Published: July 22, 2011 r2011 American Chemical Society 8870 dx.doi.org/10.1021/jp203938x | J. Phys. Chem. A 2011, 115, 8870–8876 ARTICLE pubs.acs.org/JPCA Emission and Excitation Spectra of Ce 3+ and Pr 3+ Ions in Hexafluoroelpasolite Lattices Chang-Kui Duan, †,‡ Peter A. Tanner,* ,‡ Vladimir Makhov, § and Nicholas Khaidukov || † Department of Physics, University of Science and Technology of China, 96 Jinzhai Road, Hefei 230026, Anhui. People's Republic of China ‡ Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong S.A.R., People's Republic of China § Lebedev Physical Institute, Leninsky Prospect 53, Moscow 119991. Russia ) Kurnakov Institute of General and Inorganic Chemistry, Moscow 117907, Russia ’ INTRODUCTION With the current availability of synchrotron radiation sources, and the recent theoretical developments for 4f N1 5d energy level calculations and 4f N 4f N1 5d transition intensity simulations, new experimental studies and interpretations have been forth- coming, especially for lanthanide ions (Ln 3+ ) doped into wide band gap hosts. 14 The vacuum ultraviolet (VUV) spectra of Ln 3+ ions doped at the S 4 site of LiYF 4 have received particular attention. 59 Other interconfigurational studies of the 4f 1 Ce 3+ and 4f 2 Pr 3+ ions have employed the CaF 2 1012 and KMgF 3 13,14 hosts. The 4f 1 5d 1 absorption transition of Ce 3+ is electric dipole allowed and comprises up to five bands in the ultraviolet spectral region, corresponding to transitions to the Kramers doublet levels derived from E g and T 2g orbitals of the 2 D multiplet. On the other hand, the spectra of Pr 3+ are more complex since the 4f 1 5d 1 configuration comprises the 10 multi- plets 1,3 P, 1,3 D, 1,3 F, 1,3 G, and 1,3 H. The present study concerns the 4f5d VUV excitation spectra and ultraviolet emission spectra of Ce 3+ and Pr 3+ at octahedral (O h ) symmetry sites, for which the energy level degeneracies are high: up to four (for Ce 3+ ) and three (for Pr 3+ ). Potential applications of these systems concern tunable ultraviolet upcon- version lasers 15 and X-ray storage phosphors. 16 On the theore- tical side, recent attempts have signaled an improvement of ab initio calculations for these ions in crystals. 17,18 Some previous studies of Ce 3+ and Pr 3+ at octahedral (O h ) symmetry sites have been carried out but provided fairly limited information content since the spectral features were broad. This prompted our investigations because the spectra of the corre- sponding chloride systems were well-resolved. 19,20 Aull and Jenssen 21,22 investigated the excitation and emission spectra of Rb 2 NaYF 6 doped with Ce 3+ . Two different crystal sites were distinguished for Ce 3+ . Excitation into the “blue site” bands, with excitation maxima at 240, 295 nm, gave a broad emission band peaking at 340 nm. On the other hand, excitation into the broad longer-wavelength band at 310 nm gave a broad emission band with maximum at 400 nm. Kodama et al. 23 found that the center of gravity of the 5d 12 D multiplet is at ∼250 nm (40000 cm 1 ) for Ce 3+ doped into several oxides and fluorides. The energy levels of the lowest 5d states of Ce 3+ are generally lower in cubic symmetry than in octahedral symmetry because the shift of the E g state from the center of gravity is 1.5 times larger than that of the T 2g state. Schiffbauer et al. 24 considered that Pr 3+ doped into Cs 2 KYF 6 occupies three different types of sites. The substitution at the T d Cs + site afforded the possibility of quantum cutting because the 4f5d onset (at 208 nm) lies above the Pr 3+ 4f 21 S 0 energy level. Excitation into the other two sites (assigned to substitution of the K + and Y 3+ octahedral sites by Pr 3+ ) gave broad 4f5d f 4f 2 emission, with the band maximum at ∼300 nm. This study concludes our experimental and theoretical inves- tigations of the VUV spectra of Ln 3+ doped into the Cs 2 NaYF 6 lattice. 2527 Attempts have been made to interpret and Received: April 28, 2011 Revised: June 7, 2011 ABSTRACT: The emission and excitation spectra of Ce 3+ and Pr 3+ doped into the cubic host Cs 2 NaYF 6 have been recorded at room temperature and ∼10 K using synchrotron radiation. The two 5d 1 T 2g states of Ce 3+ have been located from the excitation spectra, whereas the E g state is placed above the host band gap. Decay measurements of the 5d 1 f 4f 1 Ce 3+ emission, and spectra collected using selective excitation, indicate the occupation of more than one type of site by Ce 3+ in this host lattice. By contrast, the location of features in the 4f 1 5d 1 f 4f 2 emission of Pr 3+ is independent of the excitation wavelength. Assignments are presented for some of the 4f 1 5d 1 levels and for the Pr 3+ -F  charge transfer band. The 5d emission lifetimes for Ce 3+ and Pr 3+ in the Cs 2 NaYF 6 host are 42 and 29 ( 1 ns, respectively, and are not temperature-dependent.