PhotoluminescencepropertiesofNa1.45La8.55(SiO4)6(F0.9O1.1)Eu 01

Supporting InformationPHOTOLUMINESCENCE PROPERTIES OF NA1.45LA8.55(SIO4)6(F0.9O1.1): EU FOR APPLICATIONS AS A REDDISH ORANGE PHOSPHORQUN SHI*,†, DHIA A. HASSAN*,‡ and RENJIE ZENG*,§,¶*Department of Materials Science and EngineeringXiamen University, Xiamen 361005, P. R. China†Fujian Key Laboratory of Advanced MaterialsXiamen University, Xiamen 361005, P. R. China§RJZeng@¶Corresponding authors.12The crystal structure of Na1.45La8.55(SiO4)6(F0.9O1.1), shown in Fig. S1, was determined to be a monoclinic system [space group p (1121)] with lattice constants a= 9.678, b= 9.682, c= 7.1631, a= b= 90, g= 120.04, V= 581.04, and Z= 1 (JCPDS card No. 79–2417). There are four different sites for Eu incorporation in a Na1.45La8.55(SiO4)6(F0.9O1.1) host. Although Eu ions have slightly smaller ionic radii than La ions (0.107 nm, CN = 8 versus 0.118 nm, CN = 8, respectively), the Eu ions substitute with La sites containing an inversion center as indicated by the dominant lines (5D0→7F1) of the Eu emission spectrum which only correspond to an inversion center. Thus, Eu ions are expected to substitute for La ions in the Na1.45La8.55(SiO4)6(F0.9O1.1) host, resulting in a chemical formula of Na1.45La8.55-8.55x(SiO4)6(F0.9O1.1): 8.55x Eu. When Eu ions are incorporated into the Na1.45La8.55(SiO4)6(F0.9O1.1) host, substitution of Eu ions for La ions might induce vacancy defects to compensate for the excess positive charge. The SiO4 tetrahedral can fill in the gaps in the three dimensional structure of La–O. As a consequence, the crystal lattice for Na1.45La8.55(SiO4)6(F0.9O1.1) might exhibit slight deformation from monoclinic symmetry due to the nonequivalent substitution. The compound Na1.45La8.55(SiO4)6(F0.9O1.1) is particularly suitable as model for fundamental studies of certain physical properties due to the simplicity of the crystal structure.The emission energy level scheme of the Eu–doped Na1.45La8.55(SiO4)6(F0.9O1.1) phosphor under 254 nm excitation is depicted in Fig. S2. Eu ions with 4f7 configuration have complicated energy levels and multiple possible transitions between the f levels.1 The energy levels depicted in Fig. S2 are determined from the calculated energy levels reported by Carnall et al.2-3 Eu ions are excited from the ground 5D0 state to the excited 5D2 state when the sample is excited with 254 nm light. Due to the small energy differences between higher energy levels, electrons relax to the 5D2 level by cascade nonradioactive relaxation (NR) processes. Thus, we observe five intense emission peaks centered at 575 nm, 587 nm, 595 nm, 611 nm, and 619 nm corresponding to the 5D0 to 7F j (j = 0–2) emissions of Eu ions.4 The energies corresponding to the excitation spectral lines are higher than the excitation energy for these levels. Thus, these levels may also be populated by a relaxation process similar to the 5D0 level.4Figure S3 displays the diffuse reflectance spectrum of Na1.45La8.55-8.55x(SiO4)6(F0.9O1.1): 8.55x Eu (x= 0.000 and 0.035) samples in the spectral region from 200 to 800 nm at room temperature [UV–visible spectrophotometer (Cary 5000, Varian, America) using BaSO4as a reference]. The Na1.45La8.55-8.55x(SiO4)6(F0.9O1.1): 8.55x Eu (x= 0.035) sample has a wide and strong near ultraviolet (NUV) absorption before 400 nm. The absorption band does not overlap with the LED blue phosphor emission wavelength. In order to use this phosphor for NUV LED applications, the photon absorption must occur at lower wavelengths. However, the absorption of the Eu ion is overlapped by the charge transfer (CT) transition. Therefore, Na1.45La8.55(SiO4)6(F0.9O1.1): Eu could be applied for use NUV–based WLEDs.Fig. S4 shows the fluorescence decay curve of our standard sampl e at λem = 610 nm and λe x = 254 nm [The decay curve of the Eu ion in the Na 1.45La 8.55(SiO 4)6(F 0.9O 1.1): Eu phosphor was measured by an FLS920–Combined with Time Resolved & Steady State Fluorescence Spectrometer (Edinburgh Instruments) with a 450 W xenon lamp as a light source]. There are two transition superpositions in the fluorescence decay curve for the 5D 0→7F 1 transition of the Eu ions in the sample. The emission decay curves of the Eu ions are fit by the second–order exponential equation (1):1212()A exp()A exp()t t I t t t =-+- (1)where I is the luminescence intensity, t is the time, τ1 and τ2 are the show and fast components of the decay lifetimes, respectively, and A 1 and A 2 are their corresponding fit parameters.5 On the basis of Eq. (1), the lifetimes are determined to be τ1 = 735.70 m s and τ2 = 1014.63 m s.References1.S. S. Babu et al ., J. Lumin . 126, 109 (2007). 2.W. T. Carnall et al ., J. Chem. Phys . 49, 4412 (1968). 3.W. T. Carnall et al ., J. Chem. Phys . 90, 3443 (1989). 4.R. J. Xie et al ., Appl . Phys . Lett . 90, 191101 (2007). 5. P. Waltereit et al ., Nature . 406, 865 (2000).。