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Commendable Eu2+ doped oxide based matrix-LiBa12(BO3)7F4 red broad emission phosphor excited by NUV light: Electronic and Crystal Structures, Luminescence properties Xin Ding, and Yuhua Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b06612 • Publication Date (Web): 27 Jun 2017 Downloaded from http://pubs.acs.org on June 28, 2017

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ACS Applied Materials & Interfaces

Commendable Eu2+ doped oxide based matrix-LiBa12(BO3)7F4 red broad emission phosphor excited by NUV light: Electronic and Crystal Structures, Luminescence properties Xin Ding, Yuhua Wang* Key Laborary of Special Function Materials and Structure Design, Ministry of Education, Department of Materials Science, School of Physical Science and Technology, National & local Joint Engineering Laboratory for Optical Conversion Materials and Technology, Lanzhou University, Tianshui South Road No. 222, Lanzhou, Gansu 730000, PR China Abstract In this work, we synthesized a new Eu2+ doped oxide matrix based-LiBa12(BO3)7F4 broad red emission phosphor. It can emit red light peaking at ~644 nm under NUV excitation with the coordinate at (0.6350, 0.3586) and a sensitive color gamut for eyes. This phosphor with a kind special tunnel crystal structure and layered distribution of Ba2+ is contributed to longer wavelength emission. By theoretical calculation and analysis using local state density energy band structure simulation of Eu2+ doped in different site, the origin of the observed emission center is distinguished. Furthermore, decay curves analysis also indicated there are three possible Ba2+ sites for Eu2+ to occupy. Temperature dependent PL spectra appeared anomalous phenomena that the intensity increases firstly and then decreases, which is due to the traps energy level’s contribution of electron’s transition. The phosphor also has CL property which the spectra take on typical current saturation phenomenon. And the CL curves indicated that this phosphor has a very good stability under much electron beam bombardment time. After fabricated combing with BAM, (Sr, Ba)2SiO4 and our red phosphor excited under 405 nm NUV chips, warm light LED was gotten, and, its CIE coordinate is (0.3475, 0.3416) and the CCT, Ra and luminous efficiency is 4856 K, 84.1 and 72.6 lm/W. Keywords: Oxide, Structure, Luminescence, LED, Red light *Corresponding author at: Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Lanzhou, 730000, PR China. Tel.: +86 931 8912772; fax: +86 931 8913554. Corresponding author’ email: [email protected]

1. Introduction With time going on, energy and environmental issues gradually aroused people's consciousness. White light emitting diodes (W-LEDs) as a new kind light sources, have attracted much attention and been used in many areas for their numerous advantages such as small volume, long lifetime, high efficiency, energy saving and environmental friendliness1, 2. To realize white light, “phosphor conversion method” called PC-LEDs has been commercialization and widely used. It is used blue or UV (NUV) chips combining with some phosphors which can be excited by these chips. For instance, YAG: Ce3+ yellow phosphor excited by a blue InGaN chip can generate white light by yellow emission from the phosphor and blue light from the chip3, 4. Though it has been commercialization and widely used, it cannot satisfy the optimum requirements. Lack of red light component leads to high correlated color temperature (CCT) (7765K) and poor color rendering index which restricts its much broad applications5, 6. To compensate red component, Mn2+ co-doped or some quantum dot phosphors are used. But, weak efficiency of Mn2+ emission, bad stability and productivity of quantum dot phosphors are still difficult to solve7-10. RGB+NUV chips as another alternative way to get white light can be fabricated by combing of the ultraviolet 1

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(NUV) LED (350–420 nm) with blue, green and red phosphors (it is generally agreed that using NUV~405 nm chips can get most efficient emission). As compared to YAG: Ce3+ yellow phosphor excited by a blue InGaN chip, this type of W-LEDs has low correlated color temperature and high color rendering index (Ra > 90) because of its three primary colors11, 12. Among the numerous phosphors, rare-earth-doped red emitted phosphors is considered to be the most difficult to achieve, especially, in oxide matrix based phosphor, because, it needs strong crystal field strength and coordinated ion’s covalency. Though, some sulfide matrix based phosphors, like Y2O2S and La3Br(SiS4)2: Eu2+ can emit red light, under high temperature conditions, they will generate harmful sulfur oxides gas and lead to human or environment damage13-15. Other red phosphors, like Eu2+ or Ce3+ doped nitrides (CaAlSiN3: Eu2+, M2Si5N8:Ce3+ (M =Ca, Sr, Ba), Li2(Ca1-xSrx)2[Mg2Si2N6]: Eu2+ and Sr[LiAl3N4]: Eu2+)16-19, a well-known defect is that the synthesis of nitride phosphors needs a critical condition, such as high pressure and high temperature (typically prepared under 1800 °C, 0.5 MPa N2 pressure). And the broad absorption of them will lead to serious photon re-absorption phenomenon (the photons emitted from the yellow or green phosphor can be absorbed by the red one, causing color change and luminous reduction)20. Therefore, it is necessary and also a challenge to explore and study some oxide matrix based long wavelength emission phosphors excited by NUV light to satisfy urgent requirement. According to necessary conditions getting red emission, it is very important to find some matrix with special electron and crystal structure with strong crystal field strength and coordinated ion’s covalency. Fortunately, refer to the structural characteristics of some nitride-based phosphor21-24, we synthesized a oxide based-LiBa12(BO3)7F4 (LBBF) matrix with a big tunnel in its crystal structure for Ba2+ to arrange and a uniform layer distribution of Ba2+, which is considered to be an important contribution for getting longer wavelength emission. Therefore, in this work, we doped Eu2+ in this host to verify its structure and luminescence properties.

2. Experiment 2.1 Materials and utensil As the raw materials, Li2CO3 (99.9%), H3BO3 (99.9%) and Eu2O3 (99.99%) are stoichiometric and the molar ratio of BaCO3 (99.8%) and BaF2 (99.9%) is 3:1. Aluminum oxide crucibles (3 mL) and porcelain boat are utensils for sintering. High temperature tube atmosphere reduction furnace is the reaction instrument. 2.2 Synthesis LiBa12(BO3)7F4 matrix and series of xEu2+ doped LiBa12(BO3)7F4 (0.1% ≤ x ≤ 4%) samples are synthesized by two-step traditional high temperature solid-sated reaction. The relative amounts of materials are calculated and then are weighed by electronic balance. Furthermore, 3wt% carbon is calculated and weighed at the same time, and then, mix it with the raw materials at mortar. Carbon powders are used to enhance reducing action. Put all the mixture and the flux into agate mortar with 10 mL ethanol added in it at the same time. Grind the mixture for half an hour until they are evenly dry and homogeneous. After the mixture blended, transfer the mixture into aluminum oxide crucibles (3 mL) and prefired them at 500 °C for 2 h under air atmosphere and then calcined them at 940 oC for 6 h under reducing atmosphere (N2/H2 = 6/45) in the horizontal tube furnace. When they are cooled with 4 °C /min speed to room temperature, grind them to powders, getting the resulting phosphor powder. 2.3 Characterization 2


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The phase formation and crystal structure were analyzed by the powder X-ray powder diffraction (XRD) (D2 PHASER X-ray Diffractometer ,Germany) with graphite monochromator using Cu Kα radiation (λ = 1.54056 A), operating at 30 kV and 15 mA. The investigation range for the series LiBa12(BO3)7F4:xEu2+ phosphors and the structural refinement data are 10 o to 80 o with scanning step width 0.03 and 5 o-90 o with scanning step width 0.01. LiBa12(BO3)7F4 sample for TEM, SAED (selected area electronic diffraction) and HRTEM (High-resolution transmission electron microscopy) pattern and EDX (Energy Dispersive X-Ray Spectroscopy) measurements are carried out on a transmission electron microscope at an operating voltage of 200 kV. The ultraviolet-visible (UV-vis) diffuse reflectance (DR) spectra were measured using a Perkin Elmer 950 spectrometer, while BaSO4 was used as a reference. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the samples are measured by a Fluorlog-3 spectrofluorometer equipped with 450 W xenon lamps (Horiba Jobin Yvon). The temperature-dependence luminescence properties are measured on the same spectrophotometer, which is combined with a self-made heating attachment and a computer-controlled electric furnace from room temperature (25 °C) to 250 °C with a heating rate of 50 °C/min and a holding time of 5 min for each temperature point. The thermo-luminescence (TL) curve was collected using an FJ-427A1 meter (Beijing Nuclear Instrument Factory) at a heating rate of 1 K*s-1. The luminescence decay curves and Time-resolved photoluminescence (TRPL) were obtained by FLS-920T fluorescence spectrophotometer as well. All the testes are carried out at room temperature. The w-LEDs were fabricated by SH2012 Ultrasonic wire welding machine. The EL properties of w-LEDs were tested by PMS-80 UV-VIS-near IR spectrophotocolorimeter. The CL (cathodoluminescence) properties of the samples were obtained using a modified Mp-Micro-S instrument (Horiba Jobin Yvon).

3. Results and Discussion 3.1 Structure of LBBF

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Figure 1 Rietveld refinement of the powder XRD profile of LiBa12(BO3)7F4 Figure 1 illustrates the experimental and refined XRD patterns of LiBa12(BO3)7F4 host sample, and, the Eu2+ doped XRD refinement data are also carried out, which the results are shown in Figure S1-S3 . The “×” marks represent the measured diffraction data. The red solid curves indicate the calculated diffraction data and the pink vertical lines show the positions of the simulated diffraction patterns. The green solid line denotes the deviation between the measured and calculated values. By comparing the calculated data with experimental spectra, we found that each peak is in good agreement. There is no impurity phase in the samples, which reveals that it is good single-phase. The calculated residual factor value is Rp = 9.36% and Rwp = 11.53% for LiBa12(BO3)7F4 host. The relative small refinement index means LiBa12(BO3)7F4 crystalline to nice structure successfully.

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Figure 2 (a) TEM image of LiBa12(BO3)7F4; (b) HRTEM image of LiBa12(BO3)7F4; (c) SAED image of LiBa12(BO3)7F4; (d) EDX of LiBa12(BO3)7F4. To confirm the structure of LiBa12(BO3)7F4, we choose the LiBa12(BO3)7F4 matrix as the delegate to test TEM, HRTEM, SAED and EDX which are shown in Figure 2. Figure 2a shows the morphology of the LiBa12(BO3)7F4 crystal. It is an irregular shape particle with about 400 nm in diameter. In HRTEM image of LiBa12(BO3)7F4 (Figure 2b), it is clearly put up that the image possesses distinct crystallographic planes with two directions which indicated that LiBa12(BO3)7F4 obtains nice crystallinity. After measurement and calculated, these two planes belong to (040) and (233). The calibrated crystallographic planes are coincident to the refinement crystal structure data and imply the results are credible25. To further ensure the structure of LiBa12(BO3)7F4, SAED measurement is carried out and the results are shown in Figure 2c. The SAED puts on point-like distribution which demonstrates that the LiBa12(BO3)7F4 presents almost single crystal characteristic in this area. And the dots have typical characteristics of the tetragonal distribution. After estimating, three nearest neighbor planes are attributed to (002), (130) and (132), respectively, which their included angle are 59.4o (for (002) and (132)) and 90 o (for (130) and (002)). This result is also coincident to the refinement crystal structure data. The chemical composition of this compound is further determined by EDX as shown in Figure 2d. These signals of barium (Ba), boron (B), oxygen (O) and fluorine (F) suggest the presence of the corresponding element in the sample (the carbon and Cu signal are due to 5



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the carbon film bracket). The signal of Li element doesn’t appear in the EDX because of its light relative molecular mass.

Figure 3 (a) Conventional unit cell structure of LiBa12(BO3)7F4 from [001] direction; (b) Unit cell structure of LiBa12(BO3)7F4 from [010] direction; (c) Inversion symmetry structure of LiBa12(BO3)7F4 and the coordination situation of Ba2+. According to Rietveld refinement and TEM analysis, we make a structure schematic diagrams of LiBa12(BO3)7F4 shown in Figure 3. LiBa12(BO3)7F4 is assigned to tetragonal crystal system and belonging to I 4/m c m (140) space-group25. The refinement unit cell parameters of a = 13.5317(6) Å, c = 14.9702(13) Å for it. In this crystal structure, [LiF4] forms the vertex of the conventional unit cell. And some isolated LiF4−BO3 units formed by LiF4O square pyramids and BO3 groups sharing a O atom are found occupying the octagonal tunnels built by Ba3 (3 site) and BO3 groups along the c axis. In the center of this tunnel is a kind strand arrangement mode of LiF4−BO3. Ba1 ion (1site) is taking on uniform distribution in this tunnel. This type crystal characteristic can be clearly noticed from [001] direction (a). From [010] direction (b), another apparent structure character appears, which all the Ba ions (1, 2 and 3 site) are taking on parallel arrangement by [100] direction. Among them, Ba1 and Ba2 sites are in the same layer and Ba3 forms a separate layer. From Figure 3c, we can see that the crystal structure is center inversion symmetry by the symmetrical center A site. There are three kinds of Ba3 ions existing in the crystal and its coordination is 6 O-1F for Ba1, 6O for Ba2 and 8 O for Ba3, respectively. As we all know, Ba2+ has the same positive charge with Eu2+ and its radius is a little bigger than Eu2+ even it occupies different coordination site. Their radius difference value is small than 30%. Therefore, in this structure, Ba2+ site can provide appropriate position for Eu2+ substituted. In other word, LiBa12(BO3)7F4 is an appropriate host for Eu2+ doping and obtaining good emitted phosphor. It is worth noting that tunnel structure and layer arrangement of Ba2+ ion should be gotten attention. In many other phosphors with good properties, especially some apatite and nitride-matrix host doping with Eu2+ are always possessing tunnel structure, like β-sialon, Sr4[LiAl11N14]:Eu2+, Ca6BaP4O17: Eu2+, 1113 (CaAlSiN3: Eu2+), etc.16, 26-28. These phosphors always have strong crystal field strength and long wavelength emission. Though, in nitride-matrix host, N3--Eu2+ has stronger covalency and leads to strong crystal field strength, and, tunnel structure will also enhance electron cloud delocalized, then, leads to longer wavelength emission. 6


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In the LiBa12(BO3)7F4 crystal structure octagonal tunnels built by Ba3 (3 site) and BO3 groups along the c axis are existed, which is considered to enhance electron cloud delocalized extremely and lead to long wavelength emission when doping with Eu2+.

Figure 4 Band structure and band gap of LiBa12(BO3)7F4 calculated by Materials Studio (Local density approximation)

Figure 5 (a) DR spectra of series LiBa12(BO3)7F4: xEu2+ phosphors and (b) Extrapolation of the band gap energy for the LiBa12(BO3)7F4. The band structure of LiBa12(BO3)7F4 calculated by Materials Studio (Local density approximation) is shown in Figure 4. From the image, we can see that the lowest energy position of the conduction band and the highest energy position of the valence band are at the same abscissa site (X) and the band gap is 3.67 eV, which means it is an indirect optical band gap. At the same time, the DR spectra of series content Eu2+ doped LiBa12(BO3)7F4 samples and its host are measured, as shown in Figure 5a. The doped samples have obvious absorption characteristics 7



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at the range of 300 to 500 nm which indicates that they possess a broad luminescence excitation at the range of UV and NUV light. In addition to doping phosphors DR spectra, LiBa12(BO3)7F4 host is also tested and its experimental band gap extrapolated from the DR spectra are also calculated, which are shown in Figure 5b. The band gap of the LiBa12(BO3)7F4 host can be estimated according to equal as below29. where hν is the photon energy; A is a proportional constant; Eg is the value of the band gap; n = 2 for a direct transition or 1/2 for an indirect transition; and F(R∞) is a Kubelka−Munk function defined as F

1 / 2

where R, K, and S are the reflection, absorption, and scattering coefficient, respectively. From the linear extrapolation of [F(R∞)hν]2 = 0 in Figure 5b, the Eg value is the point of intersection of the double tangent line and estimated to be about 3.65 eV for the host. The theoretical calculated band gap and the experimental one are consistent. The relative bigger band gap for this host and the stronger broad absorption at the range of UV and NUV light indicate that LiBa12(BO3)7F4 would be an interesting and suitable host for Eu2+ doping luminescent materials. 3.2 Luminescence Properties

Figure 6 (a) XRD patterns of LiBa12(BO3)7F4 series samples; (b) Peak shift of series XRD patterns. In order to study the phase stability of Eu2+ doped LiBa12(BO3)7F4 host, series LiBa12(BO3)7F4:Eu2+ samples doping with different content Eu2+ were synthesized and their crystalline were investigated, which the XRD patterns of LiBa12(BO3)7F4: xEu2+ are shown in Figure 6. As is given in Figure 6a image, it can be seen that all of the diffraction peaks of the samples can be basically indexed to the corresponding standard data (Rietveld refinement data), suggesting that LiBa12(BO3)7F4: xEu2+ with different Ba/Eu ratios can be formed in the practical single-phased structure. In the meantime, the diffraction peaks shift to higher angles with 8


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increasing Eu2+ content (shown in Figure 6b) owing to the different ionic radius between Ba2+ and Eu2+. This shift can be explained by bragg equation (2dsinθ = λ), If Eu2+ substitutes Ba2+, the interplanar spacing (d) becomes short, due to smaller radius of Eu2+ than Ba2+ (1.52 Å)30. To keep λ coincident, θ will shift to larger range then the XRD peaks will shift to larger range. Well-deserve crystalline of the series LiBa12(BO3)7F4: xEu2+ phosphor indicated that Eu2+ have been doped into the crystal lattices of the LiBa12(BO3)7F4 instead of forming the impurity phase.

Figure 7 (a) PLE of LiBa12(BO3)7F4: 1%Eu2+; (b) PL of series LiBa12(BO3)7F4: xEu2+ phosphors (0.1% ≤ x ≤ 4%); (c) PL spectra peak position and relative intensity depended on Eu2+ content; (d) Gaussian components fitted of LiBa12(BO3)7F4: Eu2+ spectra. In order to evaluate the photoluminescence properties of LiBa12(BO3)7F4: Eu2+, different content of Eu2+ are doped in to LiBa12(BO3)7F4: Eu2+, which the PLE and PL spectra are shown in Figure 7. From Figure 7a, it is clearly seen that, the phosphors possess a very broad excitation band at the range of 325 to 450 nm, which is almost cover UV and NUV light area and is keeping with the DR spectra shown in Figure 5. It indicates that this phosphor can match UV and NUV LED chips effectively. Figure 7b shows the PL spectra properties of series Eu2+ doping phosphors. We can see that under 405 nm NUV light, the samples can emit red light peaking at about ~644 nm which is due to the 4f65d→4f7 transition of Eu2+. The full-width at half-maximum (FWHM) is 89 nm and the quantum efficiency is 26.6% for the brightest sample (LiBa12(BO3)7F4: 1%Eu2+). Figure 7c indicates that the PL spectra peaks have an apparent trace of red shift from 641 to 651 nm with the increasing of Eu2+ content. It can be explained that with the increasing of Eu2+ content, the energy transfer of intra-Eu2+ becomes to be significant, this kind energy transfer that leads to red shift of emission spectra. Besides, in LiBa12(BO3)7F4 host, the relative smaller dopant Eu2+ occupying Ba2+ site will lead to red shift of emission spectra by this following equation31. 9



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D Ze

Where Dq is a measure of the energy level separation, Z is the anion charge, e is the electron charge, r is the radius of the d wave function, and R is the bond length. When the Ba2+ ion is substituted and occupied by a smaller Eu2+ ion, the distance between the Eu2+ and O2- ion becomes shorter. Since crystal field splitting is proportional to 1/R5, this shorter Eu2+–O2-distance also leads to the enhancement of crystal field strength surrounding the Eu2+ ion and further results in a larger crystal field splitting of Eu2+ 5d energy levels, which makes the lowest 5d state of Eu2+ closer to its ground state and finally gives a red shift of the PL emission peak of the Eu2+. To detail analysis the PL properties, Gaussian components fitted of the brightest phosphor’s PL spectrum is also investigated shown in Figure. 7d. It is apparently seen that the PL spectrum can be fitted to three single peak of LiBa12(BO3)7F4: 1%Eu2+ sample which the peaks are at 615, 657 and 690 nm, respectively. According to above crystal structure analysis, it is known that there are three possible Ba2+ sites for Eu2+ substituted in the crystal structure. These three single fitted spectrum means that there are three luminescence centers in this host which is consistent with the structure analysis.

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Figure 8 Band structure of LiBa12(BO3)7F4 (x=1%) calculated by MS (Local density approximation), (a) doped in Ba1 site; (b) doped in Ba2 site; (c) doped in Ba3 site. To further distinguish the origin of the observed emission center (550-800 nm) in the LiBa12(BO3)7F4:1%Eu2+ phosphor, the well-known empirical Van Uitert equation was always considered to analyze the experimental results on the level of qualitative. For Eu2+ in suitable host, #

%

*+,./

the following equation32 could provide a dependable referE Q1 & 10) $

. But, in this

equation “ea” is the electron affinity of the atoms that form anions (in eV), which is different when Eu2+ is introduced into different anion complexes. In this phosphor, Ba1 is coordinated with two kind anions (O, F) and their “ea” is different. Therefore, using above equation in this system to distinguish the origin of the observed emission center may obtain confusing results. Hence, we try to find another way that using MS program to calculate the band structure’s difference of Eu2+ doping phosphor to differentiate the origin of the emission center, and, the results are shown in Figure 8. From the calculated band structure diagram of Eu2+ doped in different Ba sites, we can get a most distinction from the un-doped host’s band structure shown in Figure 4, the Fermi level presents at highest energy position of the valence band, however, in the doped band structure, the Fermi level (0 eV) presents inner conduction level. That indicates both of the whole energy bands of conduction & valence are shift to lower energy area, then, leads to Fermi level’s shift. The similar phenomenon has already appeared in other reported works33, 34. Furthermore, compared with un-doped host’s band structure, there are two apparent energy bands appearing in the band gap area of these three doped band structures. One is close to conduction band and another is close to valence band. After calculation and measurement, we found that the energy difference value of this two extra bands are 1.87, 1.96 and 2.12 eV for Eu2+doped in Ba1, Eu2+ doped in Ba2 and Eu2+ doped in Ba3 sites, respectively. Transforming above energy unit “eV” to “wavelength” by E=hc/λ equation, we can get these three energy values that are 688, 659 and 615 nm, respectively. Interestingly, they are very close to above Gaussian components fitted of the brightest phosphor’s PL spectrum. Therefore, we can get a conclusion that the extra bands appearing in Eu2+ doped phosphor’s band structure are the excited band (5d1) which is close to conduction band and the ground state band (4f7) which is close to valence band of Eu2+. It is noticed that when Eu2+ doped in Ba1 site, the phosphor’s emission is at the longest wavelength position (690 nm). From the crystal structure and Ba site arrangement, we could deduce out the PL characteristic. Ba1 site (1site) is taking on uniform distribution in the crystal structure tunnel (above mentioned) from [001] direction and in every [010] layer, there are eight Ba1 ions taking on uniform distribution. The distribution in tunnel and layer of Ba1 will get strong electron cloud delocalized, then, leads to longer wavelength emission. On the other hand, there are two F- around Ba3 site seen from Figure 3c. As we know, F has stronger electronegativity than O, and, the electron around Ba3-F bond will be prone to F. This situation will weaken electron cloud delocalized around Ba3. Therefore, when Eu2+ doped into Ba3 site, the emission position will be at a little short wavelength (615 nm). Last, we distinguished the origin of the observed emission center by calculating the Eu2+ doped phosphor’s band structure successfully.

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Figure 9 PL decay curves of (a) LiBa12(BO3)7F4: xEu2+ phosphors with 405 nm excitation and 650 nm emission; (b) Comparison of different emission decay curves with identical excitation (Eu1-615 nm, Eu2-657 nm and Eu3-690 nm).

Figure 10 Time-resolved photoluminescence (TRPL) emission spectra of LiBa12(BO3)7F4: 1%Eu2+. Figure 9 shows the PL decay curves by taking LiBa12(BO3)7F4: xEu2+ phosphors as the example. From the Figure 9a, we can see that with increasing of Eu2+ doping contents, the decay curves move down gradually under 405 nm excitations. After exponential fitting and calculation, we find that triple-exponential fitting obtains better fitting degree, which the Chi-squared is close to 1.That means the calculation of decay times is convincing. The entire decay curve can be well fitted to decay model by the following equation35: 13



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It exp 4

5 5 5 7 + exp 4 7 + 9 exp 4 7 6 6 69

Where I is the luminescence intensity; A1, A2 and A3 are constants; t is time; and τ1, τ2 and τ3 are the lifetimes for the exponential components. Further, the average lifetime constant (τ*) can be calculated as:

6∗

6 + 6 + 9 69 6 + 6 + 9 69

The calculated average lifetimes of the LiBa12(BO3)7F4: xEu2+ phosphors with different Eu2+ contents are 2.643, 2.618, 2.568, 2.523, 2.501 and 2.482 µs, respectively. The calculated lifetimes of Eu2+ are in a microsecond range, which is indicative of the character of the 5d energy level transitions in Eu2+ ions. As expected, with the increment of Eu2+ content, the decay curves gradually decreases from 2.643 to 2.482 µs. As the concentration of Eu2+ ions increases, the distance between Eu2+ ions becomes shorter and the probability of the non-radiative energy migration among the Eu2+ increases. Furthermore, to prove the three emission spectra belonging to three luminescent centers, decay curves monitored at 615, 657 and 690 nm with same excitation 405 nm are shown in Figure 9b. It is seen that three curves monitored at 615, 657 and 690 nm are not coincided and they are also different with the curve monitored at 650 nm. And the decay times calculated for them are 2.589, 2.544 and 2.511µs, respectively. The difference of them indicated that the emission spectrum peaking at 650 nm is coming from three different luminescent centers certainly. In addition, the TRPL spectra shown in Figure 10 were obtained by slicing them. Obviously, the TRPL spectra are not symmetrical, which have not been found from the emission spectra shown in Figure 7. Simultaneously, with the time interval prolonging, it was interesting to observe that the ratio of intensity of these three peaks varied significantly, confirming that there are three light luminescent centers. The occurrence of the three emission peaks further demonstrates Eu2+ occupying the three different cationic lattice sites. 3.3 Temperature quenching properties

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Figure 11 (a) Temperature dependence properties of LiBa12(BO3)7F4: 1%Eu2+ phosphor; (b) PL spectra peak position and relative intensity depended on different temperature; (c) TL curve of LiBa12(BO3)7F4: 1%Eu2+; (d) The schematic diagram of the mechanism for temperature-increasing resultant emission enhancement. The temperature stable property of the phosphor is an important factor of its application. We choose 1% Eu2+ doped sample (LiBa12(BO3)7F4: 1%Eu2+) to investigate it by testing the PL spectra at different temperature under 405 nm excitation and the results are shown in Figure 11. From the Figure 11a, we can see that an unconventional phenomenon appears, which the emission intensity increases firstly up to 75 oC and then decrease til 250 oC. This special intensity variation is shown in Figure 11b. We defined the intensity is 100 at 25 oC and the intensity at 50 and 75 oC are both exceeding triple compared with room temperature’s. Then the intensity deceases gradually, but, when the temperature increases up to 125 oC, the intensity still keeps 163, bigger than room temperature’s. After that, the intensity are lower than 100. And the emission peaking position shifts to short wavelength from 644 to 623 nm. The blue shift of the temperature dependent emission spectra is a common phenomenon, which can be explained in two aspects: (1) With temperature increasing, the crystal structure has a certain expansion. The structure expansion will loose crystalline field. Then the weak crystalline field at high temperature will lead to blue shift of the PL spectra according to previous work36; (2) It can be described in terms of back tunneling from the excited states of low-energy emission band to the excited states of high-energy emission band by assistance of thermally active phonon37. To explore the unconventional phenomenon of the intensity variation dependent on temperature, we make a further test of TL curve of LiBa12(BO3)7F4: 1%Eu2+, which the result is shown in Figure 11c. It is clearly seen that there is a relative strong TL peak at about 37 oC and a relative weak peak before at 150 oC. The TL spectrum indicated that the LiBa12(BO3)7F4: 1%Eu2+ phosphor can emit light under thermal effect at 37 and 150 oC. This type emission is always given rise to traps existing in the crystal. Figure 11d can make an explicit explanation for above unconventional phenomenon. The extra energy level generated by traps is existing in the band gap and its depth can be calculated by following equation 38. 15



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E ;< /500 Where E represents the activation energy, called, the trap depth. Tm refers to the temperature peak (Kelvin temperature) of the TL curve. Thus the trap depth is determined to be 0.62 eV. The traps energy level can store electron, and, with temperature increasing, the stored electron will be released from the traps affected by thermal disturbance and this type electron will arrive the excited energy level 4f65d1 of Eu2+ in a relaxation way. After that, this type electron as the excited electron will also take part in the transition process of Eu2+ from 4f65d1 to 4f7, then, generate luminescence emission. Therefore, besides the contribution produced from the normal transition and emission process of Eu2+ luminescence centers, extra traps electron will also contribute the emission. Hence, before 125 oC, the emission intensity is stronger than room temperature’s, after that, the electron in the traps is relaxed utterly and the temperature quenching effect will dominate the emission intensity. So, the decreasing trace appears after 125 oC. 3.4 CL Properties

Figure 12 (a) CL spectra of LiBa12(BO3)7F4: 1%Eu2+ phosphor as a function of probe current under 5 kV electron-beam excitation; (b) CL spectra of LiBa12(BO3)7F4: 1%Eu2+ phosphor with varied voltage under 60 mA probe current; (c) CL spectra intensity dependent on different probe current; (d) CL spectra intensity dependent on different voltage.

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Figure 13 (a) CL spectra of LiBa12(BO3)7F4: 1%Eu2+ dependent on different electron beam bombardment time; (b) CL intensity and chromaticity coordinate of LiBa12(BO3)7F4: 1%Eu2+ phosphor with the electron-beam bombardment time (min). To check if the LiBa12(BO3)7F4: Eu2+ red phosphor possessing CL properties, further measurements are performed on the phosphors with the results shown in Figure 12 and Figure 13. They are CL spectra of LiBa12(BO3)7F4: 1%Eu2+, applying fixed voltage as 5 kV with increasing probe current (10 mA-100 mA) and increasing accelerating voltage (1kV-10kV) with probe current as 60 mA, respectively. When voltage is fixed as 5 kV, CL intensity meets a decline after 60 mA (Figure 12a,c) while no decline is observed with the increasing of voltage (Figure 12b,d). CL decline caused by increasing current is so called current saturation phenomenon and it is common to occur, for example, in Ca19Mg2(PO4)14:Eu3+ 39, Li2CaSiO4:Eu2+ 40, SrSiAl2O3N2:Eu2+ 41, etc.. There are several possible reasons for this decline type42. (1): Surface lattice damage. When the bombarding current increases, more electrons possessing much energy will be interact with the lattice. As a result, the structure of the sample surface lattice even inner part destroys or changes, decreasing the amount of efficient luminescence center, so the emission intensity decreases. (2): Thermal unstable property (thermal quenching). More electrons with higher energy will lead to charge accumulation which can both cause temperature rising of the sample, (temperature increasing will decrease emission intensity distinctly as above part 3.3 analysis). (3): Ionization or other reasons. Combining with structure and thermal stable property characteristic, we think the first two reasons are the main effect to act on this current saturation phenomenon. The stability of the sample’s CL is investigated by measure bombarding time dependent CL intensity of LiBa12(BO3)7F4: 1%Eu2+. Degradation property is known significant when evaluate a phosphor for its FED application. Bombarding time is performed from 0 to 90 min. From Figure 13a, we can see that the shape of the CL curves does not change visibly with time going on. Specially, the bombarding time dependent CL intensity of the sample keeps constant as well. Furthermore, the calculated CIE coordinates plotted as a function of bombarding time are almost invariable according to Figure 13b. It means the phosphor will not put up color purity drift with bombarding time going on. The bombarding time measurement indicated that the LiBa12(BO3)7F4: 1%Eu2+ phosphor has a very stable CL property. 3.5 Performance of LED devices

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Figure 14 CIE chromaticity diagram of the LiBa12(BO3)7F4: 1%Eu2+ red phosphor and white LEDs fabricated by BAM: Eu2+, (Sr, Ba)2SiO4: Eu2+ and LiBa12(BO3)7F4: 1%Eu2+ phosphors (inset: The EL spectra of white emitting LEDs composed of a 405 nm NUV chip (GaN)).

To verify the potential applied value of LiBa12(BO3)7F4: Eu2+ red phosphor, we choose the brightest sample (1%Eu2+ doped) to fabricate white LED mixing with BAM: Eu2+ blue phosphor, (Sr, Ba)2SiO4: Eu2+ green phosphor and 405 nm GaN chip. We also take a photo of the red phosphor under 365 nm UV light. Their patterns, EL spectrum of white LED and CIE coordinates are shown in Figure 14. First, we can see that LiBa12(BO3)7F4: Eu2+ under 365 nm UV light takes on homogeneous and bright red light and its CIE coordinate is (0.6350, 0.3586). From its colour area position, it locates at the red-orange region and this part is most sensitive for the human eyes. Moreover, it is clearly seen that after fabricated, the white LED, we adjust the weight rate of these three RGB phosphors and can get warm white light, which its CIE coordinate is (0.3475, 0.3416) and the CCT, Ra and luminous efficiency is 4856 K, 84.1 and 72.6 lm/W with 50 mA and 7 V working current. Furthermore, the parameter of the w-LEDs at different current are also measured and the results are shown in Figure S4. Under higher current, the luminous efficiency is not increasing as expected. At higher current, it may generate more thermal than “current at 70 mA”, but, the higher current can also excite more emission. These two opposite factors may affect luminous efficiency together. All of the tested data indicated that 18


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LiBa12(BO3)7F4: Eu2+ can be as a potential candidate for the NUV-excitable warm white-emitting phosphor.

4. Summary In summary, a novel oxide matrix LiBa12(BO3)7F4 material and its Eu2+ doped phosphors are synthesized successfully by traditional high temperature solid-state reaction. After TEM, XRD Rietveld refinement analysis, it is found that LiBa12(BO3)7F4 has a special tunnel and layered arrangement of Ba2+.According to theoretical calculation and PL properties analysis, it has three kinds of Ba2+ that can be occupied by Eu2+. LiBa12(BO3)7F4: Eu2+ has a very broad excitation band at the range of 300-450 nm and a red emission band peaking at ~644 nm with the FWHM 89 nm. Temperature dependent PL spectra of LiBa12(BO3)7F4: 1%Eu2+appeared anomalous phenomena that the intensity increases firstly and then decreases, which is due to the traps energy level’s contribution of electron’s transition. The phosphor also has CL property, which it can emit red light under cathode. And the CL curves indicated that this phosphor has a very good stability under much electron beam bombardment time. After fabricated combing with BAM, (Sr, Ba)2SiO4 and our red phosphor excited under 405 nm NUV chips, warm light LED was gotten, and, its CIE coordinate is (0.3475, 0.3416) and the CCT, Ra and luminous efficiency is 4856 K, 84.1 and 72.6 lm/W. Ultimately, the unusual oxide based Eu2+ doped red emission phosphor were synthesized successfully and it can get warm white-emitting device by fabricating with chips and other NUV-excitable phosphors.

Acknowledgement This work is supported by Specialized Research Fund for the Doctoral Program of Higher Education (no. 20120211130003), the National Natural Science Funds of China (Grant no. 51372105). At the same time, thanks for the support of Gansu Province Development and Reform Commission Supporting Information The refinement XRD data by three different occupying situations in Ba sites and fabricated LEDs’ properties under different current are introduced in detail in the supporting information, which named Figure S1-S3 and Figure S4.

Reference (1) Phillips, J. M.; Coltrin, M. E.; Crawford, M. H.; Fischer, A. J.; Krames, M. R.; Mach, R. M.; Mueller, G. O.; Ohno, Y.; Rohwer, L. E. S.; Simmons, J. A.; Tsao, J. Y. Research Challenges to Ultra-efficient Inorganic Solid-State Lighting, Laser Photonics Rev. 2007, 1, 307-333. (2) Kitai, A. Luminescent Materialsand Applications, John Wiley & Sons, Ltd ISBN: 978-0-470-05818-3 (2008) (3) Ye, S.; Xiao, F.; Pan, Y. X.; Ma, Y. Y.; Zhang, Q. Y. Phosphors in Phosphor-Converted White Light-Emitting Diodes: Recent Advances in Materials, Techniques and Properties, Mater. Sci. Eng. R. 2010, 71, 1-34. (4) Smet, P. F.; Parmentier, A. B.; Poelman, D. Selecting Conversion Phosphors for White Light-emitting Diodes. J. Electrochem. Soc. 2011, 158, R37-R54. (5) Bachmann, V.; Ronda, C.; Meijerink, A. Temperature Quenching of Yellow Ce3+ Luminescence in YAG:Ce. Chem. Mater. 2009, 21, 2077-2084. (6) Takahashi, K.; Hirosaki, N.; Xie, R. J.; Harada, M.; Yoshimura, K.; Tomomura, Y. Luminescence Properties of Blue La1-xCexAl(Si6-zAlz)(N10-zOz) (z˜1) Oxynitride Phosphors and Their Application in White Light-emitting Diode. Appl. Phys. Lett. 2007, 91, 091923-091926. (7) Lin, C. C.; Liu, R. S. Advances in Phosphors for Light-emitting Diodes. J. Phys. Chem. Lett. 2011, 2, 1268-1277. 19



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

(8) G. F. Ju, Y. H. Hu, L. Chen, X. J. Wang, Persistent Luminescence and Its Mechanism of Ba5(PO4)3Cl:Ce3+,Eu2+. J. Appl. Phys. 2012, 111, 113508-113513. (9) Liu, Y. F.; Zhang, X.; Hao, Z. D.; Wang, X. J.; Zhang, J. H. Color Point Tuning of Y3Al5O12: Ce3+ Phosphor via Mn2+–Si4+ Incorporation for White Light Generation. J. Mater. Chem. 2012, 22, 15146-15152. (10) Singh, V.; Chakradhar, R. P. S.; Rao, J. L.; Kwak, H. Y. Green Luminescence and EPR Studies on Mn-activated Yttrium Aluminum Garnet Phosphor. Appl. Phys. B. 2010, 98, 407-415. (11) Liu, Y. F.; Zhang, X.; Hao, Z. D.; Wang, X. J.; Zhang, J. H. Crystal Structure and Luminsescence Properties of (Ca2.94-xLuxCe0.06)(ScMg)Si3O12 Phosphors for White LEDs. Chin. J Lumin. 2011, 32, 445-450. (12) Li, J. K.; Li, J. G.; Liu, S. H.; Li, X. D.; Sun, X. D.; Sakkab, O. Greatly Enhanced Dy3+ Emission via Efficient Energy Transfer in Gadolinium Aluminate Garnet (Gd3Al5O12) Stabilized with Lu3+. J. Mater. Chem. C. 2013, 1, 7614-7622. (13) Lee, S. P.; Liu, S. D.; Chan, T. S.; Chen, T. M. Synthesis and Luminescence Properties of Novel Ce3+- and Eu2+- doped Lanthanum Bromothiosilicate La3Br(SiS4)2 Phosphors for White LEDs. ACS Appl. Mater. Interfaces. 2016, 8, 9218–9223. (14) Yang, L. Y.; Wang, J. X.; Dong, X. T.; Yu, W. S. Synthesis of Y2O2S:Eu3+ Luminescent Nanobelts via Electrospinning Combined with Sulfurization Technique. J. Mater. Sci. 2013, 48. 644–650. (15) Kuang, J. Y.; Liu, Y. L.; Yuan, D. S. Preparation and Characterization of Y2O2S : Eu3+ Phosphor via One-Step Solvothermal Process. Electrochem. Solid-State Lett. 2005, 8, 72-74. (16) Piao, X. Q.; Machida, K.; Horikawa, T.; Hanzawa, H.; Shimomura, Y.; Kijima, N. Preparation of CaAlSiN3:Eu2+ Phosphors by the Self-Propagating High-Temperature Synthesis and Their Luminescent Properties. Chem. Mater. 2007, 19, 4592-4599. (17) Chung, S. L.; Chou, W. C. Combustion Synthesis of Ca2Si5N8: Eu2+ Phosphors and Their Luminescent Properties. J. Am. Ceram. Soc. 2013, 96, 086–2092. (18) Strobel, P.; Weiler, V.; Hecht, C.; Schmidt, P. J.; Schnick, W. Luminescence of the Narrow-Band Red Emitting Nitridomagnesosilicate Li2(Ca1–xSrx)2[Mg2Si2N6]: Eu2+ (x= 0–0.06). Chem. Mater. 2017, 29, 1377-1383. (19) Pust, P.; Weiler, V.; Hecht, C.; Tücks, A.; Wochnik, A. S.; Henß, A. K.; Wiechert, D.; Scheu, C.; Schmidt, P. J.; Schnick, W. Narrow-band Red-emitting Sr[LiAl3N4]:Eu2+ as a Next-generation LED-phosphor Material. Nat. Commun. 2014, 13, 891-896. (20) Cui, D. P.; Xiang, Q. C.; Song, Z.; Xia, Z. G.; Liu, Q. L. The Synthesis of Narrow-band Red-emitting SrLiAl3N4:Eu2+ Phosphor and Improvement of Its Luminescence Properties. J. Mater. Chem. C. 2016, 4, 7332-7338. (21) Mu, Z. F.; Hu, Y. H.; Wu, H. Y.; Fu, C. J.; Kang, F. W. The Structure and Luminescence Properties of a Novel Orange Emitting Phosphor Y3MnxAl5−2xSixO12. Physica B: Condensed Matter. 2011, 406, 864-868. (22) Sun, C.; Zhang, Y.; Ruan, C.; Yin, C. Y.; Wang, X. Y.; Wang Y. D.; Yu, W. W. Efficient and Stable White LEDs with Silica-Coated Inorganic Perovskite Quantum Dots. Adv. Mater. 2016, 28, 10088-10094. (23) Zhang, F.; Zhong, H. Z.; Chen, C.; Wu, X. G. ; Hu, X. M.; Huang, H. L.; Han, J. B.; Zou, B. S.; Dong, Y. P. Brightly-Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X=Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS nano. 2015, 9, 4533-4542. 20


Page 20 of 22

Page 21 of 22

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


(24) Zhu, Z. Y.; Yang, Q. Q.; Gao, L. F.; Zhang, L.; Shi, A. Y.; Sun, C. L.; Wang Q.; Zhang, H. L. Solvent-Free Mechanosynthesis of Composition-Tunable Cesium Lead Halide Perovskite Quantum Dots. J. Phys. Chem. Lett. 2017, 8, 1610-1614. (25) J. Zhao and R. K. Li, Two New Barium Borate Fluorides ABa12(BO3)7F4 (A = Li and Na), Inorg. Chem., 2014, 53, 2501-2505. (26) Kimoto, K.; Xie, R. J.; Matsui, Y.; Ishizuka, K.; Hirosaki, N.; Direct Observation of Single Dopant Atom in Light-emitting Phosphor of β-SiAlON: Eu2+. Appl. Phys. Lett. 2009, 94, 041908-041911. (27) Wilhelm, D.; Baumann, D.; Seibald, M.; Wurst, K.; Heymann G.; Huppertz, H. Narrow-Band Red Emission in the Nitridolithoaluminate Sr4[LiAl11N14]:Eu2+. Chem. Mater. 2017, 29, 1204– 1209. (28) Komuro, N.; Mikami, M.; Shimomura, Y.; Bithell E. G.; Cheetham, A. K. Synthesis, Structure and Optical Properties of Cerium-doped Calcium Barium Phosphate–a Novel Blue-green Phosphor for Solid-state Lighting. J. Mater. Chem. C. 2015, 3, 204-210. (29) Chen, X.; Dai, P. P.; Zhang, X. T.; Li, C.; Lu, S.; Wang, X. L.; Jia, Y.; Liu, Y. C. A Highly Efficient White Light (Sr3,Ca,Ba)(PO4)3Cl:Eu2+, Tb3+, Mn2+ Phosphor via Dual Energy Transfers for White Light-Emitting Diodes. Inorg. Chem. 2014, 53, 3441−3448. (30) Sato, M.; Tanaka, T.; Ohta, M.; Photostimulated Luminescence and Structural Characterization of Ba5(PO4)3Cl:Eu2+ Phosphors. J. Electrochem. Soc.1994, 141, 1851-1855. (31) Huang, Y. L.; Gan, J. H.; Zhu, R.; Wang, X. G.; Seo, H. J. Structural Phase Formation and Tunable Luminescence of Eu2+-Activated Apatite-Type (Ca,Sr,Ba)5(PO4)2(SiO4). J. Electrochem. Soc. 2011, 158, J334-J340. (32) Xin, S. Y.; Wang, Y. H.; Zhu, G.; Zhang, F.; Gong, Y.; Wen, Y.; Liu, B. T. Tunable White Light Emitting from Mono Ce3+ Doped Sr5(PO4)2SiO4 Phosphors for Light Emitting Diodes. Mater. Res. Bull. 2013, 48, 1627–1631. (33) Chen, L.; Fei, M.; Zhang, Z.; Jiang, Y.; Chen, S. F.; Dong, Y. Q.; Sun, Z. H.; Zhao, Z.; Fu, Y. B.; He, J. H.; Li, C.; Jiang, Z. Understanding the Local and Electronic Structures Towards Enhanced Thermal Stable Luminescence of CaAlSiN3:Eu2+, Chem. Mater., 2016, 28, 5505–5515 (34) Zhu, Q. Q.; Wang, L.; Hirosaki, N.; Hao, L. Y.; Xu, X.; Xie, R. J. An Extra-Broad Band Orange-Emitting Ce3+-doped Y3Si5N9O Phosphor for Solid-State Lighting: Electronic and Crystal Structures, Luminescence Properties, Chem. Mater., 2016, 28, 4829–4839. (35) Wang, X. G.; Gan, J. H.; Huang, Y. L.; Seo, H. J. The Doping Concentration Dependent Tunable Yellow Luminescence of Sr5(PO4)2(SiO4):Eu2+. Ceram. Int. 2012, 38, 701–706. (36) Yu, H.; Deng, D. G.; Li, Y.Q.; Xu, S. Q.; Li, Y. Y.; Yu, C. P.; Ding, Y. Y.; Lu, H. W.; Yin, H. Y.; Nie, Q. L. Electronic Structure and Luminescent Properties of Ca5(PO4)2(SiO4):Eu2+ Green-emitting Phosphor for White Light Emitting Diodes. Opt. Commun.2013, 289, 103–108. (37) Shi, Y. R.; Zhu, G.; Mikami, M.; Shimomura, Y.; Wang, Y. H. Photoluminescence of Green-emitting Ca7(PO4)2(SiO4)2:Eu2+ Phosphor for White Light Emitting Diodes. Opt. Mater. Express. 2014, 4, 280-287. (38) Pust, P.; Wochnik, A. S.; Baumann, E; Schmidt, P. J.; Wiechert, D.; Scheu, C.; Schnick, W. Ca[LiAl3N4]:Eu2+-A Narrow-Band Red-Emitting Nitridolithoaluminate. Chem. Mater. 2014, 26, 3544-3549. (39) Zhu, G.; Ci, Z. P.; Shi, Y. R.; Que, M. D.; Wang Q.; Wang, Y. H. Synthesis, Crystal Structure and Luminescence Characteristics of a Novel Red Phosphor Ca19Mg2(PO4)14: Eu3+ for Light 21



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

Emitting Diodes and Field Emission Displays. J. Mater. Chem. C. 2013, 1: 5960-5969. (40) Xu, X. G.; Chen, J.; Deng, S. Z. ; Xu, N. S.; Liang, H. B.; Su, Q.; Lin, J. High Luminescent Li2CaSiO4: Eu2+ Cyan Phosphor Film for Wide Color Gamut Field Emission Display. Opt. Express. 2012, 20, 17701-17710. (41) Wang, X. C.; Zhao, Z. Y.; Wu, Q. S.; Li, Y. Y.; Wang, C.; Mao A. J.; Wang, Y. H. Synthesis, Structure, and Luminescence Properties of SrSiAl2O3N2: Eu2+ Phosphors for Light-emitting Devices and Field Emission Displays. Dalton Trans. 2015, 44, 11057-11066. (42) Blass, G.; Grabmaier, B. C. A General Introduction to Luminescent Materials[M]//Luminescent materials. Springer Berlin Heidelberg. 1994: 1-9.

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