IR luminescence of thulium-activated crystals of double sodium yttrium fluoride Na0.4Y0.6F2.2:Tm3+: Self-quenching of luminescence from the 3H4 level

Na_0.4Y_0.6F_2.2:Tm³⁺ crystals with thulium contents of 0.5–20% have been grown by the Stockbarger-Bridgman method. The concentration dependences of the steady-state spectra and luminescence kinetics from the ³ H ₄ and ³ F ₄ thulium levels upon selective laser excitation of a series of Na_0.4Y_0.6F_2.2:Tm³⁺ crystals (0.5–20% Tm) are investigated. It is shown that the luminescence from the ³ H ₄ level becomes significantly quenched with an increase in the concentration due to the nonradiative energy transfer. No concentration quenching of luminescence from the ³ F ₄ level is observed. Possible schemes of self-quenching are considered for the ³ H ₄ thulium level, the self-quenching microparameters and macrorates are estimated using model quantum-mechanical calculation, and the most likely self-quenching mechanisms and schemes are found from comparison of the calculated and experimental self-quenching rates. Good agreement is obtained between the experimental and calculated kinetic curves. It is shown that, under pumping near ∼0.8 μm, self-quenching of the ³ H ₄ thulium level leads to effective occupation of the ³ F ₄ level and increases the luminescence intensity in the range of 1.7–1.9 μm. It is concluded that Na_0.4Y_0.6F_2.2:Tm³⁺ crystals are promising active media for tunable lasers in the range of 1.7–1.9 μm, with small thermal loss under laser-diode pumping near 0.8 μm. Original Russian Text ? S.é. Ivanova, A.M. Tkachuk, A.A. Mirzaeva, F. Pellé, 2009, published in Optika i Spektroskopiya, 2009, Vol. 106, No. 6, pp. 922–930.     

Intense blue-emitting Ca5Al8O14: Eu phosphor for mercury free lamp

The calcium aluminates doped with Eu ions, Ca₅Al₈O₁₄: Eu, phosphors are prepared by the combustion method. The formation of crystalline aluminates was confirmed by X-ray diffraction pattern. The prepared phosphors were characterized by SEM, TGA, DTA, particle size analyzer and Photoluminescence (PL) techniques. From the UV-excited luminescence spectra it was found that the Eu ions acts as a luminescent centre with luminescence at the blue (λ _max = 470 nm) region due to 4f ⁶5d ¹ → 4f ⁷ transition. The excitation spectra show the broad band at 355 nm wavelength (λ _em = 470 nm). The excitation 355 nm is a mercury free excitation and therefore Ca₅Al₈O₁₄: Eu may be useful for the solid state lighting phosphor in lamp industry.      

Vibronic and Raman spectra of Y(Eu3+) polytantalate, EuxY1?xTa7O19

Luminescence spectra, luminescence excitation spectra, and Raman spectra of polycrystalline Eu_0.9Y_0.1Ta₇O₁₉ were studied. Zero-phonon lines and vibronic sidebands of the ⁷ F ₀−⁵ D ₂ and ⁷ F ₀−⁵ D ₀ transitions were identified and the Stark splittings of several ⁷ F _J and ⁵ D _J , states of Eu³⁺ ions were investigated. The details of the structure of lanthanide polytantalates and the reduction of the luminescence quenching are discussed. Original Text ? Astro, Ltd., 2007.     

Recombination luminescence of CaSO4:Tb3+ and CaSO4:Gd3+phosphors

A comparative study of the excitation of luminescence by VUV radiation as well as of thermally and photostimulated luminescence has been carried out for CaSO₄:Tb³⁺ and CaSO₄:Gd³⁺ phosphors, where Na⁺ or F⁻ ions are used for charge compensation. The distinction in hole processes for the phosphors with Na⁺ or F⁻ compensators is determined by the differing thermal stability of the holes localized at/near Tb³⁺Na⁺ and Gd³⁺Na⁺ (up to 100–160 K) or at/near Tb³⁺F⁻ V _Ca and Gd³⁺F⁻ V _Ca centers involving also a cation vacancy (up to 400–550 K). Tunnel luminescence in the pairs of localized electrons and holes nearby Tb³⁺ or Gd³⁺ has been detected. The mechanisms of electron-hole, hole-electron and tunnel recombination luminescence as well as a subsequent released energy transfer to RE³⁺ ions are considered.     

Spontaneous and stimulated red luminescence of Lu2O3: Eu nanocrystals

The spectra of spontaneous and stimulated luminescence of Lu₂O₃: Eu (7 at %) nanopowders at different optical pumping intensities have been investigated. The obtained results—changes in the shape of the red luminescence spectra and in the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions—indicate the onset of superluminescence with an increase in the excitation power. It has been found that an increase in the optical pumping intensity leads to a decrease in the luminescence decay time of the Lu₂O₃: Eu (7 at %) phosphor in the stimulated luminescence regime and to an increase in the quantum efficiency of red luminescence with a maximum at 611 nm.     

Growth and the luminescence properties of a lutetium gadolinium garnet doped with Ce3+ and Pr3+ ions

Crystals of lutetium gadolinium garnet solid solutions (Lu_{1 − x} Gd _x )Al₅O₁₂ (0 ≤ x ≤ 0.6) doped with Ce³⁺ and Pr³⁺ ions have been prepared by the horizontal directional crystallization method, and their optical and luminescence properties have been investigated. It has been established that the introduction of gadolinium into the lutetium garnet lattice leads to a decrease in the antisite luminescence (Lu_Al centers) in the UV spectral range and to sensitization of the Ce³⁺ ion luminescence. By contrast, the presence of gadolinium results in the quenching of the Pr³⁺ luminescence due to the nonradiative excitation transfer from Pr³⁺ ions to Gd³⁺ ions.     

Time-resolved luminescence spectroscopy of pure and doped with Ce3+ ions SrAlF5 crystals

The results of a study of time-resolved photoluminescence (PL) and energy transfer in both pure and doped with Ce³⁺ ions SrAlF₅ (SAF) single crystals are presented. The time-resolved and steady-state PL spectra in the energy range of 1.5–6.0 eV, the PL excitation spectra and the reflectivity in the energy range of 3.7–21 eV, as well as the PL decay kinetics were measured at 8.8 and 295 K. The lattice defects were revealed in the low temperature PL spectra (emission bands at 2.9 and 4.5 eV) in the undoped SAF crystals. The luminescence spectra of the doped Ce³⁺:SAF crystals demonstrate a new selective emission bands in the range of 3.7–4.5 eV with the exponential decay kinetics (τ ≈ 60 ns at X-ray excitation). These bands correspond to the d-f transitions in Ce³⁺ ions, which occupy nonequivalent sites in the crystal lattice.     

Eu3+-based optical centers with a high efficiency of the 5D0 → 7F4 transition in alumina gel films

A record peak luminescence intensity of the ⁵ D ₀ → ⁷ F ₄ transition in Eu³⁺ ions and broadening of their UV excitation band are obtained by doping of Eu-containing alumina gel films with bismuth oxyfluoride and subsequent thermal treatment at T ≥ 700°C. The results obtained are explained by the formation of complex Eu—Bi centers with C _3V symmetry in the Al₂O₃ structure, efficient migration of excitations from EuAlO₃ crystallites to these centers, and the sensitization of the luminescence of the rare-earth activator by Bi³⁺ ions. __________ Translated from Optika i Spektroskopiya, Vol. 98, No. 2, 2005, pp. 224–228. Original Russian Text Copyright ? 2005 by Malashkevich, Shevchenko, Bokshits, Kornienko, Pershukevich.     

Synthesis and photoluminescence properties of MZr2(PO4)3:Eu3+; Bi3+ (M=Na; K) phosphors

A series of new red phosphors, MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K), were synthesized using the solidstate reaction method, and their photoluminescence spectra were measured. The MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors were efficiently excited by an ultraviolet (UV; 395 nm) source, and showed intense orange-red emission at 595 nm. Further investigation of the concentration-dependent emission spectra indicated that the MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors exhibit the strongest luminescence intensity when y = 0.01 in NaZr_2(0:95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ and y = 0.09 in NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺, whereas the relative PL intensity decreases with increasing Bi³⁺ concentration due to concentration quenching. The addition of Bi³⁺ widens the excitation band of NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ around 320 nm, which provides the useful idea of broadening the excitation band around 300–350 nm to fit the ultraviolet chip.     

Photoluminescent properties of Eu 3 +(Dy 3 +)-activated YNb x Ta 1 - x O 4 and REVTa 2 O 9 (RE?=?Y, La, Gd) phosphors from the hybrid precursors

In the context, Eu³⁺ (Dy³⁺)-doped YNb_xTa_1-xO₄ and REVTa₂O₉ (RE=Y, La, Gd) phosphors have been synthesized from the hybrid precursors. Both XRD and SEM indicated the particles present good crystalline state, whose crystalline grain sizes were in the range of 0.5 to 1 μm. Besides, XRD patterns of YNb_xTa_1-xO₄ (x=0.1, 0.2, 0.3, 0.5, 0.9) have shown that the phase has been changed from M^′-type YTaO₄ to M-type YNbO₄ with increasing niobium content. Furthermore, from the luminescent spectra of Eu³⁺-doped YNb_xTa_1-xO₄, it was observed that the ⁵ D ₀–⁷ F ₂ transition of Eu³⁺ was predominated and its intensity increases with increasing niobium content, as well as the intensity ratio of ⁵ D ₀–⁷ F ₂ transition to ⁵ D ₀–⁷ F ₁ transition for Eu³⁺. The optimum concentrations of Eu³⁺ and Dy³⁺ in YNb_0.5Ta_0.5O₄ have been found to be 6 and 5 mol %, respectively. At the same time, the luminescent properties of Eu³⁺ and Dy³⁺ in REVTa₂O₉ (RE=Y, La, Gd) have also been investigated that GdVTa₂O₉:Eu³⁺ (Dy³⁺) presents high luminescence, while LaVTa₂O₉:Eu³⁺ (Dy³⁺) shows weak luminescence. PACS 78.20.-e; 78.55.-m; 61.72.Ss; 32.50.+d; 81.40 Tv     

Emission analysis of RE3+ (Eu3+, Tb3+ & Ho3+): B2O3-BaO-LiF/AIF3 glasses

We report here the luminescence spectra of certain rare earth ions (Eu³⁺, Tb³⁺ & Ho³⁺) doped B₂O₃-BaO-LiF/AiF₃ based on the measurements of emission and decay curves of prominent emission transitions. For both the reference host glasses, FTIR, XRD, DTA-TG profiles have been recorded to understand their structural and thermal properties. Eu³⁺ doped glasses have shown five emission transitions of ⁵D₀ → ⁷F_{01,2,3 & 4} located at 580nm, 593nm, 615nm, 655nm and 704nm respectively with an excitation at λ_exci = 392 nm (⁷F₀ → ⁵L₆). Also under an UV source, these europium glasses have displayed a bright red emission from their surfaces. Tb³⁺ glasses have exhibited four emission bands of ⁵D₄ → ⁷F_6,5,4,3 at 491nm, 547nm, 588nm and 625nm respectively with an excitation at λ_exci = 376 nm (⁷F₆ → ⁵G₆). Intense green emission from the glass surfaces has been noticed upon exposure to the UV source. Prominently bluish-green emission has been noticed from the surfaces of the holmium glasses under an UV source and same emission transition (⁵F₄ → ⁵I₈) at 519 nm with an excitation at λ_exci = 389 nm (⁵I₈ − ⁵G₄) has also been obtained from their measured emission spectra. For all the prominent emissions of the rare earth glasses, decay curves have been measured to compute their lifetimes.     

Calculation of the probability of the 4 T 2→4 A 2 transition in luminescence spectra of the Mn4+ ion in gadolinium-gallium garnet

The ⁴ T ₂→⁴ A ₂ transition of the Mn⁴⁺ ion has been observed in the luminescence spectrum of Mn⁴⁺:Cd₃Ga₅O₁₂ upon intense laser pumping. It is shown that an increase in the intensity of the ⁴ T ₂→⁴ A ₂ transition with respect to the ² E→ ⁴ A ₂ transition in these crystals with increasing pumping power relates to the increased role of induced transitions. The intensity of this process is greater in the region where the ² E→⁴ A ₂ and ⁴ T ₂→⁴ A ₂ transition bands overlap most, which leads to an increase of the zero-phonon line of the latter transition, peaking at a wavelength of 694 nm. The rates of radiative and nonradiative recombination involving the ⁴ T ₂, ² E, and ⁴ A ₂ terms of the Mn⁴⁺ ion in gallium-gadolinium garnet (GGG) are calculated using data from luminescence spectra measured at different temperatures. The Mn⁴⁺:GGG crystal is proposed for use as an active element of lasers with continuous frequency tuning. __________ Translated from Optika i Spektroskopiya, Vol. 94, No. 4, 2003, pp. 590–596. Original Russian Text Copyright ? 2003 by Bulyarskiĭ, Zhukov, Prikhod’ko.     

Comparative Raman study of the Ti complex Cp2Ti(η2-C60) · C6H5CH3 and TixC60 films

Raman spectra from the first Ti fullerene complex Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ are presented. Compared to spectra of pure C₆₀, the spectra of the Ti complex exhibit a number of new peaks due to the symmetry lowering for C₆₀. The A _g(2) mode is downshifted by 12 cm⁻¹ compared to C₆₀, which corresponds to a charge transfer of one electron per Ti-C₆₀ bond. This value (6 cm⁻¹ for one transferred electron) is identical to the downshift of the A _g(2) mode in alkali metal fullerides with ionic bonding. The spectra of Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ were compared to the spectra of evaporated Ti_xC₆₀ films. The A _g(2) mode in Ti₄C₆₀ showed a downshift of about 25 cm⁻¹ compared to pure C₆₀, which corresponds to a charge transfer of one electron per Ti atom; this is similar to the ionic alkali metal fullerides and different from η²-C₆₀-type bonding. From Fizika Tverdogo Tela, Vol. 44, No. 3, 2002, pp. 483–485. Original English Text Copyright ? 2002 by Talyzin, Jansson, Usatov, Burlakov, Shur, Novikov. This article was submitted by the authors in English.     

Cr-related centers in Gd3Ga5O12 polycrystals

The luminescence excitation spectra, emission spectra under photo- and X-ray excitation, luminescence decay kinetics and thermostimulated luminescence (TSL) of Gd₃Ga₅O₁₂ garnet (GGG) polycrystalline samples have been investigated. It was established that the spectrum of Cr³⁺ ion emission were present in all TSL peaks. The activation energies of traps that are responsible for appearance of TSL in the region 295-600 K were estimated. It is shown that delocalization of electrons from the Cr³⁺e traps leads to the appearance of thermoluminescence (TL) glow peak at 390 K. The nature of other TSL peaks is discussed. The influence of visible light on the TSL intensity of the preliminary X-ray-irradiated samples is shown.     

Photoluminescence properties of Eu3+-doped Gd2MoB2O9 phosphors for LED-based solid-state-lighting

Investigation was performed on luminescent properties of novel Gd_2−x Eu _x MoB₂O₉ (0.02≤x≤2.0) phosphors. The excitation spectra consist of broad band and intense narrow lines. The 4f-4f transitions are situated in a favorable position for excitation by GaN chip emission. The emission spectra consist of transitions from the ⁵D₀ level to the lower ⁷F manifold, and the emission shows no concentration quenching at higher doping level. The decay time spectra of the ⁵D₀ → ⁷F₂ emission are recorded. Under 395 nm excitation, the intensity of ⁵D₀ → ⁷F₂ transition of GdEuMoB₂O₉ is 1.2 times stronger than that of commercial Eu³⁺:Y₂O₂S phosphor. Gd₂MoB₂O₉:Eu³⁺ phosphors are promising candidates for near-UV-based solid-state-lighting (SSL).     

Upconversion properties of Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glasses

The Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glass is prepared by conventional melting method, and its upconversion spectra are measured. The intense green upconversion luminescence upon excitation with a 976 nm laser diode is observed with the naked eyes. The dependence of luminescence intensity on the ratio of Yb^3＋/Er^3＋ is discussed in detail, and the relationship between the ratio of green luminescence intensity to red luminescence intensity and the ratio of Yb^3＋/Er^3＋ is also studied, The luminescence intensity increases with the ratio of Yb^3＋/Er^3＋ increasing. The ratio of Yb^3＋/Er^3＋ plays a more important role than the concentration of Er^3＋ in determining the upconversion luminescence intensity. The ratio of green luminescence intensity to red luminescence intensity reaches a maximum when ratio of Yb^3＋/Er^3＋ is 3. Thus the glass could be one of the potential candidates for LD pumping solid-state lasers.     

Up-conversion emission in triply-doped Ho/Yb/Tm KGd(WO4)2 single crystals

Detailed spectroscopic studies of the triply doped KGd(WO₄)₂:Ho³⁺/Yb³⁺/Tm³⁺ single crystals (which exhibit multicolor up-conversion fluorescence) are reported for the first time. The absorption spectra of crystals were measured at 10 and 300 K; the room temperature luminescence spectra were excited at 980 nm wavelength. The dependence of the intensity of luminescence on the excitation power for three different concentration of Ho³⁺, Yb³⁺ and Tm³⁺ ions was investigated. Efficient green and red up-converted luminescence of Ho³⁺ ions and weak blue up-conversion luminescence of Tm³⁺ ions were observed in spectra. The red emission of Ho³⁺ ions is more intensive than their green emission. Dependence of the up-conversion luminescence intensity on the excitation power and impurities concentration was also studied; the number of phonon needed for efficient up-conversion was determined for each case. All possible energy transfer processes between different pairs of the impurity ions' energy levels are also discussed.     

Preparation and luminescent characteristic of Li3NbO4 nanophosphor

Synthesis and luminescence properties of Li₃NbO₄ oxides by the sol-gel process were investigated. The products were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and absorption spectra. The PL spectra excited at 247 nm have a broad and strong blue emission band maximum at 376 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectra of the samples sintered at temperatures of 600 and 700 °C exhibited the band-gap energies of 4.0 and 4.08 eV.     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.     

Growth and characterization of Nd-doped disordered Ca3Gd2(BO3)4 crystal

A high-quality disordered Nd³⁺:Ca₃Gd₂(BO₃)₄ (Nd³⁺:CGB) laser crystal was grown by the Czochralski method. The space group and effective segregation coefficient of Nd³⁺ were determined to be Pnma and 1.06, respectively. The thermal properties, including the average linear thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity were systematically measured for the first time. It was found that the thermal conductivity increases with increasing temperature, indicating glasslike behavior. The polarized spectral properties of the crystal were investigated, including the polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay. The spectroscopic parameters of Nd³⁺ ions in Nd³⁺:CGB crystal have been obtained based on Judd–Ofelt theory. The anisotropy of the spectral properties for different polarized directions was discussed. Additionally, the continuous-wave (CW) laser performance at 1.06 μm was demonstrated for the first time. The maximum output power of 603 mW was achieved with corresponding optical conversion efficiency of 8.33% and slope efficiency of 9.95%.