Electron transfer from excited F centres to F+, F+A and F+AA centres in CaO studied by optically detected magnetic resonance (ODMR)

ODMR measurements via the magnetic circular polarization of the emission (MCPE) of F_A(Mg) centres in CaO at 1.6 K showed besides the known F_A-ODMR lines a non zero MCPE, which vanishes at g ? 2. From the dynamical behaviour of this MCPE and the F_A luminescence is shown that an electron tunneling takes place from the excited T_1u F centre state to F⁺_A centres forming excited F_A centres. The ground state back tunneling rate is 10⁷ times smaller and cannot explain the observed electron transfer cycle. The back tunneling is also going via excited states. The results can be understood assuming a random centre distribution. A new luminescence band at 785 nm could be identified by ODMR as being due to tetragonal F_AA centres. The electron transfer is also observed between F and F⁺ and F⁺_AA centres.     

New aspects of the luminescence of magnesiumtitanate part II: Activation with manganese

Measurements of the emission and excitation spectra of powdered Mg₂TiO₄:Mn⁴⁺ phosphors reveal that single Mn⁴⁺ ions are not responsible for the luminescence — as assumed till now — but so-called N centres. These centres are excited either by direct UV absorption or by radiationless energy transfer from the excited ²E state of the Mn⁴⁺ ions to the N centres. The Mn⁴⁺ ions absorb the energy corresponding to the transition ⁴A_2g→ ²E which is used for the excitation of the N centres, but do not emit the corresponding lines. The observed different luminescence spectra (sharp lines or broad bands) depend on the annealing conditions and indicate that the N centres consist of Mn⁴⁺ ions associated with unknown lattice defects. The annealing process does not only form the tetravalent state of the manganese, but creates above all the N₁ centres, which emit sharp lines. Two more lines observed at 697.8 nm and 699.4 nm, called R^m lines, are due to a certain amount of MgTiO₃:Mn⁴⁺ in the phosphor.     

Self-consistent analysis of absorption and emission data forF A centres in alkali halides

Summary A theory which explains self-consistently the emission and the polarization rotation of transmitted light has been developed forF _A centres in crystals with cubic symmetry. Azimuthal dependences ofF _A luminescence in alkali halides are very informative for determining the electron-phonon interaction as well as the parameters related to the structural and optical quality for coulour centre lasers crystals. The theoretical results are applied to the interpretation of the luminescence properties ofF _A (Li) centres in KCl, RbCl and KF.     

Spectroscopy of multisites Cr3+ and Nd3+ in yttrium aluminium garnet

Cr³⁺ and Nd³⁺ non-equivalent crystal field sites were observed. By use of a high-resolution dye laser,²E and⁴A₂ splittings, zero-phonon⁴A₂ →²E,²T₁,⁴T₂ transitions and vibronic levels of²E doublets of Cr³⁺ non-equivalent centres were recorded. Energy transfers from Cr³⁺ multisites to Nd³⁺ were studied by site-selective spectroscopy and fluorescence decays.     

Cr+ centres in mixed polytype ZnS single crystal

The glow peaks of mixed polytype ZnS: Cu, Cr, Cl crystals were identified as produced by three Cr⁺ centres observed by electron paramagnetic resonance (EPR): one cubic (C) and two axial (H₁ and H₂). The characteristics of these centres were partly found by the methods of interrupted thermoluminescence, infrared stimulation, “thermo-EPR” (variation of the EPR signal with heating of a previously excited crystal) and also by decay of glow areas and of the three Cr⁺EPR signals after excitation at different temperatures. Moreover, these measurements showed the important part played by the non-thermal emptying of the Cr⁺ traps. This emptying occurs through photoexcitation of the trapped electrons by the reabsorbed luminescence light or through recombination of these electrons with free holes. Both of these processes diminish the efficiency of phosphorescence when the crystal is cooled; so it was necessary to take them into account when analysing the experimental results. The percentage of H₁ and H₂ found by EPR and luminescence is in agreement with the percentage of the hexagonalicity as found from the birefringence measurements. The crystal field calculation gives account of three centres in such a mixed polytype crystal.     

Mise en evidence sous hautes pressions d'une transition electronique dans le fluorure Pd2F6

The pressure coefficient dE/dP appears to be sensitive to the ZnS lattice symmetry for the SA donor-acceptor pair, but not for the Mn²⁺ centres emission.The HP variation of the relative intensities for the SA and Mn emissions suggests a resonant transfer between these centres. The classical Dexter's formula for P_dd does not explain the results for the cubic crystal, whereas the preferential transfer from the SA centers to the ⁴E(⁴G) level in Mn²⁺ follows all reported observations.     

New aspects of the luminescence of magnesiumtitanate part I: Activation with chromium

Mg₂TiO₄:Cr³⁺ annealed at 560°C shows luminescence properties which differ considerably from those of the unannealed phosphor used so far. In both cases the regular Cr³⁺ ions only absorb the irradiated energy transferring it radiationless to the real luminescence centres, but the annealed phosphor reveals a new spectrum consisting of a few sharp lines. The radiance of the single lines can be influenced by powdering, which in connection with the annealing effect shows that the centres of both types of phosphors consist of clusters of lattice defects and octahedrally coordinated Cr³⁺ ions. These clusters or associates form themselves by thermal diffusion during the annealing process. Furthermore criteria have been found showing that the R lines do not come from only one but from two Cr³⁺ ions situated in non-equivalent lattice sites.     

Photoluminescence studies of γ-irradiated CaF2:Dy:Pb:Na single crystals

The optical absorption (OA) and photoluminescence (hereafter referred to as luminescence) studies were made on CaF₂:Dy:Pb:Na single crystals (Dy—0.005 at%, Pb—0.188 at% and Na—0.007 at%) before and after γ-irradiation. The unirradiated crystal exhibited a strong OA band around 6.36 eV attributed to the ‘A’ band absorption of Pb²⁺ ions. The γ-irradiated crystal exhibited OA bands around 2.06, 3.28, 3.75 (broad shoulder) and 2.48 eV. The first three bands could be tentatively attributed to M_Na centre when compared with that of the coloured CaF₂:Na. The origin of 2.48 eV band was not explicitly known. Luminescence emission and excitation of Pb²⁺ and Dy³⁺ ions were negligible in the unirradiated crystal. Irradiated crystal exhibited a strong excitation spectrum with overlapping bands, due to different colour centres, in the UV-vis region for the 2.15 eV emission characteristic of Dy³⁺ ion. When excited, the absorbed energy (may be a part) was transferred from a colour centre to nearby Dy³⁺ ions and Dy³⁺ characteristic emission was observed. Exciting the irradiated crystal around 3.28 eV yielded emission at 2.56, 2.15 and 1.76 eV. The first two emission bands were due to Dy³⁺ ions. The excitation spectrum for the 1.76 eV emission showed two prominent bands around 2.02 and 3.08 eV and hence the emission was attributed to the M_Na centre. The luminescence mechanism was described.     

Luminescence of an M center in ZnS?

Selected, differently doped and annealed cubic ZnS monocrystals exhibit a structured luminescence in the spectral region between 815 and 1150 nm. At 4 K more than 70 lines with typical linewidths of only 3–5 cm^?1 could be resolved. The influence of temperature, of magnetic fields up to B = 10T, and of irradiation with additional light were studied, and the excitation spectrum was recorded. The experiments indicate for the luminescence center a three-fold excited state and a singlet ground state with a strong phonon coupling, and allow the determination of the position of the involved electronic levels between valence band and conduction band. The results can be explained satisfactorily under the assumption that the center of luminescence consists of two adjacent F⁺ centers, the so-called M center. The present work marks the first time that any such center has been found in a II–VI compound.     

Spectroscopy of multisites Cr3+ and Nd3+ in yttrium aluminium garnet

Cr³⁺ and Nd³⁺ non-equivalent crystal field sites were observed. By use of a high-resolution dye laser,²E and⁴A₂ splittings, zero-phonon⁴A₂ ²E,²T₁,⁴T₂ transitions and vibronic levels of²E doublets of Cr³⁺ non-equivalent centres were recorded. Energy transfers from Cr³⁺ multisites to Nd³⁺ were studied by site-selective spectroscopy and fluorescence decays.     

Ti离子注入和退火对ZnS薄膜结构和光学性质的影响

利用真空蒸发法在石英玻璃衬底上制备了ZnS薄膜,将能量80 keV,剂量1×10¹⁷ cm^-2的Ti离子注入到薄膜中,并将注入后的ZnS薄膜进行退火处理,退火温度500—700 ℃.利用X射线衍射（XRD）研究了薄膜结构的变化,利用光致发光（PL）和光吸收研究了薄膜光学性质的变化.XRD结果显示,衍射峰在500 ℃退火1 h后有一定程度的恢复;光吸收结果显示,离子注入后光吸收增强,随着退火温度的上升,光吸收逐渐降低,吸收边随着退火温度的提高发生蓝移;PL显示,薄 关键词： ZnS薄膜 离子注入 X射线衍射 光致发光     

B+注入HgCdTe快速热退火的研究

借助二次离子质谱和俄歇电子能谱对B⁺注入HgCdTe有无ZnS膜包封在快速热退火条件下表层的Hg损失进行了深入的分析-快速热退火温度为300，350和400℃，退火时间为10s-ZnS膜厚度为160nm-结果表明，300℃，10s快速热退火后，有ZnS膜包封的HgCdTe表层没有Hg损失-对B⁺注入HgCdTe N⁺-P结快速热退火工艺流程进行了优化-结果表明，快速热退火放在光刻金属电极之后进行，可以改善结的特性- 关键词：     

Absorption and emission properties of Nd in lithium cesium mixed alkali borate glasses

Lithium cesium mixed alkali borate glasses of the composition 67B₂O₃·xLi₂O·(32−x)Cs₂O (where x=8, 12, 16, 20 and 24) containing 1 mol% Nd₂O₃ were prepared by melt quenching. The absorption spectra of Nd³⁺ were studied from the experimental oscillator strengths and the Judd-Ofelt intensity parameters were obtained. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) (A_T), branching ratios (β) and integrated absorption cross-sections (Σ) of the Nd³⁺ transitions from the excited state J manifolds to the lower lying J′ manifolds. Radiative lifetimes (τ_R) are estimated for certain excited states of Nd³⁺ in these mixed alkali borate glasses. Luminescence spectra were measured and the emission cross-sections (σ_p) were evaluated for the three emission transitions. The variation of luminescence intensity with x was recorded for the three transitions at different excitation power to see the effect of mixed alkalies in these borate glasses.     

Electronic and vibrational absorption spectra in otwayite,a new nickel mineral

The optical absorption spectrum of Ni²⁺ ion in otwayite crystal has been studied at room and liquid nitrogen temperatures. From the nature and positions of the observed bands a successful interpretation of all the bands could be made assuming octahedral symmetry for the Ni²⁺ ion in the crystal. The splittings observed for the ³T_1g(F) band at liquid nitrogen temperature have been interpreted due to spin-orbit interaction. The observed band positions in the crystal have been fitted with four parameters B, CDq and ξ. NIR and IR spectra of the otwayite sample are presented. The fundamental vibrational modes of H₂O and CO^2-₃ ion are identified in the IR region. The bands observed in NIR spectrum are due to overtones and combination tones of water and carbonate ion.     

Spectral properties of Nd<Superscript>3+</Superscript> ions in samples of transparent Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

The spectral and luminescent characteristics of samples of Y₂O₃:Nd³⁺ ceramics obtained from different precursors under different preparation conditions (the concentration of an HfO₂ compacting additive, the temperature and time of synthesis) are studied at 300 and 77 K. It is shown that the spectral positions of absorption and luminescence lines of ceramics correspond to those of a Y₂O₃:Nd³⁺ single crystal. At the same time, the absorption and luminescence spectra show an inhomogeneous broadening, characteristic of disordered crystals and glass. The energies of the ⁴ I _9/2 and ⁴ F _3/2 Stark states of the Nd³⁺ ion are calculated. The calculation results nearly coincide with the data from the literature for the Y₂O₃:Nd³⁺ single crystal and transparent ceramics. Samples containing the compacting additive show additional lines, whose intensities correlate with its concentration and the method of preparation of Y₂O₃:Nd³⁺ ultradispersed powders. It is assumed that these lines are related to the fact that either Nd³⁺ ions enter the composition of the HfO₂ compacting additive or Hf⁴⁺ ions are present in the nearest environment of Nd³⁺ ions at the boundaries of granules enriched with HfO₂.     

TL, OSL and ESR studies on beryllium oxide

Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the thermoluminescence (TL) and optically stimulated luminescence (OSL) processes in BeO phosphor. Two defect centres were identified in irradiated BeO phosphor by ESR measurements, which were carried out at room temperature and these were assigned to an O⁻ ion and Al²⁺ centre. The O⁻ ion (hole centre) correlates with the main 190 °C TL peak. The Al²⁺ centre (electron centre), which acts as a recombination centre, also correlates to the 190 °C TL peak. A third centre, observed during thermal annealing studies, is assigned to an O⁻ ion and is related to the high temperature TL at 317 °C. This centre also appears to be responsible for the observed OSL process in BeO phosphor.     

Effects of neon matrix environment on three vibronic emission systems of PbS

Laser sources have been used to explore three emission band systems of the PbS molecule in solid neon matrices. The D → X emission (origin near 29 630 cm^?1), excited biphotonically, consists of broad bands originating from V′ = 0. With laser excitation tuned into the region of the band system origin near 21 860 cm^?1, the B → X system shows emission narrowing of inhomogeneously broadened absorption. Hot luminescence from the B state is also reported. In the a → X system near 14 625 cm^?1 the intensities of phonon sidebands on the high-frequency side of the zero-phonon lines are found to be very sensitive to laser power. Lifetimes of the a, A, and B states of PbS in solid argon have been measured as 260, 0.95, and 1.8 μsec.     

Synthesis,characterisation, luminescence and defect centres in solution combustion synthesised CaZrO3:Tb3+ phosphor

Tb³⁺ doped CaZrO₃ has been prepared by an easy solution combustion synthesis method. The combustion derived powder was investigated by X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy techniques. A room temperature photoluminescence study showed that the phosphors can be efficiently excited by 251 nm light with a weak emission in the blue and orange region and a strong emission in green light region. CaZrO₃:Tb³⁺ exhibits three thermoluminescence (TL) glow peaks at 126 °C, 200 °C and 480 °C. Electron Spin Resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the centres responsible for the TL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0233 is identified as an O^? ion. Centre II with an axial symmetric g-tensor with principal values g_=1.9986 and g_?=2.0023 is assigned to an F⁺ centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F⁺ centre) seems to originate from an F centre (oxygen vacancy with two electrons). The F centre and also the F⁺ centre appear to correlate with the observed high temperature TL peak in CaZrO₃:Tb³⁺ phosphor.     

Luminescence of Bi3+-activated LaOBr,a system with emission from different states

The luminescence properties of LaOBr-Bi³⁺ are reported. Two luminescent centres are observed. These are ascribed to isolated Bi³⁺ ions and to a second BiOBr-rich phase. The emission of the isolated Bi³⁺ ion shows a remarkable temperature dependence. At low temperatures the emission is in the UV region. At higher temperatures the UV emission disappears and an emission in the visible region appears. At still higher temperatures the visible emission disappears and the UV emission reappears. The emission in the visible region is ascribed to a charge-transfer transition.     

Spectral studies of Nd3+ and Er3+ ions in POCl3:SnCl4 laser liquid

The optical absorption spectra of triply ionized neodymium and erbium ions in POCl₃SnCl₄ laser liquid have been studied for the first time in the UV-VIS and NIR regions. Spectroscopic and Judd-Ofelt intensity parameters are evaluated from the observed band positions and their intensities. Radiative lifetimes and the luminescent branching ratios for the excited fluorescent levels of Nd³⁺ and Er³⁺ ions are theoretically estimated and the possible laser transitions are indicated. From the observed splittings of certain bands in the second-derivative spectrum of the Nd³⁺ ion, the crystal field (A ₂₀,A ₄₀) parameters are evaluated assumingC _3h symmetry for the ion.