60 th International Symposium on Molecular Spectroscopy Experiment

60 th International Symposium on Molecular Spectroscopy Experiment Discovery: Ga. As: Er system, 1983 JAdvantages: The coincidence of the transition wavelength with the absorption minimum of semiconductor-based fibers The sharp spectrum lines The temperature insensitive wavelength LDisadvantages: The temperature quenching of the emission intensity H. Ennen, J. Schneider, G. Pomrenke, A. Axmann, Appl. Phys. Lett. 43, 943 (1983)

60 th International Symposium on Molecular Spectroscopy Experiment Improvement: intensity vs. band gap, 1989 üConclusion: Semiconductor hosts with larger band gaps exhibit less temperature quenching of Er 3+ luminescence. P. N. Favennec, H. L’Haridon, M. Salvi, D. Moutonnet, Y. L. Guillou, Electron. Lett. 25 (1989)

60 th International Symposium on Molecular Spectroscopy Experiment M. Thaik, U. Hömmerich, R. N. Schwartz, R. G. Wilson and J. M. Zavada, Appl. Phys. Lett. 71, 2641 (1997)

60 th International Symposium on Molecular Spectroscopy Theory üThe detailed energy splitting of Er 3+ center is unknown. Spin-orbit interaction needs to be considered. Ligand field effect under different local symmetries should be studied. üTheoretical calculations are helpful to study transition mechanism. Possible transition frequencies under certain local symmetry could be estimated. Transition moment needs to be computed explicitly.

60 th International Symposium on Molecular Spectroscopy Theory Calculations Outline ü ab initio spin-orbit configuration interaction singles (CIS) and singles and doubles (CISD) excitation calculations based on relativistic effective core potentials (RECP) are applied to calculate energies of the ground and excited states for a series of Er 3+-centered clusters. ü Transition dipole moment calculations are performed based on the CI calculation results. ü All of the calculations are carried out by COLUMBUS package.

60 th International Symposium on Molecular Spectroscopy Theory Ga. N Structure Ga. N crystals have two crystal structures: zinc blende and wurtzite Theoretical estimate of Ezinc blende-wurzite= 0. 952 k. J/mol Er substitutes the Ga site Second Shell 12 Ga 3+ added Td Symmetry C T 3 v Symmetry d Symmetry (zinc blende) (wurtzite)

60 th International Symposium on Molecular Spectroscopy Theory Er. N 49 - (Td) Er. N 4 Ga 1227+ (Td) Er. N 4 Ga 12 N 129 - (Td) Er. N 4 Ga 1227+ (C 3 v) Er. N 4 Ga 12 N 12 Ga 69+ (Td)

60 th International Symposium on Molecular Spectroscopy Theory Brief Review for Er 3+ ü The atomic number of Erbium is 68. ü The electron configuration for Er 3+ is 1 s 22 p 63 s 23 p 63 d 104 s 24 p 64 d 104 f 115 s 25 p 6 ü The ground state term symbol for Er 3+ is 4 I 15/2. ü The 1. 54 µm PL corresponds to 4 I 13/2 4 I 15/2 transition. 4 I 13/2 4 I 15/2 Schematic diagram of the energy levels of a free Er 3+ ion and splitting of the 4 f subshell levels in the field of Td symmetry.

60 th International Symposium on Molecular Spectroscopy Theory RECP and Basis Set ü Erbium 36 -electron core developed by Ermler (unpublished) 1 s 22 p 63 s 23 p 63 d 104 s 24 p 6 Core Corresponding contracted Gaussian cc-p. VDZ basis set (Our group) (5 sd 3 p 6 f 1 g)/[3 sd 2 p 2 f 1 g] ü Nitrogen 2 -electron core developed by Christiansen (1985) 1 s 2 Core Corresponding contracted Gaussian cc-p. VDZ basis set (Pitzer) (4 s 4 p 1 d)/[3 s 2 p 1 d] ü Gallium 28 -electron core developed by Ermler (1986) 1 s 22 p 63 s 23 p 63 d 10 Core

60 th International Symposium on Molecular Spectroscopy Theory

60 th International Symposium on Molecular Spectroscopy Theory ü For virtual p orbital: Augmented primitive is used. ü For virtual f orbital: Freeing diffuse primitive method is applied. ü For g polarization orbital: CISD method is employed to optimize the exponent. P. A. Christiansen, J. Chem. Phys. 112 , 10070 (2000)

60 th International Symposium on Molecular Spectroscopy Theory Reference Space 4 f orbitals of Er 3+ (small reference, 57, 239 CSFs) CIS 5 s, 5 p, 4 f orbitals of Er 3+ and 2 s, 2 p orbitals of N 3(large reference, 888, 979 CSFs) 4 f orbitals of Er 3+ (small reference, 6, 504, 680 CSFs) CISD 5 s, 5 p, 4 f orbitals of Er 3+ and 2 s, 2 p orbitals of N 3(large reference, over one billion CSFs)

60 th International Symposium on Molecular Spectroscopy Theory State Energy (cm-1) 4 I 4 I 13/2 15/2 29 atoms 35 atoms E 1/2 6137. 55 6159. 12 G 3/2 6117. 12 6135. 64 E 5/2 6090. 93 6104. 59 E 5/2 6009. 36 6016. 82 G 3/2 5990. 28 5994. 71 G 3/2 215. 00 238. 31 G 3/2 196. 71 212. 71 E 5/2 33. 49 49. 11 G 3/2 18. 63 22. 13 E 1/2 0. 00

60 th International Symposium on Molecular Spectroscopy Theory Electric Transitions ü Electric dipole moment operator belongs to F 2 irreducible representation under Td symmetry. E 1/2—E 5/2 E 1/2—G 3/2 E 5/2—G 3/2—G 3/2 ü 22 possible transitions wavelengths correspond to 4 I 13/2 4 I 15/2. ü Need to know the initial populations of the upper sublevels to compare to the spectrum.

60 th International Symposium on Molecular Spectroscopy Theory Transition Moments Squares G 3/2: from 4 I 13/2 G 3/2: from 4 I 15/2 2 nd G 3/2 ->2 nd G 3/2 Er. N 4 Ga 12 N 12 Ga 69+ Cluster

60 th International Symposium on Molecular Spectroscopy Conclusions and Future Work [ Td clusters show a converged splitting pattern with the E 1/2 state as the ground state. [ 1. 54 µm PL is tentatively assigned to the transition between 2 nd G 3/2 of 4 I 13/2 and 2 nd G 3/2 of 4 I 15/2. [ Large clusters for both zinc blende and wurzite should be studied.