B. L. Wang

Bin Fan

C. S. McCamy

D. Wang

D. Y. Wang

F. Zhang

G. Blasse

H. H. Lin

J. C. Zhang

J. D. Liu

J. G. Pan

J. P. Zhong

J. Schanda

J. Y. Lu

M. B. Xie

P. Flesch

Q. Su

S. Y. Stefanovich

ShengLi An

SongBo Li

SongWei Gao

WenYu Zhao

Z. Y. Zhang

English

Crossref

    © The Author(s) 2012. This article is published with open access at Springerlink.com csb.scichina.com   www.springer.com/scp                       *Corresponding author (email: san@imust.cn) Article SPECIAL TOPICS:  Materials Science December 2012  Vol.57  No.34: 45134516  doi: 10.1007/s11434-012-5418-2 The luminescence properties of Sr3Gd(BO3)3: Tb3+ phosphors under vacuum ultraviolet excitation ZHAO WenYu1,2, GAO SongWei3, AN ShengLi2,3*, FAN Bin1 & LI SongBo1 1 School of Chemistry and Chemical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China; 2 School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China; 3 School of Material and Metallurgical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China Received February 22, 2012; accepted July 2, 2012; published online August 27, 2012  Tb3+-activated Sr3Gd(BO3)3 green phosphors were prepared by conventional solid-state reaction. The vacuum ultraviolet (VUV) excitation, photoluminescence (PL) and decay properties of the phosphors in the visible range were investigated. The excitation spectrum showed a strong broad band from 160 to 200 nm with a maximum at 183 nm which was adjacent to the VUV excitation light source of 172 nm. Under excitation at 172 nm, the optimum co-doping concentration of Tb3+ was 10 mol%, and the emission intensity of Sr3Gd0.9(BO3)3:0.1Tb3+ was comparable to that of commercial Zn2SiO4:Mn2+. The strongest emission peak of Sr3Gd0.9(BO3)3:0.1Tb3+ was at 543 nm with chromaticity coordinates of (0.2626, 0.4922) and a lifetime of 2.32 ms. The optical properties of the green phosphor Sr3Gd(BO3)3: Tb3+ make it suitable for use in Hg-free fluorescent lamps and plasma display panels. phosphor, vacuum ultraviolet, optical properties, photoluminescence  Citation:  Zhao W Y, Gao S W, An S L, et al. The luminescence properties of Sr3Gd(BO3)3:Tb3+ phosphors under vacuum ultraviolet excitation. Chin Sci Bull, 2012, 57: 45134516, doi: 10.1007/s11434-012-5418-2    Plasma display panels (PDPs) are a promising type of flat panel display that have attracted great interest because of advantages such as fast response, large screen size, good environment durability, low energy consumption, good col-or purity, wide viewing angle, and good temperature stabil-ity. Phosphors play an important role in the performance of PDPs. A commercial green vacuum ultraviolet (VUV) phosphor from Asa, Zn2SiO4:Mn2+ (ZSM), has high lumi-nous efficiency and good color purity, but a long decay time (~4–23 ms), which causes a serious lag in image transfor-mation [1]. It is necessary to overcome this shortcoming by improving existing phosphors and/or developing new green phosphors for PDPs.  Lanthanide-doped borate phosphors are good candidates for PDPs because of their high chemical stability, low syn-thesis temperature, short decay time, intense luminescence and high efficiency. Examples include the red phosphor (Y,Gd)BO3:Eu and green phosphors (Y,Gd)BO3:Tb, and GdMgB5O10:Ce, Tb [2]. A number of rare earth-activated M3Ln(BO3)3 (M=Ba, Sr and Ln=La–Lu, Y, Sc) double bo-rate materials have been developed, such as laser host mate-rials Sr3Tb(BO3)3 [3] and Yb3+-doped Sr3Gd(BO3)3 [4], nonlinear optical materials Ba3R(BO3)3 (R = Y, Ho–Lu) [5], magneto-optical materials Sr3Gd(BO3)3 and Sr3TbxGd1−x- (BO3)3 [6]. The photoluminescence (PL) properties of Tb3+- doped Ba3Ln(BO3)3 (Ln = Lu and Gd) phosphors under VUV excitation have been studied [7]. However, the VUV- excited luminescence of Sr3TbxGd1−x(BO3)3 has not been reported to date. Tb3+ ions as luminescence centers can not only emit green light, but also have a short decay time [8−10], their materials show potential for application as phosphors in PDPs. In this paper, Tb3+-activated Sr3Gd(BO3)3 green VUV phosphors are prepared and their PL properties investigated. 1  Experimental 1.1  Synthesis of Sr3Gd(BO3)3:Tb3+ Sr3Gd1–x(BO3)3: xTb3+ (0≤x≤1) samples were prepared by conventional solid-state reaction. Using appropriate stoi-4514 Zhao W Y, et al.   Chin Sci Bull   December (2012) Vol.57 No.34 chiometric ratios, SrCO3 (strontia, AR grade, Sinopharm Chemical Reagent Co. Ltd., China), H3BO3 (boric acid, AR grade, Sinopharm Chemical Reagent Co. Ltd.), Gd2O3 (gadolinia, 99.99%, Baotou Research Institute of Rare Earths, China) and/or Tb4O7 (terbia, 99.99%, Baotou Re-search Institute of Rare Earths) were thoroughly ground in an agate mortar; an 8 wt% excess of H3BO3 was used to compensate for its evaporation at high temperature. The mixture was heated at 800°C for 3 h in air. The mixture was reground and then reheated at 1000°C for 12 h in a reducing atmosphere (5% H2/95% N2) for the Tb3+-doped samples and Sr3Tb(BO3)3 or in air for the undoped host compound. The final samples were obtained by cooling down to room temperature. 1.2  Characterization X-ray power diffraction (XRD) patterns were recorded on a Rigaku D/max-IIIB diffractometer (Rigaku Corporation, Tokyo, Japan) with Cu Kα radiation (λ= 0.15405 nm) oper-ating at 35 kV and 60 mA. VUV PL spectra were measured at the VUV spectroscopy experimental station on beam line U24 of the National Synchrotron Radiation Laboratory (Hefei, China). The electron energy of the storage ring and beam current was 800 MeV and about 150–250 mA, re-spectively. A Seya-Namioka monochromator (1200 g mm−1, 100–400 nm) was used for the photons produced by syn-chrotron radiation excitation, an Acton-275 monochromator (1200 g mm−1, 330–700 nm) was used for the emitted pho-tons, and the signal was detected by a Hamamatsu H5920-01 photomultiplier. The resolution of the instru-ments was about 0.2 nm. The working pressure was main-tained at about 1×10−3 Pa. The relative VUV excitation in-tensities of the samples were corrected by dividing the measured excitation intensities of the samples by the excita-tion intensities of sodium salicylate (o-C6H4OHCOONa) under the same excitation conditions. The luminescence decay curve was recorded with an Edinburgh FLS 920 combined fluorescence lifetime and steady-state spectrome-ter. The sample was excited by an nF900 nanosecond flash lamp with a pulse width of 1 ns and pulse repetition rate of 40–100 kHz. All measurements were recorded at room temperature. 2  Results and discussion XRD patterns of Sr3Gd(BO3)3, Sr3Gd0.9(BO3)3: 0.1Tb3+ and Sr3Tb(BO3)3 powder [3] are compared in Figure 1. The XRD patterns of the samples prepared in this work were consistent with that of Sr3Tb(BO3)3, indicating that they are a single pure phase. The doped Tb3+ ions prefer to occupy the Gd3+ sites in the crystal structure of Sr3Gd (BO3)3: Tb3+ because Tb3+ and Gd3+ ions possess similar ionic radii and the same valence [11]. Sr3Gd(BO3)3 and Sr3Tb(BO3)3 form   Figure 1  XRD patterns of Sr3Gd(BO3)3, Sr3Gd0.9(BO3)3:0.1Tb3+ and Sr3Tb(BO3)3 [3]. a complete solid solution because of their similar crystal structure. The diffraction peaks show shift to slightly higher angle when Gd3+ ions are substituted with Tb3+ ions because the radius of Gd3+ is a little larger than that of Tb3+. The relative intensity of the diffraction peaks varies slightly as the doping concentration of Tb3+ ions increases, which may be related to the preferential growth of microcrystal parti-cles. The change in luminescence intensity at 543 nm with the doping concentration x of Sr3Gd1−x(BO3)3:xTb3+ (0≤x≤0.2) is presented in Figure 2 (λex = 172 nm). The luminescence in-tensity increases as x increases until it reaches a maximum at 10 mol%. As x continues to increase, the luminescence intensity begins to decrease. In general, a low dopant con-centration results in weak luminescence, while a high do-pant concentration causes luminescence quenching. For Tb3+, when x exceeds a critical value, the 5D4→7FJ transi-tions of Tb3+ are quenched by non-radiative energy transfer between Tb3+ ions and cross-relaxation between the 5D3→   Figure 2  Change in luminescence intensity at 543 nm with doping con-centration x (λex=172 nm).  Zhao W Y, et al.   Chin Sci Bull   December (2012) Vol.57 No.34 4515 5D4 and 7F0→7F6 transitions [10]. These results show that the optimum co-doping concentration of Tb3+ for these sys-tems is 10 mol%. Excitation spectra measured for Sr3Gd0.9(BO3)3:0.1Tb3+, Sr3Tb(BO3)3 and Sr3Gd(BO3)3 are depicted in Figure 3. For Sr3Gd0.9(BO3)3: 0.1Tb3+, the sharp peaks at about 273 and 312 nm are attributed to the 8S7/2→6IJ and 8S7/2→6PJ transi-tions of Gd3+ ions, respectively. This indicates that energy transfer occurs from Gd3+ to Tb3+ in Sr3Gd0.9(BO3)3:0.1Tb3+. By comparison with the spectra for Sr3Tb(BO3)3 and Sr3Gd(BO3)3, the two broad bands located at 232 and 183 nm can be assigned to the f-d transition of Tb3+ ions and a host-related absorption, respectively [7]. In addition, the f-f transition of Tb3+ and Gd3+ ions may also appear in the re-gion of 130–280 nm [12]. When an electron is promoted from the 4f8 ground state to the 4f75d1 excited level within Tb3+ ions, it can give rise to two groups of 4f-5d transitions: spin-allowed (SA) transi-tions that are stronger and appear at higher energy, and spin-forbidden (SF) transitions that are weaker and appear at lower energy [13]. In the spectrum for Sr3Gd(BO3)3, the broad excitation bands located at 232 and 273 nm are from the SA and SF transitions of Tb3+ ions, respectively. There-fore, for Sr3Gd(BO3)3:Tb3+, the transition from the 8S7/2 en-ergy level to the 6IJ levels of Gd3+ with a maximum at about 273 nm overlaps with the 4f-5d transition of Tb3+. This pro-vides further evidence for efficient energy transfer from Gd3+ to Tb3+ in Sr3Gd(BO3)3:Tb3+. Emission spectra obtained for Sr3Gd(BO3)3:Tb3+, Sr3Gd(BO3)3, Sr3Gd(BO3)3:Y3+ and commercial phosphor ZSM upon excitation at 172 nm are compared in Figure 4. For Sr3Gd(BO3)3:Tb3+, the emission peaks at 380–460 nm and 480–650 nm are assigned to the 5D3→7FJ and 5D4→7FJ transitions of Tb3+, respectively. The main emission peak at 543 nm corresponds to the 5D4→7F5 transition of Tb3+. On the basis of this data and that in [14], the Commission In-ternationale de l’Eclairage (CIE) chromaticity coordinates for the emission from Sr3Gd(BO3)3:Tb3+ are x = 0.2626 and    Figure 3  Excitation spectra obtained for Sr3Gd0.9(BO3)3: 0.1Tb3+ (a), Sr3Tb(BO3)3 (b) and Sr3Gd(BO3)3 (c).  Figure 4  Emission spectra determined for Sr3Gd0.9(BO3)3:0.1Tb3+ (a), Sr3Gd(BO3)3 (b), Sr3Gd0.9(BO3)3: 0.1Y3+ (d) and ZSM (e). y = 0.4922, indicating it is green phosphor. According to the approximate formula (T=−437n3+3601n2 −6861n+5514.31, n = (x−0.3320)/(y−0.1858)) [15,16], the relative color tem-perature of Sr3Gd0.9(BO3)3:0.1Tb3+ is 7258.1550 K. In addi-tion, as is shown in Figure 4, the luminescent intensity of Gd3+ at 314 nm weakens when substituted by non-luminous Y3+. In contrast, when Gd3+ is replaced by Tb3+ at the same concentration, the luminescent intensity at 314 nm decreas-es greatly. This indicates that part of the energy is trans-ferred to Tb3+. Thus, compared with the spectrum for Sr3Gd(BO3)3, the decrease of emission at 314 nm for Sr3Gd0.9(BO3)3:0.1Tb3+ is generated not only from energy transfer from Gd3+ to Tb3+, but also from the decrease in the concentration of Gd3+. Comparing the spectra for Sr3Gd0.9(BO3)3:0.1Tb3+ and ZSM, the emission intensity of Sr3Gd0.9(BO3)3:0.1Tb3+ at 543 nm is about 145% that of ZSM at 525 nm upon excitation at 172 nm. The light inten-sity for the range 380–650 nm of Sr3Gd0.9(BO3)3:0.1Tb3+ is about 98% that of ZSM. For PL, the radiant efficiency (η) is defined as the ratio of emitted luminescent power and the power absorption of the material from the exciting radiation [17]. The luminous efficiency (L) is defined as the ratio of the luminous flux Φ(v) emitted by the material and the ab-sorbed power [17]. In general, Φ(v) is given by the folding or weighting of the spectral power distribution Φ(λ) with the normalized photopic response curve V(λ) and the constant factor Km [18]. Φ(λ) is directly proportional to the intensity of PL emission. Therefore, η and L can be also determined roughly from the PL emission peak areas and the weighting of PL emission intensity with the normalized photopic re-sponse curve V(λ), respectively. According to the experi-mental data, the emission peak area of the Sr3Gd0.9(BO3)3: 0.1Tb3+ phosphor is similar to that of ZSM. The weighting of the PL emission intensity with V(λ) of Sr3Gd0.9(BO3)3: 0.1Tb3+ is higher than that of ZSM. Therefore, η of Sr3Gd0.9(BO3)3:0.1Tb3+ might be similar to that of ZSM, and L of Sr3Gd0.9(BO3)3:0.1Tb3+ might be higher than that of ZSM. 4516 Zhao W Y, et al.   Chin Sci Bull   December (2012) Vol.57 No.34  Figure 5  PL decay curves determined for Sr3Gd0.9(BO3)3:0.1Tb3+ and commercial phosphor ZSM (λex= 232 nm). PL decay curves measured for Sr3Gd0.9(BO3)3:0.1Tb3+ and commercial phosphor ZSM upon excitation at 232 nm are presented in Figure 5. The decay curve for Sr3Gd0.9(BO3)3:0.1Tb3+ can be fitted to the single exponen-tial equation I = I0exp(−t/τ), in which I0 is the initial inten-sity at t = 0 and τ is the decay lifetime. Using this equation, the excited state lifetime for Sr3Gd0.9(BO3)3:0.1Tb3+ was determined to be 2.32 ms (the time to decay 1/e of the orig-inal intensity). According to [20], τ1/e of commercial phos-phor ZSM is 4.56 ms, so Sr3Gd0.9(BO3)3:0.1Tb3+ has a shorter decay time. Although the above results were ob-tained following excitation at 232 nm, it is believed that the activator decay under VUV excitation will be around this value in the present case. 3  Conclusions Sr3Gd(BO3)3:Tb3+ phosphors were prepared by solid-state reaction. XRD revealed that Tb3+ ions act as luminescent centers, inhabiting the sites of Gd3+ ions. Upon excitation at 172 nm, the emission intensity of Sr3Gd0.9(BO3)3:0.1Tb3+ is the strongest of the investigated dopant concentrations. A strong excitation band located at 183 nm is caused by host-related absorption. For Sr3Gd(BO3)3:Tb3+, SA and SF f-d transitions were located at 232 and 273 nm, respectively. The excitation peaks at about 273 and 312 nm were at-tributed to 8S7/2→6IJ and 8S7/2→6PJ transitions of Gd3+ ions, respectively. Energy transfer from Gd3+ to Tb3+ was ob-served. The emission intensity of Sr3Gd0.9(BO3)3:0.1Tb3+ at 543 nm was about 145% that of commercial phosphor ZSM at 525 nm. The light intensity for the range 380–650 nm of Sr3Gd0.9(BO3)3:0.1Tb3+ was similar to that of ZSM upon excitation at 172 nm. The lifetime of Sr3Gd(BO3)3:Tb3+ was 2.32 ms, so it is considered promising as a green phosphor for use in PDPs, Hg-free lamps or LCD backlights. This work was supported by the “111 Talents Project” Foundation of Inner Mongolia, and the Innovation Fund of Inner Mongolia University of Science and Technology (2010NC026). 1 Zhang Z Y, Wang Y H, Zhang J C. A novel green-emitting VUV phosphor Na3YSi3O9: Tb3+. Mater Lett, 2008, 62: 846–848 2 Lin H H, Liang H B, Zhang G B, et al. The luminescence of Eu3+ ac-tivated Ba2Mg(BO3)2 phosphors. Appl Phys A, 2011, 105: 143–147 3 Lu J Y, Guo F Y, Chen J Z. Growth and characteristic of Sr3Tb(BO3)3 crystal. J Crystal Growth, 2011, 314: 157–162 4 Pan J G, Hu Z S, Lin Z B. Growth of Yb3+-doped Sr3Gd(BO3)3 crystal. J Cryst Growth, 2004, 262: 527–530 5 Stefanovich S Y, Khamaganova T N. Nonlinear optical properties of Ba3R(BO3)3(R = Y, Ho–Lu) polar crystals. Inorg Mater, 2002, 38: 66–68 6 Lu J Y, Chen J Z. Growth and magnetic-optical properties of Sr3Gd(BO3)3 andSr3TbxGd1-x(BO3)3 single crystals. Cryst Res Technol, 2010, 45: 1137–1140 7 Wang D Y, Chen T M, Cheng B M. Host sensitization of Tb3+ ions in tribarium lanthanide borates Ba3Ln(BO3)3 (Ln = Lu and Gd). Inorg Mater, 2012, 51: 2961–2968 8 Zhang F, Wang Y H, Liu B T, et al. Investigation of Na3GdP2O8:Tb3+ as a potential green-emitting phosphor for plasma display panels. Mater Res Bull, 2011, 46: 722–725 9 Wang D, Wang Y H. Optical properties of (Y,Tb)PO4 under VUV excitation. Mater Chem Phys, 2009, 115: 699–702 10 Zhang J C, Wang Y H, Zhang Z Y, et al. The concentration quench-ing characteristics of 5D3-7FJ and 5D4-7FJ (J=0–6) transitions of Tb3+ in YBO3:Tb3+ phosphor. Chin Sci Bull, 2007, 52: 2297–2300 11 Su Q. Rare Earth Chemistry (in Chinese). Kaifeng: Science and Technology of Henan Press, 1993. 8–12 12 Xie M B, Liang H B, Han B, et al. Ca6Gd1.5Tb0.5Na2(PO4)6F2—An intense green-emitting phosphor under vacuum ultraviolet and low- voltage cathode ray excitation. Opt Lett, 2009, 34: 3466–3468 13 Zhong J P, Liang H B, Han B, et al. NaGd(PO3)4:Tb3+—A new promising green phosphor for PDPs application. Chem Phys Lett, 2008, 453: 192–196 14 Schanda J. Colorimetry: Understanding the CIE System. Hoboken: John Wiley & Sons, 2007 15 McCamy C S. Correlated color temperature as an explicit function of chromaticity coordinates. Color Res Appl, 1992, 17: 142–144 16 Wang B L, Sun L Z, Ju H D, et al. Sol-gel synthesis of single-phase Ca5MgSi3O12: Eu2+, Mn2+ phosphors for white-light emitting diodes. Mater Lett, 2009, 63: 1329–1331 17 Blasse G, Grabmaier B C. Luminescence Materials. Berlin: Springer- Verlag, 1994 18 Flesch P. Light and Light Sources: High-Intensity Discharge Lamps. Berlin Heidelberg: Springer-Verlag, 2006 19 Liu J D, Wang Y H, Yu X, et al. Enhanced photoluminescence prop-erties of Zn2SiO4:Mn2+ co-activated with Y3+/Li+ under VUV excita-tion. J Lumin, 2010, 130: 2171–2174  Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.  

Chinese Science Bulletin

The luminescence properties of Sr3Gd(BO3)3: Tb3+ phosphors under vacuum ultraviolet excitation

https://link.springer.com/content/pdf/10.1007%2Fs11434-012-5418-2.pdf

The luminescence properties of Sr3Gd(BO3)3: Tb3+ phosphors under vacuum ultraviolet excitation

Abstract

Similar works

Full text

Available Versions

Crossref