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In this paper, Ho3+/Yb3+ co-doped Sodium Gadolinium Fluoride (NaGdF4) phosphors were synthesized by a facile and efficient hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy spectrum (EDS), and photoluminescence (PL). The results of XRD and SEM indicated that the prepared NaGdF4 samples have the hexagonal structure and good orientation in the case of changing the concentration of Yb3+. The results of pump power dependence of up-conversion intensity indicated that the energy transfer mechanism from Yb3+ to Ho3+ is a two-photon process. The energy transfer between Ho3+ and Yb3+ under 448 nm excitation was determined by PL spectra and fluorescence lifetimes. All the results proved that the doping of Yb3+ ions can effectively improve the up-conversion luminescence of NaGdF4 phosphors and achieve quantum cutting efficiency of up to 179.8%. Overall, NaGdF4:Ho3+/Yb3+ have potential application in the field of optoelectronic materials. [ABSTRACT FROM AUTHOR]

Single-phased white light-emitting YNbO: Bi, Eu phosphors were synthesized by conventional solid-state reaction. YNbO: Bi phosphor exhibits a broad excitation band ranging from 220 to 360 nm and a blue light emission band peaking at 457 nm, originating from the P-S transition of Bi, whereas YNbO: Eu phosphor exhibits the typical red emission aroused from the D → F, D → F, D → F, D → F transitions of Eu. Under the excitation at 330 nm, the YNbO: Bi, Eu exhibits both the blue emission band of Bi and the red emission of Eu due to the energy transfer from Bi to Eu ions. By tuning the Bi/Eu ratio via the energy transfer, the emission hue of YNbO: Bi, Eu varied from blue (0.16, 0.18) to white (0.33, 0.24) and eventually to red (0.62, 0.33). The mechanism of energy transfer from a sensitizer Bi to an activator Eu in YNbO: Bi, Eu phosphors was demonstrated to be an exchange interaction. [ABSTRACT FROM AUTHOR]

Novel single-phase and color-tunable Ca 2 Y 3 Sb 3 O 14 : Bi 3+ , Eu 3+ phosphors were synthesized by conventional solid-state reaction. The obtained Ca 2 Y 3 Sb 3 O 14 : Bi 3+ phosphor exhibits a blue light emission band peaking at 460 nm due to the 3 P 1 – 1 S 0 transition of Bi 3+ , whereas Ca 2 Y 3 Sb 3 O 14 : Eu 3+ phosphor exhibits the typical red emission aroused from the 5 D 0 → 7 F J (J = 0, 1, 2) transitions of Eu 3+ . Due to the energy transfer from Bi 3+ to Eu 3+ ions, Ca 2 Y 3 Sb 3 O 14 : Bi 3+ , Eu 3+ exhibits both the blue emission of Bi 3+ and the red emission of Eu 3+ under 350 nm excitation. By tuning the Bi 3+ /Eu 3+ ratio, the emission color of Ca 2 Y 3 Sb 3 O 14 : Bi 3+ , Eu 3+ could vary from blue (0.16, 0.18) to red (0.62, 0.38), and white-light emission with superior CIE chromaticity coordinates (0.35, 0.30) and low correlated color temperature (CCT ≈ 3500 K) was obtained as a result of color tuning. The mechanism of energy transfer from the sensitizer Bi 3+ to the activator Eu 3+ in Ca 2 Y 3 Sb 3 O 14 : Bi 3+ , Eu 3+ phosphors was demonstrated to be an exchange interaction. [ABSTRACT FROM AUTHOR]

A novel Ca 2 Y 3 Sb 3 O 14 : Bi 3+ phosphor was synthesized and its crystal structure, photoluminescence (PL) properties was investigated. Ca 2 Y 3 Sb 3 O 14 crystallized as a monoclinic structure with a space group of I2m/11 and lattice constants of a = 7.4129(7) Å, b = 10.4428(1) Å, c = 7.3898(8) Å and α = 90.049°. Ca 2 Y 3 Sb 3 O 14 : Bi 3+ could be efficiently excited in the wavelength range of 270–400 nm. With the increase of Bi 3+ concentration, the most efficient excitation wavelength of the phosphors moved from 320 to 350 nm. When excited under 310–350 nm, the phosphors emit a broad band with a maximum intensity appearing at about 420–460 nm due to the 3 P 1 – 1 S 0 transition of Bi 3+ . The relationship between the PL properties and the crystal structure was discussed. Due to the efficient excitation in the near UV region and the strong blue to cyan emission, Ca 2 Y 3 Sb 3 O 14 : Bi 3+ would be a potential blue phosphor for near UV white light-emitting diodes, or a potential donor system for designing single-composition white-light phosphors based on energy transfer. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sr12Al14O32Cl2:Eu2+ was synthesized by solid state reaction method. [•] Sr12Al14O32Cl2 crystallizes as a cubic structure with a space group of . [•] Sr12Al14O32Cl2:Eu2+ could be efficiently excited by near UV lights. [•] Sr12Al14O32Cl2:Eu2+ gives bright green emission band under near UV excitation. [ABSTRACT FROM AUTHOR]

A novel Bi3+ activated double perovskite CaLaMgTaO 6 phosphor was synthesized and its photoluminescence properties were investigated. CaLaMgTaO 6 : Bi3+ could be efficiently excited in the wavelength range of 270–400 nm, and exhibit a blue emission band ascribing to the 3P 1 –1S 0 transition of Bi3+. The maximum intensity of the excitation moves from 332 to 351 nm, and the emission band moves from 443 to 434 nm as the concentration of Bi3+ increases from 0.5 to 20 mol %, corresponding to the overlapped luminescence of Bi3+ substituting for La3+ and Ca2+ with substitution preference. Due to the energy transfer between Bi3+ ions, the concentration quenching of Bi3+ in the CaLaMgTaO 6 host occurred when the concentration of Bi3+ exceeded 7.5 mol %. The energy transfer mechanism of CaLaMgTaO 6 : Bi3+ was estimated to be dipole-dipole interaction. Furthermore, the thermal stability of the phosphor was investigated and the corresponding activation energy ΔE was determined to be 0.26 eV. Due to the efficient excitation in near ultraviolet (n -UV) region and the strong blue emission, CaLaMgTaO 6 : Bi3+ would be a potential blue phosphor for n -UV pumped light-emitting diodes. Image 1 • Non-rare-earth activated double perovskite phosphor CaLaMgTaO 6 : Bi3+ was synthesized. • CaLaMgTaO 6 : Bi3+ could be efficiently excited at 270–400 nm. • CaLaMgTaO 6 : Bi3+ gives blue emission with a peak at about 440 nm. • CaLaMgTaO 6 : Bi3+ exhibited good thermal stability. [ABSTRACT FROM AUTHOR]

Ca2Y3-xSb3O14: Bi3+x (x = 0.0225-0.75) phosphors are prepared by firing stoichiometric amounts of CaCO3, Y2O3, Sb2O3, and Bi2O3 (Al2O3 crucible, 1400 °C, 8 h). [ABSTRACT FROM AUTHOR]

Abstract: Long afterglow phosphors (Ca1−x Eu x )2MgSi2O7 (0.002≤ x ≤0.02) were prepared by solid-state reactions under a weak reductive atmosphere. X-ray diffraction pattern, photoluminescence spectra, decay curve, afterglow spectra and thermoluminescence curves were investigated. The phosphors showed two emission peaks when they were excited by 343nm, due to two types of Eu2+ centers existing in the Ca2MgSi2O7 lattice. However, only one emission peak can be found in their afterglow spectra. Energy transfer between Eu2+ ions in inequivalent sites was found. A possible mechanism was presented and discussed. The afterglow decay time of Ca1.998MgSi2O7:Eu0.002 was nearly 12.5h which means it was a good long lasting phosphor. [Copyright &y& Elsevier]

Bi 3+ and Eu 3+ ions co-doped Ca 2 YSbO 6 have been prepared via high temperature solid–state reaction. Its crystal structure and photoluminescence properties were investigated by X-ray diffraction patterns, diffuse reflection spectra, photoluminescence excitation and emission spectra. The results indicated that the Ca 2 YSbO 6 crystallizes as a monoclinic structure with a space group of P21/n, with the lattice parameters related to that of the double perovskite by a = 5.5995 Å, b = 5.7964 Å, c = 8.0507 Å, α = γ = 90.00°, β = 89.8943°. The Ca 2 YSbO 6 :Eu 3+ can be excited by ultraviolet, near-ultraviolet, and blue lights, and a strong red emission located at 614 nm ( 5 D 0 → 7 F 2 ) of Eu 3+ ions was observed in all samples. By co-doping Bi 3+ ions in Ca 2 YSbO 6 :Eu 3+ , the excitation band shifts to the long-wavelength region, and the red emission intensity was remarkably enhanced. With 5 mol% Bi 3+ doped in Ca 2 YSbO 6 :Eu 3+ , the relative intensity of Ca 2 Y 0.80 Bi 0.05 Eu 0.15 SbO 6 was enhanced by 327%, 389% and 348% excited at 290 nm, 400 nm and 470 nm compared with those of Ca 2 Y 0.85 Eu 0.15 SbO 6 , respectively. The composition-optimized Ca 2 Y 0.8 SbO 6 :0.15Eu 3+ , 0.05Bi 3+ phosphor with strong red emission and good CIE chromaticity coordinate shows great potential for applications in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: The Ho3+/Yb3+ co-doped NaGd(WO4)2 phosphors with different concentrations of Yb3+ were prepared by a facile hydrothermal route. X-ray diffraction and scanning electron microscopy were used to study the structure of the samples. The upconversion (UC) emission spectra of the samples were measured under 980nm excitation with different pumping power. Intense red luminescence at 625–675nm, weak blue luminescence at 458–492nm, green luminescence at 523–565nm and near infrared luminescence at 736–770nm emitted by Ho3+ were observed, and their emission intensities changed with the Yb3+ concentration. The transition mechanisms of the UC luminescence were also discussed. [Copyright &y& Elsevier]

A series of NaYF 4 :0.2Yb/0.02Ho microcrystals co-doped with various K+ and Gd3+ concentrations were synthesized by hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and upconversion (UC) spectroscopy were used to study the effects of co-doped ions on the phase structure, morphology, size and up-conversion luminescence (UCL) properties of microcrystals in detail. The results show that the K+ and Gd3+ co-doping do not evoke the change in crystal structure, but the UCL intensities of NaYF 4 :0.2Yb/0.02Ho are significantly enhanced. Compared to K+ and Gd3+-absent sample, UCL intensities of green emission (541 nm) and red emission (643 nm) in NaYF 4 :0.2Yb/0.02Ho microcrystals via 15 mol% K+ and 15 mol% Gd3+ co-doping are increased by 2.4 times and 3.3 times, respectively. The temperature sensing characteristics and thermal quenching properties of the microcrystals were also explored. Significantly, the maximum relative sensitivity of the studied sample reaches 0.0127 K−1 at 298 K, which indicates that NaYF 4 :0.2Yb/0.02Ho phosphors can be suitable for temperature sensing. [Display omitted] • The K+/Gd3+ co-doped NaYF 4 :0.2Yb/0.02Ho microcrystals have been prepared by a simply hydrothermal synthesis procedure. • The up-conversion transition mechanism of the crystallites is attributed to the two-photon absorption process. • Explore the average lifetime of K+/Gd3+ co-doped microcrystals under 980 nm excitation. • Explore the optical temperature measurement and thermal quenching performance of K+/Gd3+ co-doped microcrystals. [ABSTRACT FROM AUTHOR]