Journal of Luminescence 102–103 (2003) 391–394 Nanomaterials containing rare-earth ions Tb, Eu, Er and Yb: preparation, optical properties and application potential T Kim Anha,b,*, L Quoc Minha, N Vua, T Thu Huonga, N Thanh Huonga, C Barthouc, W Strekd a Institute of Materials Science, NCST of Vietnam, 18 Hoang Quoc Viet Road, Cau Giay, Hanoi, Viet Nam International Training Institute for Materials Science, Dai hoc Bach Khoa, Dai Co Viet, Hanoi, Viet Nam c Lab d Optique des Solides UMR7601, Univ P & M Curie, Place Jussieu, F 75252 Paris Cedex 05, France d Institute of Low Temperature and Structure Research, PAS, Okolna, Wroc!aw, Poland b Abstract This paper focuses on preparation, optical properties and application potential of some nanomaterials based on Y2O3:Eu,Tb,Er,Yb and SiO2–TiO2 and SiO2–ZiO2 doped with Er and Yb Y2O3 nanophosphors are prepared by the combustion method with different doped concentrations The nanocrystal size of Y2O3:Eu is from 4.4 to 72.2 nm depending on the technology condition The luminescent spectra, up-conversion and lifetimes were measured and compared The influence of the technological conditions on the luminescent properties was investigated in detail The energy transfer effect was studied by the luminescent spectra and the lifetimes in the temperature dependence for the samples with rare-earth concentrations of mol%, The relative concentration between Eu and Tb is 8/2 for energy transfer from Tb to Eu The SiO2–TiO2 and SiO2–ZiO2 thin films containing Er rare-earth ion were prepared by the sol– gel technique Optical properties were investigated and the influence of the Er concentration on the luminescent spectra as well as the influence of the Ti concentration on the refractive index of thin films was presented r 2003 Elsevier Science B.V All rights reserved Keywords: Nanophosphors; Sol–gel; Rare earths; Waveguide Introduction Materials with nanostructure are increasingly interesting for optoelectronics and also for photonics Nanomaterials display novel, often enhanced, properties compared to traditional materials, nanophosphors: synthesis, properties and applica*Corresponding author Institute of Materials Science, NCST of Vietnam, 18 Hoang Quoc Viet Road, Cau Giay, Hanoi, Viet Nam Tel.: +84-4-7560371; fax: +84-4-7562039 E-mail address: kimanh@ims.ncst.ac.vn (T.K Anh) tions were presented [1,2] Luminescence properties of nanocrystalline Y2O3:Eu3+ in different host materials were studied [3] High-definition displays call for sub-micron particle sizes to maximize screen resolution and screen efficiency Nanophosphors codoped with Tb, Eu for high intensity of red region by energy transfer between Tb and Eu as well as Y2O3:Er,Yb for infrared region and upconversion effect are interesting SiO2–TiO2 system offers the possibility of producing a material with a controllable refractive index from 1.46 (the refractive index of pure silica) to 2.2 (pure 0022-2313/02/$ - see front matter r 2003 Elsevier Science B.V All rights reserved PII: S 0 2 - 3 ( ) 0 - 392 T.K Anh et al / Journal of Luminescence 102–103 (2003) 391–394 amorphous TiO2) SiO2–ZiO2 thin films doped with rare earth are currently of much interest in planar waveguides application, because they are homogeneous and have the ability to tune the refractive index and wavelength [4] Sol–gel chemistry, where all chemicals mix in the matrices in a molecular scale combined with the spincoating or dip-coating technique, is a good method for producing rare-earth-doped planar waveguides [5] We report the preparation, structure and optical properties of SiO2–TiO2:Er or SiO2– ZiO2:Er thin films and discuss briefly the possibility of the development of nanomaterials for active waveguides Experiment The Y2O3:Eu, Y2O3:Tb,Eu and Y2O3:Er,Yb nanophosphors with different concentrations of RE were obtained from the calcination of the basic carbonate Eu3+, Tb3+or Er3+ and Yb3+ (RE) ions are easily hydrolyzed and then the precipitation of basic carbonate in an aqueous solution of urea or glycine SiO2–TiO2:Er and SiO2–ZiO2:Er thin films were prepared via the hydrolysis and condensation of tetraethoxysilane Si (OC2H5)4 (TEOS) 98% Merck with Tetraisopropylorthotitanate Ti(OC3H7)4 Fluka [6] or Zr (OC3H7)4 Aldrich The spin coating method on Si substrates in the clean room of the class 100, dip coating method and rapid thermal annealing were used The photoluminescence spectra were studied by the monochromator Jobin-Yvon HR 460, and a multichannel CCD detection from Instruments SA model Spectraview-2D and Triax 320 for infrared range measurements The decay were analyzed by a PM Hamamatsu R928 and Nicolet 490 scope with a time constant of the order of ns N2, diode, Ti-Sapphire or argon lasers were used as excitation sources for the different wavelengths The morphology and particle sizes of Y2O3:RE was observed by using a high-resolution transmission electron microscope (TEM) Philips CM 200 The Y2O3: RE powder, SiO2–TiO2:Er and SiO2– ZiO2:Er were checked by the X-ray diffractometer D 5000 (Siemens) and Atom Force Microscope E+ Digital (AFM) Results and discussion The value for crystallite size can be extracted according to the Warren–Averbach theory The particle sizes are 4.4, 5.6, 15.2, 46.1 and 72.2 nm for Y2O3:Eu nanophosphors with various annealing times and temperatures 5501C, 60 min, 6001C, 30 min, 7001C, 30 min, 9001C, 30 and 9001C, 60 min, respectively The high-resolution TEM images of Y2O3:Er mol% nanophosphors, 6001C, 30 annealing was presented in Fig The development of efficient nanophosphors has been one of the key issues in commercializing the new type of flat panel display with respect to potentially higher display resolution The optical efficiency of prepared spherical Y2O3:Eu as red phosphor was twice as much as that of commercial products in cathode luminescent according to Cho et al [7] In order to increase efficient luminescence in the red phosphor, Eu is codoped with Tb for energy transfer effect The luminescent spectra of Y2O3:Tb,Eu mol% for three ratios 9/ 1, 8/2 and 7/3 are shown in Fig and relative ratio 8/2 has the strongest energy transfer The fullwidth at half-maximum (FWHM) is also greater for the nanoparticles Under 337.1 nm excitation, Fig High-resolution TEM image of Y2O3:Er (5 mol%) 6001C, 30 T.K Anh et al / Journal of Luminescence 102–103 (2003) 391–394 Y0.95 : EuxTby Nanophosphors Intensity (norm.) 1.6 20 Y2O3 :Er 3+ λ exc= 982 nm P = 96 mW T = 300 K 1.4 Tann = 600˚C (30 min) 1.2 15 Intensity (rel.) 393 1.0 0.8 8/2 0.6 10 0.4 9/1 0.2 0.0 7/3 1450 540 570 600 630 λ (nm) Fig Luminescent spectra of Y2O3:Tb,Eu with the mole ratio of Eu/Tb: 7/3, 8/2, 9/1 lexc ¼ 337:1 nm 1500 1550 λ (nm) 1650 Fig Luminescent spectra in the infrared region of Y2O3:Er3+ (10 mol%) nanophosphors lexc ¼ 982 nm (1) 6001C, 30 and (2) 7001C, 30 NanoScope Scan size Setpoint Scan rate Number of samples Nanophosphores Y2O3:Er3+ (YERU2) 1600 λexc = 799.8 nm AFM 15.97 µm 0V 20.35 Hz 512 Intensity (a.u.) T = 300 K 15 10 500 SZAE500 600 x z µm 5.000 µm/div 270.457 nm/div 700 λ (nm) Fig Emission spectra of Y2O3:Er3+ (10%) nanophosphor lexc ¼ 799:8 nm Power laser: 550 mW Y2O3:Tb,Eu presents for the 5D0 excited level of Eu3+ lifetimes of 360, 640 and 940 ms for the ratio of Eu/Tb 8/2, 7/3 and 9/1, respectively The upconversion effect is observed for both Y2O3:Er and Y2O3:Er,Yb Fig presents the up-conversion spectra of Y2O3:Er 10 mol% at 799.8 nm excitation The infrared luminescent spectra of Y2O3:Er 10 mol% is presented in Fig for two annealing temperatures : 6001C and 7001C To compare the green and the red up-conversion, we can propose two mechanisms First mechanism for dominant green luminescence: the laser light brings the ion Er3+ into 4I9/2 level, which then non-radiatively decays to the 4I11/2 and 4I13/2 levels Energy transfer processes bring the ion into 4F3/2 and H11/2, non-radiative decay to the lower levels and Fig AFM of the Er3+-doped 83Silica/17Zirconia/Alumina (15%) sample was annealed at 8801C the 2H11/2, 4S3/2 transitions to 4I15/2, and 4F9/2 transitions to 4I15/2 occur The second mechanism is red luminescence stronger than green one Laser beam brings the ion to the excited 4I9/2 level One ion non-radiatively decays to the 4I13/2 level, and second one decays to the 4I11/2 level Energy transfer processes bring the ion to the 4F9/2 and a red emission can be observed For codoped samples with Yb, an energy transfer from the 2F5/2 excited state of Yb3+ to Er 4I11/2 can occur For thin films prepared by dip coating, the AFM of the Er3+-doped 83 Silica/17 Zirconia/ Alumina (15%) sample annealed at 8801C is shown in Fig One can notice that the roughness is about 51 nm compared to the value of 24 nm for T.K Anh et al / Journal of Luminescence 102–103 (2003) 391–394 394 Intensity (a.u.) Si/Ti & Si/Zr : Er3+ λexc = 976 nm T = 300 K Si/Zr Si/Ti 1450 1500 1550 1600 1650 λ (nm) Fig Luminescent spectra of the Er3+ (5%) in Silica/Titania codoped with Yb3+ (12.5%) and Al (10%) annealed at 9501C and Silica/Zirconia samples codoped with Yb3+ (15%) and Al (6%) annealed at 8501C conditions SiO2–TiO2:Er and SiO2–ZiO2:Er thin films were deposited by the spin coating and dip coating methods in order to study the optical properties as well as the possible application for planar waveguide The typical transitions of trivalent Er and Eu were observed and discussed Energy transfer and up-conversion mechanisms were studied Refractive index for SiO2–TiO2 thin films can be tailored in a wide range by controlling the relative quantity of the two precursors The emission depends on the temperature of the thermal processing and on the Er,Yb concentrations This material will be promising for active waveguides in telecommunication application Acknowledgements the case without Alumina This value is convenient for planar waveguide application Fig represents the luminescent spectra of the Er3+ (5%) in Silica/ Titania codoped with Yb3+(12.5%) and Al (10%) annealed at 9501C and the Er3+ (5%) in Silica/ Zirconia samples codoped with Yb3+ (15%) and Al (6%) annealed at 8501C The FWHM of the corresponding band from the 4I13/2–4I15/2 transition is above 50 nm The adding of alumina increases the process of densification of the silica–zirconia and silica–titania system The refractive index varied from 1.49 to 1.60 with respect to the Ti concentration Refractive index and thickness of 90SiO2–10TiO2, 85SiO2–15TiO2 and 80SiO2– 20TiO2 thin films at different annealing temperatures are presented in Ref [8] For example, for 9001C annealing temperature, the measured refractive indexes are 1.53, 1.56 and 1.60, respectively The SiO2–TiO2:Er thin films and SiO2–ZiO2:Er thin films show the transitions from 4I13/2 to 4I15/2 of Er3+ in the infrared region (1530 nm ) and 4S3/2 level to 4I15/2 in the visible region (550 nm) Conclusion Nanophosphor Y2O3:RE (Tb, Eu, Er, Yb) 5– 10 mol% samples were prepared by combustion method and the crystal size can be monitored in the range of 10–80 nm depending on technology We would like to thank Prof Nguyen Van Hieu, Prof Clement Sanchez, and Dr Paul Simons for their help Our work was financially supported by the project Franco-Vietnamese 2001, the Institute of Materials Science, NCNST of Vietnam, the International Training Institute for Materials Science, the National Basic Research Programs of Vietnam 2001–2002 References [1] G.Y Hong, S.H Kwon, J.S Yoo, C.J Summers, Extended Abstracts of the Fifth International Conference on the Science and Technology of Display Phosphors, San Diego, CA, November, 1999, pp.187–190 [2] B.R Ratna, A.D Dinsmore, Y Tian, S.B Qadri, D.S Hsu, H.F.Gray, Extended Abstracts of the Fifth International Conference on the Science and Technology of Display Phosphors, San Diego, CA, November 1999, pp 295–296 [3] R Schmechel, M Kennedy, H von Seggern, H Winkler, M Kolbe, A Fischer, L Xaomao, A Benker, M Winterer, H Hahn, J Appl Phys 89 (3) (2001) 1679 [4] C Sanchez, B Lebeau, MRS Bull 26 (2001) 377 [5] X Orignac, D Barbier, X.M Du, R.M Almeida, Appl Phys Lett 69 (7) (1996) 895 [6] L.Q Minh, T.K Anh, P Benalloul, C Barthou, in: E Giacobino, et al (Eds.), Advances in Optics and Spectroscopy, National University Press, Hanoi, 2001, pp 505–509 [7] S.H Cho, L.S Yoo, J.D Lee, J Electrochem Soc 145 (3) (1998) 1017 [8] L.Q Minh, N.T Huong, C Barthou, P Benaloul, W Strek, T.K Anh, Mater Sci 20 (2) (2002) 63 ... with Yb3 + (15%) and Al (6%) annealed at 8501C conditions SiO2–TiO2 :Er and SiO2–ZiO2 :Er thin films were deposited by the spin coating and dip coating methods in order to study the optical properties. .. well as the possible application for planar waveguide The typical transitions of trivalent Er and Eu were observed and discussed Energy transfer and up-conversion mechanisms were studied Refractive... possibility of the development of nanomaterials for active waveguides Experiment The Y2O3 :Eu, Y2O3:Tb,Eu and Y2O3 :Er, Yb nanophosphors with different concentrations of RE were obtained from the calcination