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Persistent Luminescence from Eu3+ in SnO2 Nanoparticles Jintao Kong,ab Wei Zheng,a Yongsheng Liu,a Renfu Li,a En Ma,a Haomiao Zhu,a and Xueyuan Chenab*

Received 00th xx 2015, Accepted 00th xx 2015 DOI: 10.1039/x0xx00000x www.rsc.org/

Persistent luminescence phosphors, which are capable of emitting light for a long time after ceasing the excitation, have shown great promise in areas as diverse as bioprobes, lighting and displays. Exploring new materials to realize efficient persistent luminescence is a goal of general concern. Herein, we report a novel persistent luminescence phosphor based on Eu3+ -doped SnO 2 nanoparticles (NPs). The afterglow decay behaviour, the trap depth distribution as well as the underlying mechanism for persistent luminescence of the NPs were comprehensively surveyed by means of thermoluminescence and temperaturedependent afterglow decay measurements. It was found that the thermal activation mechanism is responsible for the afterglow decay of the NPs with inverse power-law exponent of 1.0 (or 1.7) in the temperature region below (or above) 220 K. Particularly, the co-existence of uniform and exponential distributions in trap depths may result in such a unique afterglow decay behaviour. These results reveal the great potential of SnO 2 NPs as an excellent host material for Eu3+ doping for the generation of efficient persistent luminescence.

1. Introduction Persistent luminescence is a phenomenon whereby light emission from a material lasts for a long time after ceasing the excitation. Starting from the first scientific description published in 1602, there have been continuous efforts to unveil this interesting light-emitting phenomenon, and also to develop promising materials with bright persistent luminescence.1 A substantial breakthrough was accomplished with the realization of ultra-long afterglow (over 30 h) in the green-emitting SrAl2O4:Eu2+,Dy3+ phosphor, developed by Matsuzawa et al. in the mid-1990s.2 Stimulated by this pioneering work, the past two decades have witnessed the surge of various visible and near-infrared (NIR) persistent luminescence phosphors and their versatile applications as night or dark-light vision materials in many technological fields.3-10 Recently, persistent luminescence materials with particle size down to nanoscale have attracted particular attention. These so-called persistent luminescence nanoparticles (PLNPs) are capable of continuing emitting light for hours after a few minutes of excitation, thus allowing sensitive biological imaging and detection free of interference from blood and tissue autofluorescence arising from in situ excitation.11-18 Despite the rapid advances in material development, the underlying mechanism for persistent luminescence has not been well understood yet,9, 19 which makes it difficult to design novel persistent luminescence phosphors and optimize their optical performance. Long before the appearance of SrAl2O4:Eu2+,Dy3+, researchers had noticed the important role

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of traps in the generation of persistent luminescence.20 Through capturing charge carriers (electrons or holes), the traps, with energy levels located in the bandgap of the material, are capable of storing the excitation energy and gradually releasing it to luminescent centers when the excitation is ended.21 So far, there are generally two kinds of mechanisms proposed for persistent luminescence: thermal activation22 and tunnelling.23 In the former, the stored excitation energy is thermally activated and released from the electron (or hole) traps via the conduction (or valence) bands to the excited states of emitters, with an activation rate dependent on the energy depth of the traps. By contrast, the stored excitation energy of the traps can also reach the emitters through direct tunnelling, with a rate determined by the distance between them. However, currently it remains challenging to provide the solid evidence for identifying the dominant mechanism in one practical material, which is fundamentally important for the optimization of the persistent luminescence of the phosphors. To the best of our knowledge, a vast majority of persistent luminescence phosphors are restricted to those emitters with allowed electric-dipole (ED) transitions such as Eu2+.9 Eu3+, an excellent activator in a variety of phosphors, had never been reported for its persistent luminescence properties in SnO2 NPs. Herein, we demonstrated for the first time the persistent luminescence from Eu3+ in SnO2 NPs. The persistent luminescence (or afterglow) decay behaviour, the trap depth distribution as well as the underlying mechanism for persistent luminescence of the NPs were comprehensively studied through a series of thermoluminescence (TL) measurements

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and temperature-dependent afterglow decay analysis. Furthermore, a rational theoretical model based on the thermal activation mechanism was proposed to reveal the unique afterglow decay with inverse power-law exponents of 1.0 (or 1.7) in the temperature region below (or above) 220 K, in an effort to gain new insights into the trapping and de-trapping mechanistic processes involved in the PLNPs.

2. Experimental 2.1. Chemicals and materials SnCl4·5H2O, SnCl2·2H2O, (NH4)2C2O4·H2O, and ethylene glycol (EG) were purchased from Sinopharm Chemical Reagent Co., China. EuCl3·6H2O (99.99%) was purchased from Aladdin Chemistry, China. All chemical reagents were of analytical grade and used as received without further purification. 2.2. Synthesis of SnO2:Eu3+ NPs SnO2:Eu3+ NPs were synthesized via a modified solvothermal method in combination with high-temperature annealing.24 In a typical synthesis, 0.19 M of SnCl4·5H2O and 1.9 mM of EuCl3·6H2O (Eu:Sn = 1:100 at.%) were dissolved in 30 mL of EG under vigorous stirring for 2 h. The precursor solution was then transferred to a Teflon-lined autoclave and maintained at 180 °C for 5 h. The obtained precipitates were centrifuged and washed with ethanol for several times. After drying at 60 °C for 10 h, the precipitates were annealed in air at 1000 °C for 1 h to yield the final SnO2:Eu3+ NPs. 2.3. Synthesis of SnO2:Eu3+ microparticles SnO2:Eu3+ microparticles (MPs) were synthesized via an oxalate coprecipitation method followed by high-temperature annealing.25 To ensure identical Eu3+ content in SnO2:Eu3+ MPs to that in their NP counterparts, 0.5 M of SnCl2·2H2O and 0.05 mM of EuCl3·6H2O were dissolved in 16 mL of ethanol, and 0.33 M (NH4)2C2O4·H2O was dissolved in 30 mL of water. The chloride solution was then added to the oxalate solution at 60 °C under vigorous stirring, and the suspension was further stirred for 5 min. The obtained white precipitates were filtered, washed, dried, and finally annealed in air at 1300 °C for 2 h to yield the the final SnO2:Eu3+ MPs. Higher annealing temperature usually yields larger particles. 2.4. Structural and optical characterization The actual concentration of Eu3+ ions in SnO2 was determined by Ultima2 inductively coupled plasma optical emission spectrometer (ICP-OES). Powder X-ray diffraction (XRD) patterns of the samples were collected using a RIGAKU DMAX2500PC powder diffractometer with Cu Kα1 radiation (λ = 0.154 nm). The morphology of SnO2:Eu3+ NPs was characterized by a JEOL-2010 transmission electron microscope (TEM). Photoluminescence (PL) emission and excitation spectra as well as PL decays were recorded on an Edinburgh Instruments FLS920 spectrofluoremeter equipped with both continuous (450 W) and pulsed xenon lamps. For the measurements of the PL transients over short time window (1000 ms) and the afterglow decay over long time window (>1000 s), two distinct experimental setups, namely the multichannel scaling (MCS) and the kinetic scan, were used, respectively. In the MCS, the excitation source was the pulsed

2 | Nanoscale, 2015, xx, x-x

Journal Name DOI: 10.1039/C5NR01961C xenon lamp operating at a repetition frequency of 1 Hz. In the kinetic scan, the samples were irradiated by the continuous xenon lamp for 10 s. The temporal changes of the sample luminescence at certain wavelength were recorded with time resolution of 0.2 s. For temperature-dependent measurements, samples were mounted on a closed-cycle cryostat (10–350 K, DE202, Advanced Research Systems). To measure the PL transient decays of SnO2:Eu3+ NPs with varied surrounding media, the NPs were immersed into different solvents in a thin quartz tube, which were further vacuumed to remove the residual air in the solvents. All the spectra were corrected for lamp fluctuations and detector response. For TL measurements, the samples placed on a thermal stage (77–873 K, THMS 600, Linkam Scientific Instruments) were exposed to a continuous excitation for a period of time at 100 K, and after the stoppage of the excitation, the temperature was allowed to decrease to 80 K and then increase to 373 K with a heating rate of 120 K/min. Meanwhile, the persistent luminescence decay of Eu3+ by monitoring at 588 nm was collected. The final TL glow curves were obtained by transforming the time base of the decay curves to a temperature base utilizing the linear heating rate employed in the experiments.

3. Results and Discussion 3.1. Structure and persistent luminescence properties Eu3+-doped SnO2 NPs were synthesized by using a solvothermal method coupled with a subsequent annealing procedure as previously reported.24 All the samples can be determined as rutile-phase SnO2 (JCPDS No. 77-0449) without any other impurities such as Eu2O3 or Eu2Sn2O7 based on the powder XRD analysis (Figure S1, Supporting Information). The corresponding TEM image (Figure S2) shows that most of the NPs have the particle sizes ranging from 50 to 100 nm. The high-resolution TEM (HRTEM) image shows clear lattice fringes for an individual NP, with an observed d spacing of 0.26 nm, which is in good agreement with the lattice spacing of the (101) plane of rutile SnO2. The actual concentration of Eu3+ in the NPs was determined to be 0.01 at.% by ICP-OES analysis. Figure 1a shows PL excitation and emission spectra of SnO2:Eu3+ NPs at room temperature (RT). Upon ultraviolet (UV) excitation at 300 nm, characteristic and sharp emission peaks centered at 588.0, 592.8 and 599.0 nm that correspond to the 5D0→7F1 MD transitions of Eu3+ were detected. By monitoring the Eu3+ emission at 588.0 nm, an UV broad excitation band centered at ~300 nm orginating from the bandgap absorption of SnO2 NPs was observed,26 which indicates an efficient energy transfer from the host to the Eu3+ emitters. It is worthy of emphasizing that the direct 4f-4f excitation lines of Eu3+ were hardly observable in the excitation spectum, which is ascribed to the centrosymmetric site symmetry (most likely to replace Sn4+ at D2h) of Eu3+ in SnO2 NPs.26 According to the selection rule for the 4f-4f transitions of trivalent lanthanide ions, the ED transitions are strictly forbidden, while the MD transitions are allowed with the condition of ∆J = 0, ±1 (0→0 forbidden) for a site with a center of inversion. As a result, only much weaker emission lines from the 5D0→7F2 transitions of Eu3+ were detected owing to their ED nature. Figure 1b displays the PL decay curves of SnO2:Eu3+ NPs in the temperature range of 100-300 K by monitoring the Eu3+:5D0→7F1 emission at 588.0 nm. At 300 K, a nearly mono-




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Figure 1. (a) Normalized PL excitation and emission spectra of SnO2:Eu3+ NPs at 300 K. The emission spectrum was measured under UV excitation at 300 nm and the excitation spectrum was recorded by monitoring the Eu3+ emission at 588.0 nm. In the following measurements, the excitation and monitored wavelengths were used throughout. (b) Temperature-dependent PL decays of Eu3+ in the temperature range of 100-300 K. The inset shows the decay at 300 K and the fitting curve using single-exponential function (red line). (c) Persistent emission spectra of SnO2:Eu3+ NPs acquired at 200 K and at different time intervals after the stoppage of the excitation. (d) Evolution of the integrated Eu3+:5D0→7F1 emission intensity as a function of temperature. exponential decay was observed, with a fitted 5D0 lifetime of Eu3+ as long as 15.9 ms, which is much longer than that in SnO2:Eu3+ MPs (8.1 ms; Figure S3). Such a long 5D0 lifetime of Eu3+ in SnO2 NPs results mainly from the decreased MD transition rate, due to the decrease of the photon density of states by the non-solid medium (air) surrounding the NPs,27, 28 as verified by the decreased 5D0 lifetime of Eu3+ with the increased refractive indices of the surrounding media (Figure S4). Surprisingly, it was found that the PL of Eu3+ in SnO2 NPs exhibits a temperture-dependent long-lasting decay that far exceeds the time window available (1000 ms) when the temperature was lower than 250 K, indicating a persistent luminescence feature of SnO2:Eu3+ NPs. The corresponding persistent emission spectra (Figure 1c), recorded at different time intervals after the stoppage of the excitation at 200 K, exhibit the essentially same profile as that of the steady-state emission spectrum (Figure 1a), thereby confirming that the persistent luminescence of SnO2:Eu3+ NPs originated from the Eu3+ emitters. Similar persistent luminescence from MD tansitions of Eu3+ was also found in their MP counterparts (Figure S5). To the best of our knowledge, this is the first demonstration for the persistent luminescence of Eu3+ in SnO2 lattice, either in NPs or MPs. 3.2. TL properties and trap depth distribution To gain more insights into the trapping and de-trapping processes involved in the persistent luminescence of SnO2:Eu3+ NPs, we conducted a series of TL measurements by varying the following four experimental parameters: i) excitation duration;


ii) excitation intensity; iii) thermal cleaning temperature; and iv) delay time.10 In order to rule out the effect of nonradiative transitions on the TL spectra, we first recorded the integrated Eu3+:5D0→7F1 emission intensity at different temperatures for SnO2:Eu3+ NPs, based on which the TL spectra were corrected.29 As shown in Figure 1d, the integrated PL intensity of Eu3+ undergoes an initial increase and then a decrease with the temperature, with the maximum at ~250 K. The initial increase of the PL intensity with the temperature suggests that the energy transfer from the SnO2 NPs to Eu3+ may be attributed to the thermal activation process, since the scattering (and thereby the absorption) of the NPs to the excitation light did not change with the temperature (Figure S6). The decrease in the PL intensity above 250 K is due presumably to the nonradiative thermally activated energy back transfer from the Eu3+:5D0 excited state to SnO2 NPs. Specifically, the calibration curve for the TL spectra was obtained by fitting the experimental data using the empirical formula,30  I0 Et  I( T ) = )  （1） 1 + At exp( − 1 + Aq exp( − Eq / k BT )  k BT  where kB is the Boltzmann constant, Et and Eq are thermal activation energies for the energy transfer from the NPs to Eu3+ and from Eu3+ to the NPs, respectively.The fitting yielded Et = 25.3 meV and Eq = 0.28 eV. Figure 2a shows the influence of the excitation duration on the TL glow curves of SnO2:Eu3+ NPs. The curves can be deconvoluted into three Gaussian peaks centered at 145, 180, and 220 K, corresponding to traps with different depths. The TL intensity increased with the increase of excitation duration from 10 to 300 s, indicating that the larger number of charge carriers were captured by the traps with longer excitation durations. However, neither the positions of the Gaussian peaks nor their relative intensities change with varying excitation durations, which means that a 10 s duration is enough for all the traps to reach a trapping / de-trapping equilibrium, and that once the charge carriers leave the traps re-trapping is neglegible (the so-called first-order kinetics).29 The absense of re-trapping would greatly facilitate the analysis of the trapping and detrapping processes in SnO2:Eu3+ NPs.31 Apart from the excitation duration, the excitation intensity also significantly affects the trapping process. As shown in Figure 2b, when the excitation intensity was attenuated, not only the TL intensity was markedly reduced but also the shape of the TL glow curves was altered. This is because at the lower excitation intensity, the shallower traps would be relatively less filled due to their larger de-trapping rates, which resulted in more prominent intensity decrease in the low-temperature side of the TL glow curves. To further probe the energy distribution of these traps, we conducted TL measurements by using the preheating technique.32 The samples were first irradiated for 10 s at 100 K and then heated to a certain temperature (Tstop) to partially clean the occupied traps. Thereafter, the samples were subjected to TL measurements, and a series of TL glow curves that contain information of both the depth and the density of the traps were recorded (Figure 2c). The trap depth distribution in SnO2:Eu3+ NPs can thus be derived from these glow curves following the procedure outlined by Eeckhout et al.31 First, the depth of the shallowest trap occupied after each cycle of thermal cleaning was determined from the corresponding TL glow curve by the initial rise analysis (Figure S7), which was observed to increase with the rise of Tstop (Figure 2d). Then, the trap density between two adjacent depths can be estimated from the difference



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Figure 2. TL glow curves of SnO2:Eu3+ NPs measured by varying (a) excitation duration, (b) excitation intensity, and (c) thermal cleaning temperature under the excitation at 100 K with a heating rate of 120 K/min. The corresponding experimental setting for the excitation intensity: (a) I0, (b) I0 → 0.1I0, (c) I0; excitation duration: (a) 10 → 300 s, (b) 10 s, (c) 10 s; thermal cleaning temperature: (a) N/A, (b) N/A, (c) 120 → 300 K. All the TL glow curves were corrected by using the fitting curve of Figure 1d. (d) Trap depths as a function of thermal cleaning temperature derived from initial rise analysis of the TL curves in (c). (e) The integrated intensity of the TL glow curves in (c) in linear (left) and logarithmic (right) scales. The red lines are the linear (left) and exponential (right) fitting of the data points. (f) Trap depth distribution in SnO2:Eu3+ NPs derived from (d) and (e). The trap depth distribution is uniform below ~ 0.37 eV and exponential above ~ 0.41 eV, respectively. (g) Trap depths obtained from initial rise analysis of the TL curves measured under excitation at 100 and 220 K with varying delay time. between the integrated intensities of the corresponding two TL glow curves (Figure 2e) divided by the energy difference between them, because the area under the glow curve is proportional to the total number of occupied traps.31 As shown in Figures 2d and 2e, the dependence of the trap depth and the integrated TL intensity on Tstop can be divided into two stages. In Stage I, the trap depth increases linearly with Tstop, while the integrated TL intensity decreases linearly with Tstop, which yields a uniform trap depth distribution from ~0.08 to 0.37 eV (Figure 2f). In Stage II, the trap depth increases with the larger linear slope with Tstop due to the faster afterglow decay in this stage, whereas the integrated TL intensity decreases exponentially with Tstop, which yields an exponential trap depth distribution above ~0.41 eV (Figure 2f). The co-existence of both uniform and exponential distributions in trap depths is responsible for the unique afterglow decays observed in SnO2:Eu3+ NPs, as will be discussed in Section 3.4. It is worthy of noting that the shapes of the TL curves were almost identical for the samples synthesized at different annealing temperatures (900-1200 °C, Figure S8), indicating that the traps and their depth distributions are independent of the annealing temperature we investigated.


3.3. Persistent luminescence decay To better understand the persistent luminescence mechanism, we measured the persistent luminescence decays of SnO2:Eu3+ NPs in longer time window at various temperatures (100-300 K). As shown in Figure 3a, all the decays observed in the time window of 1000 s exhibit an initial rapid decline that corresponds to the exponential decay of Eu3+, followed by an inverse power-law decay in the long time tail. For a typical persistent luminescence decay, the afterglow intensity can be expressed in an inverse power-law function22

I(t ) = I0t −a

(2) By fitting the decay curves with equation (2), the averaged inverse power-law exponent a was determined to be approximately 1.01 and 1.65 in the temperature regions below and above 220 K, respectively (Figure 3b). To reveal the evolution of these decays, we further investigated the afterglow decay at 100-220 K in longer time window of 104 s under higher excitation power (Figure 3c). It was found that the decay curves recorded at temperatures below 200 K obeyed an inverse



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The inset displays the afterglow decay curve of Eu3+ at 300 K in the time window of 10 – 103 s. (b) The fitted inverse power-law exponent as a function of temperature. (c) Persistent luminescence decays at 100-220 K in longer time window of 104 s. The red lines in (a) and (c) are the fitting of the afterglow decays with inverse power-law functions. power law of t-1.2, whereas that recorded at 220 K exhibited a clear transition from an inverse power law of t-1.2 to t-1.8. It was observed that such a power-law transition in the afterglow decay of the NPs is indeed temperature-dependent, which occurred at the shorter afterglow time as the temperature was increased. As a result, this power-law transition in afterglow decays disappeared at the temperature above 240 K (Figure 3a), while it occurred at longer afterglow time that exceed the time window available at lower temperatures below 220 K (Figure 3c). It should be noted that the slight increase of the inverse power-law exponents in Figure 3c is due to the larger excitation intensity employed in the measurements (Figure S9). 3.4. Persistence luminescence mechanism Based on the above TL and persistent luminescence decay analyses, we propose a theoretical model to unveil the persistent luminescence mechanism of Eu3+ in SnO2 NPs (Figure 4). In the model, the traps are supposed to be electron traps lying below the conduction band (CB) of SnO2 NPs, with their nature ascribed to some lattice defects intrinsic to SnO2, such as oxygen vacancies and/or tin interstitials. Upon abovebandgap excitation of SnO2 NPs at 300 nm, electrons are promoted from the valence band (VB) to the CB, leaving holes in the VB. The recombination of electrons and holes excited the 5 D0 (and/or higher) state of Eu3+ that located within the forbidden band of SnO2 NPs through energy transfer, resulting in the PL from 5D0 of Eu3+ to its low-lying states (mainly 7F1). Meanwhile, in the CB, the electrons can move freely until they are captured by the traps. When the excitation is ended, the captured electrons are slowly released to the CB by thermal activation, followed by nonradiative recombination with the holes and transferring the recombination energy to Eu3+, giving rise to the persistent luminescence. The de-trapping rate of electrons is a function of the depth (E) of the traps in the form of 22

p = se- E/ kBT


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where s is a constant and kB is Boltzman’s constant. The lifetime τ of a trapping level is inversely proportional to the electron de-trapping rate. With the known trap depth distribution, the decay kinetics of the persistent luminescence can be theoretically predicted. According to the theoretical work by Randall and Wilkins,22 the uniform trap distribution gives the persistent luminescence decay following t-1 law and the exponential trap distribution gives t-1.7 decay in SnO2:Eu3+ NPs. To verify this model, we measured the TL glow curves of SnO2:Eu3+ NPs at 100 K and 220 K with delay time of 1, 10, 100, and 1000 s, from which the trap depths for the corresponding delay time can be derived from the initial rise analysis (Figure 2g and Figure S10). For the excitation at 100 K, the trap depth was found to increase from 0.08 to 0.17 eV with increasing delay time (Figure 2g), corresponding to the traps distributed uniformly in depth (Figure 2f), which is consistent with the observed t-1 decay of the persistent luminescence at 100 K (Figure 3c). For the excitation at 220 K, the trap depths for the delay time of 1 and 10 s (0.33 and 0.35 eV) were determined to fall in the uniform distribution region, while those for the delay time of 100 and 1000 s (0.42 and 0.55 eV) were in the exponential distribution region; this trap depth evolution is in consistence with the inverse power-law decay transition from t-1 to t-1.7 observed at the afterglow time of ~90 s (Figure 3c).

4. Conclusions In summary, we have discovered a new persistent luminescence phosphor based on Eu3+-doped SnO2 NPs and systematically investigated its underlying afterglow mechanism. Through a series of TL and persistent luminescence decay measurements, two distinct trap depth distributions, namely, uniform and exponential distributions, were determined in the NPs, which account for the persistent luminescence decay of Eu3+ obeying the inverse power law of t-1.0 and t-1.7 in the temperature regions below and above 220 K, respectively. The thermal activation mechanism was found to be responsible for the persistent



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Figure 4. A schematic representation of the persistent luminescence mechanism in SnO2:Eu3+ NPs. CB and VB denote the conduction and valence bands of SnO2 NPs, respectively. The green solid-line and blue dash-line arrows in the CB represent the trapping and detrapping of electrons respectively. The trap density (nE) takes the profile of trap depth distribution in Figure 2f. luminescence of Eu3+ in the NPs. Finally, a theoretical model based on the trap depth distribution was proposed to give a clear physical picture on the trapping and de-trapping processes involved in the persistent luminescence of the NPs. These findings reveal the great potential of SnO2:Eu3+ NPs as an excellent persistent luminescence phosphor. Nevertheless, the afterglow luminescence of SnO2:Eu3+ PLNPs at room temperature is currently not efficient enough for applications such as in vitro luminescent bioassay. Future efforts towards the practical applications of SnO2:Eu3+ NPs lie in the significant improvement of the persistent luminescence intensity and the afterglow time at room temperature, which can be realized by controlling the trap depth distribution of the NPs through, for example, intentional cation incorporation under the guidance of the proposed mechanism. The analytical methods for probing the persistent luminescence mechanism established in this work can be extended to the investigation of other persistent luminescence phosphors, thus laying an foundation for future rational design of novel persistent luminescence materials.

10. 11. 12.

13.

14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

Acknowledgements This work is supported by the 973 program of MOST (No. 2014CB845605), Special Project of National Major Scientific Equipment Development of China (No. 2012YQ120060), the NSFC (Nos. 11304314, U1305244, and 21325104), the CAS/SAFEA International Partnership Program for Creative Research Teams.

28. 29. 30. 31. 32.

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Notes and references a

Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China. E-mail: [email protected]; Fax: +86 591 63179421; Tel: +86 591 63179421 b

University of Chinese Academy of Sciences, Beijing 100049, China.




† Electronic Supplementary Information (ESI) available: Figures S1-S9.

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A novel persistent luminescence phosphor based on magneticdipole transitions (5D0→7F1) of Eu3+ in SnO2 nanoparticles was discovered. The thermal activation process associated with the distinct uniform and exponential trap depth distributions was revealed to account for its unique afterglow decay behavior.

