Bahram Zandi | University of Maryland Global Campus (original) (raw)
Papers by Bahram Zandi
ABSTRACT We report crystal-field splitting investigations of Gd3+(4f7) energy levels determined f... more ABSTRACT We report crystal-field splitting investigations of Gd3+(4f7) energy levels determined from high resolution energy (Stark) level cathodoluminescence (CL) spectroscopy of Gd-implanted 2H-aluminum nitride (AlN) in the wavelength range 250 to 320 nm and at temperatures 12, 77, and 300 K. The CL spectra are interpreted in terms of lattice-sum and crystal-field splitting models that assume implanted Gd replaces Al substitutionally in cationic sites in AlN having C3v point group symmetry. The CL spectra are associated with Gd3+ ions in a single site. A rms deviation of 7 cm-1 was obtained between 43 observed and calculated Stark levels. The intense UV emission at 318 nm (the 6P7/2-->8S7/2 transition) can be understood in terms of multiplet-to-multiplet branching ratios.
![Research paper thumbnail of Crystal-field splitting of Pr[sup 3+] (4f [sup 2]) energy levels in GaN](https://attachments.academia-assets.com/48642923/thumbnails/1.jpg)
](Journal of Applied Physics, 2001
We have calculated the crystal-field splitting of the energy levels of Pr 3ϩ in GaN and have comp... more We have calculated the crystal-field splitting of the energy levels of Pr 3ϩ in GaN and have compared these results to an analysis reported recently of the photoluminescence and the cathodoluminescence spectra of Pr 3ϩ implanted in GaN by metal organic chemical vapor deposition on sapphire substrates. The lattice location of Pr in GaN determined recently by the emission channeling technique, provides direct evidence that substitutional Ga sites are thermally stable lattice positions for Pr. The lattice-sum calculations with Pr occupying Ga sites include effective ionic charges, multipole polarizabilities, and structural information also available in the literature. From the calculations, we conclude that the majority of the reported emission spectra is associated with Pr 3ϩ ions in a common site with transitions from excited 3 P 0 and 3 P 1 states to crystal-field split multiplets, 3 H 4 ͑the ground state͒, 3 F J , and 1 G 4 .
Aps Texas Sections Fall Meeting Abstracts, Oct 1, 2000
Absorption spectra suggest that Cr4+:GGG, though interesting as a saturable absorber for passive ... more Absorption spectra suggest that Cr4+:GGG, though interesting as a saturable absorber for passive Q-switching of lasers near one micron, should be less effective in that task than Cr4+:YAG. By our estimates the absorption cross section near that wavelength is only about one half as large in Cr:GGG as in Cr:YAG, yet the upper state lifetime of Cr:GGG is shorter. We have made a direct comparison of the two materials as Q-switches in the same Nd:YLF laser cavity with diode pumping. The output pulse energy was consistently higher and the pulse duration consistently shorter with Cr:YAG Q-switches. Because we observed evidence that the optical quality of the Cr:GGG material was poorer, we also performed one-dimensional modeling of the passively Q-switched performance of this laser. The model results agree qualitatively with the observed material dependence, supporting the conclusion that intrinsic material properties are responsible.
Journal of Applied Physics, Mar 15, 2003
We report a detailed spectroscopic analysis of Nd3+(4f3) as a dopant in single crystals of LaSc3(... more We report a detailed spectroscopic analysis of Nd3+(4f3) as a dopant in single crystals of LaSc3(BO3)4 (LSB). Absorption spectra were obtained between 570 and 1750 nm at temperatures as low as 8 K. Fluorescence spectra and lifetimes were obtained at similar temperatures from 4F3/2 to 4I9/2, 4I11/2, and 4I13/2 multiplet manifolds. The observed spectra are similar to spectra reported earlier for Nd3+ as a dopant in the alpha phase of LSB. The observed crystal-field splitting of the 2S+1LJ multiplet manifolds of Nd3+ was modeled using a Hamiltonian, which includes atomic and crystal field terms. A least-squares fitting between 57 calculated-to-observed energy (Stark) levels gave a root mean square deviation of 8 cm-1 for the 13 lowest-energy multiplet manifolds. With wave functions obtained from the modeling studies, multiplet-to-multiplet and line-to-line branching ratios were calculated as well as the radiative lifetime for emission from 4F3/2. The results are compared with experimental values obtained in the present study and also with results reported for Nd3+ in the beta phase of LSB.
Journal of Applied Physics
ABSTRACT
Journal of Applied Physics
We report the absorption and fluorescence spectra of divalent cobalt (Co 2ϩ ) in a series of rela... more We report the absorption and fluorescence spectra of divalent cobalt (Co 2ϩ ) in a series of related spinels Mg (1Ϫx) Co x Al B O C , where Bϭ2, 4, 6, Cϭ4, 7, 10, and x represents the amount of Co 2ϩ that substitutes for Mg 2ϩ in tetrahedral sites of T d symmetry. The spectra support the assumption that both Mg 2ϩ and Co 2ϩ prefer the tetrahedral cation sites during the growth of these crystalline materials. These observations also support earlier conclusions obtained from crystallographic and thermodynamic studies of the MgO and Al 2 O 3 phase diagram. The observed spectra are analyzed and compared to calculated electronic levels derived from lattice-sum models using crystallographic data determined from the crystals grown in the present studies. Comments are made in relevance to the use of these crystals as saturable absorbers for near infrared Q-switched lasers.
2007 Quantum Electronics and Laser Science Conference, 2007
... 4453692 abstract; Rights And Permissions; Nash, KL; Yow, RM; Gruber, JB; Nijjar, AS; Zandi, B... more ... 4453692 abstract; Rights And Permissions; Nash, KL; Yow, RM; Gruber, JB; Nijjar, AS; Zandi, B.; Kokta, MR; Sardar, DK; Univ. of Texas at San Antonio, San Antonio. This paper appears in: Lasers and Electro-Optics, 2007. CLEO 2007. ...
Physical Review B, 2001
The absorption spectra of Co 2ϩ incorporated into crystals of Zn 4 O͑BO 2 ͒ 6 , zinc oxide metabo... more The absorption spectra of Co 2ϩ incorporated into crystals of Zn 4 O͑BO 2 ͒ 6 , zinc oxide metaborate, have been obtained at room temperature and at 8 K between 300 and 2600 nm. The fluorescence spectrum has been observed at 8 K between 555 and 855 nm. Room-temperature infrared spectra obtained between 4000 and 400 cm Ϫ1 are compared to previously reported Raman spectra of the zinc metaborate. The fundamental modes of vibration that are both Raman active and infrared active are confirmed in this study. Zinc metaborate is cubic (I4 3m) with Zn 2ϩ ions occupying sites of T 3d symmetry. It is presumed that Co 2ϩ substitutes for Zn 2ϩ during the crystal-growth process. The observed spectra of Co 2ϩ are analyzed, and the identified energy levels are compared to calculated levels derived from lattice-sum models and the crystal-field, three-parameter theory. Twenty-six experimental Stark ͑electronic͒ energy levels of Co 2ϩ (3d 7 ) are compared to calculated levels with a final rms deviation of 26 cm Ϫ1 . The atomic parameters for Co 2ϩ (3d 7 ), including the Slater, spin-orbit, and interconfigurational parameters, are in general agreement with the corresponding parameters obtained for divalent cobalt in other host crystals. The initial crystal-field parameters B nm determined from the lattice-sum calculations represent an excellent starting set for the splitting analyses and undergo only modest changes to a final set of parameters. Comments are also made in relation to the use of the crystal as a saturable absorber for near-infrared Q-switched solid-state lasers.
Laser Source Technology for Defense and Security III, 2007
ABSTRACT
Physical Review B, 2002
The complex crystallographic, spectroscopic, and laser properties of Dy 3+ ions in α-KY(WO 4 ) 2 ... more The complex crystallographic, spectroscopic, and laser properties of Dy 3+ ions in α-KY(WO 4 ) 2 and α-KGd(WO 4 ) 2 single crystals are investigated. Individual Stark levels for many of the 2S+1 L J manifolds of Dy 3+ (4f 9 ) ions in these monoclinic tungstates are obtained ...
2010 3rd International Conference on Advanced Computer Theory and Engineering(ICACTE), 2010
Page 1. 2010 3rd International Conference on Advanced Computer Theory and Engineering(ICACTE) E-p... more Page 1. 2010 3rd International Conference on Advanced Computer Theory and Engineering(ICACTE) E-portfolio Role to Satisfy Technical Students Job Demands Samaneh Salehi Nasab Faculty of computer science and information ...
2010 Second International Conference on Computer Research and Development, 2010
... Malaysia e-mail: samanehsalehy@yahoo.com Mazdak Zamani Universiti Teknologi Malaysia Universi... more ... Malaysia e-mail: samanehsalehy@yahoo.com Mazdak Zamani Universiti Teknologi Malaysia Universiti Teknologi Malaysia, Kuala Lumpur, Malaysia e-mail: mazdak_zamani @yahoo.com Abstract-This paper presents a comprehensive ...
Laser Technologies for Defense and Security, 2004
Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 19... more Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 1960. Lasers are used as scientific tools as well as for a wide variety of applications for both commercial industry and the military. Today lasers come in all types, shapes and sizes depending on their application. The solid-state laser has some distinct
Physical Review B, 2004
We have calculated the crystal-field splitting of the energy levels of Er 3ϩ (4 f 11 ) in charge-... more We have calculated the crystal-field splitting of the energy levels of Er 3ϩ (4 f 11 ) in charge-compensated sites having C 3 symmetry in the host crystal of lithium niobate, LiNbO 3 ͑LN͒, with crystal-field parameters obtained from lattice-sum calculations. The charge-compensation model assumes that Er 3ϩ substitutes into Li ϩ sites that are shifted from the Li ϩ positions in the undoped lattice with excess charge compensated for by niobium vacancies and defect complexes. The calculated splitting of 11 multiplet manifolds 2Sϩ1 L J including the ground state 4 I 15/2 of Er 3ϩ (4 f 11 ) is compared with existing data in the literature, as well as with polarized absorption and fluorescence spectra obtained in the present study between 8 K and room temperature. The calculated splitting is compared with the experimental splitting without least-squares adjustments to the crystal-field splitting parameters, although the centroids between multiplet manifolds are adjusted to account for J mixing between states. The calculated splitting supports site symmetries for Er 3ϩ as C 3 , in agreement with magnetic resonance studies. The calculation also predicts the symmetry label of the ground-state Stark level as 2 ⌫ 6 or ͑Ϯ3/2͒, in agreement with the observed polarized absorption and fluorescence spectra.
ABSTRACT We report crystal-field splitting investigations of Gd3+(4f7) energy levels determined f... more ABSTRACT We report crystal-field splitting investigations of Gd3+(4f7) energy levels determined from high resolution energy (Stark) level cathodoluminescence (CL) spectroscopy of Gd-implanted 2H-aluminum nitride (AlN) in the wavelength range 250 to 320 nm and at temperatures 12, 77, and 300 K. The CL spectra are interpreted in terms of lattice-sum and crystal-field splitting models that assume implanted Gd replaces Al substitutionally in cationic sites in AlN having C3v point group symmetry. The CL spectra are associated with Gd3+ ions in a single site. A rms deviation of 7 cm-1 was obtained between 43 observed and calculated Stark levels. The intense UV emission at 318 nm (the 6P7/2-->8S7/2 transition) can be understood in terms of multiplet-to-multiplet branching ratios.
Journal of Applied Physics, 2001
We have calculated the crystal-field splitting of the energy levels of Pr 3ϩ in GaN and have comp... more We have calculated the crystal-field splitting of the energy levels of Pr 3ϩ in GaN and have compared these results to an analysis reported recently of the photoluminescence and the cathodoluminescence spectra of Pr 3ϩ implanted in GaN by metal organic chemical vapor deposition on sapphire substrates. The lattice location of Pr in GaN determined recently by the emission channeling technique, provides direct evidence that substitutional Ga sites are thermally stable lattice positions for Pr. The lattice-sum calculations with Pr occupying Ga sites include effective ionic charges, multipole polarizabilities, and structural information also available in the literature. From the calculations, we conclude that the majority of the reported emission spectra is associated with Pr 3ϩ ions in a common site with transitions from excited 3 P 0 and 3 P 1 states to crystal-field split multiplets, 3 H 4 ͑the ground state͒, 3 F J , and 1 G 4 .
Aps Texas Sections Fall Meeting Abstracts, Oct 1, 2000
Absorption spectra suggest that Cr4+:GGG, though interesting as a saturable absorber for passive ... more Absorption spectra suggest that Cr4+:GGG, though interesting as a saturable absorber for passive Q-switching of lasers near one micron, should be less effective in that task than Cr4+:YAG. By our estimates the absorption cross section near that wavelength is only about one half as large in Cr:GGG as in Cr:YAG, yet the upper state lifetime of Cr:GGG is shorter. We have made a direct comparison of the two materials as Q-switches in the same Nd:YLF laser cavity with diode pumping. The output pulse energy was consistently higher and the pulse duration consistently shorter with Cr:YAG Q-switches. Because we observed evidence that the optical quality of the Cr:GGG material was poorer, we also performed one-dimensional modeling of the passively Q-switched performance of this laser. The model results agree qualitatively with the observed material dependence, supporting the conclusion that intrinsic material properties are responsible.
Journal of Applied Physics, Mar 15, 2003
We report a detailed spectroscopic analysis of Nd3+(4f3) as a dopant in single crystals of LaSc3(... more We report a detailed spectroscopic analysis of Nd3+(4f3) as a dopant in single crystals of LaSc3(BO3)4 (LSB). Absorption spectra were obtained between 570 and 1750 nm at temperatures as low as 8 K. Fluorescence spectra and lifetimes were obtained at similar temperatures from 4F3/2 to 4I9/2, 4I11/2, and 4I13/2 multiplet manifolds. The observed spectra are similar to spectra reported earlier for Nd3+ as a dopant in the alpha phase of LSB. The observed crystal-field splitting of the 2S+1LJ multiplet manifolds of Nd3+ was modeled using a Hamiltonian, which includes atomic and crystal field terms. A least-squares fitting between 57 calculated-to-observed energy (Stark) levels gave a root mean square deviation of 8 cm-1 for the 13 lowest-energy multiplet manifolds. With wave functions obtained from the modeling studies, multiplet-to-multiplet and line-to-line branching ratios were calculated as well as the radiative lifetime for emission from 4F3/2. The results are compared with experimental values obtained in the present study and also with results reported for Nd3+ in the beta phase of LSB.
Journal of Applied Physics
ABSTRACT
Journal of Applied Physics
We report the absorption and fluorescence spectra of divalent cobalt (Co 2ϩ ) in a series of rela... more We report the absorption and fluorescence spectra of divalent cobalt (Co 2ϩ ) in a series of related spinels Mg (1Ϫx) Co x Al B O C , where Bϭ2, 4, 6, Cϭ4, 7, 10, and x represents the amount of Co 2ϩ that substitutes for Mg 2ϩ in tetrahedral sites of T d symmetry. The spectra support the assumption that both Mg 2ϩ and Co 2ϩ prefer the tetrahedral cation sites during the growth of these crystalline materials. These observations also support earlier conclusions obtained from crystallographic and thermodynamic studies of the MgO and Al 2 O 3 phase diagram. The observed spectra are analyzed and compared to calculated electronic levels derived from lattice-sum models using crystallographic data determined from the crystals grown in the present studies. Comments are made in relevance to the use of these crystals as saturable absorbers for near infrared Q-switched lasers.
2007 Quantum Electronics and Laser Science Conference, 2007
... 4453692 abstract; Rights And Permissions; Nash, KL; Yow, RM; Gruber, JB; Nijjar, AS; Zandi, B... more ... 4453692 abstract; Rights And Permissions; Nash, KL; Yow, RM; Gruber, JB; Nijjar, AS; Zandi, B.; Kokta, MR; Sardar, DK; Univ. of Texas at San Antonio, San Antonio. This paper appears in: Lasers and Electro-Optics, 2007. CLEO 2007. ...
Physical Review B, 2001
The absorption spectra of Co 2ϩ incorporated into crystals of Zn 4 O͑BO 2 ͒ 6 , zinc oxide metabo... more The absorption spectra of Co 2ϩ incorporated into crystals of Zn 4 O͑BO 2 ͒ 6 , zinc oxide metaborate, have been obtained at room temperature and at 8 K between 300 and 2600 nm. The fluorescence spectrum has been observed at 8 K between 555 and 855 nm. Room-temperature infrared spectra obtained between 4000 and 400 cm Ϫ1 are compared to previously reported Raman spectra of the zinc metaborate. The fundamental modes of vibration that are both Raman active and infrared active are confirmed in this study. Zinc metaborate is cubic (I4 3m) with Zn 2ϩ ions occupying sites of T 3d symmetry. It is presumed that Co 2ϩ substitutes for Zn 2ϩ during the crystal-growth process. The observed spectra of Co 2ϩ are analyzed, and the identified energy levels are compared to calculated levels derived from lattice-sum models and the crystal-field, three-parameter theory. Twenty-six experimental Stark ͑electronic͒ energy levels of Co 2ϩ (3d 7 ) are compared to calculated levels with a final rms deviation of 26 cm Ϫ1 . The atomic parameters for Co 2ϩ (3d 7 ), including the Slater, spin-orbit, and interconfigurational parameters, are in general agreement with the corresponding parameters obtained for divalent cobalt in other host crystals. The initial crystal-field parameters B nm determined from the lattice-sum calculations represent an excellent starting set for the splitting analyses and undergo only modest changes to a final set of parameters. Comments are also made in relation to the use of the crystal as a saturable absorber for near-infrared Q-switched solid-state lasers.
Laser Source Technology for Defense and Security III, 2007
ABSTRACT
Physical Review B, 2002
The complex crystallographic, spectroscopic, and laser properties of Dy 3+ ions in α-KY(WO 4 ) 2 ... more The complex crystallographic, spectroscopic, and laser properties of Dy 3+ ions in α-KY(WO 4 ) 2 and α-KGd(WO 4 ) 2 single crystals are investigated. Individual Stark levels for many of the 2S+1 L J manifolds of Dy 3+ (4f 9 ) ions in these monoclinic tungstates are obtained ...
2010 3rd International Conference on Advanced Computer Theory and Engineering(ICACTE), 2010
Page 1. 2010 3rd International Conference on Advanced Computer Theory and Engineering(ICACTE) E-p... more Page 1. 2010 3rd International Conference on Advanced Computer Theory and Engineering(ICACTE) E-portfolio Role to Satisfy Technical Students Job Demands Samaneh Salehi Nasab Faculty of computer science and information ...
2010 Second International Conference on Computer Research and Development, 2010
... Malaysia e-mail: samanehsalehy@yahoo.com Mazdak Zamani Universiti Teknologi Malaysia Universi... more ... Malaysia e-mail: samanehsalehy@yahoo.com Mazdak Zamani Universiti Teknologi Malaysia Universiti Teknologi Malaysia, Kuala Lumpur, Malaysia e-mail: mazdak_zamani @yahoo.com Abstract-This paper presents a comprehensive ...
Laser Technologies for Defense and Security, 2004
Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 19... more Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 1960. Lasers are used as scientific tools as well as for a wide variety of applications for both commercial industry and the military. Today lasers come in all types, shapes and sizes depending on their application. The solid-state laser has some distinct
Physical Review B, 2004
We have calculated the crystal-field splitting of the energy levels of Er 3ϩ (4 f 11 ) in charge-... more We have calculated the crystal-field splitting of the energy levels of Er 3ϩ (4 f 11 ) in charge-compensated sites having C 3 symmetry in the host crystal of lithium niobate, LiNbO 3 ͑LN͒, with crystal-field parameters obtained from lattice-sum calculations. The charge-compensation model assumes that Er 3ϩ substitutes into Li ϩ sites that are shifted from the Li ϩ positions in the undoped lattice with excess charge compensated for by niobium vacancies and defect complexes. The calculated splitting of 11 multiplet manifolds 2Sϩ1 L J including the ground state 4 I 15/2 of Er 3ϩ (4 f 11 ) is compared with existing data in the literature, as well as with polarized absorption and fluorescence spectra obtained in the present study between 8 K and room temperature. The calculated splitting is compared with the experimental splitting without least-squares adjustments to the crystal-field splitting parameters, although the centroids between multiplet manifolds are adjusted to account for J mixing between states. The calculated splitting supports site symmetries for Er 3ϩ as C 3 , in agreement with magnetic resonance studies. The calculation also predicts the symmetry label of the ground-state Stark level as 2 ⌫ 6 or ͑Ϯ3/2͒, in agreement with the observed polarized absorption and fluorescence spectra.