English

• 0.   Introduction

  Lanthanide doped phosphors have attracted great attention for its high feasibility applications in lighting and display systems^[1-5]. Green phosphors are of capital importance in solid-state lighting for white light sources, and most of green luminescent materials are Tb³⁺ activated phosphors because of its predominant ⁵D₄-⁷F₅ transition^[6-8]. Tb³⁺ shows a strong UV excitation characteristic due to its spin-allowed 4f-5d transition, and an intense visible emission can be achieved in an appropriate host lattice upon the UV excitation^[9-10]. Therefore, Tb³⁺ doped phosphors are widely used in fluorescent lamps^[6-10].

  Recently, double perovskite oxides (A₂BB′O₆) have been widely used as host materials because of their advanced luminescence and thermal stability^[11]. In a typical structure with double perovskite, B site coordinated by six oxygen atoms is occupied by orderly arranged B and B′. A site possesses various coordination numbers (8~12) depending on the distortion degree of the crystal structure^[12-14]. Therefore, the local crystal environment, which is critical for luminescence, can be modulated by changing composition elements. Recently, many M3+ activated (M3+=rare earth element ion) phosphors with double perovskite have been investigated owing to their good luminescence properties, such as Sr₂LaSbO₆∶Eu^3+[12], La₂MgTiO₆∶Eu^3+[13], CaLaMgSbO₆∶Eu^3+[14], Ca₂GdTaO₆∶Eu^3+[15], Ca₂YTaO₆∶ Dy^3+[16], Ca₂LaTaO₆∶Tb³⁺ and Ba₂LaTaO₆∶Tb^3+[17]. Ca₂GdTaO₆ belongs to the A₂BB′O₆ structure with double perovskite, which has the monoclinic crystal structure^{[15, 18-19]}. In Ca₂GdTaO₆ lattice, Ca²⁺ occupies the A site, while Gd³⁺ and Ta⁵⁺ situate respectively at the B and B′ sites. And Gd³⁺ and Ta⁵⁺ ions occupied the octahedral sites by sharing one oxygen atom, Ca²⁺ ions were situated in the center of the alternation between octahedrons^[18-19].

  Herein, we report the preparation of double perovskite-type Ca₂Gd_1-xTaO₆∶xTb³⁺(CGTO∶xTb³⁺) phosphors by a high temperature solid state reaction method. The luminescence properties of CGTO∶xTb³⁺ phosphors were investigated by changing doping concentration of Tb³⁺ ions in the host. Our results show that CGTO∶xTb³⁺ has good properties as a green phosphor for lighting and display application.

  1.   Experimental

  The samples of CGTO∶xTb³⁺(x=0, 0.05, 0.1, 0.15, 0.2, 0.3 and 0.4) were synthesized using a hightemperature solid -state method. Stoichiometric quantities of CaCO₃ (99.9%), Tb ₄O₇(99.99%), Gd₂O₃ (99.99%) and Ta₂O₅ (99.99%) used as the starting materials were finely ground in an agate mortar and transferred into the alumina crucibles to be calcined at 1 500 ℃ for 6 h. Then, the samples were cooled down to room temperature and reground for further measurements.

  The phase purity of the samples was checked by powder X-ray diffraction (XRD) performed on a Panalytical X′ Pert diffractometer with Cu Kα₁ radiation (λ=0.154 187 nm) operating at 40 kV and 40 mA in 2θ range of 10°~80°. The morphology and particle size of CGTO∶0.15Tb³⁺ were characterized by a field emission scanning electron microscope (FE-SEM, Tescan Orsay Holding, MIRA3 LMH) equipped with the energy dispersive spectra (EDS, Thermo Scientific, UltraDry) operated at 20 kV. Photoluminescence luminescence (PL), photoluminescence excitation (PLE), and decay curves were measured on a spectrophotometer (FLS980) equipped with both a xenon lamp (450 W) and a pulse xenon lamp (450 W) as the lighting source.

  2.   Results and discussion

  2.1   Crystal structure and morphology

  Fig.1 shows the XRD patterns of CGTO∶xTb³⁺(x= 0, 0.05, 0.1, 0.15, 0.2, 0.3 and 0.4). It could be seen that all the diffraction peaks of the samples were identified to the standard card of Ca₂GdTaO₆ (PDF No. 73 0085) except for a relatively weak peak at 2θ =28.5° marked with the symbol (*). This impurity peak can be attributed to Gd₃TaO₇ (PDF No. 38-1409) impurity phase. The Tb³⁺ ions are proposed to occupy the Gd³⁺ sites because the effective radius of Tb³⁺ ions (0.092 3 nm for CN=6) is very close to that of Gd³⁺ ions (0.093 8 nm for CN=6) (CN=coordination number)^[20].

  Figure 1

  

  Figure 1.  XRD patterns of CGTO∶xTb³⁺

  下载: 全尺寸图片 幻灯片

  Rietveld refinement analysis was further performed from the powder XRD data using the General Structure Analysis System (GSAS) program. Fig. 2a shows the fitted Rietveld refinement data and the difference between the calculated and experimental data of the typical CGTO∶0.15Tb³⁺ phosphor. The detailed refinement results for CGTO∶0.15Tb³⁺ phosphor are listed in Table 1. The smaller residual parameters (R_wp=2.36% and R_p=1.5%) and goodness of fit (χ2=3.494 8) for all the fitting data, together with the tiny fluctuation in the difference curves shown in Fig.2, indicate high reliability of the refinement results. The schematic of CGTO crystal structure is shown in Fig.2b. Gd³⁺ ions occupy B sites with six-folded coordination.

  Figure 2

  

  Figure 2.  (a) Rietveld refinement for XRD patterns of CGTO∶0.15Tb³⁺ phosphor; (b) Crystal structure of CGTO∶0.15Tb³⁺ phosphor

  下载: 全尺寸图片 幻灯片

  Table 1

  

  Table 1.  Refined crystallographic parameters of CGTO∶0.15Tb³⁺ phosphor

  下载: 导出CSV

  Formula	Ca2(Gd0.85Tb0.15)TaO6
  Crystal system	Monoclinic
  Space group	P21/n
  a/nm	0.557 516(4)
  b/nm	0.584 742(5)
  c/nm	0.808 356(6)
  β/(°)	90.306 1(2)
  Volume/nm3	0.263 523
  Rwp/%	2.36
  Rp/%	1.50
  χ2	3.494 8

  Fig. 3a and 3b show SEM images of CGTO∶ 0.15Tb³⁺ phosphor. The morphology of the sample was ovaloid-like and the particle size was 2~3 μm. In addition, Fig. 3c~3g show the distribution of each element of one phosphor particle. The results indicate that Ca, Gd, Ta, O and Tb are evenly distributed. The EDS was used to further characterize the chemical composition of the as prepared product, and the result of CGTO∶ 0.15Tb³⁺ phosphor shown in Fig.3h was 39∶17∶3∶19 of n_Ca∶n_Gd∶n_Tb∶n_Ta, which was close to the chemical formula of CGTO∶0.15Tb³⁺. The results confirm that Tb³⁺ ions have been effectively incorporated into the CGTO host lattice, consisting with the XRD analysis above.

  Figure 3

  

  Figure 3.  (a, b) SEM images of CGTO: 0.15Tb³⁺; (c~g) Distribution of the elements in CGTO: 0.15Tb³⁺; (h) EDS spectrum of CGTO: 0.15Tb³⁺

  下载: 全尺寸图片 幻灯片

  2.2   Photoluminescence properties

  Fig.4a shows the PLE spectrum of CGTO∶0.15Tb³⁺ at room temperature. The PLE spectrum of CGTO: 0.15Tb³⁺, which monitored the PL peak at 543 nm, exhibited an intense peak at 255 nm assigned to the allowed 4f-5d transition of Tb³⁺. The PL spectra of CGTO∶xTb³⁺ samples under UV (255 nm) excitation are shown in Fig.4b. The Tb³⁺ luminescence was composed of two series of emission peak at 400~470 nm and 470~700 nm (Fig.4b), which are attributed to Tb³⁺ ions transitions from ⁵D₃-⁷F_J (J=5, 4, 3) and ⁵D₄-⁷F_J(J= 6, 5, 4, 3), respectively^[21]. Owing to the obvious concentration quenching of the Tb³⁺ luminescence at ⁵D₃-⁷F_J(J =5, 4, 3) transitions, the emission at 400~470 nm region was very weak^[21]. Where blue and green as well as red emission centered at 490, 543, 588 and 623 nm are attributed to the ⁵D₄-⁷F_J(J=6, 5, 4, 3) transitions of Tb³⁺, respectively^[22]. As shown in the inset of Fig. 4b, the relative integrated intensity of the dominant emission from ⁵D₄-⁷F₅ transition increased with the increasement of the Tb³⁺-concentration, reaching maximum at x =0.15 Tb³⁺ doping, and then decreased with the further increasing Tb³⁺ concentration.

  Figure 4

  

  Figure 4.  Photoluminescence spectra of CGTO∶xTb³⁺: (a) excitation spectrum of CGTO∶0.15Tb³⁺, λ_em=543 nm; (b) emission spectra (λ_ex=255 nm) with the inset showing the relative integrated intensity of the dominant emission from ⁵D₄-⁷F₅ transition

  下载: 全尺寸图片 幻灯片

  The CIE chromaticity coordinates for the emission of CGTO∶0.15Tb³⁺ under 255 nm excitation is shown in Fig. 5, and the inset at the top right corner is luminescence image of CGTO∶0.15Tb³⁺ irradiated by 254 nm UV lamp. The color coordinates (x, y) of CGTO∶ 0.15Tb³⁺ phosphor was calculated as (0.348 6, 0.562 0). The CIE coordinates belong to green region. The corresponding color temperature can be calculated using the following formula^[23]:

  $ T = - 437{n^3} + 360\;\;1{n^2} - 686\;\;1n + 5514.31 $

  (1)

  Figure 5

  

  Figure 5.  CIE chromaticity coordinates of CGTO∶0.15Tb³⁺(λ_ex=255 nm) and luminescence image (Inset) of CGTO∶0.15Tb³⁺ irradiated by 254 nm UV lamp

  下载: 全尺寸图片 幻灯片

  where n=(x-0.332)/(y-0.185 8). The color temperature of CGTO∶0.15Tb³⁺ phosphor was 5 219 K.

  To investigate the luminescence concentration quenching, the critical distance (R_c) between two Tb³⁺ ions in CGTO∶xTb³⁺crystalline can be estimated by the formula^[24]: R_c=2[3V/(4πNx_c)]^1/3 (2), where V is the volume of the unit cell, x_c is the critical concentration and N is the number of available crystallographic sites occupied by the activator ions in the unit cell. The Rietveld refinement analysis values of V and N for CGTO∶0.15Tb³⁺ crystalline were 0.263 523 nm³ and 2, respectively. The critical distance of two Tb³⁺ ions in CGTO∶x Tb³⁺ was 1.188 1 nm. It is known that the nonradiative energy transfer mechanism consists of exchange interaction and electric multipolar interaction. The exchange interaction comes into effect only when the typical critical distance between the activators is shorter than 0.5 nm. Here, the critical distance is much longer than 0.5 nm, so the concentration quenching is dominated by the multipole-multipole interaction in CGTO∶xTb³⁺. According to Dexter theory, the type of electric multipolar interaction among Tb³⁺ ions can be deduced by the following equation^[25]:

  $ \frac{I}{x} = K{\left( {1 + {x^{\frac{\theta }{3}}}} \right)^{ - 1}} $

  (3)

  where K and β are constants; x is the activator Tb³⁺ concentration; I is the dominant emission intensity from ⁵D₄-⁷F₅ transition of CGTO∶xTb³⁺ phosphors; θ equals 6, 8 or 10 corresponding to dipole dipole, dipole quadrupole or quadrupole-quadrupole interaction, respectively. Fig.6 demonstrated that the relationship between lg(I/x) and lg x was approximately linear, and the slope was around -1.94, which meant that θ was about 6.0. The result indicates that the mechanism of concentration quenching for Tb³⁺ luminescence centers is the dipoledipole interaction in the CGTO∶xTb³⁺ host lattice.

  Figure 6

  

  Figure 6.  Relationship between lg(I/x) and lg x for CGTO∶xTb³⁺ phosphor

  下载: 全尺寸图片 幻灯片

  Thermal stability is an important parameter of a phosphor. In order to investigate the thermal stability of CGTO∶0.15Tb³⁺ phosphor, we measured PL spectra of CGTO∶0.15Tb³⁺ phosphor with UV excitation 255 nm at different temperatures (25~300 ℃), as shown in Fig. 7. The PL intensity of CGTO∶0.15Tb³⁺ phosphor decreased along with the temperature increasing, which is due to thermal quenching. In the process of thermal quenching, the activation energy (ΔE) can be determined by the following Arrhenius equation^[26]: I_T= I₀/{1+cexp[-ΔE/(kT)]}(4), where I₀ and I_T stand for the initial emission intensity and the luminescence intensity of the dominant emission from ⁵D₄-⁷F₅ transition at temperature T, respectively; c is a constant for a designated host and k is the Boltzmann constant (8.617×10^-5 eV·K^-1). The activation energy (ΔE) can be calculated by plotting ln[(I₀/I_T)^-1] vs 1/(kT), as shown in Fig. 8, and the ΔE of CGTO∶0.15Tb³⁺ that equals the minus slope of the fitting line was determined to be 0.181 9 eV, which was close to the value of 0.2 eV for Ca₃Ga₂Ge₃O₁₂∶Tb³⁺ phosphor^[27].

  Figure 7

  

  Figure 7.  Temperature dependent emission intensity spectra of CGTO∶0.15Tb³⁺

  Inset: integrated intensity of the dominant emission from ⁵D₄-⁷F₅ transition

  下载: 全尺寸图片 幻灯片

  Figure 8

  

  Figure 8.  Plot of ln[(I₀/I_T)-1] vs 1/(kT) for thermal quenching of CGTO∶0.15Tb³⁺

  下载: 全尺寸图片 幻灯片

  To further clarify the concentration quenching of Tb³⁺ in CGTO host, the luminescence decay curves of CGTO∶xTb³⁺ phosphors (λ_ex=255 nm, λ_em=543 nm) are shown in Fig. 9. The luminescence decay curves of Tb³⁺ doped with different Tb³⁺ concentrations can be well fitted into a single­ exponential function as I=Aexp(-t/τ)+B (5), where I is the relative intensity; t is time; A and B are constants; τ is the lifetime of the Tb³⁺ ions.The fitting results are listed in Table 2. The lifetime of the Tb³⁺ ions decreased with increasing Tb³⁺ concentration. The decay time decreased from 4.181 7 to 1.719 1 ms, when the Tb³⁺ doping concentration increased from 0.05 to 0.4. It can be attributed to the increased non-radiative energy migration among Tb³⁺ ions.

  Figure 9

  

  Figure 9.  Luminescence decay curves of CGTO∶xTb³⁺ phosphors under 255 nm excitation

  下载: 全尺寸图片 幻灯片

  Table 2

  

  Table 2.  Lifetime (τ) of Tb³⁺ 543 nm emission in CGTO∶xTb³⁺ phosphors under 255 nm excitation

  下载: 导出CSV

  Tb doping concentration (x)	0.05	0.1	0.15	0.2	0.3	0.4
  A	4.519 4	4.293 9	4.723 8	4.504 4	4.369 8	4.297 3
  B	4.369 2	4.408 6	4.404 3	4.446 3	4.394 7	4.431 1
  τ/ms	4.181 7	4.068 9	4.020 6	3.587 2	2.646 8	1.719 1

  In order to investigate the luminescence efficiency, quantum efficiency (η) of CGTO∶0.15Tb³⁺ was tested under 255 nm excitation, which is shown in Fig.10, and the value was obtained by the following equation^[28]:

  $ \eta = \frac{{\int {{L_{\rm{S}}}} }}{{\int {{E_{\rm{R}}}} - \int {{E_{\rm{S}}}} }} $

  (6)

  Figure 10

  

  Figure 10.  Excitation line of BaSO₄ reference and emission spectrum of CGTO∶0.15Tb³⁺ under 255 nm excitation collected using an integrating sphere

  下载: 全尺寸图片 幻灯片

  where L_S and E_S are the emission and excitation spectra of objective samples; E_R is the spectrum of the excitation light without the samples in the integrating sphere. The quantum efficiency of CGTO∶0.15Tb³⁺ was calculated to be 32.32%, which was close to that of LiLaSiO₄∶Tb³⁺(39.8%)^[29].

  3.   Conclusions

  In summary, we synthesized CGTO∶xTb³⁺ phosphors by a high­temperature solid­state reaction method. The intense green luminescence corresponding to ⁵D₄­⁷F₅ transition of Tb³⁺ of the sample was clearly observed under 255 nm excitation. The optimum doping concentration of Tb³⁺ was 0.15. The quantum efficiency of CGTO∶0.15Tb³⁺ was calculated to be 32.32%. CGTO∶Tb³⁺ phosphor exhibited an intensive green emission and high activation energy as well as low thermal quenching occurring under UV light excitation. These results suggest that CGTO∶Tb³⁺ phosphor is a promising green­emitting phosphor for optical devices.

  
  Acknowledgement: This work was financially supported by the National Natural Science Foundation of China (Grant No. 51862012) and the Natural Science Foundation of Jiangxi Province (Grants No. 20202BAB204008, 20165ABC28010) as well as the Innovation Leadership Program of Ganzhou.
• 1. [1]

     McKittrick J, Shea-Rohwer L E. J. Am. Ceram. Soc. , 2014, 97(5): 1327-1352 doi: 10.1111/jace.12943

  2. [2]

     Liu X M, Lin J. J. Mater. Chem. , 2008, 18(2): 221-228 doi: 10.1039/B709929K

  3. [3]

     Sahu N K, Singh N S, Ningthoujam R S, Bahadur D. ACS Photonics, 2014, 1(4): 337-346 doi: 10.1021/ph4001718

  4. [4]

     Zhao W Y, An S L, Fan B, Li S B. Appl. Phys. A, 2013, 111(2): 601-604 doi: 10.1007/s00339-012-7271-1

  5. [5]

     Sotiriou G A, Franco D, Poulikakos D, Ferrari A. ACS Nano, 2012, 6(5): 3888-3897 doi: 10.1021/nn205035p

  6. [6]

     Weg V D W F, Popma T J A, Vink A T. J. Appl. Phys. , 1985, 57(12): 5450-5456 doi: 10.1063/1.334821

  7. [7]

     Panse V R, Kokode N S, Dhoble S J, Yerpude A N. Luminescence, 2016, 31(3): 893-896 doi: 10.1002/bio.3049

  8. [8]

     Yu H L, Yu X, Xu X H, Jiang T M, Yang P H, Jiao Q, Zhou D C, Qiu J B. Opt. Commun. , 2014, 317: 78-82 doi: 10.1016/j.optcom.2013.12.008

  9. [9]

     Carnall W T, Fields P R, Rajnak K. J. Chem. Phys. , 1968, 49: 4447-4449 doi: 10.1063/1.1669895

  10. [10]

      Yu R J, Wang C F, Chen J T, Wu Y K, Li H J, Ma H L. ECS J. Solid State Sci. Technol. , 2014, 3(3): R33-R37 doi: 10.1149/2.013403jss

  11. [11]

      Li K, Lian H Z, Van Deun R. Dalton Trans. , 2018, 47(8): 2501-2505 doi: 10.1039/C7DT04811D

  12. [12]

      Zhong J S, Xu M, Chen D Q, Xiao G H, Ji Z G. Dyes Pigm. , 2017, 146: 272-278 doi: 10.1016/j.dyepig.2017.07.019

  13. [13]

      Bondzior B, Stefanska D, Vu T H Q, Miniajluk-Gawel N, Deren P J. J. Alloys Compd. , 2021, 852: 157074 doi: 10.1016/j.jallcom.2020.157074

  14. [14]

      Liu Q, Wang L X, Huang W T, Li X B, Yu M X, Zhang Q T. Ceram. Int. , 2018, 44(2): 1662-1667 doi: 10.1016/j.ceramint.2017.10.091

  15. [15]

      Wang S Y, Sun Q, Devakumar B, Liang J, Sun L L, Huang X Y. J. Alloys Compd. , 2019, 804: 93-99 doi: 10.1016/j.jallcom.2019.06.388

  16. [16]

      Sun P F, Liu S H, Shu S, Ding K, Wang Y, Liu Y Y, Deng B, Yu R J. Opt. Mater. , 2019, 96: 109300 doi: 10.1016/j.optmat.2019.109300

  17. [17]

      Ueda K, Tanaka S, Yamamoto R, Shimizu Y, Honma T, Massuyeau F, Jobic S. J. Phys. Chem. C, 2020, 124(1): 854-860 doi: 10.1021/acs.jpcc.9b09260

  18. [18]

      Ghosh B, Dutta A, Brajesh K, Sinha T P. Indian J. Pure Appl. Phys. , 2015, 53(2): 125-133

  19. [19]

      Momma K, Izumi F. J. Appl. Crystallogr. , 2008, 41: 653-658 doi: 10.1107/S0021889808012016

  20. [20]

      Shannon R D. Acta Crystallogr. , 1976, 32: 751-767 doi: 10.1107/S0567739476001551

  21. [21]

      Zhang J C, Wang Y H, Zhang Z Y, Wang D Y, Ci Z P, Sun Y K. Chin. Sci. Bull. , 2007, 52(16): 2297-2300 doi: 10.1007/s11434-007-0329-3

  22. [22]

      Teng X, Li J K, Duan G B, Liu Z M. J. Lumin. , 2016, 179: 165-170 doi: 10.1016/j.jlumin.2016.06.029

  23. [23]

      Mccamy C S. Color Res. Appl. , 1992, 17(2): 142-144 doi: 10.1002/col.5080170211

  24. [24]

      Blasse G. J. Solid State Chem. , 1986, 62: 207-211 doi: 10.1016/0022-4596(86)90233-1

  25. [25]

      Dexter D L. J. Chem. Phys. , 1953, 21: 836-850 doi: 10.1063/1.1699044

  26. [26]

      Xie R J, Hirosaki, N, Kimura N, Sakuma K, Mitomo M. Appl. Phys. Lett. , 2007, 90(19): 191101 doi: 10.1063/1.2737375

  27. [27]

      Sawada K, Nakamura T, Adachi S. Ceram. Int. , 2017, 43(16): 14225-14232 doi: 10.1016/j.ceramint.2017.07.170

  28. [28]

      Van Deun R, Ndagsi D, Liu J, Van Driessche I, Van Hecke K, Kaczmarek A M. Dalton Trans. , 2015, 44(33): 15022-15030 doi: 10.1039/C5DT02112J

  29. [29]

      Wu X L, Du L, Zheng Y L, Pei M K, Ren Q, Hai O. J. Lumin. , 2021, 235: 118027 doi: 10.1016/j.jlumin.2021.118027

• 

  Figure 1  XRD patterns of CGTO∶xTb³⁺

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) Rietveld refinement for XRD patterns of CGTO∶0.15Tb³⁺ phosphor; (b) Crystal structure of CGTO∶0.15Tb³⁺ phosphor

  下载: 全尺寸图片 幻灯片
  

  Figure 3  (a, b) SEM images of CGTO: 0.15Tb³⁺; (c~g) Distribution of the elements in CGTO: 0.15Tb³⁺; (h) EDS spectrum of CGTO: 0.15Tb³⁺

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Photoluminescence spectra of CGTO∶xTb³⁺: (a) excitation spectrum of CGTO∶0.15Tb³⁺, λ_em=543 nm; (b) emission spectra (λ_ex=255 nm) with the inset showing the relative integrated intensity of the dominant emission from ⁵D₄-⁷F₅ transition

  下载: 全尺寸图片 幻灯片
  

  Figure 5  CIE chromaticity coordinates of CGTO∶0.15Tb³⁺(λ_ex=255 nm) and luminescence image (Inset) of CGTO∶0.15Tb³⁺ irradiated by 254 nm UV lamp

  下载: 全尺寸图片 幻灯片
  

  Figure 6  Relationship between lg(I/x) and lg x for CGTO∶xTb³⁺ phosphor

  下载: 全尺寸图片 幻灯片
  

  Figure 7  Temperature dependent emission intensity spectra of CGTO∶0.15Tb³⁺

  Inset: integrated intensity of the dominant emission from ⁵D₄-⁷F₅ transition

  下载: 全尺寸图片 幻灯片
  

  Figure 8  Plot of ln[(I₀/I_T)-1] vs 1/(kT) for thermal quenching of CGTO∶0.15Tb³⁺

  下载: 全尺寸图片 幻灯片
  

  Figure 9  Luminescence decay curves of CGTO∶xTb³⁺ phosphors under 255 nm excitation

  下载: 全尺寸图片 幻灯片
  

  Figure 10  Excitation line of BaSO₄ reference and emission spectrum of CGTO∶0.15Tb³⁺ under 255 nm excitation collected using an integrating sphere

  下载: 全尺寸图片 幻灯片

  Table 1.  Refined crystallographic parameters of CGTO∶0.15Tb³⁺ phosphor

  Formula	Ca2(Gd0.85Tb0.15)TaO6
  Crystal system	Monoclinic
  Space group	P21/n
  a/nm	0.557 516(4)
  b/nm	0.584 742(5)
  c/nm	0.808 356(6)
  β/(°)	90.306 1(2)
  Volume/nm3	0.263 523
  Rwp/%	2.36
  Rp/%	1.50
  χ2	3.494 8

  下载: 导出CSV

  Table 2.  Lifetime (τ) of Tb³⁺ 543 nm emission in CGTO∶xTb³⁺ phosphors under 255 nm excitation

  Tb doping concentration (x)	0.05	0.1	0.15	0.2	0.3	0.4
  A	4.519 4	4.293 9	4.723 8	4.504 4	4.369 8	4.297 3
  B	4.369 2	4.408 6	4.404 3	4.446 3	4.394 7	4.431 1
  τ/ms	4.181 7	4.068 9	4.020 6	3.587 2	2.646 8	1.719 1

  下载: 导出CSV
•