Spectroscopy of Luminescent Crystals Containing Rare Earth Elements Meng-Ling Chen, Kwang-Hwa Lii, and Bor-Chen Chang Department of Chemistry National Central University Jhongli 32001, Taiwan

Trivalent Lanthanides (Ln 3+ )? Eu 3+, Ce 3+, Tb 3+ are luminescent centers of fluorescent/phosphorescent powders. Strong emission from visible to near-infrared wavelengths. Unlike the ligand field splitting in the d orbitals of transition metals, the spectroscopy of 4f elements principally attributes to perturbed atomic transitions. Any given compound of the rare earth element is likely to crystallize with the same structure as any other rare earth elements. 2

Energy Levels of Eu 3+ Selection Rules Electric Dipole (ED) ∆J= ± 2, ± 4, ± 6 Magnetic Dipole (MD) ∆J= 0, ± 1 Forbidden 0↔0 ENERGY ━ ﹝ Xe ﹞ 4 f 6 7F7F 7F67F6 7F57F5 7F47F4 7F37F3 7F27F2 7F17F1 5D5D 5D05D0 5D15D1 5D25D2 5D45D4 5D35D3 Spin–Orbit Coupling 7F07F0 Stark Levels Strong Red Luminescence Racah, Phys. Rev. 76, 1352 (1949). Carlos and Videira, Phys. Rev. B 49, 49, (1994). 3

R 2 (C 8 H 10 O 4 ) 3 4 R= Y, Eu, Tb C 8 H 10 O 4 = 1,4-cyclohexanedicarboxylate (CHDC)

Emission of R 2 (CHDC) 3 5

Photoluminescence (PL) Spectra Y 2 (CHDC) 3 π*→n Eu 2 (CHDC) 3 5 D 0 → 7 F J 6 J= 0 J= 1 J= 2 J= 3J= 4 J= 6 J= 5 J= 4J= 3 Tb 2 (CHDC) 3 5 D 4 → 7 F J

5D15D1 5D25D2 5L65L6 5D45D4 5D45D4 Eu 2 (CHDC) 3 Tb 2 (CHDC) 3 Excitation Spectra 7

* PL Spectra Eu 2 (CHDC) 3 Tb 2 (CHDC) 3 Y 1.06 Eu 0.39 Tb 0.55 (CHDC) D 4 → 7 F 6 5D0→7F15D0→7F1 5D0→7F25D0→7F2 5D0→7F35D0→7F3 5D0→7F45D0→7F4 5 D 4 → 7 F 5 5 D 4 → 7 F 4 5 D 4 → 7 F 3 5D0→7F05D0→7F0

Excitation Spectra of Y 1.06 Eu 0.39 Tb 0.55 (CHDC) 3 Eu 3+ 5 D 1 Eu 3+ 5 D 2 Eu 3+ 5 L 6 Tb 3+ 5 D 4 Eu 3+ 5 D 4 9 Detected Emission Eu 3+ Tb3 +

PL Spectra at 355 nm Excitation 10 Eu 3+ 5 D 4 → 7 F 0 Eu 3+ 5 D 0 → 7 F 1 Tb 3+ 5 D 4 → 7 F 4 Tb 3+ 5 D 4 → 7 F 5 Eu 0.08 Tb 1.92 (CHDC) 3 Tb 2 (CHDC) 3 Tb 3+ 5 D 4 → 7 F 6

Temporal Waveforms of Emission in Eu 0.08 Tb 1.92 (CHDC) 3 11 Eu 3+ Tb 3+

Energy Transfer Tb 3+ 5 D 4 → 7 F 5 Eu 3+ 5 D 2 ← 7 F 4 5 D 1 ← 7 F D45D4 5DJ5DJ Eu 3+ Tb FJ7FJ 7FJ7FJ

Eu 3+ Emission Lifetime 13 Y 1.96 Eu 0.04 (CHDC) 3 Y 1.9 Eu 0.1 (CHDC) 3 Eu 0.08 Tb 1.92 (CHDC) 3 Y 1.06 Eu 0.39 Tb 0.55 (CHDC) 3 Y 1.64 Eu 0.36 (CHDC) 3 Eu 2 (CHDC) 3

Tb 3+ Emission Lifetime 14 Y 0.97 Tb 1.03 (CHDC) 3 Y 1.06 Eu 0.39 Tb 0.55 (CHDC) 3 Tb 2 (CHDC) 3 Eu 0.08 Tb 1.92 (CHDC) 3

Silicates and Germanates KEuGe 2 O 6 τ = 0.81 ms R (Eu-Eu) ～ 3.9 Å Cs 3 EuSi 6 O 15 τ = 5.5 ms R (Eu-Eu) ～ 7.2 Å 15 Chen et al. Dalton Trans. 2008, Huang et al. Chem. Mater. 2005, 17, 5743

KEu x Nd 1-x Ge 2 O 6 16 x= 1 x= 0.98 x= 0.96 x= 0.94 x= 0.84 Eu 3+ Emission Lifetime

5D0 → 7F15D0 → 7F1 5 D 0 → 7 F 2 5 D 0 → 7 F 3 5 D 0 → 7 F 4 5 D 0 → 7 F 0 x= 1 x= x= 0.96 x= 0.95 PL Spectra of Cs 3 Eu x Nd 1-x Si 6 O 15 17

Ligand Effects Cs 3 Eu x Nd 1-x Si 6 O 15 KEu x Nd 1-x Ge 2 O 6 18 XLifetime (ms) XLifetime (μs)

562.3 nm Excitation of Ligands PL Spectra 19 Cs 3 EuSi 6 O 15 KEuGe 2 O 6

Summary Unidirectional energy transfer from Tb 3+ to Eu 3+ was found. Concentration quenching was observed in Eu 2 (CHDC) 3 as well as in Tb 2 (CHDC) 3. In R 2 (CHDC) 3, the ligand has no significant impact on the energy transfer (ET). On the other hand, the ligands play an important role in ET in the silicate and germanate compounds containing Eu 3+. $$$ Supports: National Science Council, Taiwan National Central University Many thanks for your attention!