Charge-exchange processes in titanium-doped sapphire crystals. I. Charge-exchange energies and titanium-bound excitons

Wong, William; McClure, Donald S.; Basun, S. A.; Kokta, Milan R.

doi:10.1103/physrevb.51.5682

Cited by 81 publications

(54 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The intensity of this band increases with the concentration of dopant while the centroid of the excitation spectrum is positioned in the energy range of the O-Ti 4þ charge transfer transitions. These transitions exhibit a threshold at 4.17 eV and are located around 5.4-6.8 eV, 3 which is consistent with the luminescence excitation spectra (see Fig. 6).…”

Section: -4supporting

confidence: 74%

“…Since the blue emission of Ti 4þ ions is a characteristic emission of wide-gap hosts 7,8 stimulated through charge-transfer transitions, the corresponding assignment of the 420 nm (3 eV) luminescence band of sapphire has been the subject of many publications since the end of the last century. 1,3,4,[9][10][11][12][13][14] Another hypothesis attributes this band to the emission of F þ or F defect centers (an oxygen vacancy occupied by one or two electrons, respectively) ever-present in aluminum oxide. [15][16][17] The existing ambiguity in the assignment of this luminescence has been acknowledged 2,18 and it has been suggested that there are several clear features permitting to discriminate between the impurity and defect emission, such as band half-width, excitation spectra, lifetimes etc.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Studies of concentration dependences in the luminescence of Ti-doped Al2O3

Mikhailik

Stefano

Henry

et al. 2011

Journal of Applied Physics

View full text Add to dashboard Cite

The variation of luminescence and excitation spectra of titanium doped Al 2 O 3 for the concentration of Ti ranging from 10 to 1000 ppm was investigated using synchrotron radiation. In the lightly doped Al 2 O 3 -Ti (<100 ppm) samples we identified several emission bands. These are the emission of the excitons localized at Ti (290 nm), the emission due to F þ centers (325 nm), the band around 420 nm traditionally attributed to F center emission, and the luminescence of Ti 3þ ions at 720 nm. The emphasis in this study is on the clarification of the nature of the blue emission band in the samples with high concentration of Ti (!100 ppm), where the luminescence and excitation spectra of the blue emission exhibit noticeable variability. This is explained by a model of the luminescence process of Ti 4þ -F centers that includes the photoionization of Ti 3þ , the subsequent capture of electrons at F þ -centers, formation of excited F-centers and, finally, the emission of a blue photon. The quenching of the blue emission with increasing Ti concentration is interpreted in terms of competition between oxygen vacancies and Ti 4þ centers in the capture of the electron.

show abstract

Section: -4supporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Studies of concentration dependences in the luminescence of Ti-doped Al2O3

Mikhailik

Stefano

Henry

et al. 2011

Journal of Applied Physics

View full text Add to dashboard Cite

show abstract

“…This idea was previously suggested by Wong et al [11] and later used by Happek et al [12,13] In Ref. [4] an elaborate study of such relationship was made and the assumption that the energy E CT can be used for the energy E Vf of the lowest 4f state above the top of the valence band was further motivated.…”

Section: Charge Transfer Energies and Absolute Lanthanide Level Locationmentioning

confidence: 96%

Lanthanide charge transfer energies and related luminescence, charge carrier trapping, and redox phenomena

Dorenbos

2009

Journal of Alloys and Compounds

130

121

View full text Add to dashboard Cite

“…Such an excited state is referred to as an impurity trapped exciton. 4,9 From this study, it is clear that the temperature dependence of the photoconductivity provides valuable information about these exciton states.…”

mentioning

confidence: 99%

Temperature dependent spectroscopic studies of the electron delocalization dynamics of excited Ce ions in the wide band gap insulator, Lu2SiO5

Kolk

Basun

Imbusch

et al. 2003

Applied Physics Letters

View full text Add to dashboard Cite

Electron delocalization processes of optically excited states of Ce 3ϩ impurities in Lu 2 SiO 5 were investigated by means of a temperature and spectrally resolved photoconductivity study. By monitoring separately the strength of the photocurrent resulting from excitation into each of the Ce 3ϩ 5d absorption bands, over a broad temperature region, three different delocalization processes, namely direct photoionization, thermal ionization, and tunneling, have been identified. The relative probabilities and temperature dependencies of each of these processes are discussed. The observed exponential temperature increase in the photocurrent, which spans six orders of magnitude, allows for the exact placement of the lowest energy 5d levels of the Ce 3ϩ ions within the band gap. For Lu 2 SiO 5 :Ce 3ϩ , the lowest 5d state is determined to be 0.45 eV below the conduction band edge. Electron delocalization processes involving optically excited transition metal (3d) or lanthanide (4 f ) impurity ions in wide band gap insulators play a central role in determining the utility of insulating materials in various technical applications, such as in scintillators, phosphors, and tunable solid state lasers. For the 5d excited states of lanthanides, delocalization can result in the total quenching of the luminescence and appears to be directly related to the precise location of the exited 5d states relative to the intrinsic bands of the crystalline host. 1,2 One way of locating the impurity ion ground state relative to the conduction band ͑CB͒ edge is to deduce the photoionization threshold energy from the onset of photoconductivity. 3-5 These onsets, however, are inherently difficult to define and can be easily misinterpreted. In this letter, we show that, instead of using the photoionization threshold energy, the energy level structure of the impurity ion can be determined with more precision using the temperature dependence of thermal ionization from the lowest 5d state to the CB edge.A 10ϫ10ϫ0.5 mm Ce-doped Lu 2 SiO 5 crystal was mounted between two 90% transparent nickel mesh electrodes and two sapphire plates. Photocurrents were measured with a femtoampere stability using a Keitley 6517A electrometer. 1000 V was applied across the electrodes using the stabilized voltage supply of the same electrometer. Temperature control was achieved by using a cold finger, liquid nitrogen, a cartridge heater, a thermocouple, and a proportional integral differential controller. Tunable monochromatic light was provided by a 300 W cw xenon lamp and a 0.15 m monochromator. Photoconductivity ͑PC͒ and photostimulated luminescence ͑PSL͒ excitation spectra were corrected for the spectral intensity distribution of the excitation source.Lu 2 SiO 5 :Ce 3ϩ has been studied extensively since its successful use as a scintillating material in positron emission tomography scanners. [6][7][8] It is useful to compare PC spectra with the absorption, excitation, and luminescence spectra. Both absorption and luminescence properties are dominated by the vibroni...

show abstract

Charge-exchange processes in titanium-doped sapphire crystals. I. Charge-exchange energies and titanium-bound excitons

Cited by 81 publications

References 35 publications

Studies of concentration dependences in the luminescence of Ti-doped Al2O3

Studies of concentration dependences in the luminescence of Ti-doped Al2O3

Lanthanide charge transfer energies and related luminescence, charge carrier trapping, and redox phenomena

Temperature dependent spectroscopic studies of the electron delocalization dynamics of excited Ce ions in the wide band gap insulator, Lu2SiO5

Contact Info

Product

Resources

About