Spectroscopic Characteristics of Ca₂Al₂Sio₇: RE³⁺ Phosphors

Spectroscopic Characteristics of Ca₂Al₂Sio₇: RE³⁺ Phosphors

Nguyen Manh Son Department of Physics, University of Sciences, Hue University

Hue City, Vietnam

Do Thanh Tien

Faculty of Basic Science, University of Agriculture and Forestry

Department of Physics, University of Sciences Hue University, Hue City, Vietnam

Duong Tan Tien

Son My High School

Tinh Khe District, Quang Ngai Province, Vietnam

Pham Ngoc Luyen

Nguyen Cong Tru High School

Mo Duc District, Quang Ngai Province, Vietnam

Nguyen Van Tam

Tra Bong High School

Tra Bong District, Quang Ngai Province, Vietnam

Nguyen Van Hung

Huynh Thuc Khang High School, Quang Ngai City,

Vietnam

Le Trung Cang

Vo Nguyen Giap High School Quang Ngai City, Vietnam

Abstract– Different rare-earth ion single doped Ca2Al2SiO7 materials have been successfully synthesized by solid state reaction method. The emission of Ce3+ ion doped Ca2Al2SiO7 phosphor is a broad band, while these of Dy3+, Tb3+, Sm3+ or Eu3+ ion single doped materials are the narrow lines that characterised by transitions in the 4f electron configuration. The maximum emission intensity of each rare earth ion depends on the excitation radiation wavelength. Spectroscopic properties of Ca2Al2SiO7 phosphors doped with rare earth ion (Ce3+, Dy3+, Tb3+, Sm3+ or Eu3+) have been presented and discussed.

Keywords– Ca2Al2SiO7, RE3+, luminescence

1. INTRODUCTION

   Earth alkaline alumino silicate luminescent materials (M2Al2SiO7 with M = Ca, Sr) doped with rare earth ions have been interested because their high luminescent efficiency and its spectral characteristic suitable for many applications, especially in lighting technology and display [1-4]. Researches on the luminescent characteristic of luminescent materials base on (Ca, Sr)2Al2SiO7 lattice shows that the materials have many advantages such low cost, thermal stability and chemical stability, especially their high absorbance to near UV radiation which make it is suitable for a wide range of application. Therefore, researches on luminescent characteristic of materials base on CaAl2SiO7 lattice attract lots of attention and have great significance in basic and applied research. A few recent years, there are

   many investigations on the Ca2Al2SiO7 single doped/codoped with rare earth ion that could use for fabricating laser, wLED as explaining mechanism of the photoluminescence and thermoluminescence [5- 8]. This paper presents systematic research results on the luminescent characteristics of RE3+ ion doped Ca2Al2SiO7 (CAS) phosphors with RE3+: Ce3+, Sm3+, Dy3+, Eu3+, Tb3+ that were synthesized by solid state reaction method. Effects of the excitation radiation to the emission intensity of phosphors also were considered.

2. EXPERIMENT

   RE3+ (Ce3+, Sm3+, Dy3+, Eu3+, Tb3+) ion single doped Ca2Al2SiO7 materials have been synthesized by solid state reaction method. Initial materials used include CaCO3, Al2O3, SiO2 and CeO2, Dy2O3, Eu2O3, Sm2O3, Tb4O7 are weighted according to molar ratio, the concentration of RE3+ ion was constantly choose at 0.5 %mol. Then, the reagent mixture was grinded in an agate mortar for 2 hours, later was annealed at temperature 1280oC for 1 hour. The X-ray diffraction diagrams were taken by Brucker D8-Advance diffractometer. The Photoluminescent (PL) and Photoluminescent excitation (PLE) spectra were taken by FL3-22 fluorescence spectrometer, Horiba with a Xenon lamp 450 W.

3. RESULTS AND DISCUSSION
   1. Crystalline structure

      Intensity (a. u.)

      Intensity (a. u.)

       

      RE = Sm RE = Tb

      RE = Eu RE = Ce

      RE = Dy

      Ca2Al2SiO7 (JCPDS: 35-0755)

      Figure 3(b) shows PL spectrum of CAS: Sm3+ excited by the radiation at wavelength 350 nm. The spectrum has narrow lines ranging from 550 715 nm with maximum at 563 nm, 602 nm, 645 nm and 710 nm that correspond to the transitions in the 4f5 electronic configuration of Sm3+ ion from 4G5/2 excitation state to 6HJ/2 ground states (J = 5, 7, 9,

      11 respectively) [9]. Figure 2(a) shows PLE spectrum of Sm3+ in the wavelength range of 325 500 nm. The spectrum shows the transitions from the ground state 6H5/2 to the 4I9/2 (478 nm), 4I11/2 (470 nm), 4I13/2 (459 nm), 4M17/2, 4G9/2, 4I15/2 (438 nm), 6P5/2, 4L13/2 (421 nm), 4F7/2 (412 nm), 6P3/2 (405 nm), 4G11/2 (390 nm), 4L17/2 (374 nm), 4D5/2 (359 nm), 4H9/2 (344 nm) and 4G9/2 (331 nm) excited states of Sm3+ ion. The

      20 40 60 80

      2 Degree

      Fig. 1. XRD diagrams of samples CAS: RE3+ (RE = Sm, Tb, Eu, Ce, Dy)

      highest emission intensity with peak at Ex = 405 nm, corresponds to the 6H 6 transition which is usually used

      P

      P

       

      5/2 3/2

      5/2 3/2

       

      3+

      in the fluorescent stimulation of Sm ions. The results show

      The crystalline structure of rare earth ions doped Ca2Al2SiO7 luminescent material was investigated by X-ray diffraction method. The XRD diagram of Samples CAS: RE3+ (RE: Dy, Ce, Eu, Tb, Sm) are shown in Figure 1.

      The analysis results show that all of the samples have the desiring tetragonal phase structure of Ca2Al2SiO7. On the other hand, the XRDs show no characteristic peaks of rare earth ion as well as of initial reagents. The observation indicates that the small amount of rare earth dopant did not change the phase structure of the material.

   2. Spectral characteristics of Ca2Al2SiO7: RE3+ phosphors

      Figure 2(b) is the PL spectrum of CAS: Ce3+ excited by UV radiation at = 350 nm. The result shows that emission of sample CAS: Ce3+ has a broad band ranging from 360 nm to

      500 nm with maximum at 420 nm, correspond to the transition from 5d to 4f (5F5/2 and 2F7/2) electronic states of Ce3+ ion in the host lattice. Figure 2(a) shows the PLE spectrum of CAS: Ce3+ at emission wavelength of 420 nm, correspond to the excitation transition of Ce3+ in CAS lattice. The PLE spectrum has two broad bands peaking at 280 nm and 350 nm, correspond to the absorption due to the transition from the ground state of 4f to the excited state 4f05d1 of Ce3+ ion [2, 4]. The broad band emission locates in wavelength 360 500 nm shows that Ce3+ ion not only is suitable for using as an activator but also a sensitizer in codoped materials that can emit visible light.

      Fig. 2. PLE spectra (a) and PL spectra (b) of CAS: Ce3+

      that CAS: Sm3+ samples emit strong reddish orange light when being stimulated by blue LED. Therefore, this material has potential application in LED manufacture or reddish orange fluorescent lamp if stimulated with blue light.

      Fig. 3. PLE spectra (a) and PL spectra (b) of CAS: Sm3+

      The PL spectrum of CAS: Dy3+ Figure 4(b) consists of the narrow lines at = 478 nm, 575 nm and 664 nm. Peaks at =

      478 nm, 575 nm have high intensity correspond to the 4F9/26H15/2 and 4F9/26H13/2 transitions of Dy3+ ion. Meanwhile, peak at 664 nm has lower intensity which corresponds to the 4F9/26H11/2 transition. The PLE spectrum of CAS: Dy3+ with a radiation wavelength of 575 nm is shown in Figure 4(a). The PLE spectrum has narrow lines peak at 322 nm (6H15/26P3/2), 350 nm (6H15/24M15/2,6P7/2), 363 nm (6H15/24I11/2), 383 nm (6H15/24I13/2, 4F7/2), 425 nm (6H15/24G11/2,), 451 nm (6H15/24I15/2), 472 nm (6H15/24F9/2), correspond to the transitions from the ground state 6H15/2 to different excited states of Dy3+ ion in the 4f9 electronic configuration [3].

      Fig. 4. PL spectra (a) and PLE spectra (b) of CAS: Dy3+

      In the figure 5(b), the PL spectrum of CAS: Eu3+ excited by a radiation at 393 nm that consists of narrow lines correspond tothe transitions of Eu3+ ion from the excited state 5D0 to the ground states 7FJ (J = 0, 1, 2, 3, 4). The peak at 586 nm corresponds to the 5D0 7F1 electric dipolar transition of Eu3+

      Fig. 6. PLE spectra (a) and PLE spectra (b) of CAS: Tb3+

      Figure 6(b) shows the PL spectrum of CAS: Tb3+ excited by the radiation at 379 nm. The spectrum has narrow lines correspond to the transitions of Tb3+ ion. The peak at 545 nm has the highest intensity that corresponds to the 5D4 7F5 transition. The other peaks at 440 nm, 462 nm, 494 nm, 590

      nm and 622 nm are relatively weak, correspond to the 5D

      ion. The peak at 617 nm corresponds to the 5D0 7F2 7 5 7 5 7 5 7 5 7 3

      magnetic dipolar transition of Eu3+ ion which depends of the symmetry of the crystal field. Other peaks at 578 nm, 656 nm and 702 nm are relatively weak, corresponds to the 5D0 7F0, 5D0 7F3 and 5D0 7F4 transitions [1, 5]. The characteristic broad band of Eu2+ ion was not observed in the PL spectrum. Figures 5(a) shows the PLE spectrum of CAS: Eu3+ monitored at wavelength of 617 nm. The spectrum has a strong broad band at about 260 nm (not depicted in the figure) and a few narrow lines in the range of 310 nm 550 nm. The peak that has the strongest intensity at 393 nm corresponds to the 7F05L6 transition of Eu3+ ion. Other weak

      F4, D3 F3 D4 F6, D4 F4 and D4 F3 transitions, respectively [4, 7]. The PLE spectrum of CAS: Tb3+ monitored at wavelength 545 nm is shown in the figure 6(a). The spectrum has a board band in UV region and narrow lines in the range of 310 nm 500 nm. The peak has the

      strongest intensity at 368 nm correspond to the 7F6 5G5

      transition of Tb3+ ion. Other weak peaks at 315 nm, 338 nm, 347 nm and 376 nm, 481 nm that were assumed to be the 4f – 4f interconfiguration transition of Tb3+ ion in the host lattice,

      could be assigned to 7F0 5D0, 7F6 5L8, 7F6 5L8,

      7F 5D , 7F 5D transitions, respectively.

      6 3 6 4

      peaks at 360 nm, 374 nm, 380 nm, 412 nm, 463 nm, 523 nm and 530 nm were ascribed to be the 4f – 4f interconfiguration transitions of Eu3+ ion in the lattice that consist of the

      7F05D4, 7F05G2, 7F15L7, 7F05D3, 7F05D2, 7F05D1,

      7F15D1 transitions, respectively.

      Fig. 5. PLE spectra (a) and PL spectra (b) of CAS: Eu3+

   3. Effect of excitation radiation to the luminescence of Ca2Al2SiO7: RE3+

      Fig. 7. PL spectra of CAS: RE3+ excited by a radiation at 365 nm

      Fig. 8. PL spectra of CAS: RE3+ excited by a radiation at 405 nm

      Luminescent efficiency and intensity of all phosphors can be change by the excitation radiation. Therefore, the influence of 365 nm and 405 nm excitation radiation to the CAS: RE3+ phosphors as show in the figure 7 and 8. The luminescent intensity of the phosphors are different when they are excited by the radiation of 365 nm and alternates CAS: Eu3+ > CAS: Tb3+ > CAS: Dy3+ > CAS: Sm3+. On the other hand, when exciting by a radiation of 405 nm, the luminescent intensity of CAS: Sm3+ is much higher than that of CAS: Eu3+, CAS: Tb3+, CAS: Dy3+. It means that CAS: Sm3+ phosphor can use to produce wLED that is pumped blue LED.

4. CONCLUSION

RE3+ ion single doped Ca2Al2SiO7 phosphors have been successfully synthesized by solid state reaction method. The emission of CAS: RE3+ phosphor locates the visible band, i.e. these of CAS: Ce3+ phosphor is blue light, these of CAS: Dy3+ is yellow light, these of CAS: Sm3+ is yellow-red light, these of CAS: Eu3+ is red light and these of CAS: Tb3+ is green light. The emission of these phosphors is produced by the electronic transitions of RE3+ ion in the lattice. The emission intensity of CAS: Sm3+ phosphor is strongest when

excited by the radiation with wavelength 405 nm. This material can use to make wLED.

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