expected distribution of activation barriers indeed exists, the effect will be seen in the


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temperature dependence of the singlet emission intensity as well, according to Eq. (5). In contrast to the expectation, the temperature dependence of is satisfactorily reproduced by assuming only two activation energies, as shown in Fig. 2(a). This indicates that the distribution of the activation energy is not so continuously wide as to explain the observed temperature dependence of $% . Thus, we consider that the previous model based on the conformational disorder cannot be applied to the present case. Although the previous model based on the structural inhomogeneity may not be relevant in explaining the non-Arrhenius characteristics of the ISC rate, it is likely that the model is still useful to explain the broad spectral features as well as the monotonous temperature-induced change in the peak position and spectral shape of the GLPC.35,36

5. CONCLUSIONS We have demonstrated from detailed PL and PLE measurements that there exist at least three excited triplet states that can contribute respectively to the ISC processes of the GLPC. Stationary emission models allow us to obtain kinetic information on the emission scheme of the GLPC. The S1→T1 channel is a temperature independent process because the T1 state is weakly coupled to the S1 state with a relatively large



adiabatic energy difference between their respective potential minima, leading to nested potential energy surfaces. On the other hand, the S1→T2 and S1→T3 channels are the temperature dependent ones and are assumed to be in the strong coupling limits, characterized by thermal activation energies of ~40 and ~170 meV. We further have shown that at least two non-radiative relaxation channels with different activation energies are present in the T1→S0 relaxation process. One of the activation energies is ~5 meV, and the other is ~350 meV. These extremely small and large activation energies will explain the reason why these non-radiative relaxation channels have not been noticed in previous studies. The resulting configuration coordinate diagram is given in Fig. 5. This diagram will not only disentangle the controversial temperature dependence of the ISC rate without assuming a wide distribution of the activation energies governing the ISC process, but will also shed light on the entire emission scheme of the GLPC in Ge-doped silica glass.

ASSOCIATED CONTENT Supporting Information Additional PL data and details of the derivation of Eqs. (5)−(8). (PDF)

ACKNOWLEDGMENT


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Financial support from Nippon Sheet Glass Co., Ltd. is greatly acknowledged.

References 1

Kasha, M. Phosphorescence and the Role of the Triplet State in the Electronic Excitation of Complex Molecules. Chem. Rev. 1947, 41, 401– 419.

2

Forste, L. S. Intersystem Crossing in Transition Metal Complexes. Coord. Chem. Rev. 2006, 250, 2023−2033.

3

El-Sayed, M. Spin Orbit Coupling and the Radiationless Processes in Nitrogen Heterocyclics. J. Chem. Phys. 1963, 38, 2834– 2838.

4

Marian, C. M. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2, 187−203

5

Penfold, T. J.; Gindensperger, E.; Daniel, C.; Marian, C. M. Spin-Vibronic Mechanism for Intersystem Crossing, Chem. Rev. 2018, 118, 6975−7025.

6

Capano, G.; Chergui, M.; Rothlisberger, U.; Tavernelli, I.; Penfold, T. J. A Quantum Dynamics Study of the Ultrafast Relaxation in a Prototypical Cu(I)-Phenanthroline. J. Phys. Chem. A 2014, 118, 9861– 9869.

7

Bergmann, L.; Hedley, G. J.; Baumann, T.; Bräse, S.; Samuel, I. D. W. Direct Observation of Intersystem Crossing in a Thermally Activated Delayed Fluorescence Copper Complex in the Solid State. Sci. Adv. 2016, 2, e1500889.

8

Hofbeck, T.; Lam, Y. C.; Kalbáč, M.; Záliš, S.; Vlček, A., Jr; Yersin, H. Thermally Tunable Dual Emission of the d8-d8 Dimer [Pt2(µ-P2O5(BF2)2)4]4–. Inorg. Chem.

2016, 55, 2441–2449. 9

Lam, Y. C.; Gray, H. B.; Winkler, J. R. Intersystem Crossing in Diplatinum Complexes. J. Phys. Chem. A 2016, 120, 7671– 7676.



10

Mai, S.; Marquetand, P.; González, L. Intersystem Crossing Pathways in the Noncanonical Nucleobase 2-Thiouracil: A Time-Dependent Picture. J. Phys. Chem. Lett. 2016, 7, 1978– 1983.

11

Sanchez-Rodriguez, J. A.; Mohamadzade, A.; Mai, S.; Ashwood, B.; Pollum, M.; Marquetand, P.; González, L.; Crespo-Hernandez, C. E.; Ullrich, S. 2-Thiouracil Intersystem Crossing Photodynamics Studied By Wavelength-Dependent Photoelectron And Transient Absorption Spectroscopies. Phys. Chem. Chem. Phys.

2017, 19, 19756– 19766. 12

Mai, S.; Marquetand, P; González, L. A General Method to Describe Intersystem Crossing Dynamics in Trajectory Surface Hopping. Int. J. Quant. Chem. 2015, 115, 1215−1231.

13

Pacchioni, G. In Defects in SiO2 and Related Dielectrics: Science and Technology; Pacchioni, G.; Skuja, L.; Griscom, D. L., Eds.; Kluwer: Dordrecht, the Netherlands, 2000; pp.161−195.

14

Griscom, D L. Trapped-Electron Centers in Pure and Doped Glassy Silica: A Review and Synthesis. J. Non-Cryst. Solids 2011, 357, 1945−1962.

15

Skuja, L. J. Non-Cryst. Solids Isoelectronic Series of Twofold Coordinated Si, Ge, and Sn Atoms in Glassy SiO2: A Luminescence Study. 149, 77−95 (1992).

16

Gallagher M.; Osterberg, Spectroscopy of Defects in Germanium-Doped Silica Glass. U. J. Appl. Phys. 1993, 74, 2771−2778.

17

Anedda, A.; Carbonaro, C. M.; Clemente, F.; Corpino, R. Ultraviolet Excitation Fine Tuning of Luminescence Bands of Oxygen-Deficient Centers in Silica. J. Appl. Phys. 2001, 92, 3034−3038.


Page 28 of 33

Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


18

Zhang, B. L.; Raghavachari, K. Photoabsorption and Photoluminescence of Divalent Defects in Silicate and Germanosilicate Glasses: First-Principles Calculations Phys. Rev. B 1997, 55, R15993−R15996.

19

Pacchioni, G; Ieranò, G. Ab initio Formation Energies of Point Defects in Pure and Ge-Doped SiO2. Phys. Rev. B 1997, 56, 7304−7312.

20

Uchino, T.; Takahashi, M.; Yoko, T. Structure and Formation Mechanism of Ge

! 9 Center from Divalent Defects in Ge-doped SiO2 Glass. Phys. Rev. Lett. 2000, 84, 1475−1478. 21

Nishii, J.; Fukumi, K.; Yamanaka, H.; Kawamura, K.; Hosono, H.; Kawazoe, H. Photochemical Reactions in GeO2-SiO2 Glasses Induced by Ultraviolet Irradiation: Comparison between Hg Lamp and Excimer Laser. Phys. Rev. B 1995, 52, 1661−1665.

22

Griscom, D. L. On the Natures of Radiation-Induced Point Defects in GeO2-SiO2 glasses: Reevaluation of a 26-Year-Old ESR and Optical Data set. Opt. Mater. Exp.

2011, 1, 400−412. 23

Giacomazzi, L.; Martin-Samos, L.; Boukenter, A.; Ouerdane, Y.; Girard, S.; Alessi, A.; de Gironcoli, S.; Richard, N. Photoactivated Processes in Optical Fibers: Generation and Conversion Mechanisms of Twofold Coordinated Si and Ge Atoms. Nanotechnology, 2017, 28, 195202.

24

Hill, K. O.; Fujii, Y.; Johnson, D. C.; Kawasaki, B. S. Photosensitivity in Optical Fiber Waveguides: Application to Reflection Filter Fabrication. Appl. Phys. Lett.

1978, 32, 647−649. 25

Mihailov, S. J.; Smelser, C. W.; Lu, P.; Walker, R. B.; Grobnic, D.; Ding, H.;



Henderson, G.; Unruh, J. Fiber Bragg Gratings Made with a Phase Mask and 800-nm Femtosecond Radiation. Opt. Lett. 2003, 38, 995−997. 26

Österberg, U.; Margulis, W. Dye Laser Pumped by Nd:YAG Laser Pulses Frequency Doubled in a Glass Optical Fiber. Opt. Lett. 1986, 11, 516−518.

27

Kazansky, P. G.; Inouye, H.; Mitsuyu, T.; Miura, K.; Qiu, J.; Hirao, J.; Starrost, F. Anomalous Anisotropic Light Scattering in Ge-Doped Silica Glass. Phys. Rev. Lett. 1999, 82, 2199−2202.

28

Fujimaki, M.; Ohki, Y.; Nishikawa, H. Energy States of Ge-doped SiO2 Glass Estimated through Absorption and Photoluminescence. J. Appl. Phys. 1997, 81, 1042−1046 (1997).

29

Anedda, A.; Carbonaro, C. M.; Corpino, R.; Serpi, A.; Low Temperature Time Eesolved Photoluminescence of the 3.1 and 4.2 eV Emission Bands in Ge-Soped Silica. J. Non-Cryst. Solids 1997, 216, 19−25.

30

Leone, M.; Boscaino, R.; Cannas, M.; Gelardi, F. M. Low Temperature Photoluminescence Spectroscopy Relationship between 3.1 and 4.2 eV Bands in Vitreous Silica. J. Non-Cryst. Solids 1997, 216, 105−110.

31

Agnello, S.; Boscaino, R.; Cannas, M.; Cannizzo, A.; Gelardi, F. M.; Grandi, S.; Leone, M. Temperature and Excitation Energy Dependence of Decay Processes of Luminescence in Ge-Doped Silica. Phys. Rev. B 2003, 68, 165201.

32

Alessi, A.; Agnello, S.; Ouerdane, Y.; Gelardi, F. M. Dependence of the Emission Properties of the Germanium Lone Pair Center on Ge doping of Silica. J. Phys. Condens. Matter 2011, 23, 015903 (2011).

33

Alessi, A.; Agnello, S.; Messina, F.; Gelardi, F. M. Irradiation Induced


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Germanium Lone Pair Centers in Ge-Doped Sol–Gel SiO2: Luminescence Lifetime and Temperature Dependence. J. Lumin. 2010, 130, 1866−1871. 34

Leone, M.; Agnello, S.; Boscaino, R.; Cannas, M.; Gelardi, F. M. Conformational Disorder in Vitreous Systems Probed by Photoluminescence Activity in SiO2. Phys. Rev. B 1999, 60, 11475−11481.

35

DʼAmico, M.; Messina, F.; Cannas, M.; Leone, M.; Boscaino, R. Isoelectronic Series of Oxygen Deficient Centers in Silica: Experimental Estimation of Homogeneous and Inhomogeneous Spectral Widths. J. Phys. Chem. A 2008, 112, 12104−12108.

36

DʼAmico, M.; Messina, F.; Cannas, M.; Leone, M.; Boscaino, Homogeneous and Inhomogeneous Contributions to the Luminescence Linewidth of Point Defects in Amorphous Solids: Quantitative Assessment Based on Time-Resolved Emission Spectroscopy. Phys. Rev. B 2008, 78, 014203.

37

Cannizzo, A.; Agnello, S.; Grandi, S.; Leone, M.; Magistris A.; Radzig, V. A. Luminescence Activity of Surface and Interior Ge–Oxygen Deficient Centers in Silica. J. Non-Cryst. Solids 2005, 351, 1805−1809.

38

Cannizzo A.; Leone, M. Conformational Disorder and Optical Properties of Point Defects in Vitreous Silica. Phil. Mag. 2004, 84, 1651−1657.

39

Skuja, L. Direct Singlet-to-Triplet Optical Absorption and Luminescence Excitation Band of the Twofold-Coordinated Silicon Center in Oxygen-Deficient Glassy SiO2. J. Non-Cryst. Solids 1994, 167, 229−238.

40

Nagayoshi Y.; Uchino, T. Enhanced Ultraviolet Emission and Its Irreversible Temperature Antiquenching Behavior of Twofold Coordinated Silicon Centers in



Silica Glass. Appl. Phys. Lett. 2016, 109, 181103. 41

Gupta, B. K.; Thanikaivelan, P.; Narayanan, T. N.; Song, L.; Gao, W.; Hayashi, T.; Reddy, A. L.; Saha, A.; Shanker, V.; Endo, M. et al. Optical Bifunctionality of Europium-Complexed Luminescent Graphene Nanosheets. Nano Lett. 2011, 11, 5227−5233.

42

Milder, S. J.; Brunschwig, B. S. Factors Affecting Nonradiative Decay: Temperature Dependence of the Picosecond Fluorescence Lifetime of Pt2(pop)44−. J. Phys. Chem. 1992, 96, 2189−2196.

43

van der Burgt, M. J.; Jansen, L. M. G.; Huizer, A.; Varma, C. A. G. O. Effects of Solvent Induced Modulation of Energy Gaps on Electronic Relaxation of Excited Hydrogen Bonded Complexes of Some Aromatic Carbonyl Compounds. Chem. Phys. 1995, 201, 525−538.

44

Thomaz, M. F.; Barradas, M. I.; Stevens, B. Comments on Activated Intersystem Crossing. Chem. Phys. Lett. 1972, 17, 160−162.

45

Biczók L.; Bérces, T. Temperature Dependence of the Rates of Photophysical Processes of Fluorenone. J. Phys. Chem. 1988, 92, 3842−3845.

46

Renger, T.; Madjet, M. E.; Müh, F.; Trostmann, I.; Schmitt, F.-J.; Theiss, C.; Paulsen, H.; Eichler, H. J.; Knorr A.; Renger, G. Thermally Activated Superradiance and Intersystem Crossing in the Water-Soluble Chlorophyll Binding Protein. J. Phys. Chem. B 2009, 113, 9948−9957.

47

Englman, R.; Jortner, J. The Energy Gap Law for Radiationless Transitions in


Page 32 of 33

Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Large Molecules. Mol. Phys. 1970, 18, 145−164.

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Multiple Intersystem Crossing Processes in Ge-Doped Silica Glass

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