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Luminescence of the compounds Y0.5−xLi1.5VO4:(Dy3+,Eu3+)x
Journal of Alloys and Compounds 351 (2003) 84–86
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Luminescence of the compounds Y 0.52x Li 1.5 VO 4 :(Dy 31 ,Eu 31 ) x Yaqin Yu, Shihong Zhou, Siyuan Zhang* Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China Received 13 July 2002; received in revised form 30 August 2002; accepted 30 August 2002
Abstract In this paper for the first time the compounds Y 0.52x Li 1.5 VO 4 :(Dy 31 ,Eu 31 )x (YLV:Dy,Eu) (0.01,x,0.1 mol) were synthesized by the simple method of solid state reaction. The temperature to synthesize YLV:Dy,Eu is about 600 8C and 400 8C lower than that to synthesize rare earth vanadates. Their structures were analyzed by X-ray powder diffraction experiment. The excitation and emission spectra were measured at room temperature. The blue, the yellow and the red emission from the 4 F 9 / 2 – 6 H 15 / 2 (474.2–484.2 nm) transitions and 4 F 9 / 2 – 6 H 13 / 2 (568–576.4 nm) transitions of Dy 31 and the 5 D 0 – 7 F 2 (608–619.2 nm) transitions of Eu 31 , respectively, are very strong in multiwavelength. 2002 Elsevier Science B.V. All rights reserved. Keywords: Inorganic materials; Chemical synthesis; Luminescence; Optical spectroscopy
1. Introduction
2. Experimental details
Rare earth vanadates have been studied extensively [1–4]. They are of interest as better hosts for luminescence and laser materials. The europium activated yttrium vanadate (YVO 4 :Eu) has been earliest used in color television as red phosphor. To obtain red emission higher concentrations of Eu 31 must be used by cross relaxation in which the blue and green luminescence could be quenched. In 1974 blue, green and red phosphors, in which narrow emission lines occur, could be mixed for improving luminescent efficiency and obtaining excellent color phosphor. If possible there should be a new excellent luminescent material with wide wavelength, it is a ideal material for great application potentials. In the present paper for the first time we reported the new compounds of Y 0.52x Li 1.5 VO 4 :(Dy 31 ,Eu 31 ) x (YLV:Dy,Eu) (0.01,x,0.1 mol), which were prepared by the simple method of solid state reaction. To synthesize YLV:Dy,Eu it takes about 600 8C for several hours and 400 8C lower than that to synthesize rare earth vanadates. The characteristics of multiwavelength emission and structure were measured and analyzed as well.
The YLV:Dy,Eu samples were prepared by mixing stoichiometric amounts of the starting compounds: viz. R 2 O 3 (purity 99.99%) and V2 O 5 , Li 2 CO 3 (spectral purity). After grinding the mixtures were fired at 600 8C in air atmosphere for several hours, and a series of Dy 31 and Eu 31 activated yttrium lithium vanadates were obtained. The phase and the structure of all samples were checked by X-ray powder diffraction. Excitation was with a MPF-4 UV–Vis spectrophotometer.
*Corresponding author. E-mail address: [email protected] (S. Zhang).
3. Results and discussion
3.1. Spectrum and multiwavelength emission The excitation and the emission spectra of Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01 (mol) are shown in Fig. 1a,b at room temperature. The excitation spectra were recorded with an excitation wavelength of 574 nm. From Fig. 1a it can be seen that in the ultraviolet the broad excitation peak at 322.4–324.4 nm is very strong, corresponding to the excitation of the vanadate group VO 32 4 . If the slit width is larger the characteristic excitation peaks of Dy 31 and Eu 31 ions were observed at 353.4 nm and 393 nm from the
0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )01031-9
Y. Yu et al. / Journal of Alloys and Compounds 351 (2003) 84–86
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in relation to the other Stark components. As mentioned above the yellow and the red group emissions are from the 4 F 9 / 2 – 6 H 13 / 2 transitions of Dy 31 and the 5 D 0 – 7 F 2 transi31 4 6 tion of Eu , respectively. Both the F 9 / 2 – H 13 / 2 and the 5 7 D 0 – F 2 transitions are D j 52, which is called hypersensitive transition. The emission intensity of hypersensitive transition change about two to four times. The fourth and the fifth groups have peaks at 586, 591, 593, 697.4 and 702 nm, respectively, and these emission intensities are very weak from 5 D 0 – 7 F 1 and 5 D 0 – 7 F 4 transitions of Eu 31 . As compared with the intensities of the other emissions, the emission intensities for the 5 D 0 – 7 F 3 (645 nm) transitions are a weak broad. It is very interesting to note that the emission of the 5 D 1 – 7 F 0 (538 nm) transition produces an observable intensity in YLV:Dy,Eu. In general, this emission is difficult to be observed, because the populations of 5 D 1 level can decay to the 5 D 0 level by a relaxation process.
3.2. Energy transfer
Fig. 1. The excitation (a) and emission (b) of Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01 .
H 15 / 2 – 6 P7 / 2 transition of Dy 31 and the 7 F 0 – 5 L 6 transition of Eu 31 , respectively. Both Dy 31 and Eu 31 ions produce the excitation intensities, which were so weak that measurements proved difficult under the same condition as the measurement used for VO 32 as shown in Fig. 1a. 4 When the Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01 were excited with 322.4 nm, the multiwavelength luminescence of Dy 31 and Eu 31 in the visible can be classified into five groups as follows: In the first group there are three resolved lines at 474.2, 482.0 and 484.2 nm from the 4 F 9 / 2 – 6 H 15 / 2 transitions of Dy 31 in the blue range. In the second group the yellow emissions consist of four peaks at 569, 571, 574 and 576.4 nm, respectively. The third group lies in the typical red line emission as shown in Fig. 1b and contains four peaks at 608, 614, 619.2 and 626 nm, respectively, and the intensities of the red emission are weaker than that of the yellow emission. In our work a total of four lines were observed for the 7 F 2 multiplet. The red lines in YLV:Dy,Eu correspond to transitions between 5 D 0 and the Stark levels of the 7 F 2 multiplet. These lines have electric dipole character which accounts for their strong intensity
The emission intensity of the vanadate group VO 32 is 4 markedly strong. Once the vanadate center becomes excited, it can either emit the energy as luminescence or transfer the energy to a rare earth center which subsequently emits its own characteristic radiation. The latter mechanism is phonon regulated, and also the excitation transition probably involves a charge transfer process, such as 11 uV 15 O 22n u→uV 14 O 22n u. It is particularly noteworthy n n 31 31 that Dy and Eu are the most efficient activators in the 31 YLV:Dy,Eu, and the VO 32 energy transfer is higher 4 R efficiency. In a series of YLV:Dy,Eu the phenomenon of concentration quenching occurs with increasing Dy 31 and Eu 31 concentrations due to mutual R31 –R31 interactions.
6
3.3. Structure The structure of YLV:Dy,Eu consists of YVO 4 and b p -Li 3 VO 4 phase as derived from X-ray powder diffraction (Fig. 2). The structure of YVO 4 is known to belong to the tetragonal crystal system with I41 /amd as the space group, in which the rare earth cation is coordinated by eight oxygen atoms in an arrangement of two interpenetrating tetrahedral yielding D2d as the point symmetry of the single R31 site. The structure of b p -Li 3 VO 4 which lacks a center of symmetry, possesses a wurtzite–crystal type structure.
4. Conclusion Y 0.52x Li 1.5 VO 4 :(Dy,Eu) x compounds were prepared by solid state reaction at 600 8C for several hours. Its structure consists of the YVO 4 and b p -Li 3 VO 4 phase. The multiwavelength luminescence of Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01
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Y. Yu et al. / Journal of Alloys and Compounds 351 (2003) 84–86
(mol) in the visible are blue (474.2, 482, 484 nm, Dy 31 ), yellow (569, 571, 574 nm, Dy 31 ), and red (608, 614, 619.2 nm, Eu 31 ) emissions. The energy transfer from VO 32 to R31 has a high efficiency. 4
References
Fig. 2. The spectrum of X-ray powder diffraction. (a) YVO 4 ; (b) YLV:Dy,Eu; (c) Li 3 VO 4 .
[1] F.C. Palilla, A.K. Levine, M. Rinkevics, J. Eletrochem. Soc. 112 (8) (1965) 776–779. [2] J.L. Sonnerdijk, A. Bril, J. Eletrochem. Soc. 122 (7) (1975) 952– 954. [3] J. Loriers, M. Vichr, J. Crystal Growth 13 / 14 (1972) 593–596. [4] Y. Yaqin, L. Mei, Proceedings of the 2nd International Conference on Rare Earth Development and Application, International Academic Publishers, Beijing, 1991, pp. 762–764.
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Luminescence of the compounds Y 0.52x Li 1.5 VO 4 :(Dy 31 ,Eu 31 ) x Yaqin Yu, Shihong Zhou, Siyuan Zhang* Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China Received 13 July 2002; received in revised form 30 August 2002; accepted 30 August 2002
Abstract In this paper for the first time the compounds Y 0.52x Li 1.5 VO 4 :(Dy 31 ,Eu 31 )x (YLV:Dy,Eu) (0.01,x,0.1 mol) were synthesized by the simple method of solid state reaction. The temperature to synthesize YLV:Dy,Eu is about 600 8C and 400 8C lower than that to synthesize rare earth vanadates. Their structures were analyzed by X-ray powder diffraction experiment. The excitation and emission spectra were measured at room temperature. The blue, the yellow and the red emission from the 4 F 9 / 2 – 6 H 15 / 2 (474.2–484.2 nm) transitions and 4 F 9 / 2 – 6 H 13 / 2 (568–576.4 nm) transitions of Dy 31 and the 5 D 0 – 7 F 2 (608–619.2 nm) transitions of Eu 31 , respectively, are very strong in multiwavelength. 2002 Elsevier Science B.V. All rights reserved. Keywords: Inorganic materials; Chemical synthesis; Luminescence; Optical spectroscopy
1. Introduction
2. Experimental details
Rare earth vanadates have been studied extensively [1–4]. They are of interest as better hosts for luminescence and laser materials. The europium activated yttrium vanadate (YVO 4 :Eu) has been earliest used in color television as red phosphor. To obtain red emission higher concentrations of Eu 31 must be used by cross relaxation in which the blue and green luminescence could be quenched. In 1974 blue, green and red phosphors, in which narrow emission lines occur, could be mixed for improving luminescent efficiency and obtaining excellent color phosphor. If possible there should be a new excellent luminescent material with wide wavelength, it is a ideal material for great application potentials. In the present paper for the first time we reported the new compounds of Y 0.52x Li 1.5 VO 4 :(Dy 31 ,Eu 31 ) x (YLV:Dy,Eu) (0.01,x,0.1 mol), which were prepared by the simple method of solid state reaction. To synthesize YLV:Dy,Eu it takes about 600 8C for several hours and 400 8C lower than that to synthesize rare earth vanadates. The characteristics of multiwavelength emission and structure were measured and analyzed as well.
The YLV:Dy,Eu samples were prepared by mixing stoichiometric amounts of the starting compounds: viz. R 2 O 3 (purity 99.99%) and V2 O 5 , Li 2 CO 3 (spectral purity). After grinding the mixtures were fired at 600 8C in air atmosphere for several hours, and a series of Dy 31 and Eu 31 activated yttrium lithium vanadates were obtained. The phase and the structure of all samples were checked by X-ray powder diffraction. Excitation was with a MPF-4 UV–Vis spectrophotometer.
*Corresponding author. E-mail address: [email protected] (S. Zhang).
3. Results and discussion
3.1. Spectrum and multiwavelength emission The excitation and the emission spectra of Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01 (mol) are shown in Fig. 1a,b at room temperature. The excitation spectra were recorded with an excitation wavelength of 574 nm. From Fig. 1a it can be seen that in the ultraviolet the broad excitation peak at 322.4–324.4 nm is very strong, corresponding to the excitation of the vanadate group VO 32 4 . If the slit width is larger the characteristic excitation peaks of Dy 31 and Eu 31 ions were observed at 353.4 nm and 393 nm from the
0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )01031-9
Y. Yu et al. / Journal of Alloys and Compounds 351 (2003) 84–86
85
in relation to the other Stark components. As mentioned above the yellow and the red group emissions are from the 4 F 9 / 2 – 6 H 13 / 2 transitions of Dy 31 and the 5 D 0 – 7 F 2 transi31 4 6 tion of Eu , respectively. Both the F 9 / 2 – H 13 / 2 and the 5 7 D 0 – F 2 transitions are D j 52, which is called hypersensitive transition. The emission intensity of hypersensitive transition change about two to four times. The fourth and the fifth groups have peaks at 586, 591, 593, 697.4 and 702 nm, respectively, and these emission intensities are very weak from 5 D 0 – 7 F 1 and 5 D 0 – 7 F 4 transitions of Eu 31 . As compared with the intensities of the other emissions, the emission intensities for the 5 D 0 – 7 F 3 (645 nm) transitions are a weak broad. It is very interesting to note that the emission of the 5 D 1 – 7 F 0 (538 nm) transition produces an observable intensity in YLV:Dy,Eu. In general, this emission is difficult to be observed, because the populations of 5 D 1 level can decay to the 5 D 0 level by a relaxation process.
3.2. Energy transfer
Fig. 1. The excitation (a) and emission (b) of Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01 .
H 15 / 2 – 6 P7 / 2 transition of Dy 31 and the 7 F 0 – 5 L 6 transition of Eu 31 , respectively. Both Dy 31 and Eu 31 ions produce the excitation intensities, which were so weak that measurements proved difficult under the same condition as the measurement used for VO 32 as shown in Fig. 1a. 4 When the Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01 were excited with 322.4 nm, the multiwavelength luminescence of Dy 31 and Eu 31 in the visible can be classified into five groups as follows: In the first group there are three resolved lines at 474.2, 482.0 and 484.2 nm from the 4 F 9 / 2 – 6 H 15 / 2 transitions of Dy 31 in the blue range. In the second group the yellow emissions consist of four peaks at 569, 571, 574 and 576.4 nm, respectively. The third group lies in the typical red line emission as shown in Fig. 1b and contains four peaks at 608, 614, 619.2 and 626 nm, respectively, and the intensities of the red emission are weaker than that of the yellow emission. In our work a total of four lines were observed for the 7 F 2 multiplet. The red lines in YLV:Dy,Eu correspond to transitions between 5 D 0 and the Stark levels of the 7 F 2 multiplet. These lines have electric dipole character which accounts for their strong intensity
The emission intensity of the vanadate group VO 32 is 4 markedly strong. Once the vanadate center becomes excited, it can either emit the energy as luminescence or transfer the energy to a rare earth center which subsequently emits its own characteristic radiation. The latter mechanism is phonon regulated, and also the excitation transition probably involves a charge transfer process, such as 11 uV 15 O 22n u→uV 14 O 22n u. It is particularly noteworthy n n 31 31 that Dy and Eu are the most efficient activators in the 31 YLV:Dy,Eu, and the VO 32 energy transfer is higher 4 R efficiency. In a series of YLV:Dy,Eu the phenomenon of concentration quenching occurs with increasing Dy 31 and Eu 31 concentrations due to mutual R31 –R31 interactions.
6
3.3. Structure The structure of YLV:Dy,Eu consists of YVO 4 and b p -Li 3 VO 4 phase as derived from X-ray powder diffraction (Fig. 2). The structure of YVO 4 is known to belong to the tetragonal crystal system with I41 /amd as the space group, in which the rare earth cation is coordinated by eight oxygen atoms in an arrangement of two interpenetrating tetrahedral yielding D2d as the point symmetry of the single R31 site. The structure of b p -Li 3 VO 4 which lacks a center of symmetry, possesses a wurtzite–crystal type structure.
4. Conclusion Y 0.52x Li 1.5 VO 4 :(Dy,Eu) x compounds were prepared by solid state reaction at 600 8C for several hours. Its structure consists of the YVO 4 and b p -Li 3 VO 4 phase. The multiwavelength luminescence of Y 0.44 Li 1.5 VO 4 :Dy 0.05 Eu 0.01
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Y. Yu et al. / Journal of Alloys and Compounds 351 (2003) 84–86
(mol) in the visible are blue (474.2, 482, 484 nm, Dy 31 ), yellow (569, 571, 574 nm, Dy 31 ), and red (608, 614, 619.2 nm, Eu 31 ) emissions. The energy transfer from VO 32 to R31 has a high efficiency. 4
References
Fig. 2. The spectrum of X-ray powder diffraction. (a) YVO 4 ; (b) YLV:Dy,Eu; (c) Li 3 VO 4 .
[1] F.C. Palilla, A.K. Levine, M. Rinkevics, J. Eletrochem. Soc. 112 (8) (1965) 776–779. [2] J.L. Sonnerdijk, A. Bril, J. Eletrochem. Soc. 122 (7) (1975) 952– 954. [3] J. Loriers, M. Vichr, J. Crystal Growth 13 / 14 (1972) 593–596. [4] Y. Yaqin, L. Mei, Proceedings of the 2nd International Conference on Rare Earth Development and Application, International Academic Publishers, Beijing, 1991, pp. 762–764.