Effect of Eu³⁺ion Doping Concentration to Luminescent Properties of Ca₂Al₂SiO₇ Phosphor

Effect of Eu³⁺ion Doping Concentration to Luminescent Properties of Ca₂Al₂SiO₇ Phosphor

Nguyen Manh Son

Department of Physics,

University of Sciences, Hue University, Vietnam

Do Thanh Tien

Le Van Thanh Son

University of Science and Education University of Danang, Vietnam

Faculty of Basic Science, University of Agriculture and Forestry Department of Physics, University of Sciences

Hue University, Vietnam

Abstract–Eu3+ ion doped Ca2Al2SiO7 phosphors were synthesized by solid state reaction method that were sintered at 12800C for 1 hour. X-ray diffraction diagram showed the materials have single-phased tetragonal structure. The

photoluminescent spectra of Ca2Al2SiO7: Eu3+ have narrow lines, correspond to the transition of Eu3+ ions. Dipole-dipole

(d-d) interaction plays a main role in concentration quenching of the material. The luminescent characteristics of the material will be presented and discussed.

Keywords–Ca2Al2SiO7: Eu3+; photoluminescence; concentration quenching

1. INTRODUCTIONMany red fluorescence materials were synthesised from Eu3+ doped the different lattices as Y2O3, earth alkaline aluminate, earth alkaline silicate, borate,… which can use to produce the fluorescence lamp because these materials could absorb 254 nm radiation of mercury.

   In recent years, white LED stimulated by near-UV radiation combined with red and green luminescent materials have attracted interest from many scientists. Materials could emit visible light with high efficiency under the stimulation of near UV radiation have been used to produce white LED. Earth alkaline alumino silicate materials have attracted a lot of attention from many scientists and became an interesting research orientation because its high chemical stability and better water-resistance than other materials synthesized on sulphide and aluminates lattice [1-3]. Earth alkaline alumino silicate phosphors doped with different rare earth ions (Eu3+, Dy3+, Tb3+, Ce3+,…) could emit different emission in the visible. Inside, there are very many researches that introduced on the luminescence of this lattice doped Eu3+ ion [4-6] .

   This paper presents results studied on the luminescent characteristics of the Eu3+ ion doped Ca2Al2SiO7 red luminescent material that synthesized by solid state reaction method. Influence of Eu3+ doping concentration and mechanism of concentration quenching was discussed too.

2. EXPERIMENTThe Eu3+ ion doped Ca2Al2SiO7 (CAS) phosphors are synthesized by the solid state reaction. The starting materials include CaCO3, Al2O3, SiO2 and Eu2O3 are weighted according to molar ratio and mixed with 4%wt of

   B2O3 as fluxing agent. The mixtures is grinded in an agate mortar for 1 hour, later is annealed at 1280oC for 1 hour. CAS samples doped with Eu3+ion that concentration can change from 0.25 to 3.0 %mol. The crystalline structure has been characterized by X-ray diffraction method by Brucker D8-Advandce diffractometer. Photoluminescence of the material has been taken by FL3-22 fluorescence spectrometer Horiba Jobin Yvon, USA with XFOR 450W Xenon lamp.

3. RESULTS AND DISCUSSION
   1. Crystalline structure of Eu3+ doped Ca2Al2SiO7 phosphorsThe X-ray diffraction diagram of samples CAS: Eu3+ (x

      %mol) with x = 0.25; 0.5; 1.0; 1.5; 2.0; 3.0 are shown in Fig.

      1. All results of XRD diagrams show that the materials have Ca2Al2SiO7 single-phased structure with pure tetragonal phase.

      x = 3.0

      Intensity (a. u.)

      Intensity (a. u.)

       

      x = 2.0

      x = 1.5

      x = 1.0

      x = 0.5

      x = 0.25

      Ca2Al2SiO7 (JCPDS: 35-0755)

      20 30 40 50 60 70 80

      2/Degree

      Fig 1. The XRD diagram of CAS: Eu3+ (x %mol) phosphors

   2. Spectroscopic properties of CAS phosphors doped with different Eu3+ ion concentrationFigure 2 show PL spectra of CAS: Eu3+ (x %mol) materials with x = 0.25; 0.5; 1.0; 1.5; 2.0; 3.0 excited by UV radiation at = 393 nm. The Spectra have narrow lines of Eu3+ ions. The spectra consist narrow lines, correspond to the transitions of Eu3+ ion, from 5D0 excited state to 7FJ (J = 0, 1, 2, 3, 4) ground states. The emission at = 586 nm

      corresponds to magnetic dipole transition 5D0 7F1. The emission at = 617 nm correspond to electric dipole transition 5D0 7F2 which depends on the symmetry of the

      (1) x=0.25 (2) x=0.5

      (3) x=1.0

      (4) x=1.5

      (5) x=2.0

      (6) x=3.0

      (1) x=0.25 (2) x=0.5

      (3) x=1.0

      (4) x=1.5

      (5) x=2.0

      (6) x=3.0

       

      (3)

      (4)

      (5)

      (6)

      (2)

      (1)

      (3)

      (4)

      (5)

      (6)

      (2)

      (1)

       

      1.0×106

      PL Intensity (a. u.)

      PL Intensity (a. u.)

       

      8.0×105

      6.0×105

      4.0×105

      2.0×105

      The shape and the peak position of both PL and PLE spectra remain unchanged as the concentration of Eu3+ dopant ion change. The emission intensity increases as the concentration of Eu3+ in the host lattice increase and reaches

      617 nm

      617 nm

       

      1.0×106

      PL Intensity (a. u.)

      PL Intensity (a. u.)

       

      8.0×105

      6.0×105

      4.0×105

      2.0×105

      0.0

      0.0

      560 580 600 620 640 660 680 700 720

      Wavelength (nm)

      Fig 2. PL spectra of CAS: Eu3+ (x %mol), ex=393 nm

      (1) x=0.25

      (2) x=0.5

      (3) x=1.0

      (4) x=1.5

      (5) x=2.0

      (6) x=3.0

      (1) x=0.25

      (2) x=0.5

      (3) x=1.0

      (4) x=1.5

      (5) x=2.0

      (6) x=3.0

       

      1.0×108

      (3)

      (3)

       

      PL Intensity (a. u.)

      PL Intensity (a. u.)

       

      8.0×107

      (5)

      (4)

      (6)

      (2)

      (1)

      (5)

      (4)

      (6)

      (2)

      (1)

       

      6.0×107

      4.0×107

      2.0×107

      0.0

      0.0 0.5 1.0 1.5 2.0 2.5 3.0

      Concentration ion Eu3+(mol%)

      Fig 4. The dependence of maximum emission intensity vs the concentration of Eu3+ ions

      the maximum value with concentration of Eu3+ ion at 1.0

      %mol. Later, the maximum emission intensity decreases due to concentration quenching effect. The relation between the maximum emission intensity and the Eu3+ concentration is shown in Figure 4.

   3. Mechanism of concentration quenching

   The mechanism of concentration quenching in CAS: Eu3+ material occurs when the concentration of Eu3+ ions over 1.0

   %mol (as show in Figure 4). According to the theory of concentration quenching by Dexter and Blasse, the critical radius (RC) of the energy transfer is given by [3, 7]:

   260 280 300 320 340 360 380 400 420 440 460 480

   Wavelength (nm)

   R 2 3V

   1/ 3

   Fig 3. PLE spectra of CAS: Eu3+ (x %mol), = 617 nm

   c 4x N

   (1)

   em c

   crystalline field. Other peaks at = 578 nm, 656 nm and 702 nm are relatively weak, corresponding to the transitions 5D0 7F0, 5D0 7F3 and 5D0 7F4 [2], [4], [6-7]. Broad band

   emission of Eu2+ ion was not observed in the PL spectra of

   CAS: Eu3+.

   Figure 3 show PLE spectra of CAS: Eu3+(x %mol) at emission wavelength = 617 nm. The spectra have a wide band in the UV region and narrow lines in the range from 310 nm to 550 nm. The PLE spectrum consists of 2 main parts: (1) – A wide band with strongest intensity at = 260 nm characteristics for charge transfer (CTB) due to Eu3+- O2- interaction, (2) – narrow lines in the range from 310 nm to 550 nm, which are assigned to the f-f transition of Eu3+ ions.

   Where, xc is the critical concentration i.e. the dopant concentration beyond which the luminescent intensitybegins to decrease. For CAS material, V is the unit cell volume is determined from XRD pattern, V = 299.4Ã…3, N is the number of cation ion in the unit cell, N = 2 [3] and xc = 0.01. Substituting these values to the formula (1), RC is determined about 30.6Ã…. Therefore, multipolar interaction is accounted for the concentration quenching of the CAS: Eu3+ material. At that time, the relation between luminescent intensity and concentration of activation center is given by the formula [8]:

   I = K

   The line at = 393 nm which has the high intensity is assigned to the 7F0 5L6 transition of Eu3+. Other weaker

   x 1+ (x)Q/3

   (2)

   peaks at = 360 nm, 374 nm, 380 nm, 412 nm and 463 nm,

   523 nm, 530 nm are assumed to be the 4f – 4f interconfigurational transitions of Eu3+ ion in the lattice that

   could be assign to 7F 5D , 7F 5G , 7F 5L ,

   Where, I is the luminescent intensity of CAS: Eu3+, K

   and are the constants in the same stimulation condition, while x is the concentration of activation center. The parameter Q = 6, 8, 10 corresponds to dipole-dipole (d-d),

   7 5

   7 5

   0 4

   7 5

   0 2 1

   7 5

   7 dipole-quadrupole (d-q), quadrupole-quadrupole (q-q)

   F0 D3, F0

   D2, F0

   D1, F1

   D1 transitions,

   interactions. The Q value can be determined from the graph:

   respectively [4, 6].

    

   log I

   x

   = c –

   Q logx 3

   (3)

   of Eu3+ ion at 1.0 %mol. The concentration quenching of the phosphor results by dipole-dipole interaction.

   ACKNOWLEDGMENT

   The log(I/x) vs logx graph of CAS: Eu3+with different concentration of Eu3+ ion is shown in Figure 5. The graphs slope is -2.0015. From this result, we found that Q = 6.0045,

   This research is supported by Funds for Science and Technology Development of the University of Danang under project number B2017-N03-17.

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   6.0×100

   5.8×100

   y = 6.0356 – 2.0015x R2=0.97

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4. CONCLUSION

The CAS: Eu3+ phosphors with the tetragonal phase structure have been successfully synthesized by the solid- state reaction. The PL spectra of CAS: Eu3+ have narrow lines correspond to the electronic transition of Eu3+ ions. The emission of phosphor locates at the red region of visible spectrum with high luminance. The photoluminescent intensity varies according to concentration of Eu3+ ion and reaches maximum emission intensity with the concentration

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