Identify a Cyan Ultra-Long Persistent Phosphorescence (Ba, Li) (Si

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C: Plasmonics; Optical, Magnetic, and Hybrid Materials

Identify a Cyan Ultra-Long Persistent Phosphorescence (Ba, Li) (Si, Ge, P)O: Eu , Pr via Solid Solution Strategy 2

5

2+

3+

Peng Feng, Gen Li, Haijie Guo, Dongwei Liu, Qiangfei Ye, and Yuhua Wang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b11084 • Publication Date (Web): 17 Jan 2019 Downloaded from http://pubs.acs.org on January 21, 2019

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The Journal of Physical Chemistry

Identify A Cyan Ultra-Long Persistent Phosphorescence (Ba, Li) (Si, Ge, P)2O5: Eu2+, Pr3+ Via Solid Solution Strategy Peng Feng, Gen Li, Haijie Guo, Dongwei Liu, Qiangfei Ye and Yuhua Wang*

Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Lanzhou, 730000, PR China and Key Laboratory for Special Function Materials and Structural Design of the Ministry of Education, Lanzhou University, Lanzhou 730000, China. Abstract A series of cyan emission (Ba, Li) (Si, Ge, P)2O5: Eu2+, Pr3+ long persistent phosphors (LPP) were designed by solid solution strategy and synthesized by solid state reaction, the crystal structure and photoluminescence of this long persistent phosphor have been analyzed systematically. Under 256nm light excitation, the as-prepared (Ba, Li) (Si, Ge, P)2O5: Eu2+, Pr3+ present a strong cyanemitting located at 514 nm and the decay time of samples can be elongated to about 38h (BaSi2O5:0.008Eu2+, 0.01 Pr3+), 47h (BaSi1.5Ge0.5O5:0.008Eu2+, 0.01Pr3+) and 56h (Ba0.92Li0.08 Si1.92 P0.08O5: 0.008Eu2+,0.01Pr3+) after ceasing the excitation source, respectively. A number of the excitation duration(1s≤t≤30s), decay duration(10min≤t≤10h) and temperature dependent TL experiments of (Ba, Li)(Si, Ge, P)2O5:0.008Eu2+,0.01Pr3+ were conducted, revealing that the existence of shallow and deep traps caused by Eu2+ and Pr3+ ions in samples give rise to the excellent LPP property. According to the experimental results, a feasible mechanism on persistent luminescence of (Ba, Li) (Si, Ge, P)2O5:0.008Eu2+, 0.01Pr3+ was proposed and illustrated in detail. *Corresponding

1.

author. Email: [email protected]; Tel.: +86 931 8912772; Fax: +86 931 8913554.

Introduction Long persistent phosphorescence material is an interesting phenomenon in which the long-

persistent emission of the material lasts for a long time after the removal of the excitation source,1, 2 this materials have long been of great investigation interest and are extensively commercialized as night or dark environment vision materials nowadays, such as security signs, emergency route signage, identification markers, medical diagnostics, optical storage media, drug carriers and in vivo imaging.3-6 Currently, a great many of LPP materials have been developed and commercialized successfully, for example, CaAl2O4: Eu2+,Nd3+ (blue,＞10h)7-9 , SrAl2O4:Eu2+, Dy3+ (green, ＞30h)101

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BaAl2O4:Eu2+,Dy3+ (green,

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＞ 10h), Y2O2S:Eu3+, Mg2+,Ti4+(red,

＜ 5h)13 or CaS:Eu2+,

Tm3+,Ce3+,(red, ＜4h)14. Nevertheless, The preparation condition of aluminate-based LPP materials are very strict, requiring pretty high synthesis temperature (＞1400℃), and the poor water resistance make them easy to failure in a humid environment; while sulfide-based LPP materials have deficiencies of bad chemical stability, short afterglow time, and unfriendliness to the environment. The silicate LPPs, by contrast, possess better chemical and physical stability, heat stability and facile synthesis, and they have incomparable advantage in terms of water resistance, which make them have attracted tremendous academic and commercial interest recently. Unfortunately, the silicate LPP materials are confined to Sr2MgSi2O7:Eu2+, Dy3+ (blue, >10h), (blue, >10 h),17,

18

15, 16

Sr3MgSi2O8:Eu2+,Dy3+

Sr3SiO5: Eu2+,Dy3+ (yellow,>6h),19 BaZrSi3O9:Eu2+,Pr3+(cyan,>15h),20

Ba5Si8O21:Eu2+,Dy3+ (cyan, >15 h)21 and their afterglow intensities and persistent luminescence time are not a patch on those prominent aluminate-based LPP materials. Consequently, the exploration of new silicate-based LLP materials could be urgently needed for satisfying the demand of practical utilization. A sanbornite BaSi2O5 was proposed firstly by Douglass, R.M. in 1958.22 Gilliland, J. W. et al. proposed

the phosphor BaSi2O5:Pb2+, demonstrating that BaSi2O5 is a promising host for

investigating the long persistent phosphorescence materials;23-25 T Nakanishi et al. and Cao D et al. also reported the Luminescent Properties of Eu2+ ions doped BaSi2O5 phosphors, proving that BaSi2O5:Eu2+ is an efficient phosphor for light-emitting devices.26-29 However, to the best of our knowledge, there is no report about the LLP properties of BaSi2O5:Eu2+,Ln3+( Ln=Dy, Pr, Ce, Nd, Tb, Ho, Tm, Er). As far as activator concerned, the Eu2+ is a common ion generally investigated and applied in the LPP materials as an efficient activator. Because the 5d electron state of Eu2+ ions is usually close to the conduction band of the host, which makes trapping of electrons possible.30-33 Meanwhile, traps in the material play a crucial role in the generation of afterglow, which allow the material to store energy from the excitation source, thereby slowly releasing the reserved electrons after shutting off the irradiation, resulting in the LPP performance. The distribution of the traps for Eu2+ doped LPP phosphors can be tailored by occupying the crystal site of a matrix with different valence ions such as lanthanides R3+ to make LPP phenomenon improved.34, 35 Recently band gap engineering has been used as a technique for the LPP tuning.

36, 37One

can

achieve persistent phosphorescence tunable silicate-LPPs through modifying their chemical composition and crystal structure. For instance, the Ca2Ga2GeO7:Pr3+,Yb3+ exhibits reddish orange 2


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afterglow emission about 150s; When the Ge4+ ion is partially substituted with the Si4+ ion, Ca2Ga2(Si, Ge)O7:Pr3+,Yb3+ gradually prolong its persistent decay time from 150s to around 3 hours with increasing the Si content.38 So in this paper, the silicate (BaSi2O5) is chosen as the LPP material host and studied the influence of substitution of cation (Ge4+ → Si4+, Li+ → Ba2+, P5+ → Si4+) on the LPP properties of (Ba, Li)(Si, Ge, P)2O5: Eu2+.Ln3+. Particularly, the feasible mechanism of trapping, detrapping and retrapping processes was systematically revealed with the aid of TL measurements. 2.

Experimental

2.1 Material Synthesis. A series of BaSi2O5:0.008Eu2+, 0.01Ln3+ (Ln=Dy, Pr, Ce, Nd, Tb, Ho, Tm, Er) , BaSi2O5:0.008Eu2+, xPr3+ (0≤x≤0.08), BaSi2-xGexO5:0.008Eu2+, 0.01Pr3+ (0≤x≤1), Ba1-xLixSi2-x Px O5: 0.008Eu2+, 0.01Pr3+ (0.01≤x≤0.3) samples were synthesized by the high-temperature solid-state reaction technique. The raw materials using in experiment were BaCO3(A.R.), SiO2 (A.R.), GeO2 (A.R.), Li2CO2 (A.R.), (NH4)2HPO4 (A.R.), Eu2O3(99.99%) Dy2O3(99.99%), Pr6O11(99.99%), CeO2(99.99%), Nd2O3(99.99%), Tb4O7 (99.99%), Ho2O3 (99.99%), Tm2O3 (99.99%) and Er2O3 (99.99%). The raw materials were accurately weighed out and mixed thoroughly in an agate mortar for about 30 min by adding with appropriate ethanol. Then, the mixtures were placed into an alumina crucible and sintered at 1250 ℃ for 6 h with reductive atmosphere of N2 (95%) and H2 (5%). 2.2 Characterization Methods.

The phase purity of the obtained samples was identified by a Rigaku D/Max-2400 X-ray diffractometer (XRD) using a Rigaku diffractometer with Nifiltered Cu Ka radiation at scanning steps of 0.02° in the 2θ range from 10° to 80°. The crystal structure of the series of samples was refined by adopting the Maud refinement program using the Rietveld method. The absorption spectrum was measured on a PE lambda 950 UV−vis spectrophotometer using BaSiO4 white power as a reference. The photoluminescence (PL) and PL excitation (PLE) spectra were measured by A FLS-920T fluorescence spectrophotometer equipped with a 450W xenon arc lamp (Xe 900) as the light source and the scanning step was 1 nm. Persistent decay curves were carried out with a PR305 long afterglow instrument after the samples were irradiated with ultraviolet light (254 nm and 365 nm) for 10 min, the afterglow time is defined that the time sample decayed from initial intensity to 0.32mcd/m2, which is 100 times the lowest intensity visible to the naked eye. Mcd/m2(millicandela per square meter) is unit of luminosity, meaning that the luminous flux per square meter. The thermoluminescence (TL) curves were obtained by a FJ-427A TL meter (Beijing Nuclear Instrument 3



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Factory) with a heating rate of 1 °C/s in the temperature range from 20 to 400 °C. The 0.0015 g samples were irradiated for 5 s by 254 nm and 365 nm light before the measurements. 3.

Results And Discussion As the first step in unveiling the details of the optical functionality of these LPP materials, we

set out to determine the crystal structure of the sample. Figure. 1a shows the Rietveld refinement for as-prepared sample BaSi2O5. The reliability factors of refinement are wRp=11.2%, Rp=8.9%, χ2= 1.450, respectively, which illustrate that the refined results are reliable. The compound crystallizes in the orthorhombic structure with the space group Pcmn and the refined cell parameters of BaSi2O5 are a = 4.6172(5) Å, b = 7.6580(3) Å, c = 13.4692 (3) Å, V=476.2590(3) Å3. Figure.1b displays the unit cell structure of BaSi2O5 and the coordination environment of Ba2+ and Si4+. As can be seen, the structure framework of BaSi2O5 lattice is built up by SiO4 tetrahedra connecting with each other through sharing corner and Ba-O polyhedra with connection of edge shared. Simultaneously, the SiO4 tetrahedra concatenate with the Ba-O polyhedra via sharing corner, which shapes the layer structure paralleling to (001) crystal plane. Considering the similar ionic radii, the Eu2+and R3+ ions are expected to dissolve in the host by randomly occupying the Ba2+ sites. Crystallographic data and structure date for BaSi2O5 is listed in Table S1.

Figure 1. a) XRD Rietveld refinement of as-prepared BaSi2O5 based on the data from ref 50. b) Unit cell of BaSi2O5 drawn and the coordination environment of Ba2+ and Si4+.

4


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Figure 2. (a) XRD patterns of as-prepared BaSi2O5:Eu2+, Ln3+(Ln=Dy, Pr, Ce, Nd, Tb, Ho, Tm, Er) samples and the standard data of XRD Rietveld refinement of BaSi2O5; b) Excitation and emission spectra of BaSi2O5:Eu2+, Ln3+(Ln=Dy, Pr, Ce, Nd, Tb, Ho, Tm, Er); c) TL spectra of BaSi2O5:0.008Eu2+, 0.01Pr3+; d) Persistent decay curve of BaSi2O5:0.008Eu2+, 0.01Pr3+ sample excited by UV lights(254nm) for 10 min. Inset shows persistent luminescence spectrum of the sample BaSi2O5:0.008Eu2+, 0.01Pr3+ and the digital photo under UV lights (254nm) irradiation.

Thus, a series of samples by co-doping Eu2+ and several lanthanide Ln3+ ions were prepared and the LPP properties were characterized. The XRD patterns of the BaSi2O5:Eu2+, Ln3+(Ln=Dy, Pr, Ce, Nd, Tb, Ho, Tm, Er) samples are shown in Figure 2a. Apparently, all the diffraction peaks are easily indexed to the standard date of XRD Rietveld refinement of BaSi2O5 and no peaks related to second phase is detected, which indicates that these samples obtained at 1250 ℃ have pure phase and the Eu2+ and R3+ dopants are successfully incorporated in the BaSi2O5 host lattice and aroused little influence to the crystal structure. Figure 2b depicts the excitation and emission spectra of the BaSi2O5:Eu2+, Ln3+ (Ln=Dy, Pr, Ce, Nd, Tb, Ho, Tm, Er). The excitation spectra of samples monitored at 514 nm cover a broad spectral region from 250nm to 450 nm attributed to the allowed Eu2+ transition and the partly overlaps with the solar irradiation region, indicating that these BaSi2O5:Eu2+, Ln3+ phosphors could be effectively activated by sunlight. Under 345nm excitation, 5



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the maximum corresponding to 514nm located in the dominant cyan emission band range from 380nm to 700 nm, ascribing to the transition from 4f to 5d of Eu2+. Comparing the results of the study of BaSi2O5:Eu2+ by other researchers, it is found that the excitation and emission spectra of BaSi2O5:Eu2+ are almost the same, but the excitation and emission intensities are significantly increased after co-doping with different rare earth ions, and considerable afterglow emission is generated. The LPP materials contain a certain concentration of luminescent centers and traps. Under the excitation of light, part of electrons is captured by traps. As the LPP materials were heated up, the trapped electrons are thermally excited into free carriers, and then emit light when combined with the ionized luminescent center, which can be monitored by TL spectrometer. The TL curve of BaSi2O5:0.008Eu2+, 0.01Pr3+ are presented in Figure 2c, the peak of TL curve located at about 373K, which can obtain the depth of the trap in the BaSi2O5:Eu2+, Pr3+ (about 0.75eV) according to the calculation. The depth of traps is optimum to produce excellent persistent luminescence performance, reaching about 38h after the sample is excited by UV light at 254nm for 10min and decrease to 0.32mcd/m2(Figure 2d).

Figure 3. The excitation, emission and persistent luminescence spectra of sample BaSi2O5:0.008Eu2+,0.01Pr3+; the inset shows persistent luminescence emission intensity (λex=345 nm) as a function of the doping content (x value)

In order to obtain the best LPP materials, BaSi2O5:0.008Eu2+, xPr3+ (0≤x≤0.08) were synthesized and the optimum concentration of Pr3+ ion is proved to be x=0.01 (Figure S1). Figure 3 depicts the excitation, emission and persistent luminescence spectra of BaSi2O5:0.008Eu2+, 0.01Pr3+, it is obvious that there is no difference between photoluminescence spectrum and persistent luminescence spectrum, both of which reveal only one broad cyan emission band. Noticeably, the 6


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characteristic sharp peaks of Pr3+ were not detected and thus the phosphor have only one kind of emitter that is Eu2+. As can be concluded from the persistent luminescence emission intensity at different concentration of Pr3+ ions in inset of Figure 3, the optimal concentration of Pr3+ ions for the strongest persistent luminescence intensity is same as that for photoluminescence intensity.

Figure 4. TL curves of the sample BaSi2O5:0.008Eu2+,0.01Pr3+ a) recorded after UV lights(254nm) excitation with various durations (0s≤t≤30s), inset shows the fitting results after 30s’ excitation duration; b) Delay duration(10min≤t≤10h) dependent TL curves after UV lights(254nm) excitation for 10s, inset shows the fitting results of delay duration in 10min. c) The fitting results of excitation time dependent TL glow curves; d) The fitting results of delay duration dependent TL curves;

The variation of TL curves with different excitation time(0s≤t≤30s) and delay duration(10min≤t≤10h) as well as the fitting results were observed to make a further exploration for the afterglow mechanism of BaSi2O5:0.008Eu2+,0.01Pr3+(Figure 4a, 4b).39-41 The 254 nm UV lamp is chosen to excite samples on account of the approximation to 265nm, under which samples perform the strongest afterglow intensity(Figure S2). As can be seen from Figure 4c, the peak position of shallow traps shifts slightly to the high temperature, indicating that electrons gradually filled the high 7



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energy of shallow traps with the excitation time increasing; whereas the peak of deep traps shifts towards the direction of the low temperature deviation, which means that the excited electrons would rather fill the deep traps with higher energy first to a degree than congest the lower energy deep traps due to the existence of a tunneling related process. Similar phenomena have also been reported by Guo H. et al.20 When shallow traps are filled to saturation, excess electrons continue to be trapped by deep traps from shallow traps until both the shallow traps and deep traps reach saturation, which makes the peaks of the thermoluminescence spectra shift to higher temperature; When the sample was excited under the UV light at 254nm for 10 seconds and delayed for different time from 10min to 10h, likewise, a shift to higher temperature spectrum is generated. As the delay duration increases, the electrons in the shallow traps gradually release and then the shallow traps retrap electrons from deep traps; In addition to the release of electrons through the conduction band, the deep traps also discharge electrons via the tunneling effect, which lead the peak of deep traps to low temperature (Figure 4d).

Figure 5. a) XRD patterns of as-prepared BaSi2-xGexO5:0.008Eu2+, 0.01Pr3+(0≤x≤1) samples; b) XRD peak shift of the (101) crystal face

BaSi2-xGexO5:0.008Eu2+, 0.01Pr3+(0≤x≤1) samples were fabricated and characterized. Figure 5a displays the XRD patterns of as-prepared samples and no change of crystal structure is observed with the increasement of solid solubility until that rises by 50%(x=1). As Figure 5b represents, the XRD peak of the (101) crystal face shifts to the direction of smaller angle, ascribing to the substitution of Ge4+ (r = 0.39 Å, CN=4) ions for Si4+ (r = 0.26 Å, CN=4) ions42 43, which will give rise to the lattice expansion.

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Figure 6. Persistent decay curves of BaSi2-xGexO5:0.008Eu2+,0.01Pr3+(0≤x≤1). Inset: function of reciprocal afterglow intensity (I-1) versus time (t) of BaSi1.5Ge0.5O5: 0.008Eu2+,0.01Pr3+ sample excited by UV lights(254nm) for 10 min.

We found out the applicable samples BaSi2-xGexO5: 0.008Eu2+, 0.01Pr3+(x=0.1,0.2,0.5) that are suitable for producing long afterglow by testing the thermoluminescence spectra in different solid solubility (Figure S3), which manifest a considerable afterglow time of 38h, 44h and 47h, separately, as depicted in Figure 6. The persistent decay curve of the optimum sample BaSi1.5Ge0.5O5: 0.008Eu2+, 0.01Pr3+ is plotted as a function of the reciprocal persistent luminescence intensity (I−1) versus time (t), as shown in the inset of Figure 6. The I−1-t curve prior to 16 h time can be well matched by a straight line: I−1 =51t-8.6025, which is the rapid-decay process, the 16-47 h time period can by well fitted by another straight line: I−1 =73.2t-2.36×102, which is the slow decay process. The two linear dependencies of I−1 versus t indicate that the persistent luminescence is mainly caused by two effective trap centers, which is consistent with the conclusion above.

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Figure 7. TL curves of the sample BaSi1.5Ge0.5O5:0.008Eu2+, 0.01Pr3+ a) recorded after UV lights(254nm) excitation with various durations (0s≤t≤30s), inset shows the fitting results after 30s’ excitation duration; b) Decay duration(10min≤t≤10h) dependent TL curves after UV lights(254nm) excitation for 10 s, inset shows the fitting results of delay duration in 10min. c) The fitting results of excitation time dependent TL glow curves; d) The fitting results of decay duration dependent TL curves;

Similarly, we conducted the test of TL spectra with different excitation time(1s-30s) and delay duration(10min-10h), as shown in Figure 7. Comparing with the BaSi2O5:0.008Eu2+, 0.01Pr3+ sample, the process of chargement of electrons in the BaSi1.5Ge0.5O5: 0.008Eu2+, 0.01Pr3+ remains the same. Specifically, the concentration of deep traps at 410K was greatly increased because of the substitution of Ge4+ to Si4+, which results in a large increase of electrons stored in deep traps, bringing about an improvement in the afterglow time of the sample after solution treatment.

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Figure 8. TL curves of the sample Ba0.92Li0.08Si1.92 P0.08O5:0.008Eu2+,0.01Pr3+ a) recorded after UV lights(254nm) excitation with various durations (1 s-30 s),inset shows the fitting results after 30s’ excitation duration; b) Decay duration(10min≤t≤10h) dependent TL curves after UV lights(254nm) excitation for 10 s, inset shows the fitting results of delay duration in 10min. c) The fitting results of excitation time dependent TL glow curves; d) The fitting results of decay duration dependent TL curves;

Since the solid solution can effectively improve the afterglow performance of the LPP material, the Ba1-xLixSi2-xPxO5:Eu2+,Pr3+ was investigated to inquire whether the lattice distortion to a greater degree caused by the non-equivalent cation replacement will induce more electron traps, which can enhance the luminescence phosphor's afterglow performance. As described in Figure S4, the sample maintain pure phase until the solid solubility was about 43%(x=0.3), and was also a cyan emission. The traps in the sample were distributed between 325K and 430K, which are suitable for realizing long-lasting afterglow (Figure S5). As the ionic radii of Li+ and P5+ are respectively smaller than Ba2+ and Si4+, the crystal lattice shrinkage caused by replacement introduces a plenty of traps. As a consequence, the Ba0.92Li0.08Si1.92 P0.08O5:0.008Eu2+, 0.01Pr3+ contains more traps in it both shallow and deep traps compared with the BaSi1.5Ge0.5O5:0.008Eu2+, 0.01Pr3+, as presented in Figure 8, the shallow traps have a significant 11



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increase, especially. Because of which, the sample reaches an extremely long persistent time about 56h (Figure S6).

Figure 9. Schematic illustration of the persistent luminescence mechanism

A schematic based on the above analyses is proposed to interpret the persistent luminescence processes in series of (Ba, Li) (Si, Ge, P)2O5: Eu2+, Pr3+, as illustrated in Figure 9. There is a narrow shallow trap center and rather broad deeper trap in the material according to the experiment data. When the material is irradiated by UV light, the electrons located at the ground state of Eu2+ ions are promoted to the 5d excited states (process 1); The electrons pumped to higher 5d states locating near the conduction band (CB) of the host can be trapped by the shallow traps through CB (process 2); The deep traps capture electrons from excitation source directly (process3), trap electrons via tunneling procedure (process 4) or get electrons from shallow traps (process 5) until both the shallow and deep traps become saturated,; Subsequently, when UV excitation ceases, the detrapping process occurs under the action of thermal perturbation. Shallow traps in the material gradually release the captured electrons to the 5d energy level via the CB (process 6) and recaptured electrons from the deep traps (process 7). Simultaneously, electrons also could back to the 5d energy level through tunneling effect (process 8). Finally, these electrons recombined with emission centers to generate bright persistent luminescence (process 9). In case of solid solution, due to the introduction of Ge4+, Li+ and P5+, a variety of cationic sites are generated in the matrix for Eu, it will cause the crystal lattice distortion of the sample and induce more traps, allowing more electrons are reserved in the material, which make the afterglow time extended distinctly. 4.

Conclusion

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In summary, a novel cyan ultra-long persistent phosphor BaSi2O5: Eu2+, Pr3+ was successfully realized by co-doping Pr3+ and Eu2+ in BaSi2O5. The long persistent phosphor BaSi2O5:0.008Eu2+, 0.01Pr3+ has significant persistent luminescence property, with an excellent afterglow time more than 35h.

In

addition,

the

samples,

BaSi2-xGexO5:0.008Eu2+,

0.01Pr3+

and

Ba1-xLixSi2-x

PxO5:0.008Eu2+,0.01Pr3+, constructed by solid solution show better persistent luminescence performance in that the lattice distortion caused by solid solution can produce more traps and store more excitation energy, which will improve the persistent performance. As a conclusion, BaSi2-x GexO5: Eu2+, Pr3+ (47 h), and Ba0.92Li0.08Si1.92 P0.08O5: Eu2+, Pr3+ (56 h) were designed. A doable delay mechanism was proposed, and an original insight was put forward to design new outstanding LPPs. Supporting Information Available Crystallographic data and structure date for BaSi2O5 as determined by Rietveld refinement of powder XRD data at room temperature (Table S1). PLE and PL spectra of BaSi2O5:Eu2+, xPr3+(0≤x≤0.08) (Figure S1). TL curves of as-prepared BaSi2-xGexO5:0.008Eu2+, 0.01Pr3+(0≤x≤1) samples measured after UV lights(254nm) excitation for 5s (Figure S2). XRD patterns of asprepared Ba1-xLixSi2-xPxO5:0.008Eu2+,0.01Pr3+(0≤x≤0.3) samples(Figure S3). Excitation and emission spectra, thermo luminescence spectra of Ba1-xLixSi2-xPxO5:0.008Eu2+,0.01Pr3+(0≤x≤0.3) samples(Figure S4). Persistent decay curve of Ba1-xLixSi2-xPxO5:0.008Eu2+,0.01Pr3+(0≤x≤0.3) samples(Figure

S5).

Persistent

luminescence

spectra

in

different

excitation

wavelength(220nm≤λEx≤420nm)(Figure S6). Acknowledgement The authors gratefully acknowledge the support from the National Natural Science Funds of China (Grant No. 51672115 and Grant No. 51372105), Gansu Province Development and Reform Commission, and Chengguan district lanzhou city science and technology development projects (project number: 2017-2-2). Reference [1]. Holsa, J. Persistent Luminescence Beats the Afterglow: 400 Years of Persistent Luminescence. 2009; Vol. 18. [2]. Qiu, J.; Hirao, K. Long lasting phosphorescence in Eu2+-doped calcium aluminoborate glasses. Solid State Commun. 1998, 106, 795-798. 13



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TOC Graphic


Identify a Cyan Ultra-Long Persistent Phosphorescence (Ba, Li) (Si

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