A novel Ba4Gd3K3(PO4)6F2:Eu2+ blue-white emitting phosphor for near-ultraviolet excited light-emitting diodes

Accepted Manuscript A novel Ba4Gd3K3(PO4)6F2:Eu excited light-emitting diodes

2+

blue-white emitting phosphor for near-ultraviolet

Zhihua Leng, Wei Yang, Weifeng Huang, Liping Li, Dan Zhang, Xiufeng Wu, Guangshe Li PII:

S0022-2313(19)30385-0

DOI:

https://doi.org/10.1016/j.jlumin.2019.05.020

Reference:

LUMIN 16480

To appear in:

Journal of Luminescence

Received Date: 25 February 2019 Revised Date:

28 April 2019

Accepted Date: 10 May 2019

Please cite this article as: Z. Leng, W. Yang, W. Huang, L. Li, D. Zhang, X. Wu, G. Li, A novel 2+ Ba4Gd3K3(PO4)6F2:Eu blue-white emitting phosphor for near-ultraviolet excited light-emitting diodes, Journal of Luminescence (2019), doi: https://doi.org/10.1016/j.jlumin.2019.05.020. 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 proof before it is published in its final 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.

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Graphical Abstract

ACCEPTED MANUSCRIPT Blue-White

Emitting

Phosphor

for

2

Near-Ultraviolet Excited light-emitting diodes

3

Zhihua Leng, Wei Yang, Weifeng Huang, Liping Li *, Dan Zhang, Xiufeng Wu,

4

Guangshe Li *

5

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of

6

Chemistry, Jilin University, Changchun 130026, P. R. China;

7

Abstract

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A

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Novel

Ba4Gd3K3(PO4)6F2:Eu2+

1

Exploring new phosphors with broadband emission could find potential

9

applications in white light emitting diodes (w-LEDs). However, it is still a severe

10

challenging to achieve a broadband emission in single activator doped phosphors.

11

Herein, we reported a novel apatite-type Ba4Gd3K3(PO4)6F2:Eu2+ phosphor with

12

broadband blue-white emission, which almost cover the whole visible light range.

13

Differing from previous reports, we prove that the broadband emission is originated

14

from the accommodation of Eu2+ ions in the M(1), Gd(2) and K(3) sites, respectively.

15

Emission spectrum and luminescence decay curves further confirm the existence of

16

three emission centers in Ba4Gd3K3(PO4)6F2:Eu2+ phosphor. White LED (Ra=81 and

17

CCT=3780K) can be obtained by depositing Ba4Gd3K3(PO4)6F2:Eu2+ and red-emitting

18

CaAlSiN3:Eu2+ phosphors on 395 nm LED chip. Moreover, the as-obtained

19

Ba4Gd3K3(PO4)6F2:Eu2+ phosphor can give an stable color output at high temperature,

20

demonstrating that this novel phosphor could be an potential candidate for

21

next-generation near ultraviolet excited white LEDs.

22

Key words: Phosphors, Broadband emission, Crystal field splitting, Thermal stability,

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ACCEPTED MANUSCRIPT 1

White LED

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1. Introduction In the past decades, under the background of global energy saving and

4

environmental protection, the technology and industry of w-LEDs develop rapidly

5

due to their superior merits of high efficiency, long lifetime, low energy consumption,

6

and eco-friendliness [1-4]. The current commercial w-LEDs are mainly fabricated by

7

integrating InGaN blue LED chip and yellow Y3Al5O12:Ce3+ (YAG:Ce) phosphor.

8

However, due to the absence of red-emitting component, their unsatisfactory

9

performances, such as low color rendering index (Ra) and high correlated color

10

temperature (CCT), should be further improved and perfected [5-8]. As a alternative

11

strategy,

12

aforementioned deficiency because n-UV chips can excite more versatile phosphors.

13

Therefore, n-UV excited blue, green, red and white-emitting phosphors, especially for

14

broadband-emitting ones, have been a hot topics for worldwide researchers [9-12]. It

15

is urgent to explore novel n-UV excited phosphors with broadband emission for solid

16

state lighting.

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(n-UV) pumped

LEDs

can

effectively overcome

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near-ultraviolet

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Eu2+ doped multiple cation lattice hosts could be ideal candidates for

18

broadband-emitting phosphors, because the multiple luminescence centers originated

19

from the distribution of environment-sensitive Eu2+ activator in different cation sites

20

can output versatile colors [13-16]. Recently, apatite type M10(PO4)6X2 (M=alkaline

21

metal, alkaline earth metal, or rare earth ions; X=F, Cl or Br) host materials have

22

attracted more and more attention [17-19]. They can offer multiple cation sites for the

2

ACCEPTED MANUSCRIPT accommodation of rare earths ions, especially for Eu2+ ions. As derivative structures

2

of Ba10(PO4)6F2, apatite-like Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2 were firstly

3

synthesized by step-wise replacement of Ba ions [20]. Many isostructural phosphors

4

with these apatite-like structures have been reported by rare earth/alkaline metal

5

substitution,

6

Ba4Gd3Na3(PO4)6F2:Eu2+ [21-23]. There is no consensus conclusion whether the

7

bivalent Eu2+ ions can entry into the trivalent/univalent cationic site or not. In

8

Ba6Gd2Na2(PO4)6F2:Eu2+ phosphor, Guo et al. deduce that Eu2+ ions only distribute in

9

three different Ba sites rather than Gd or Na sites [21]. On the other hand, You et al.

10

speculate that Eu2+ ions occupy Ba2+ and Gd3+ sites in Ba4Gd3Na3(PO4)6F2:Eu2+

11

phosphor [23]. However, other researchers claim that Eu2+ ions can entry into alkaline

12

metal sites (Na or K) [24-25]. Fundamentally investigate is extremely essential to

13

reveal the distribution of Eu2+ activators in these apatite type luminescence materials.

as

Ba6Gd2Na2(PO4)6F2:Eu2+,

Ba6La2K2(PO4)6F2:Tb3+,

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Inspired by alkaline metal substitution, a novel Ba4Gd3K3(PO4)6F2:Eu2+

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phosphor with blue-white emitting was successfully synthesized by solid-state

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reaction method for the first time. The site-dependent luminescence property,

17

concentration quenching mechanism, thermal stability as well as LED performances

18

were investigated in detail. Differing from previous reports, we prove that Eu2+ ions

19

can distribute in Ba, Gd and K sites, resulting in a broadband blue-white emitting.

20

Excitingly, the blue-white emission almost cover the whole visible light range. A

21

white LED can be successfully fabricated by depositing Ba4Gd3K3(PO4)6F2:Eu2+ and

22

red-emitting CaAlSiN3:Eu2+ phosphors on 395 nm LED chip. These results

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ACCEPTED MANUSCRIPT demonstrate that the as-synthesized Ba4Gd3K3(PO4)6F2:Eu2+ phosphor could be an

2

potential candidate for next-generation n-UV excited white LEDs.

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2. Experimental

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2.1. Synthesis

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A series of Ba4Gd3K3(PO4)6F2:xEu2+ (hereinafter abbreviated as BGKPOF:xEu2+) phosphors were synthesized via the solid-state reaction method. High purity BaCO3

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(99.99%), BaF2 (99.99%), Gd2O3 (99.99%), KHCO3 (99.99%), NH4H2PO4 (99.99%),

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and Eu2O3 (99.99%) were used as the raw materials. The stoichiometric amount of

9

raw materials with excessive 5 mol% BaF2 (to compensate the loss of fluorine at high

10

temperature) was weighted and thoroughly mixed by grinding in an agate mortar.

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Then the well-mixed powder mixtures were pressed into cylindrical disks and

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presintered at 500 oC for 2 h in air. After being reground thoroughly, the powder

13

mixtures were pressed into cylindrical disks with 20 mm diameter and approximately

14

1 mm height, and annealed again at 1040 oC for 3 h in tube furnace under a 10%

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H2-90% Ar reducing atmosphere. Finally, the naturally cooled samples were reground

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thoroughly for subsequent measurement.

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2.2. Characterization

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X-ray diffraction (XRD) patterns were recorded in a step-scanning mode with a

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scanning speed of 2 seconds counting time per step and step width of 0.02 degree on a

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Rigaku Mini-Flex 600 X-ray diffractometer with graphite-monochromatic Cu Kα

21

radiation

22

high-resolution transmission electron microscopy (HRTEM) images were recorded on

(λ=0.15418

nm).

Transmission

4

electron

microscopy

(TEM)

and

ACCEPTED MANUSCRIPT Tecnai G2 electron microscope. The room-temperature photoluminescent excitation

2

(PLE) and emission (PL) were recorded on an Edinburgh Instruments FLS920

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spectrofluorimeter equipped with a R928 photomultiplier tube as the detector and a

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450W xenon lamp as the excitation source. The decay time curves were measured on

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the same spectrophotometer and detectors equipped with a 100 W pulsed hydrogen

6

lamp nF900 as the excitation source. The phosphor-converted LED (pc-LED) was

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fabricated by depositing the as-obtained BGKPOF:0.06Eu2+ and red-emitting

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CaAlSiN3:Eu2+ phosphors on 395 nm LED chip.

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3. Results and discussion

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The XRD patterns of BGKPOF:xEu2+ (0.02≤x≤0.12) samples are given in Fig.

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S1. All diffraction peaks can be indexed to fluorapatite type structure with parameters

12

close to Ba4Nd3Na3(PO4)6F2 (JCPDS 71-1318), except few weak peaks from small

13

amount of unknown impurity. Previous reports have confirmed that the small amount

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of impurities have little influence on the PLE and PL properties of target phosphors

15

[26, 27]. To investigate the crystal structure of the as-synthesized sample, the XRD

16

Rietveld refinement of BGKPOF:0.06Eu2+ sample is performed by the GSAS

17

program with the fluorapatite type Ba4Nd3Na3(PO4)6F2 crystallographic data as the

18

initial model. Under the supposition that the Nd and Na ions are substituted by Gd and

19

K ions, the refinement results demonstrate that the crystal structure of

20

BGKPOF:0.06Eu2+ sample can agree well with that of fluorapatite type

21

Ba4Nd3Na3(PO4)6F2 (Fig. 1a, Table S1 and S2). Namely, the as-synthesized

22

BGKPOF:0.06Eu2+ sample is isostructural with the apatite-type Ba4Nd3Na3(PO4)6F2

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ACCEPTED MANUSCRIPT and Ba4Gd3Na3(PO4)6F2 compounds. Fig. 1b shows the unit cell structure of

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BGKPOF host together with the coordination environments of the cationic sites. As

3

reported in previous research, there are three independent crystallographic cation sites

4

in this structure (Fig. 1c), which are named as M(1), Gd(2) and K(3) sites,

5

respectively. The M(1) site contains a mixture of 2/3Ba, 1/6Gd and 1/6K, which is

6

coordinated by seven oxygen and two fluoride atoms [23]. The Gd(2) and K(3) sites

7

are coordinated by nine and six oxygen atoms, respectively. Because the ion radius of

8

K+ is larger than that of Na+ ( rK + =1.55 Å and rNa + =1.24 Å for CN=9, rK + =1.32 Å

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and rNa + =1.02 Å for CN=6, where CN stands for coordination number), the lattice

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expansion should take place when larger K+ is substituted for smaller Na+.

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Fig. 1 (a) XRD refinement result of the BGKPOF:0.06Eu2+ sample, (b) crystal

2

structure diagram of the BGKPOF host, and (c) three kinds of cation sites with

3

different coordination environment. To characterize the micro-structure of BGKPOF:0.06Eu2+ phosphor, TEM,

5

HRTEM and EDS mapping were carried out. Fig. 2a shows the TEM image obtained

6

from the selected BGKPOF:0.06Eu2+ sample. The continuous lattice fringes

7

demonstrate the high crystallization of BGKPOF:Eu2+ phosphor (Fig. 2b). The

8

interplanar spacing of 0.410 nm agree well with the corresponding (11-1) planes of

9

fluorapatite type Ba4Nd3Na3(PO4)6F2. In addition, the elemental mapping images (Fig.

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2c) indicate that Ba, Gd, K, P, O, F and Eu are homogeneously dispersed in the

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phosphor particles.

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Fig. 2 (a) TEM image, (b) corresponding HRTEM image and (c) EDS elemental

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mapping of the BGKPOF:0.06Eu2+ phosphor.

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Fig. 3 (a) Excitation and (b) emission spectra of the BGKPOF:0.06Eu2+ sample (inset

3

shows the corresponding photograph under 365 nm UV lamp), (c) intensities of Eu2+

4

as a function of Eu2+ doping concentration, and (d) linear fitting of log(x) versus

5

log(I/x) in the BGKPOF:Eu2+ samples.

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Fig. 3a and b display the PLE and PL spectra of the BGKPOF:0.06Eu2+ phosphor.

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The PLE spectrum monitored at 480 nm shows a broad band ranging from 240 to 440

8

nm, which can be attributed to the 4f7→4f65d1 transition of Eu2+ activator. The

9

emission spectrum shows a asymmetric broad band ranging from 400 to 750 nm,

10

which contains two strong emission peaks (centered at 447 and 480 nm) with a weak

11

trailing band around 580 nm. The asymmetric broad emission band can be fitted into

12

three Gaussian contributions (Fig. S2). Considering that there are three kinds of cation

13

sites in BGKPOF host, the observed two emission peaks and one trailing band may be

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ACCEPTED MANUSCRIPT attributed to the distribution of Eu2+ ions in the M(1), Gd(2) and K(3) sites,

2

respectively. To further certify the existence of ternary luminescence centers, the

3

luminescence lifetimes were measured monitored at 447, 480 and 580 nm,

4

respectively (Fig. 4). In view of the existence of ternary luminescence centers in the

5

BGKPOF:0.06Eu2+ phosphor, the average decay time (τav) can be calculated by the

6

following formula [28]:

7

∫ tI(t)dt τ av = 0∞ ∫0 I(t)dt

8

where t is the time ,and I(t) is the luminescent intensity at time t. The average decay

9

times monitored at 447, 480 and 580 nm are calculated to be about 444.8, 501.7 and

10

969.2 ns, respectively. The significant distinction in decay behavior for emissions at

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447, 480 and 580 nm confirms that there are three different luminescence centers in

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the BGKPF:0.06Eu2+ phosphor.

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Fig. 4 Decay curves of Eu2+ in the BGKPOF:0.06Eu2+ phosphor monitored at 447,

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480 and 580 nm, respectively. To correlate the local environment and emission position, the relationship

3

between the three luminescence centers and the actual cation sites occupied by Eu2+

4

ions can be explain by equation (2) reported by Van Uiterts [29]:

5

1  n× Ea ×r  − V V    E = Q 1 −   10 80   4   

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Where E (cm-1) is the emission position for Eu2+ ion, Q represents the energy position

7

for the lower d-band edge of the free Eu2+ ion (the Q value is 34000 cm-1 for Eu2+), V

8

refers to the valence of Eu2+ ion (V=2), n (coordination number) stands for the

9

number of anions in the immediate shell around Eu2+ ions, Ea is the electron affinity

10

of anion atoms (it is a constant for the identical host), and r is the radius of the host

11

cation substituted by Eu2+ ion. In other word, the emission position (E) is proportional

12

to the factor n × r . In BGKPOF:0.06Eu2+ sample, the coordination numbers of M(1),

13

Gd(2) and K(3) sites are 9, 9 and 6, respectively. The radius of M(1), Gd(2) and K(3)

14

cations are 1.42, 1.11 and 1.38 Å. For the M(1) site, the average cation radius

15

rav=2/3* rBa 2+ +1/6* rGd 3+ +1/6* rK + =1.42 Å ( rBa 2+ =1.47 Å for CN=9, rGd 3+ =1.11 Å for

16

CN=9, rK + =1.55 Å for CN=9). According to Equ. (2), the emission position for Eu(1),

17

Eu(2) and Eu(3) decreases in the sequence of E(Eu1)>E(Eu2)>E(Eu3). Hereinafter,

18

Eu(1), Eu(2) and Eu(3) stand for Eu2+ occupied at M(1), Gd(2) and K(3) sites,

19

respectively. Thus, we conclude that the emission peak at 447 and 480 nm and trailing

20

band around 580 nm are belong to the distribution of Eu2+ ions in the M(1), Gd(2) and

21

K(3) sites, respectively (Fig. 3b).

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ACCEPTED MANUSCRIPT It is quite remarkable that the trailing emission around 580 nm possesses such a

2

broad band. The full width at half-maximum (FWHM) of Eu2+ ions is closely

3

associated with the crystal field splitting, which is strongly dependent on anion

4

coordination polyhedron around Eu2+. The crystal field splitting εcfs (A) could be

5

evaluated as following [30, 31]:

6

εcfs (A) = β ployR −2 = β ploy  R av − ∆R 

7

Where R is the average distance between center metal Eu2+ ion and its ligand anions,

8

Rav is the average bond length from center metal Eu2+ ion to its ligand anions, and

9

∆R is the difference in ionic radius between Eu2+ and the cation substituted by it

10

( ∆R expresses a approximate correction for lattice relaxation around Eu2+ ion).

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β ploy is a constant dependent on the shape of coordination polyhedron. The

12

M(1)O7F2, Gd(2)O9 and K(3)O6 polyhedrons are close to tricapped trigonal prism

13

(3ctp), tricapped trigonal prism (3ctp) and octahedral (octa), respectively. According

14

to Dorenbos’ reports, the β ploy values for tricapped trigonal prism and octahedron

15

are in the ratio 0.42:1, i.e. β 3ctp =0.42 β octa [30, 31]. In addition, ∆R =0.12, 0.19

16

and 0.21 Å ( rEu 2+ =1.30 Å for CN=9, rEu 2+ =1.17 Å for CN=6) for M(1), Gd(2) and

17

K(3) sites, respectively (Table S4). In BGKPOF:0.06Eu2+ phosphor, the β ploy and

18

  R av 

19

β3ctp (M1) = β3ctp (Gd2) < β octa (K3) and (R M1 )−2 < (R Gd2 )−2 < (R K3 )−2 , respectively

20

(Table S4). That is to say, εcfs (Eu1) < εcfs (Eu2) < εcfs (Eu3) . The strongest crystal field

21

splitting of Eu(3) for the 4f65d1 level gives rise to multiple 4f65d1 excited states,

22

resulting in the broad emission band. The broad trailing emission originated from the

−2

(3)

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1 2

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are

arranged

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in

the

sequence

of

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accommodation of Eu2+ activator in the K(3) site is attributed to the overlap of

2

multiple 4f65d1→4f7 transitions. To get the optimal doping concentration of Eu2+ ions, a series of BGKPOF:xEu2+

4

(x=0−0.12) phosphors have been prepared. As displayed in Fig. S3, the emission

5

spectral profiles show no remarkable changes with increasing the Eu2+ doping

6

concentration. Fig. 3c displays the emission intensity as a function of Eu2+ doping

7

concentration (x). The PL intensity increases monotonously and reaches the maximum

8

at x=0.06. When x>0.06, the decrease of emission intensity can be attributed to the

9

concentration quenching of Eu2+ activator. When the distances among the identical

10

Eu2+ ions are less than the critical distance (Rc), the nonradiative energy migration

11

among Eu2+ ions takes place more easily, resulting in the concentration quenching

12

effect. Blasse proposed that the Rc can be estimated by the following equation [32,

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33]:

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Where V is the volume of the unit cell, x is the critical concentration, and N is the

16

number of certain cations in one unit cell for the accommodation of Eu2+ activator. In

17

the case of BGKPOF host, x=0.06 and N=10. The V value (V=622.77) of the unit cell

18

is obtained from the XRD Rietveld refinement result of BGKPOF:0.06Eu2+ sample

19

(Table S1). The Rc is calculated to be 12.6 Å.

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Nonradiative energy migration can be generally attributed to exchange

21

interaction or electric multipolar interaction. For exchange interaction, it is usually

22

predominant when the distance between the two nearest Eu2+ ions is smaller than 5 Å. 12

ACCEPTED MANUSCRIPT In this case, the calculated R are 18.1, 14.4, 12.6, 11.4, 10.6 and 10.0 Å for x=0.02,

2

0.04, 0.06, 0.08, 0.10 and 0.12, respectively. Thus, the exchange interaction can be

3

excluded because all these distances are larger than the distance (5 Å) required for the

4

exchange interaction mechanism. According to Dexter’s model, the mechanism of

5

nonradiative energy migration can be determined by the following equation [34]:

6

[

I = k 1 + β ( x)θ/ 3 x

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−1

(5)

Where I is the emission intensity, x is the doping concentration of Eu2+ ions, k and β

8

are constants for a certain host lattice and identical excitation condition, respectively.

9

θ=3, 6, 8 or 10 correspond to exchange, dipole−dipole, dipole−quadrupole or

10

quadrupole−quadrupole interactions, respectively. Fig. 3d presents the fitting line of

11

log(I/x) versus log(x) beyond the quenching concentration of Eu2+. The slope (-θ/3) of

12

this fitting line are -2.117. Namely, the value of θ are 6.351 and approximately equal

13

to 6, indicating that the concentration quenching mechanism of Eu2+ ions in the

14

BGKPOF host is electric dipole−dipole interaction.

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Fig. 5 (a) Temperature dependence of emission spectra of the BGKPOF:0.06Eu2+

3

sample,

4

temperature-dependent emission intensity of the BGKPOF:0.06Eu2+ sample in the

5

wavelength range of 400-750 nm, and (d) the plot of ln[(I0/IT)−1] varied as a

6

temperature function.

temperature

dependence

of

the

emission

intensity,

(c)

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Thermal stability is a vital technological parameter for phosphors applied in solid

8

state lighting, especially in high-power LEDs, because its working temperature can

9

usually arrive as high as 150 oC. High temperature seriously affect the performance of

10

LEDs, particularly for the light output, chromaticity, and color rendering index. To

11

evaluate the thermal quenching property of the as-obtained BGKPOF:0.06Eu2+

12

phosphor, temperature dependence of emission spectra heating from 298 to 478 K are

13

measured and displayed in Fig. 5a. The emission intensity of BGKPOF:0.06Eu2+

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ACCEPTED MANUSCRIPT phosphor gradually decreases with increasing temperature (Fig. 5b and c), which may

2

attributed to the thermal ionization of 5d electrons into the host conduction band and

3

the trapping of electrons at defect levels (Fig. 6) [35-37]. More importantly, as

4

displayed in Fig. 5a and c, there are no remarkable changes for their emission spectral

5

profiles and no obvious shift for their emission peaks. According to the classical

6

Arrhenius equation, the activation energy of thermal quenching process can be

7

calculated by following formula [35]:

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I T=

9

Where IT and I0 are the emission intensity at temperature T and 298 K, respectively; A

10

is a constant; Ea is the activation energy; k is the Boltzmann constant. The slope of

11

the fitting line is equal to −0.282 (Fig. 5d). Namely, the activation energy of thermal

12

quenching process is calculated to be 0.282 eV. These results demonstrate that the

13

as-obtained BGKPOF:0.06Eu2+ phosphor can give an stable color output at high

14

temperature.

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Fig. 6 A simplified schematic illustration of thermal quenching mechanism induced

15

ACCEPTED MANUSCRIPT 1

by thermal ionization. The broad absorption in near-ultraviolet region demonstrate that the as-obtained

3

BGKPOF:0.06Eu2+ phosphor could be efficiently excited by n-UV LED chip. In

4

addition, the broad emission of the as-obtained BGKPOF:0.06Eu2+ phosphor can

5

provide versatile color components for LEDs. To shed light on the potential

6

application of BGKPOF:0.06Eu2+ phosphor in solid state lighting, a white LED is

7

fabricated by depositing BGKPOF:0.06Eu2+ and commercial red CaAlSiN3:Eu2+

8

phosphors on 395 nm LED chip. The commercial red CaAlSiN3:Eu2+ phosphor is

9

added to remedy the insufficient red emission of BGKPOF:0.06Eu2+ phosphor. The

10

electroluminescence spectrum, photograph, and typical optical parameters of the

11

as-fabricated LED is displayed in Fig. 7. As expected, an warm white output can be

12

realized for the as-fabricated LED. The CIE color coordinates, CCT and CRI of

13

as-fabricated white LED are found to be (0.386, 0.369), 3780 K and 81, respectively.

14

The relatively high CRI and appropriate CCT values indicate that the as-obtained

15

BGKPOF:0.06Eu2+ phosphor may find potential applications in n-UV excited white

16

LEDs.

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ACCEPTED MANUSCRIPT 1

Fig. 7 (a) Electroluminescent spectrum and corresponding photograph and (b) CIE

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chromaticity coordinates of the as-fabricated LED.

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4. Conclusions In summary, a novel broadband BGKPOF:0.06Eu2+ phosphor with blue-white

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emitting were synthesized via the solid-state reaction method. The optimal Eu2+

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doping concentration in BGKPOF host is proved to be 0.06. The concentration

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quenching mechanism of Eu2+ ions in the BGKPOF host is confirmed to be electric

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dipole−dipole interaction. The two emission peaks centered at 447, 480 nm and the

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weak trailing band around 580 nm are attributed to the distribution of Eu2+ ions in

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M(1), Gd(2) and K(3) sites, respectively. The as-obtained BGKPOF:0.06Eu2+

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phosphor can remain an stable color output at high temperature. More importantly,

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white LED can be fabricated by depositing BGKPOF:0.06Eu2+ and red

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CaAlSiN3:Eu2+ phosphors on 395 nm LED chip. The high CRI (81) and appropriate

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CCT (3780 K) values indicate that the as-obtained BGKPOF:0.06Eu2+ phosphor may

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find potential applications in n-UV excited white LEDs.

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ACKNOWLEDGMENTS

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This work was financially supported by NSFC (Grants 21671077, 21771171,

21571176, 21611530688, and 21025104).

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