Excited-state absorption of ZnSe doped with cobalt

Ehlert, A.; Dreyhsig, J.; Gumlich, H.‐E.; Allen, J. W.

doi:10.1016/0022-2313(94)90084-1

Cited by 11 publications

(12 citation statements)

References 4 publications

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“…The results of this measurement are shown in Figure 1 b, where it is observed that the ESA spectrum spans a large portion of the visible window. Similar results have also been obtained for bulk Mn‐doped ZnSe16 and Co‐doped ZnSe 17. Other glasses doped with rare‐earth elements18 also show broadband impurity–host transitions that exhibit a large dependence on the particular host material.…”

supporting

confidence: 80%

Direct Light‐Driven Modulation of Luminescence from Mn‐Doped ZnSe Quantum Dots

et al. 2008

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Quantum dot (QD) nanocrystals remain at the forefront of fluorescence microscopy as they have the advantages of enhanced photostability, high quantum yield, and macromolecular size. [1][2][3] Furthermore, the ability to tune the QD fluorescence, either by changing their size [1] or by doping, [4] allows for multiplexed imaging. The range of applications extends well beyond the realm of microscopy: QDs may also play a major role in developing novel photonic devices including lasers, light-emitting diodes, and displays. [5][6][7] Despite significant advancements in nanocrystal research, the inability to directly modulate the fluorescence from QDs has precluded their implementation in several areas. In particular, emerging far-field diffraction-unlimited microscopy techniques [8] uniquely benefit from the capability to reversibly modulate/switch fluorescent ensembles from a bright "on" state to a dark "off" state. This activation must occur as a response to optical stimuli which do not contain spectral components within the excitation kernel of the fluorescent markers. With the need for optical control over QD fluorescence, indirect methods have been conceived by using hybrid QD structures [9][10][11] that incorporate a photochromic activator/quencher. Although the concept has been clearly established, hybrid QD structures suffer from inherent drawbacks, such as inadequate photostability, limited fluorescence quenching, and sensitivity to local environment/ solvent.Herein we report on the direct light-driven modulation of QD fluorescence. The mechanism for the fluorescence modulation relies only on internal electronic transitions within Mn-doped ZnSe quantum dots (Mn-QDs). It is demonstrated that the fluorescence of the QD can be reversibly depleted with efficiencies of over 90 % by using continuous-wave optical intensities of approximately 1.9 MW cm À2 . Time-domain measurements during the modulation indicate that the number of fluorescent on-off cycles exceeds 10 3 before a significant reduction in the fluorescence quantum efficiency occurs. Such robust nanometric probes having remotely controllable optical transitions are useful in many areas of research, particularly in far-field nanoscopy based on reversible saturable or switchable optical fluorescence transitions (RESOLFT).[8] Consequently, we show that implementation of Mn-QDs for imaging leads to an increase in the resolution by a factor of 4.4 over that of confocal microscopy.A schematic diagram of the electronic transitions involved in light-modulated fluorescence from Mn-QDs is shown in Figure 1 a. Initially, electrons are photoexcited from the valence band to the conduction band of the ZnSe semiconductor host. Within a short time (picosecond timescale [12][13][14] ), the excited electrons are transferred to the 4 T 1 upper florescent state of the Mn 2+ ion and decay radiatively to the 6 A 1 state within a measured fluorescence lifetime of t fluo % 90 ms (see the Supporting Information). Generally speaking, direct modulation of the fluorescence requires a...

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confidence: 80%

Direct Light‐Driven Modulation of Luminescence from Mn‐Doped ZnSe Quantum Dots

et al. 2008

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“…Figure A plots the energy of this ML CB CT transition versus that of the first excitonic feature for the entire set of Zn 1− x Co x Se and Zn 1− x Co x Se/CdSe nanocrystals. This plot yields a linear relationship across the series of Zn 1− x Co x Se and Zn 1− x Co x Se/CdSe nanocrystal samples, extrapolating close to the estimated bulk charge-transfer energy . Importantly, this plot shows that the CB energy of the Zn 1− x Co x Se/CdSe nanocrystals is close to the CB energy of bulk Zn 1− x Co x Se, i.e., that CdSe shell growth rapidly quenches the e CB − confinement energy of the ZnSe core.…”

Section: The Elusive Kinetic S−d Exchangesupporting

confidence: 60%

“…The red triangle symbol indicates the approximate energy of the ML CB CT transition in bulk Zn 1-x Co x Se. 42 The ML CB CT energy of the Zn 1-x Co x Se/CdSe core/ shell nanocrystals (dark blue square) from Figure 2B falls on the same line. (B) Data from part (A) replotted as conduction band confinement energy vs ZnSe nanocrystal diameter, referenced to bulk ZnSe.…”

mentioning

confidence: 93%

“…This plot yields a linear relationship across the series of Zn 1-x Co x Se and Zn 1-x Co x Se/CdSe nanocrystal samples, extrapolating close to the estimated bulk charge-transfer energy. 42 Importantly, this plot shows that the CB energy of the Zn 1-x Co x Se/ CdSe nanocrystals is close to the CB energy of bulk Zn 1-x Co x Se, i.e., that CdSe shell growth rapidly quenches the e CB -confinement energy of the ZnSe core. The data in Figure 4A are replotted in Figure 4B relative to the bulk conduction band energy 41 to emphasize the large stabilization of e CB -upon CdSe shell growth.…”

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confidence: 94%

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Dopant−Carrier Magnetic Exchange Coupling in Colloidal Inverted Core/Shell Semiconductor Nanocrystals

2009

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Dopant-carrier magnetic exchange interactions in semiconductor nanostructures give rise to unusually large Zeeman splittings of the semiconductor band levels, raising possibilities for spin-based electronics or photonics applications. Here we evaluate the recently highlighted possibility of confinement-induced kinetic s-d exchange coupling in doped ZnSe/CdSe inverted core/shell nanocrystals. Magneto-optical studies of a broad series of Co(2+)- and Mn(2+)-doped core, inverted core/shell, and isocrystalline core/shell nanocrystals reveal that the dominant spectroscopic effects caused by CdSe shell growth around doped ZnSe core nanocrystals arise from hole spatial relaxation, being essentially independent of the electron-dopant interaction or the heterointerface itself. The general criteria for observation of kinetic s-d exchange coupling in doped nanocrystals are discussed in light of these results.

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“…ESA measurements can, therefore, be used to obtain information about energy levels that cannot be otherwise measured. A similar way of gaining information about energy levels which cannot be measured by GSA has been reported in Co doped ZnSe but, to our knowledge, not yet in RE doped systems [25].…”

supporting

confidence: 64%

Optical Measurement of Narrow Band Rare-Earth4fLevels with Energies Greater than the Band Gap of the Host

et al. 1998

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Excited-state absorption spectra of erbium and thulium doped gallium lanthanum sulfide glasses reveal transitions whose final 4f states do not appear in the ground state absorption spectra due to resonance with the fundamental absorption of the glass host. The results give direct evidence for the model of isolated rare-earth ions with highly shielded 4f levels showing no noticeable interaction with the host material despite resonance. Only the energy splitting of the 4f levels is relevant for energy transfer processes between rare-earth ions and the host material, whereas the absolute energetic position is unimportant. [S0031-9007(98)05305-8] PACS numbers: 78.66.Jg, 31.50. + w, 42.70.HjExcited-state absorption (ESA) describes the absorption from a populated excited electronic state of a system to higher-energy states. In rare-earth (RE) doped materials, ESA at the emission or pump wavelengths can impede or completely prevent laser action. The final states of an ESA transition from an excited RE level can either be a higher lying RE level of the same configuration or the conduction band of the host material [1][2][3][4][5][6].In this Letter, we present ESA measurements on erbium ͑Er 31 ͒ and thulium ͑Tm 31 ͒ doped gallium lanthanum sulfide (GLS) glasses that can be classified as wideband-gap semiconductors with an energy gap of 2.6 eV, which corresponds to a visible transparency down to about 500 nm. The problem arises whether ESA transitions from RE 4f levels to the conduction band of the glass or to 4f levels that are "higher" than the conduction band will occur.ESA transitions from RE dopants to the host material have been observed in a variety of divalent and trivalent RE doped materials [1][2][3][4][5][6]. The reported ESA transitions into the conduction band originate from the 4f n21 5d states of the RE ions and have typical cross sections of 10 218 10 217 cm 2 [2-4]. These values are much larger than the values for the dipole forbidden 4f-4f transitions ͑10 221 10 220 cm 2 ͒ and even for the dipole allowed 4f n -4f n21 5d transitions ͑10 218 10 219 cm 2 ͒ [2-4]. ESA transitions have not been measured from highly shielded 4f n levels into the conduction band. Transitions from 4f n levels to the conduction band are expected to be weak compared to those from 4f n21 5d levels, due to the much smaller spatial overlap of the 4f n levels with the delocalized Bloch states of the conduction band. In all of the mentioned examples, the ground and excited 4f states of the RE ions lie within the wide band gaps of the insulating host materials (E gap ϳ 6 eV for yttrium aluminum garnet and 12.2 eV for CaF 2 ) [1-6]. The observed localized to delocalized transitions, i.e., the transfer of an electron from the impurity ion to the host material, while not uncommon in semiconductors, are quite rare in insulators.In this Letter, we look at chalcogenide glasses which can be classified as semiconductors, most of which have hole-type conductivity [7,8]. Interband gap states formed by extrinsic impurities and intrinsic defects cau...

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Excited-state absorption of ZnSe doped with cobalt

Cited by 11 publications

References 4 publications

Direct Light‐Driven Modulation of Luminescence from Mn‐Doped ZnSe Quantum Dots

Direct Light‐Driven Modulation of Luminescence from Mn‐Doped ZnSe Quantum Dots

Dopant−Carrier Magnetic Exchange Coupling in Colloidal Inverted Core/Shell Semiconductor Nanocrystals

Optical Measurement of Narrow Band Rare-Earth4fLevels with Energies Greater than the Band Gap of the Host

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