Mihail Nazarov

Luminescent Properties of Ca-α-SiAlON : Eu2 + Phosphors Synthesized by Gas-Pressured Sintering

Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, Ca-α-SiAlON:Eu 2+ based yellow and orange oxynitride phosphors with compositions of Ca 0.485 Eu 0.015 Si 9.2 Al 2.8 O 1.8 N 14.2 and Ca 0.94 Eu 0.06 Si 9 Al 3 ON 15 were prepared using the gas-pressured sintering method. The crystallinity and particle morphology of the prepared phosphors were characterized. The temperature dependence of photoluminescence properties was investigated from 25 to 150°C. The Stokes shift and zero-phonon line was calculated mathematically and estimated from the spectral data. The prepared Ca-α-SiAlON:Eu 2+ phosphors showed superior thermal quenching properties compared to commercially used YAG:Ce 3+ phosphors. In addition, the activation energies (ΔE) for thermal quenching of the prepared Ca-α-SiAlON:Eu 2+ phosphors were determined by Arrhenius fitting.

Luminescence and Raman studies of YNbO4 phosphors doped by Eu3+, Ga3+, and Al3+

Efficient phosphors based on YNbO4 and doped by Eu3+, Ga3+, and Al3+ were synthesized with different fluxes under different thermal conditions and investigated under x-ray excitation and Raman spectroscopy. The samples codoped by Al3+ and Ga3+ show higher intensity under x-ray excitation in comparison with YNbO4:Eu3+ phosphors. The model of redistribution energy transfer from D51 level to F7J is proposed. Monoclinic fergusonite crystal structure and excellent luminescent properties under x-ray excitation allow recommend these phosphors as good candidates for different applications.

Red Emission Properties of ( Y , M ) NbO4 : Eu3 + (M: Al, Ga) Phosphors under Near-UV Excitation

Red emission (613 nm) properties of (Y, M)NbO 4 :Eu 3+ (M: Al, Ga) powders under charge-transfer band (CTB, ~270 nm) and near-UV (397 nm) excitation were investigated. In Y 1-x Eu x NbO 4 , with an increase in the Eu content (x), the red emission intensity under 397 nm excitation increased abruptly up to x = 0.25 and then saturated at x ≥ 0.25, whereas that under CTB excitation broadly peaked at x = 0.1-0.25. The red emissions under 397 nm excitation of Y 1-y Al y NbO 4 :Eu 3+ and Y 1-x Ga z NbO 4 :Eu 3+ were drastically enhanced, showing about two times higher intensity at y = 0.2 and z = 0.1, respectively, than that of YNbO 4 :Eu 3+ . This improved emission was ascribed to the local distortion and asymmetry sites in the host lattice originating from the remarkably different ionic radii of Al 3+ and Ga 3+ from Y 3+ .

Rare earth double activated phosphors for different applications

Abstract For the purpose of development of highly energy-efficient light sources, one needs to design highly efficient green, red and yellow phosphors, which are able to absorb excitation energy and generate emissions. In this contribution, we present our results on producing some efficient phosphors with improved luminescence properties. Using double activation, energy could be transferred from one luminescent activator to the other one, resulting in more efficient or brighter device operation. Co-activators could be added to a host material to change the color of the emitted light. The incorporation of Eu 3+ or Tb 3+ ions into the CaWO 4 crystal lattice modified the luminescence spectrum due to the formation of the emission centers that generated the specific red and green light. Very efficient new red phosphors based on YNbO 4 and doped by Eu 3+ , Ga 3+ , Al 3+ allowed recommending these materials as good candidates for different applications including LED and X-ray intensifying screens. For double activated TAG with Ce 3+ and Eu 3+ and for different mole ratios of Ce/Eu, the color temperature changed from 5500 K (0.331, 0.322) up to 4200 K (0.370, 0.381) and the light became “warmer”. Application of TAG: Ce, Eu in the light emitting device showed better chromaticity coordinates of luminescence and color rendering index of LEDs.

Polarization selection rules and optical transitions in terbium activated yttrium tantalate phosphor under x-ray, vacuum-ultraviolet, and ultraviolet excitations

The terbium-activated yttrium tantalite (YTaO(4):Tb(3+)) phosphor is of great interest due to the interesting spectroscopic properties of rare earth ions in crystals and also practical use in x-ray imaging. Using the group-theoretical approach, we analyze the selection rules for the transition between Stark components of Tb(3+) in symmetry of the actual crystal field and the polarization for the allowed transitions. The luminescence upon UV, vacuum-ultraviolet (VUV), and x-ray excitation is presented and discussed. The YTaO(4):Tb(3+) phosphors are found to be efficient VUV-excited luminescent materials that could be used not only in x-ray intensifying screens, but also in mercury-free fluorescent lamps or plasma display panels.

Efficient multiphase green phosphor based on strontium thiogallate

Efficient multiphase green phosphors based on strontium thiogallate were synthesized by solid state reaction at 900–1000 °C with carbon as a reduction atmosphere. The detailed x-ray diffraction analysis, energy dispersive spectroscopy, Raman spectroscopy, and photoluminescence were carried out in order to enlarge the understanding of the radiative processes in multiphase green phosphors based on strontium thiogallate. The crystal field splitting, Stokes shift, redshift, and centroidal shift were estimated, and the results are in good agreement with mathematical calculations. Our study confirms that the proposed multiphase green phosphor based on strontium thiogallate is a good candidate for solid state lighting and display devices with higher intensity and better chromaticity coordinates in comparison with the known commercial phosphors.

Synthesis of europium- or terbium-activated calcium tungstate phosphors

Utilization of luminescent substances in various optoelectronic devices depends on their luminescent properties and sensitivity to various excitation radiation as well as on particle size distribution and crystalline structure of luminous powders. Calcium tungstate phosphors are well excited with roentgen radiation, so that they are largely used for manufacture of x-ray intensifying screens. Being sensitive to short UV-radiation as well, they could be utilized in Plasma Display Panels or in advertising signs fluorescent tubes. In order to diversify the utilization possibilities of this tungstate class, luminescent powders based on CaWO4:Eu3+ and CaWO4:Tb3+ were synthesized and characterized. As compared with the starting self-activated phosphor, larger excitation wavelength domain and emission colors from blue-to-green-to- yellow-to-red were obtained. The good UV excitability and variable luminescence color recommend these phosphors for optoelectronic device manufacture.

New High Efficient Red Phosphor (Y,M)NbO4: Eu3+(M: Ga3+, Al3+) for X-Ray and UV Excitation

Efficient phosphors based on YNbO4 and doped by Eu3+, Ga3+, Al3+ were synthesized and investigated under UV, and X-ray excitation in luminescence and Raman spectroscopy. Monoclinic fergusonite crystal structure and excellent luminescent properties under X-ray excitation allow recommend these phosphors as good candidates for different applications.

Double Activated X-ray and LED Phosphors with Improved Properties

In this paper, the current status of applied luminescent materials is reviewed together with its implication for the performance of devices based on them. Our approach is based on a consideration of fundamental aspects how to improve the luminescent properties of perspective X-ray and LED phosphors.

Terahertz and infrared spectroscopy of yttrium tantalate and niobate phosphors

Terahertz time-domain and infrared spectroscopy were used to better understand the luminescence and crystallographic data of yttrium tantalate and niobate phosphors.