ODMR Studies Research Articles

Mechanisms of exciton trapping in oxides

The self-trapping of excitons in some halide crystals is now an established phenomenon. The behaviour of excitons in oxides is less clear cut. ODMR studies show that in YAG and YA10 3 trapping of excitons is associated with lattice defects but suggest that in SiO 2 and Y 2O 3 intrinsic trapping processes may be dominant.

Phosphorescence and ODMR studies on the lowest excited triplet state of s-tetramethylpyrazine

The lowest excited triplet (T 1) state of s-tetramethylpyrazine has been examined at liquid helium temperatures in various surroundings. Well resolved phosphorescence spectra and the phosphorescence excitation spectra have been observed in several crystalline systems. The sublevel properties have also been obtained in the crystals. From the vibrational analyses of the spectra it is found that the T 1 state is a 3 B 2u (ππ*) state contrary to the 3 B 1u (ππ*) assignment for many benzene derivatives, and that the T 1 molecule is distorted towards the out of plane v 10a mode. Correlations among the zfs parameters, the triplet lifetimes and the intensities of the 2 × v 10a bands have been found and are discussed in terms of the pseudo Jahn-Teller coupling between the 3 B 2u (ππ*) and the higher 3 B 3u (nπ*) states. Rotations of fine structure axes have been observed in all the systems studied, but the magnitude of the rotation varies depending on the environment. The origin of the host effect is discussed.

Optical and ODMR studies on the color phenomenon of silver nitrite. The effect of silver(1+) perturbation on the radiative and nonradiative transitions in nitrite

Augmentation par un facteur 800 de la constante de vitesse radiative pour la phosphorescence T y du fait de la presence de Ag + dans NaNO 2 , et d'un facteur 4 pour la phosphorescence T z . Aucune influence pour les declins non radiatifs T 1 →S 0 et S 1 →T 1 . Interpretation par un transfert de charge avec promotion d'un electron de l'orbitale non liante de NO 2 − a l'orbitale 5p z de Ag +

ESR and DF ODMR studies of photoexcited triplets in single crystals of t-stilbene-1,2,4,5-tetracyanobenzene (1:2) complex

The photoexcited triplets in single crystals of the trans-stilbene-1,2,4,5-tetracyanobenzene (1:2) complex have been investigated by means of the ESR and DF ODMR techniques. The ESR lines attributed to localized species exhibit strong spin polarization whose dependence on the direction of the magnetic field has been examined. The zero-field splitting parameters have been measured: X = −308±15 MHz, Y = 2010±15 MHz, Z = −1702±15 MHz with the z axis directed along the normal to the t-stilbene phenyl rings. The negative sign of the DF ODMR signal has been attributed to annihilation of unlike triplets (exciton and X-trap), a process whose occurrence is supported also by decay measurements of the fluorescence.

ChemInform Abstract: EPR AND ODMR STUDIES OF THE LOWEST EXCITED TRIPLET STATES OF TWO TAUTOMERS OF INDAZOLE IN A BENZOIC ACID HOST CRYSTAL

Chemischer InformationsdienstVolume 15, Issue 7 Physical Organic Chemistry ChemInform Abstract: EPR AND ODMR STUDIES OF THE LOWEST EXCITED TRIPLET STATES OF TWO TAUTOMERS OF INDAZOLE IN A BENZOIC ACID HOST CRYSTAL M. NODA, M. NODASearch for more papers by this authorN. HIROTA, N. HIROTASearch for more papers by this author M. NODA, M. NODASearch for more papers by this authorN. HIROTA, N. HIROTASearch for more papers by this author First published: February 14, 1984 https://doi.org/10.1002/chin.198407045Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue7February 14, 1984 RelatedInformation

EPR and ODMR studies of the lowest excited triplet states of two tautomers of indazole in a benzoic acid host crystal

Etude de l'etat T 1 de l'indazole dans un cristal mixte d'acide benzoique par spectrometrie RPE et par les techniques ODMR a la temperature de l'helium liquide

Luminescence and magnetic resonance in post-hydrogenated microcrystalline silicon

We report photoluminescence, EPR and ODMR studies of plasma hydrogenated LPCVD microcrystalline silicon thin films. Apart from the dangling bond EPR resonance which is similar to that observed in a-Si : H, and possibly the emission at 1.3 eV, we find emission bands and resonance signals quite unlike those observed in normal c-Si and a-Si : H. We conclude that μ c-Si : H cannot be regarded purely as crystallites of pure silicon embedded in a matrix of a-Si : H.

Delayed-fluorescence ODMR and EPR studies of triplet excitons in charge-transfer molecular crystals

Triplet excitons in electron donor—acceptor charge-transfer (CT) molecular crystals are generated through the intersystem crossing process by excitation in the CT visible band and give rise to delayed fluorescence. Delayed-fluorescence optically detected magnetic resonance (DF ODMR) in magnetic field is analyzed in terms of microwave-induced transitions between energy levels of either the isolated triplet excitons or the annihilating triplet exciton pair. The spin polarization of the triplet excitons plays an important role in the described phenomena. A comparison between DF ODMR and EPR spectra of the anthracene—tetracyanobenzene and biphenyl—tetracyanobenzene systems is presented. In the former case the microwave transitions occurring between free exciton sublevels are predominantly responsible of the DF ODMR signal, whereas the transitions between energy levels of the exciton pair are the most important for biphenyl—TCNB.

Triplet emission from furil in different crystalline environments: Optical and odmr studies

The excited triplet state of furil was examined in single crystals of 4,4′-dibromodiphenyl ether and benzophenone. Phosphorescence and ODMR spectra reveal several distinct emitting species. In both crystals at low temperature furil is probably trans-planar. In benzophenone at elevated temperatures two emitting, furil species transfer energy on a 100 μs time scale.

EPR and ODMR investigations of defect centres in ZnTe:Cl

We report EPR and ODMR (optically detected EPR) studies of Cl doped ZnTe that show a fraction of the chlorine participating in complex, deep-level defects. Photoexcitation at T < 50 K creates an EPR spectrum corresponding to an S = 12 centre with nearly isotropic g factor (g = 1.96) and hyperfine interaction with a Cl nucleus. Weak, satellite EPR lines correspond to interaction with three equivalent Te nuclei and a low abundance, I = 12 nucleus X, which could be either an Sn, Pb or Cd nucleus. Our model for this trigonal symmetry defect is a Cl on a Te site with X on a neighbouring Zn site. ODMR studies at 2 K of an emission band peaking near 770 nm gives the Cl centre EPR spectrum and in addition the spectrum of a trigonal acceptor centre with highly anisotropic g-tensor (g″ = 2.65, g⊥ ≅ 0). The ODMR work shows that the 770 nm emission results from recombination of the electron of the deep Cl centre with the hole of the trigonal acceptor centre.

ODMR studies of antisite-related luminescence in GaP

By the use of ODMR, we have detected and identified two different antisite defects which contribute to newly-reported infrared luminescence observed in GaP. The antisite proper, P Ga, gives rise to a spin- 1 2 resonance; the associated luminescence originates in the DA pair recombination of an electron trapped at the deep double donor P + Ga with a distant shallow acceptor. An impurity-associated centre of the form P Ga · Y P is observed in a spin-triplet state via a distinct luminescence band which originates in electron-hole recombination localised at the defect.

Radiative triplet luminescence and metastable states in a-P

Previous ODMR studies showed a PL emission near 1eV which was associated with a triplet excited state. We discuss further the possible models for the ODMR signals, and show by measurement of the ODMR waveform and of the PL decay, that the experimental results are consistent with an assignment of this band to a spin-forbidden triplet exciton emission, with a lifetime ∼ 4 msec. We note, however, that with chopped excitation, luminescence transients are observed which are characteristic of long-lived (τ ∼ 1s) optically-created non-radiative centres.

E.P.R. and zero field ODMR studies of the lowest excited triplet states of halogen containing anilines and anisole

The molecular and electronic structures of the lowest excited triplet states of the halogen containing anilines and anisole were studied by means of E.P.R. and zero field ODMR techniques. Single crystal E.P.R. spectra of 4-fluoroaniline and 4-bromoanisole in 1,4-dibromobenzene host show well resolved hyperfine splittings due to halogen nuclei. It is shown that the fluorine hyperfine splitting and the angular dependence of the E.P.R. signal of 4-fluoroaniline can be explained on the basis of the skewed antiquinoid structure of the triplet state. The angular dependence of the E.P.R. signal and the sublevel decay rates of 4-chloroaniline in 1,4-dichlorobenzene also show that the molecule is distorted into an antiquinoid form. The analysis of the bromine hyperfine and quadrupole splittings of 4-bromoanisole indicates that the spin distribution is likely to be similar to that of 4-fluoroaniline.

Optical detection of magnetic resonance in AgCl1-xBrx

ODMR studies are reported for crystals of AgCl1-xBrx with x varying from approximately 0 to 0.3. For x=0.001 the ODMR spectrum at 4K shows resonances due to self-trapped holes which may be represented as (AgCl6)4-, nearly free electrons, self-trapped excitons which may be represented as (AgCl6)5-, and excitons trapped at bromine sites which may be represented as (AgCl5Br)5-. At 1.6K the intensity of the spectrum of (AgCl6)5- falls to a very low value and the spectrum of (AgCl5Br)5- grows. The origin of this effect is discussed. With increasing x the ODMR spectrum becomes increasingly dominated by excitons trapped in complexes containing increasing numbers of bromines until at x=0.3 the principal centre present is (AgBr6)5-. The variation of the g-value of nearly-free electrons with x is reported.

The relative importance of vibronic and spin-orbit couplings in aromatic carbonyl compounds

Optical and ODMR studies on the lowest triplet state of xanthone have revealed the presence of substantial spin-orbit and vibronic interactions between the two lowest triplet states, T 1 ≈ 3ππ ∗ and T 2 ≈ 3nπ ∗. Their energy separation δE T depends strongly on the solvent and varies in the range 27 to 1000 cm -1 in the systems studied. This severely perturbs the zero-field splitting in T 1, whereas the vibrational structure of the phosphorescence T 1→S 0 is hardly affected. The relative importance of the competing coupling mechanisms is discussed with respect to the magnitude of δE T.

Absorption, phosphorescence and ODMR studies of 1-phenyl-1-boracyclohexane

To investigate the influence of an electron-accepting sustituent on the excited states of benzene the singlet adsorption as well as the phosphorescence spectrum and the ODMR spectra of 1-phenyl-1-boracyclohexane have been analysed. In the singlet system we identified the benzenoid 1L a and 1L b bands and two low energetic CT transitions. The lowest triplet state T 1 may be characterized by two features: a considerable charge transfer from the benzene ring to the empty P π-orbital of boron and the influence of the pseudo-Jahn-Teller effect resulting in a quinoid distortion of the benzene ring and an additional rotation of the magnetic axis system.

ChemInform Abstract: ZERO‐FIELD ODMR STUDIES OF THE T1 STATES OF BROMINE‐CONTAINING 1,4‐DIHALOBENZENES

Chemischer InformationsdienstVolume 11, Issue 33 Physical Organic Chemistry ChemInform Abstract: ZERO-FIELD ODMR STUDIES OF THE T1 STATES OF BROMINE-CONTAINING 1,4-DIHALOBENZENES H. SHINOHARA, H. SHINOHARASearch for more papers by this authorN. HIROTA, N. HIROTASearch for more papers by this author H. SHINOHARA, H. SHINOHARASearch for more papers by this authorN. HIROTA, N. HIROTASearch for more papers by this author First published: August 19, 1980 https://doi.org/10.1002/chin.198033059AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue33August 19, 1980 RelatedInformation

ODMR and EPR studies of the triplet states of aliphatic and aromatic carbonyls

ODMR and EPR studies of the triplet states of aliphatic and aromatic carbonyls

Single crystal ODMR and phosphorescence studies of the 3nπ * state of aliphatic carbonyl: 2-indanone

We have made single crystal ODMR and phosphorescence studies of the T 1 state of 2-indanone. It was shown that the T 1 state of 2-indanone is very similar to that of the 3nπ * state cyclopentanone. The well resolved phosphorescence spectrum indicates that the 3nπ * 2-indanone has a distorted structure. A proposed decay scheme was confirmed from a single crystal ODMR study at low magnetic field.

Spin-orbit perturbation of the anion states by a heavy cation in NaNO 2:Ag +

Optical and ODMR studies of NaNO 2: Ag + crystals at T < 4.2 K have shown very selective spin-orbit perturbations on the properties of the nitrite triplet state T 1, by the heavy cation dopant. The perturbed T 1 — S 0 transition shows mainly z-axis polarization associated with the τ y spin state ( z- and y-axes in-plane with the z-axis bisecting the ONO angle). The fine structure splitting constants for the perturbed T 1 state are D = -3Y/2 = ± 15.508 GHz and E = (Z - X)/2 = ‡ .643 GHz.