Crystal Phosphors Research Articles

The relation of early lumen depreciation of halophosphate phosphors to antimonous and manganous ion concentrations

Plaque brightness depreciation of Ca 10F 2(PO 4) 6:Sb, Mn phosphors subjected to 185 nm radiation in a nitrogen atmosphere is found to be approximately an inverse linear function of Sb concentration and to be independent of Mn content. When irradiation is carried out in the prescence of as little as 0.2% O 2, depreciation of phosphors containing Mn may be much greater than in a pure N 2 ambient. This appears to be caused by photo-oxidation of Mn on or close to the surface of the phosphor crystal. The results of magnetic susceptibility measurements rule out the likelihood that photo-oxidation of Mn, when it occurs, involves either a redox couple with an electron acceptor in the structure or residual oxygen adhering to the surface. It is shown that both the Sb and Mn emission intensities are reduced in the same proportion following exposure to 185 nm radiation, so that loss of luminous efficiency is probably the result of dissipation of excitation energy prior to absorption by Sb and/or a non-radiative process occurring after absorption by Sb. From diffuse reflectance spectra the following radiation-induced absorptions associated with the presence of Sb are found: two unresolved peaks at 320 and 350 nm and absorption at 254 nm. The relative absorption in each of these regions increases with increasing depreciation.

Excitation mechanism of radical-recombinative luminescence of crystal phosphors with a wide forbidden band

Excitation mechanism of radical-recombinative luminescence of crystal phosphors with a wide forbidden band

Stokes and anti-stokes excitation of the resonance emission band of crystal phosphors

Anti-Stokes laser excitation has been induced by one photon absorption transitions in the resonance band of the following crystal phosphors: a natural diamond crystal in which the line structure of the spectrum is quite important, a ZnS:Mn crystal in which the line spectrum is easily observed but its intensity is smaller than that of the wide band emission, and halo-complexes of manganese in which the zero phonon line can hardly be observed. In all cases the emitted spectrum has the same shape as while using Stokes excitation; the intensity depends on temperature by means of a Boltzmann factor. Such a result is easily accounted for by the theory; however, except perhaps in the case of diamond, experiment is not in agreement with the simple theoretical model which concludes that the activation energy W involved in the excitation process is equal to the difference E 0 - hv between the energy of the zero phonon line E 0 and the exciting laser energy hv.

The decay kinetics of radical-recombination luminescence in crystal phosphors

The features of the decay kinetics of radical-recombination luminescence (RRL) in crystal phosphors excited by atomic hydrogen have been studied. It is shown that the kinetics of the RRL decay can be determined both by the processes in the gas phase (decrease in the hydrogen-atom concentration as a result of their recombination at the walls of the reaction vessel after the atom-generation source has been switched off) and by the processes in the solid itself. Some conclusions are drawn concerning the mechanism of recombination for the RRL of the experimental phosphors.

Kinetics of the radical-recombination luminescence of crystal phosphors on excitation by atomic oxygen

The kinetic characteristics of the radical-recombination luminescence of crystal phosphors with a wide forbidden band in atomic oxygen are considered. It is shown that, in order to explain the form of the kinetic curve in the initial stage, simple model representations as to the statistical character of the recombination processes are sufficient. By comparing the theoretical and experimental curves some of the microcharacteristics of recombination between the atoms are determined.

The determination of parameters for the kinetics of the luminescence of crystal phosphors by pulse methods

The determination of parameters for the kinetics of the luminescence of crystal phosphors by pulse methods

Kinetics of radical-recombination luminescence of crystal phosphors under excitation by atomic nitrogen

Kinetics of radical-recombination luminescence of crystal phosphors under excitation by atomic nitrogen

Quantitative relationships in the quenching of the luminescence of certain lanthanide ions by others in crystal phosphors based on YVO4

Quantitative relationships in the quenching of the luminescence of certain lanthanide ions by others in crystal phosphors based on YVO4

A further experiment which belies the fischer model for the electroluminescence process

Experiments have already been reported which provide evidence against the Fischer double-injection model for the a.e. electroluminescence (EL) in ZnS (1). They concern respectively the behaviour of low temperature of the EL yield (2) and the effect of a sharp UV light spot on the EL comets (a). We relate here another experiment which, as will be seen, also conflicts with the Fischer model. I t consists in studying the enhancement of the E1 brightness waves emit ted when the ZnS crystals are irradiated with UV light. This effect, which can be referred to as photoelectroluminescenee (PEL), was previously investigated by some authors (4), mainly by PATEK (5), but only in a rather quali tat ive manner and without succeeding in obtaining definite information about the mechanism of the EL process. To perform our measurements we used condenser shaped EL cells, 0.08 mm thick, filled with ZnS microcrystals embedded in araldite. The crystals were doped with 8.10 -4 Cu, C1 atoms per Zn atom. Both the cell electrodes were built with conducting quartz, to allow the UV light to reach the phosphor crystals. The cell was excited with a 1500 Hz sinusoidal voltage, while it was irradiated with light from a 250 W low-pressure UV lamp supplied with a 50 Hz stabilized voltage. The distance from the lamp to the cell was 30 cm. Light from the cell was detected with a 6810 A RCA phototube placed 20 em away. Suitable collimators and filters were used, to prevent visible light from the lampe reaching the cell and UV light scattered from the cell striking the phototube. In these conditions the EL signal, even though of relevant amplitude, was hidden by a predominant photoluminescence (PL) signal due, besides the ZnS crystals, to araldite. For this reason and taking into account that PL emission was pulsed with a frequency (100 Hz, say twice that of the voltage applied to the UV lamp) very low with respect to that of EL, we connected, after the photomultiplier, a high-pass filter to improve the EL to PL signal ratio.

Spectral-kinetic laws of the radical-recombination luminescence of crystal phosphors activated by manganese

A study was made of the spectral-kinetic laws of luminescence of a number of crystal phosphors activated by manganese in flows of atomic hydrogen and nitrogen. The data obtained were analyzed in terms of the mechanisms of luminescence arising in adsorption, bond strengthening, and the recombination of free atoms and radicals. It is shown that as a result of the specificity of the radical-recombination luminescence (RRL) of crystal phosphors activated by manganese, RRL can serve as an effective means of analyzing “manganese” dopants in crystal phosphors.

Effect of iodine anions on the spectral characteristics of tin- activated potassium chloride single crystals

The luminescence, absorption and excitation spectra of KCl.KI-Sn single crystal phosphors are investigated. By introduction of I- in KCl-Sn a strong shift of the emission band to longer waves is observed, which is ascribed to an association of Sn2+ and I-. The absorption and excitation spectra are affected too. The poorer structure of KCl. KI-Sn in comparison with KCl-Sn is assumed to be due to an increase of the absorption band number by incorporation of I-. In the course of these investigations, a dependence of the tin band position on the activator concentration in KCl-Sn is established.

Concerning the possibility of activation of zinc sulfide crystal phosphors by the explosive loading method

Concerning the possibility of activation of zinc sulfide crystal phosphors by the explosive loading method

Interaction between centers of luminescence and capture in neutron-irradiated zinc sulfide crystal phosphors

Interaction between centers of luminescence and capture in neutron-irradiated zinc sulfide crystal phosphors

A study of the flare-up and attenuation mechanisms of the x-ray luminescence of alkali halide crystal phosphors

A study of the flare-up and attenuation mechanisms of the x-ray luminescence of alkali halide crystal phosphors

Investigation of luminescence excitation processes in some oxygen-dominated compounds by 3 to 21 eV photons

The quantum efficiency of luminescence of a great majority of phosphors, when excited by photons having an energy higher than certain threshold energy hvt, increases with increasing exciting light frequency and in some cases exceeds unity. This phenomenon is due to the beginning of interband Auger transitions which leads to the generation of more than one electron-hole pair by each absorbed photon in average. In the present work the main characteristics of the excitation spectra of activator emission have been investigated for the oxides of periodic system groups 2 and 3 metals, some silicates and phosphates in the spectral region of the host crystal absorption. All phosphors investigated show at the photon energies higher than twice the band gap an increase in quantum efficiency of luminescence corresponding to the beginning of interband Auger transitions. In general the increase in efficiency of luminescence is observed on the background of surface migration losses which are a result of the absorption of the exciting light in a thin surface layer of phosphor crystals where the probability of radiationless recombination of the electron-hole pairs is very high.

Optical methods for finding the quality parameters of images produced on crystal phosphor screens

Optical methods for finding the quality parameters of images produced on crystal phosphor screens

Light transformers with photon multiplication

Crystal phosphors with photon multiplication in the optical range can be used as efficient light transformers. Their use in mercury-free luminescent gas-discharge lamps is especially promising. Analysis of the present position as regards neon discharges indicates that by using phosphors withηt=2–3 it might be possible to create light sources with an efficiency of 30–50 1m/W which would operate solely under outdoor lighting conditions. Evaluation of the prospects of developing light transformers withηt=2–3 indicates that this problem is solvable in principle.

Effect of microdefects in crystal lattice on certain luminescence relaxation processes in alkali halide phosphor crystals

A further development of ideas on an ionic mechanism for the activation of certain relaxation processes in recombination luminescence of alkali halide phosphor crystals is presented. It is shown that each stage of the thermal discoloration process in the phosphor crystals corresponds to disruption of the F-band in an isolated microsection of the specimen. The effect of the degree of plastic deformation on the relative proportions of F-center concentrations on various microregions of the crystal was investigated. The effect of impurity ions, of their concentration, arid of the crystal plastic deformation on the photothermal stability of the F-centers and on the thermal quenching of luminescence during photoexcitation of activator color centers in NaCl-Ag phosphor crystals was also studied.

Investigation of the disintegration mechanism of color centers, and recombination luminescence of the (NaCl-Ag, Ca)-crystal phosphor. II

The investigation of relaxation processes in alkali-halide phosphor crystals excited by X-rays is continued.

On the effective recombination cross‐section of charged centres in crystal phosphors

AbstractThe effective recombination cross‐section σeff of charged centres measured experimentally is found to be not always equal to the gas kinetical cross‐section σk. σeff is also dependent on the diffusion coefficient D and mobility μ. Such a dependence is enhanced at small free pass length l. In a general case the relation holds σk≦ σeff≦ σμ MD (where σμ is the pure drift cross‐section and MD is multiplication constant due to diffusion; σμ = (4 π R′l)/3, where R′ is the distance at which the potential energy of the free charge in the field of the centre becomes equal to kT). At small σk a temperature dependence can arise with “negative” activation energy σeff ∼ e−E/kT, where E < 0. The limiting case σeff = σk is not trivial because the equality is due to original mutual compensation of drift and diffusion.