Enhanced luminescence properties of Sr3−xEuxAlO4−yNyF phosphors

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Enhanced luminescence properties of Sr3-xEuxAlO4yNyF phosphors Qiangsheng Gao, Lili Meng, Lixia Zhang, Qi Pang, Lifang Liang

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Cite this article as: Qiangsheng Gao, Lili Meng, Lixia Zhang, Qi Pang, Lifang Liang, Enhanced luminescence properties of Sr3-xEuxAlO4-yNyF phosphors, Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2015.06.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Enhanced luminescence properties of Sr3-xEuxAlO4-yNyF phosphors Qiangsheng Gao1, Lili Meng1, Lixia Zhang1, Qi Pang2, and Lifang Liang1* 1. College of Chemistry and Materials Science, Guangxi Teachers Education University, Nanning 530001, China 2. School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530001, China

Abstract: Luminescent materials with the chemical formula Sr3-xEuxAlO4-yNyF were prepared by a solid-state reaction. X-ray diffraction (XRD) patterns, X-ray photoelectron

spectroscopy

photoluminescence

emission

(XPS),

scanning

electron

and

excitation

spectra,

microscopy the

(SEM),

lifetime,

the

temperature-dependent luminescence, and the effects of Eu3+ and N3- concentrations were investigated in detail. Partial substitution of Sr2+ by Eu3+ and O2− by N3- in Sr3-xEuxAlO4-yNyF contributes to form quadrangular crystals, and enhance the thermal stability against the temperature quenching effect. After the partial replacement of Sr2+ by Eu3+ and O2- by N3- ions in the Sr3AlO4F host structure, the emission intensity was enhanced and the charge-transfer band of O2p → Eu4f shifted to higher wavelength.

Keywords: Luminescence in Eu3+ ions; Oxyfluoride Sr3AlO4F; Phosphor; Nitridation

1

1. Introduction Light-emitting diodes (LEDs) have received a lot of attention in the past decade due to their high brightness, long lifetime, compact structure, material hardness, and environmental friendliness [1]. Among several techniques for the production of LED-phosphor-based white light sources [2,3], a combination of tricolor (red, green and blue) phosphors with n-UV LED chips is expected to emerge as the leader. Therefore, exploring novel red phosphor materials is integral for the development of white LEDs. It is well-known that Eu3+ is the most commonly used activator of red emitting luminescent materials. Eu3+ can function as an emission center in the host lattice and originate from predominant 5D0 → 7F2 or 5D0 → 7F1 transitions [4]. Recently, a family of anion ordered oxyfluorides, Sr3-xAxMO4F (A = Ca, Ba and M = Al, Ga, In), has been utilized as a host material for new luminescent materials [5-10]. These materials can be activated in the deep (200–250 nm) and near (300–400 nm) UV regions, and exhibit efficient luminescent properties when doped with rare-earth activators. The luminescent properties of Eu3+-doped Sr3-xAxMO4F phosphors have been reported to show red emission under UV or near-UV excitation, and the photoluminescent (PL) properties and Commission International de I’Eclairage (CIE) values can be tailored by various chemical substitutions [6-8]. Because the valence state of an activator ion depends on the coordination environment, the photoluminescent properties of phosphors can be controlled by modifying the covalency and polarizability of activator−ligand bonds in phosphors [11-14].

Moreover, the fluoride lattice provides a high coordination number for

2

doped rare earth ions, and the high ionicity of the rare-earth-fluorine bond results in a wide band gap, low vibrational energies, and low probability of inter-configurational transitions [15]. It has been previously reported that incorporating Si4+−N3− into Ce3+or Eu2+-doped phosphors will lead to a red shift in the 4f−5d emission owing to the lower electronegativity of N3− compared to O2− [11,12]. However, changing the valence state of the activator in Eu3+-activated phosphors by modifying the coordination environment of the activator site has scarcely been investigated. In this work, the luminescent properties of Sr3-xEuxAlO4-yNyF oxyfluorides are studied. When Sr2+ and O2- ions in the oxyfluoride host are replaced by Eu3+ and N3- ions, respectively, the effective charge-transfer band (CTB) and Eu3+ ion f-f transitions are monitored.

2. Experimental Chemicals and Materials. SrCO3 (strontium carbonate) and SrF2 (strontium fluoride) were purchased from Shanghai Aladdin Reagent Co., Ltd. Other chemicals, including Al2O3 (aluminium oxide), Eu2O3 (europium oxide), and AlN (aluminium nitride), were purchased from the Chinese Medicine Group Chemical Reagent Co., Ltd. All chemicals were of analytical grade and used without further purification. Sample Preparation. All Sr3-xAlO4-yNyF: xEu3+ phosphors were prepared by a conventional solid-state reaction. The starting materials, SrCO3, SrF2, Al2O3, Eu2O3, and AlN, were weighed at different stoichiometric ratios and finely ground in an agate mortar to obtain homogeneous mixtures. Each mixture was added to an alumina

3

crucible and sintered in an electric furnace at 1300 °C for 4 h in air or an N2 atmosphere. Sample Characterization. The crystalline phases of each sample were identified by powder X-ray diffraction (XRD) measurements using a XD-3 diffractometer (PERSEE) with a Cu Kα radiation source (λ = 0.154 nm). Data were collected over 2θ = 10–80o at a scan rate of 4o/min. X-ray photoelectron spectra (XPS) were obtained by an electron spectrometer with Al Kα (1486.6 eV) excitation source (Thermo VG Multilab 2000) at a working pressure lower than 5.0 x 10-6 Pa. Scanning electron microscopy (SEM) measurements were performed by a Zeiss EVO18 instrument operated at an acceleration voltage of 10 kV. Luminescent decay curves were measured by a FLS920 spectrofluorometer (Edinburgh Instruments, UK) equipped with an EPL375 pulsed laser diode. PL excitation and emission spectra were recorded using a Hitachi F-2500 spectrophotometer with a 150 W xenon lamp as the excitation source. The temperature dependence of PL was measured with a QE-1000 (Otsuka Electronics) equipped with temperature-controlled sample holders and a Xe lamp as the excitation source. Color temperature and color rendering index (Ra) were measured by a spectroradiometer (HAAS-2000, Hangzhou far photoelectric information co., LTD).

3. Results and Discussion It has been reported [5] that the Sr3AlO4F host lattice contains tenfold and eightfold coordinated strontium, Sr(1) and Sr(2) respectively (shown in Fig.1): Sr(1)

4

(10r = 1.36 Å) is coordinated by eight oxygens and two apical fluorines; Sr(2) (8r = 1.26 Ǻ) is eight coordinated by two fluorines and six oxygen atoms. Moreover, the oxyflouride host lattice consists of both strong ionic Sr-F and covalent Al-O bonds. Because the coordination environments of the two Sr sites in the compound are different, it is possible that the ordering of Sr2+ ions can be adjusted by replacing a Sr2+ ion with another alkaline earth or rare earth ion. On the basis of the above analysis and the similar ionic radii of Sr2+ and Eu3+, or N3- and O2- ions, Eu3+ and N3ions may be suitable substitutes in the Sr3AlO4F host.

The chemical compositions of phosphor powder surfaces were studied by XPS. Fig. 2(A) shows the XPS spectrum for the phosphor powder. Strontium-, aluminum-, oxygen-, fluorine-, nitrogen-, and europium-containing species are detected in the phosphor powders. Fig. 2(B) shows the contents of nitrogen and oxygen as a function of the quantity of AlN (y) added during the synthesis. XPS analysis reveals increasing nitrogen content and decreasing oxygen content with increasing AlN concentration (y). This signifies the formation of nitrogen-rich compounds, as nitrogen ions (r = 1.4 Å) are substituting for oxygen ions (r = 1.46 Å) due to their similar ionic radii.

Fig. 3(A) shows XRD patterns of the Sr2.9AlO4-yNyF: 0.1Eu3+ phosphors with increasing y. From the XRD analysis, all of the major diffraction peaks match well with the reference spectrum (JCPDS card No. 89-4485), which has tetragonal

，

structure with I4/mcm space group (a = 6.78(1) Å c = 11.14(1) Å). Because smaller

5

Eu3+ (8r = 1.07 Å) ions prefer the Sr(2) (8r = 1.26 Å) site [7], partial substitution of Sr2+ ions with Eu3+ ions results in a slight peak shift to higher angles. In contrast, the radii of O2- (r = 1.40 Å) and N3- (r = 1.46 Å) ions are similar, and partial substitution of O2- for N3- does not significantly shift on the peak positions or change the cell parameters with increasing y, Fig. 3(B).

SEM images of the Sr3-xAlO4-yNyF: xEu3+ samples annealed at 1300 °C for 4 h are shown in Fig. 4. The morphologies are composed of relatively uniform quadrangular shape and irregular particle aggregation, and the content of Eu3+ doped in the host presents obvious effect on the morphology and particle size, as shown in Fig. 4 (a, c, d, e, f). The powders of Sr3-xAlO3.95N0.05F: xEu3+ (x = 0.03) consist of numerous uniform quadrangular crystals and a few irregular particles (Fig. 4a), most quadrangular crystals have a length of the side about 1 µm and a thickness about 0.1 µm. The morphology of Sr3-xAlO3.95N0.05F: xEu3+ (x = 0.12) mainly consist of relatively uniform crystals with a square shape, in which a length of the side increases to 2−5 µm and a thickness remains at about 0.1 µm (Fig. 4d). When increasing Eu3+ doping concentration to x = 0.18, the crystals become irregular particle aggregation, and the grain size varies from 0.5 µm to 4 µm (Fig. 4f). Moreover, the SEM images of Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0) (Fig. 4b) and Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0.05) (Fig. 4c) display that partial substitution of O2− by N3- in Sr2.9AlO4-yNyF: 0.1Eu3+ contributes to form quadrangular crystals. The morphology with quadrangular shape indicates that the product has a tetragonal crystal structure.

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Fig. 5 describes the excitation and emission spectra of Sr2.9AlO3.97N0.03F: 0.1Eu3+ with a schematic of the Eu3+ energy states. The excitation spectrum under a 621 nm excitation shows a broad band in the 240−360 nm range with a maximum at ~293 nm, and is assigned as the charge transfer band (CTB) of O2p → Eu4f. In addition, several weak peaks between 360 and 400 nm are attributed to 4f−4f transitions of the Eu3+ ions, which correspond to 7F0-5D4 (364 nm), 7F0-5G3 (384 nm) and 7F0-5L6 (395 nm), respectively. The sharp emission lines in the red range under a 293 nm excitation are assigned to 5D1 → 7F1 (535 nm), 5D0 → 7F0 (580 nm), 5D0 → 7

F1 (590 nm), 5D0 → 7F2 (621 nm), 5D0 → 7F3 (652 nm), and 5D0 → 7F4 (705 nm)

transitions. Moreover, the 5D0 → 7F2 emission peak at 621 nm is strongest, indicating that Eu3+ occupies a site without inversion symmetry, which correlates well with the coordination environment of the Sr2+ ion shown in Fig. 1. This is especially true when nitrogen ions partially substitute for oxygen ions in Sr3-xAlO4-yNyF: xEu3+ structures.

Fig. 6 displays the emission spectra of Sr2.9AlO4-yNyF: 0.1Eu3+ for y = 0.0−0.05 under a 293 nm excitation. An intrinsic line emission of Eu3+ in the red range of the spectrum is observed, as discussed above. This Eu3+ emission intensity depends on AlN doping concentration (y) in Sr2.9AlO4-yNyF: 0.1Eu3+ phosphors. The emission intensity of Eu3+ increases with increasing N3- doping content, and reaches a maximum at y = 0.03. The spectra are dominated by an emission at 621 nm attributed

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to the hypersensitive

5

D0-7F2 transition that is strongly influenced by local

environment. When Eu3+ is located at a lower symmetry local site, the 5D0-7F2 transition often dominates the emission spectra. The intensity ratio between the 5

D0-7F2 and 5D0-7F1 transitions can be used to probe the local Eu3+ environment and to

estimate the degree of symmetry distortion. The intensity ratios of I621/I590 = 1.75, 1.76, 1.77, 1.78, and 1.79 for y = 0, 0.02, 0.03, 0.04, and 0.05, respectively, indicating that Eu3+ ions mainly occupy lattice sites without inversion symmetry. Since the replacement of O2- with N3- implies variation in the first coordination layer of the activation sites and steric structure of the host, an increase in N3- doping concentration subtly affects the degree of inversion symmetry distortion by the Eu3+ ion’s local environment, and results in an increase in the I621/I590 intensity ratio. The CIE chromaticity coordinates of Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0, 0.03) under 293 nm excitation are plotted in Fig. 7. The CIE coordinates of Sr2.9AlO4-yNyF: 0.1Eu3+ are slightly shifted from (0.5823, 0.395) to (0.5983, 0.3909) for y = 0 and y = 0.03, respectively. To further evaluate the performance of Sr2.9AlO4-yNyF: 0.1Eu3+ as the red component for white LEDs, the color temperature and color rendering index (Ra) of Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0) were measured to be 1374 K and 65, respectively, and that of Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0.05) were to be 1297 K and 60. Partial substitution of O2− by N3- in Sr2.9AlO4-yNyF: 0.1Eu3+ results a small loss of Ra.

The excitation spectra of the Sr2.9AlO4-yNyF: 0.1Eu3+ phosphors are shown in Fig. 8. The variation in the excitation intensity is similar to that of the emission

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spectra, and the maximum intensity occurs at y = 0.03. The peak maximum of the charge transfer band (CTB) for O2p → Eu4f is fixed at c.a. 293 nm with increasing N3doping concentration, y. As observed in Fig.1, the Sr(1) site is originally deca-coordinated with eight oxygens and two fluorines, while the Sr(2) site is octa-coordinated by two fluorines and six oxygens. Because the electronegativity of nitrogen is lower than that of oxygen, replacing O2− with N3- changes the first coordination layer of the Sr site and the steric structure. The first coordination layer of the activator is most influential on photoluminescence. The rigid nitride coordination around the rare earth ions has a stronger nephelauxetic effect and crystal field splitting, which affects the luminescent properties.

Fig. 9 shows the temperature dependence of the emission intensity in Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0) and Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0.05) under 293 nm excitation. The PL intensities of both samples decrease with an increase in the temperature from 25 °C to 250 °C, the emission intensity of the y = 0 phosphor decreases to 81% at 150 °C and 64% at 250 °C of the initial value, and that of the y = 0.05 phosphor falls to 83% and 67%, respectively. These results imply that partial substitution of O2− by N3- in Sr2.9AlO4-yNyF: 0.1Eu3+ would enhance the thermal stability against the temperature quenching effect.

Fig. 10 shows the emission intensity of Eu3+ as a function of Eu3+ doping concentration (x) in Sr3-xAlO3.97N0.03F: xEu3+ (x = 0.03, 0.06 0.09, 0.12, 0.15, and

9

0.18) phosphors under 325 nm excitation. The emission intensity of Eu3+ is improved with increasing Eu3+ doping concentration, reaching a maximum at approximately x = 0.15. The emission intensity ratios of I619/I589, I619/I580, and I589/I580 are given in Table 1. The ratios of I619/I580 and I589/I580 increase gradually with increasing Eu3+ doping concentration. Meanwhile, the I619/I589 ratio increases at low values of x up to approximately 1.93, and remains constant at higher Eu3+ concentrations. Since the ionic radii of Sr2+ and Eu3+ are similar, Eu3+ ions substitute for Sr2+ ions in the Sr3AlO4F host, and the above result is evidence that Eu3+ ions mainly occupy the Sr2+ lattice sites without inversion symmetry.

As shown in Fig. 11, the peak maximum of the CTB for O2p → Eu4f is shifted to higher wavelength with increasing x. The CTB maxima are 320, 324, 325, 326 and 327 nm for x = 0.03, 0.06, 0.12, 0.15, and 0.18, respectively. This trend differs from the effect of N3- doping concentration (y) in Sr2.9AlO4-yNyF: 0.1Eu3+ phosphors, where the CTB peak maximum for O2p → Eu4f is fixed at approximately 293 nm with increasing N3- doping concentration.

The PL decay curves for the luminescence of Eu3+ in the Sr2.98AlO3.97N0.03F: 0.02Eu3+ under an excitation of 293 nm are shown in Fig. 12. The decay profiles for 5

D0-7F0 (579 nm) and 5D0-7F2 (619 nm) are comparable, but differ from 5D0-7F1 (589

nm). The decay profiles for 5D0-7F0 (579 nm) and 5D0-7F2 (619 nm) arise from an electrical dipole transition, and the decay of 5D0-7F1 (589 nm) originates from a

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magnetic dipole transition. The decay curves associated with Eu3+ ions can be fit with a single exponential function, I = A exp(-t/τ), where I is the luminescence intensity at time t, A is constant, and τ is the decay time for the exponential components. The lifetime is 1.38 ms for the 5D0-7F2 (619 nm) emission. In the decay curve of the 5

D0-7F1 (589 nm) emission, there is an initial build-up with a time constant of about 10

ns, followed by a single exponential decay with a decay time of 75 ns.

4. Conclusions A family of Sr3-xEuxAlO4-yNyF oxyfluorides were prepared at 1300 °C in air or a nitrogen atmosphere. The XRD patterns of the oxyfluorides were measured and identified to have a tetragonal structure with I4/mcm space group. Partial substitution of O2- with N3- in Sr2.9AlO4-yNyF: 0.1Eu3+ does not significantly shift the diffraction peaks or cell parameters. XPS analysis reveals that nitrogen content increases while oxygen content decreases, indicating the formation of nitrogen-rich compounds as the nitrogen substitutes for oxygen ions. The SEM images display that partial substitution of Sr2+ by Eu3+ and O2− by N3- in Sr3-xAlO4-yNyF: xEu3+ contributes to form quadrangular crystals. It is found that the emission intensity of Eu3+ is improved with increasing AlN doping concentration (y), and the maximum emission intensity occurs at y = 0.03. Because the replacement of O2- with N3- implies variation in the first coordination layer of the activation sites and steric structure of the host, the increasing N3- concentration affects the local environment of the Eu3+ ion, and results in an increase in the I621/I590 intensity ratio. The CTB peak maximum for O2p → Eu4f is

11

shifted to higher wavelengths with increasing Eu3+ concentration (x). The CIE coordinates of Sr2.9AlO4-yNyF: 0.1Eu3+ are slightly shifted from (0.5823, 0.395) to (0.5983, 0.3909) when y increases from 0 to 0.03. Partial substitution of O2− by N3- in Sr2.9AlO4-yNyF: 0.1Eu3+ results a small loss of Ra, but enhances the thermal stability against the temperature quenching effect. The 5D0-7F2 (619 nm) emission shows a single exponential decay with a decay time of 1.38 ms. In summary, after the replacement of Sr2+ by Eu3+ and O2- by N3- ions in the Sr3AlO4F host structure, the emission intensity was enhanced and the charge-transfer band of O2p → Eu4f shifted to higher wavelength. These results demonstrate that Sr3-xAlO4-yNyF: xEu3+ is a promising red-emitting material for application in near-UV LEDs.

■ Author Information *Corresponding Author Tel: +86-771-3908065 E-mail: [email protected]. Postal address: College of Chemistry and Materials Science, Guangxi Teachers Education University, Nanning 530001, China

Notes The authors declare no competing financial interest.

■ Acknowledgments

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This project is supported financially by the National Natural Science Foundation of China (Grant No. 21161004) and the Natural Science Foundation of Guangxi (2011GXNSFA018048).

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Figure captions Fig. 1 A model of the crystal structure of Sr3AlO4F [5]. Fig. 2 (A) XPS spectrum of Sr2.9AlO3.97N0.03F: 0.1Eu3+. (B) Surface atomic percentage of elemental nitrogen and oxygen vs. nitrogen content in Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0.03, 0.04, 0.05, and 0.06). Fig. 3 (A) Powder XRD patterns of Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0−0.05), compared with JCPDS card No. 89-4485. (B) Cell parameters vs. nitrogen content in Sr2.9AlO4-yNyF: 0.1Eu3+. Fig. 4 SEM micrographs of the Sr3-xAlO4-yNyF: xEu3+ samples. (a) x = 0.03, y = 0.05; (b) x = 0.1, y = 0; (c) x = 0.1, y = 0.05; (d) x = 0.12, y = 0.05; (e) x = 0.15, y = 0.05; (f) x = 0.18, y = 0.05. Fig. 5 Excitation (λem = 621 nm) and emission (λex = 293 nm) spectra with schematic energy states of the Eu3+ ion. Fig. 6 Emission spectra of Eu3+ in Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0, 0.02, 0.03, 0.04, and 0.05) (λex = 293 nm). Fig. 7 CIE chromaticity diagram for Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0, 0.03) samples. Fig. 8 Excitation spectra of Eu3+ in Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0, 0.02, 0.03, 0.04, and 0.05) (λem = 621 nm). Fig. 9 Emission intensities of Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0) and Sr2.9AlO4-yNyF: 0.1Eu3+ (y = 0.05) in the temperature range from 25 °C to 250 °C. Fig. 10 Emission intensities of different transitions (619 nm, 589 nm and 580 nm) of Eu3+ vs. Eu3+ doping content in Sr3-xAlO3.97N0.03F: xEu3+ (x = 0.03, 0.06, 0.09, 0.12,

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0.15, and 0.18) (λex = 325 nm). Fig. 11 Excitation spectra of Eu3+ in Sr3-xAlO3.97N0.03F: xEu3+ (x = 0.03, 0.06, 0.12, 0.15, and 0.18) (λem = 619 nm). Fig. 12 Decay lifetimes of the 579 nm, 589 nm, and 619 nm emissions of the Sr2.98AlO3.97N0.03F: 0.02Eu3+ sample under an excitation of 293 nm.

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Fig. 1

18

O1s

Counts ( s )

(A)

Sr3d

Sr3p

F1s

Sr2s Al2p

0

O(A)

N1s

200

400

600

800

1000

1200

1400

Binding energy(eV)

1.3

1.2

O

N% (atomic)

1.1

1.0

(B)

0.9

0.8

N

0.7

0.6 0.030

0.035

0.040

0.045

y value

Fig. 2

19

0.050

0.055

0.060

O% (atomic)

80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60

(A)

y = 0. 0 5

Intensity (a.u.)

y = 0. 0 4 y = 0. 0 3 y = 0. 0 2 y = 0. 0 1 y = 0. 0 0 N o. 8 9 - 4 4 8 5 10

20

30

40

50

2θ (

60

70

°)

12

c

Cell parameter ( Å )

11

10

(B)

9

8

7

a

6

1

2

3

4

y value

Fig. 3

20

5

6

80

Fig. 4

21

5

L 55 D

7

3, 2, 1, 0

F 4, 3, 2, 1, 0

CTS

VB

Eu

3+

2- O CTB

5

5

5

5

4f-4f 200

300

400

7

5

7

D 1- F 1

W avelength (nm)

22

7

D 0- F 1

D 0- F 0

500

Fig. 5

7

D 0- F 2

600

7 D 0- F 3

700

1800 1400

λex = 293 nm

1200 1000 800 600 400 200 0

y=0.00 y=0.02 y=0.03 y=0.04 y=0.05 550

600

650

700

Wavelength ( nm )

Fig. 6

23

Intensity (a.u.)

1600

Fig. 7

24

1800 1400 1200

λem = 621 nm

1000 800 600 400 200 0

y=0.00 y=0.02 y=0.03 y=0.04 y=0.05 240

260

280

300

320

340

360

Wavelength ( nm )

Fig. 8

25

380

Intensity (a.u.)

1600

1.3

y=0 y = 0.05

Intensity (a.u.)

1.2

1.1

1.0

λ ex = 293 nm

0.9

0.8

0

50

100

150

T (℃)

Fig. 9

26

200

250

Intensity of different emissions (a.u.)

900 850

619 nm

800 750 700 650

λex= 325 nm

600 550

589 nm

500 450 400

580 nm

350 0.02

0.04

0.06

0.08

0.10

0.12

Eu3+ contents (x)

Fig. 10

27

0.14

0.16

0.18

0.20

900

x = 0.18 0.15 0.12 0.06 0.03

800

Intensity (a.u.)

700 600

λem=619 nm

500 400 300 200 100 0 200

220

240

260

280

300

320

340

Wavelength ( nm )

Fig. 11

28

360

380

400

420

Intensity (a.u.)

4000

3000

2000

578, 619 nm 1000

589 nm 0

0

2000000

Time ( ns )

Fig. 12

29

4000000

6000000

Table

Table 1 Emission intensity ratios of Eu3+ in Sr3-xAlO3.97N0.03F: xEu3+ 0.03

0.06

0.09

0.12

0.15

0.18

I619/I589

1.82

1.88

1.91

1.93

1.93

1.93

I619/I580

1.84

2.00

2.04

2.10

2.18

2.26

I589/I580

1.01

1.06

1.07

1.09

1.13

1.17

x

30