Photoluminescence properties of novel white phosphor of Dy3+-doped LaBSiO5 glass

A single-phased white emitting phosphor LaBSiO₅:Dy³⁺ was successfully synthesized via a solid state reaction. The X-ray diffraction results confirmed that the doped Dy³⁺ ions did not change the lattice structure. Several strong excitation peaks of LaBSiO₅:Dy³⁺ were found around 300–450 nm. Under excitation of 350 nm, the LaBSiO₅:Dy³⁺ exhibited white emission by combining the two emission peaks at 478 and 574 nm corresponding to the typical ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions. The optimal substitution proportions of Dy³⁺ for La³⁺ was determined to be 1 mol% and the critical distance of Dy³⁺ was 25.9628 Å. Moreover, the CIE chromaticity coordinates of LaBSiO₅:Dy³⁺ phosphor was (0.3116, 0.3474) which is close to the ideal white light coordinates (0.333, 0.333), indicating that the phosphor has a potential application as a single component ultraviolet-convertible white light emitting phosphor.     

Effect of MoO42− partial substitution on optical enhancement of LaNa(MoO4)2:Dy3+ phosphors for white light emitting diodes

Dy³⁺ doped LaNa(MoO₄)₂ phosphors with different anionic groups (SO₄²⁻, PO₄³⁻ and BO₃³⁻) substitution were prepared through solid state reaction at 1100 °C. X-ray diffraction patterns of the as-prepared phosphors indicate that all samples have the standard LaNa(MoO₄)₂ structure. The photoluminescence spectra consist of a blue emission at 484 nm and a yellow emission at 576 nm, which corresponding to the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ions, respectively. The luminescence intensity of LaNa(MoO₄)_1.9(BO₃)_0.1:Dy³⁺, LaNa(MoO₄)_1.8(PO₄)_0.2:Dy³⁺ and LaNa(MoO₄)_1.9(SO₄)_0.1:Dy³⁺ phosphors are 2.8, 1.8 and 3-fold higher than that of LaNa(MoO₄)₂:Dy³⁺ phosphor, respectively. In addition, the luminescence lifetime values of LaNa(MoO₄)₂:Dy³⁺, LaNa(MoO₄)_2−x(BO₃)_x:Dy³⁺, LaNa(MoO₄)_2−x(PO₄)_x:Dy³⁺, and LaNa(MoO₄)_2−x(SO₄)_x:Dy³⁺ are 0.188, 0.189, 0.186 and 0.183 ms, respectively.     

Enhanced emission at 2.85 μm of Ho3+/Pr3+ co-doped α-NaYF4 single crystal

The Ho³⁺/Pr³⁺ co-doped NaYF₄ single crystals with various Pr³⁺ concentrations and constant Ho³⁺ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho³⁺ single-doped NaYF₄ crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω ₂, Ω ₄ and Ω ₆) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τ _rad) are obtained in the meantime. The energy transfer from Pr³⁺ to Ho³⁺ and the optimum fluorescence emission of Ho³⁺ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10^-20 cm² for the NaYF4 single crystal with Ho³⁺ molar percentage of 1% and Pr³⁺ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho³⁺/Pr³⁺ co-doped NaYF₄ single crystal may have potential applications in mid-infrared lasers.     

Synthesis and Luminescence of BaWO4:Ln3+ (Ln = Eu,Tb, and Dy) Powders

BaWO₄:Ln³⁺ powders were synthesized by a solid-state reaction method. The BaWO₄:Ln³⁺ samples were characterized by x-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), and luminescence spectroscopy. The XRD patterns reveal that the BaWO₄:Ln³⁺ samples present pure tetragonal scheelite structure. The SEM observations demonstrate that the BaWO₄:Ln³⁺ powders are irregular particles with size in the range of micrometers. The excitation spectra of the BaWO₄:Ln³⁺ samples show the broad absorption band originating from charge transfer between oxygen ligands and the central tungstate ions inside WO ₄ ^2? groups in the metal tungstate. The emission spectra of the BaWO₄:Ln³⁺ samples display the bands associated to the anion molecular complex (WO ₄ ^2? ) and the f–f transitions of Ln³⁺. According to the emission spectra and the chromaticity coordinates (Commission internationale de l'éclairage, CIE), one can see that the BaWO₄:Eu³⁺, BaWO₄:Tb³⁺, and BaWO₄:Dy³⁺ samples show emission in the red, green, and yellow region, respectively. The results show that the luminescence color can be altered by changing the Ln³⁺ doping in BaWO₄ material.     

Preparation and Photoluminescence Properties of Pr3+ Ion-Doped Ca2LaTaO6 Phosphors

In this study, Pr³⁺ ion-doped Ca₂LaTaO₆ phosphors were synthesized using a vibrating milled solid-state reaction with metal oxides and calcined in air at 1100°C for 8 h. The crystal structure and photoluminescence properties were also investigated. The x-ray powder diffraction patterns show that all of the peaks can be attributed to monoclinic Ca₂LaTaO₆ phase with increasing Pr³⁺ ion doping. The scanning electron microscopy images show that the particles are irregular, with the most uniform distribution being obtained for Pr³⁺ ion concentration of 3 mol.%. The emission spectra of Ca₂(La_1?x Pr _x )TaO₆ phosphors showed a dominant green emission peak at 490 nm under excitation at 451 nm, which was due to the ³P₀ → ³H₄ transition. A series of weak emission peaks at 531 nm, 544 nm, 615 nm, 621 nm, and 652 nm were assigned to the ³P₀ → ³H₅, ¹D₂ → ³H₄, ³P₀ → ³H₆, and ³P₀ → ³F₂ transitions of Pr³⁺ ions, respectively. In addition, the emission intensities of the Ca₂(La_1?x Pr _x )TaO₆ phosphors increased then decreased as the Pr³⁺ ion concentration was increased, and the maximum emission intensity occurred for x of 0.03, corresponding to an average grain size of 41.5 nm with critical distance of 16.32 Å. The Commission Internationale de l’Eclairage color chromaticity coordinates for the Ca₂LaTaO₆:Pr³⁺ phosphors were all located in the green region, but shifted from (x = 0.145, y = 0.463) to (x = 0.119, y = 0.471) as the Pr³⁺ ion concentration was increased from 0.5 mol.% to 10 mol.%.     

Photoluminescence properties of YVO4:Eu3+,Ba2+ nanoparticles prepared by an ion exchange method

YVO₄:Ba²⁺ nanoparticles with a Ba²⁺ doping concentration x=0%, 1%, 3%, 5%, 7% and 9% were synthesized by a solvothermal method and then they were codoped with Eu³⁺ ions by an ion exchange method to form the YVO₄:Eu³⁺,Ba²⁺ nanoparticles. It was found that the photoluminescence intensity of the as-prepared YVO₄:Eu³⁺,Ba²⁺ nanoparticles steadily increased with x until x=7%, and then decreased for higher x. Thermal annealing resulted in considerable enhancement in their photoluminescence, and higher annealing temperature led to stronger photoluminescence enhancement. The emission intensity of the YVO₄:Eu³⁺,Ba²⁺ (x=7%) nanoparticles annealed at 500 °C was about 205% stronger than the sample without Ba²⁺ doping. Thermal annealing of the ion-exchanged YVO₄:Eu³⁺,Ba²⁺ nanoparticles at 500 °C and 700 °C resulted in photoluminescence enhancement of about 14 times and 27 times, respectively. The asymmetric ratio of Eu³⁺ in the ion-exchanged YVO₄:Eu³⁺,Ba²⁺ nanoparticles was found to increase after annealing.     

Preparation and luminescent properties of novel red phosphors for white-light emitting diodes (W-LEDs) application

A series of Eu³⁺–Gd³⁺ co-doped solid solution of Ca_0.54Sr_{0.46–1.5x–1.5z}Eu_zGd_x (MoO₄)_y (WO₄)_1−y (x=0.01–0.20, y=0–1.0, z=0.01–0.30) have been prepared by solid-state reactions. It is found that appropriate amount of Mo⁶⁺ or W⁶⁺, Eu³⁺ and Gd³⁺concentrations can enhance the luminescent intensity and improve crystal structure. These phosphors can be effectively excited by ultraviolet light at 394 nm and blue light at 465 nm (f–f transition) and emits red light (616 nm) with line spectrum. The wavelengths at 394 and 465 nm are nicely fitted in with the widely applied output wavelengths of ultraviolet or blue LED chips.     

Judd–Ofelt Analysis of Dy<Superscript>3+</Superscript>-Activated Aluminosilicate Glasses Prepared by Sol–Gel Method

Aluminosilicate (AS) glasses doped with different Dy³⁺ concentrations were synthesized via sol–gel method. Absorption, photoluminescence spectra and lifetime of this material have been studied. From analytical results of absorption spectra, the Judd–Ofelt (JO) parameters of prepared samples have been determined. These JO parameters combined with photoluminescence spectra have been used to evaluate transition probabilities (A_R), branching ratios (β) and the calculated oscillator strengths of AS:Dy³⁺ glasses. The radiative branching ratio of ⁴F_9/2 → ⁶H_13/2 transition has a minimum value at 62.2% for β_R which predicts that this transition in AS:Dy³⁺ glasses can give rise to lasing action. JO parameters show that the Ω₂ increases with the increasing of Dy³⁺ ion concentration due to the increased polarizability of the average coordination medium and decreased average symmetry.     

Visible emission from ZnO doped with rare-earth ions

We report the results of a cathodoluminescence (CL) and photoluminescence (PL) study of ZnO-bulk single crystals and epilayer thin-film samples grown on a sapphire (0001) substrate and doped by implantation with rare-earth ions (RE³⁺): Pr³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺ (bulk crystals, co-doped with Li), Sm³⁺, Dy³⁺, and Er³⁺ (epilayers). The PL and PL excitation (PLE) spectra of polycrystalline ZnO doped with RE³⁺ ions (Nd³⁺, Dy³⁺, Er³⁺, and Tm³⁺) and codoped with Li⁺, Cl⁻, and N⁻ ions have also been studied.     

Simultaneously Excited Downshifting/Upconversion Luminescence from Lanthanide‐Doped Core/Shell Fluoride Nanoparticles for Multimode Anticounterfeiting

This work presents a novel anticounterfeiting strategy based on a material changing its emission color in response to a change in the excitation sources—where a single ultraviolet (UV) or near‐infrared (NIR) light source are employed or simultaneously using two excitation sources (xenon lamp and NIR laser). Following this approach, various combinations of lanthanide (Ln³⁺)‐doped LiLuF₄/LiYF₄ core/shell nanoparticles are prepared, providing a promising route to design flexible nanomaterials, as well as already a small library of luminescent materials, which change color when varying the excitation source (UV, NIR or both UV and NIR). Aside from excitation source‐dependent color change, these materials additionally show excitation‐source power‐dependent color change. This work exploits the possibility of developing a new class of multimode anticounterfeit nanomaterials, with excellent performance, which would be almost impossible to mimic or replicate, providing a very high level of security.     

Luminescence properties of Ca4GdO(BO3)3:Eu in ultraviolet and vacuum ultraviolet regions

The luminescent properties of Ca₄GdO(BO₃)₃:Eu³⁺ were investigated under excitation of UV and VUV light. Separate two broad bands at around 259 and 184 nm were observed in the excitation spectrum of Ca₄GdO(BO₃)₃:Eu³⁺. These peaks were assigned to the charge transfer transition of Eu³⁺-O²⁻ and Gd³⁺-O²⁻, respectively. Owing to the favorable spectral position in their broad intense excitation band, Eu³⁺ ions show a intense emission under 258 nm excitation in Ca₄GdO(BO₃)₃:Eu³⁺. This spectral position was determined by the free oxygen ions O (1). Ca₄GdO(BO₃)₃ doped with Eu³⁺ ion seems to be a preferable candidate as red lamp phosphor. On the other hand, a weak band with a maximum at about 184 nm was observed below 200 nm in the excitation spectrum of Ca₄GdO(BO₃)₃:Eu³⁺. This phosphor do not emit effectively under the 147 nm excitation. This unfavorable profile was also due to the O (1) ions, which played a role to the shifting towards the lower energy sides. The luminescence of Eu³⁺ ions in Ca₄GdO(BO₃)₃ was somewhat different from that observed in the other borates phosphors, but resembled to those observed in the oxide phosphors (e.g. Gd₂O₃, Y₂O₃ and Gd₂SiO₅). Such behavior was recognized by the detailed analysis of crystallographical surroundings around activator.     

Fluorescence enhancement of single-phase red-blue emitting Ba3MgSi2O8:Eu2+,Mn2+ phosphors via Dy3+ addition for plant cultivation

Fluorescence enhancement of red and blue concurrently emitting Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺ phosphors for plant cultivation has been investigated by Dy³⁺ addition. The Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺,Dy³⁺(BMS-EMD) phosphors have two-color emissions at the wavelength peak values of 437 nm and 620 nm at the excitation of 350 nm. The two emission bands are coincident with the absorption spectrum for photosynthesis of plants. An obvious enhancement effect has been observed upon addition of Dy³⁺ with amount of 0.03 mol%, in which the intensities of both blue and red bands reach a maximum. The origin of red and blue emission bands is analysed. The photochromic parameters of the samples at the nearly UV excitation are tested. This fluoresence enhancement is of great significance for special solid state lighting equipment used in plant cultivation. This work has been supported by National Natural Science Foundation of China (Grant No 50872091) and the Natural Science Foundation of Tianjin, China (06YFJMJC02300, 06TXTJJC14602).     

Luminescence Properties of Cobalt-Doped ZnO Films Prepared by Sol–Gel Method

Pure ZnO and Co-doped ZnO films have been deposited on coverslip substrates by sol–gel spin coating. The morphological, structural, and optical properties of the films were investigated. The microstructure of the ZnO films became increasingly fine and the crystalline size decreased with Co doping. Analysis of x-ray diffraction (XRD) and Raman spectra reveals that Co²⁺ ions are substituted for Zn²⁺ ions in the ZnO lattice without changing its wurtzite structure. Co doping induces a decrease of the band-gap energy and fluorescence quenching of the emission bands. The spectra related to transitions within the tetrahedral Co²⁺ ions in the ZnO host crystal were observed in absorption and luminescence spectra. Photoluminescence (PL) spectra under different excitation energies and PL excitation spectra for the visible emissions suggest that the orange–red emission and green emission could be related to interstitial zinc (Zn_i) shallow donors and oxygen vacancy (V _O) deep donors, respectively. The red emission of Co-doped ZnO film could be assigned to the radiative transitions within the tetrahedral Co²⁺ ions in the ZnO host crystal after band-to-band excitation. A consistent explanation for the pure and Co-doped ZnO films is that the red emission under the excitation energy below the band gap is probably associated with extended Zn_i states.     

Luminescent property and energy transfer from Ce3+ to Tb3+ in YAl3(BO3)4

A series of Ce³⁺, Tb³⁺ or Ce³⁺/Tb³⁺ doped YAl₃(BO₃)₄ phosphors are synthesized by a high temperature solid-state reaction, and their luminescent properties are investigated. YAl₃(BO₃)₄:Ce³⁺ shows a broad emission band at 422 nm under the 367 nm radiation excitation. YAl₃(BO₃)₄:Tb³⁺ can be efficiently excited by the ultraviolet (UV) light, and produces green emission. The emission intensity of YAl₃(BO₃)₄:Tb³⁺ can be enhanced by adjusting Tb³⁺ doped content, and reaches the maximum at 0.06 mol Tb³⁺. When Ce³⁺ is codoped, the emission intensity of Tb³⁺ in YAl₃(BO₃)₄ can be enhanced, but the commission international del’eclairage (CIE) chromaticity coordinates of YAl₃(BO₃)₄:Tb³⁺ have almost no change. Moreover, the energy transfer from Ce³⁺ to Tb³⁺ in YAl₃(BO₃)₄ is studied.     

Structural and magnetic properties of Dy3+ doped Y3Fe5O12 for microwave devices

The Dy³⁺ doped Y_3−xDy_xFe₅O₁₂ (x=0–3) nanopowders were prepared using microwave hydrothermal route. The structural and morphological studies were analyzed using transmission electron microscope, X-ray diffractometer and field emission scanning electron microscope. The nanopowders were sintered at 900 °C/90 min using microwave furnace. Dense ceramics with theoretical density of around 95% was obtained. Ferro magnetic resonance (FMR) spectrum and microwave absorption spectrum of Dy³⁺ doped YIG were studied, the signal exhibits a resonance character for all Dy³⁺ variations. It was observed that the location of the FMR signal peak at the field axes monotonically shifts to higher field with increasing Dy³⁺ content. The dielectric and magnetic properties (ε′, ε′′, µ′ and µ′′) of Dy³⁺ doped YIG were studied over a wide range of frequency (1–50 GHz). With increase of Dy³⁺ both ε′ and µ′ decreased. The low values of dielectric, magnetic properties and broad distribution of FMR line width of these ceramics are opening the real opportunity to use them for microwave devices above K- band frequency.     

Novel Red-Emitting Microwave-Assisted-Sintered LiSrPO4: Eu3+ Phosphors for Application in Near-UV White Light-Emitting Diodes

Novel red-emitting LiSr_1?x PO₄:xEu³⁺ phosphors with various concentrations (x = 0.03, 0.05, 0.07, 0.1) of Eu³⁺ ions were synthesized by microwave-assisted sintering at 1200°C for 3 h in air. The microstructural and luminescent characteristics of the LiSrPO₄:Eu³⁺ phosphors were investigated and are discussed here. x-Ray diffraction (XRD) results showed that the prepared LiSr_1?x PO₄:xEu³⁺ phosphors presented an impurity phase of Eu₂O₃ when the Eu³⁺ ions exceeded x = 0.05. Photoluminescence (PL) results showed a series of emission states ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃, and ⁵D₀ → ⁷F₄ (corresponding to the typical 4f → 4f intraconfiguration forbidden transitions of Eu³⁺) with a major emission peak at around 617 nm. The optimum concentration of Eu³⁺ for LiSr_1?x PO₄:xEu³⁺ prepared by microwave-assisted sintering was found to be 0.05. The lifetime values of LiSr_1?x PO₄:xEu³⁺ phosphors with doping concentrations of Eu³⁺ ions of 0.03, 0.05, 0.07, and 0.1 were found to be 3.32 ms, 3.30 ms, 2.84 ms, and 2.60 ms, respectively. Moreover, the chromaticity values (x, y) of all of the LiSr_1?x PO₄:xEu³⁺ phosphors were located in the red region (0.65, 0.34).     

Thermoelectric Properties of Ca3−x Dy x Co4O9+δ with x = 0.00, 0.02, 0.05, and 0.10

Polycrystalline samples of Ca_3?x Dy _x Co₄O_9+δ (x = 0.00, 0.02, 0.05, and 0.10) have been prepared by conventional solid-state synthesis. The x-ray diffraction (XRD) results revealed that all the samples are single phase. The thermoelectric properties were measured at 25 K to 300 K. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity of all the samples exhibited the nonmetal-to-metal transition at below 75 K. The electrical resistivity decreased and the thermopower increased with increasing Dy³⁺ content. Among all the samples, Ca_2.9Dy_0.10Co₄O_9+δ had the highest dimensionless figure of merit of 0.044 at 300 K.     

First Evidence of Electron Trapped Ln2+ Promoting Afterglow on Eu2+, Ln3+ Activated Persistent Phosphor-Example of BaZrSi3O9:Eu2+, Sm3+

BaZrSi₃O₉:Eu²⁺, Sm³⁺ (Em:525 nm) is prepared. The role played by the trivalent co-doping ion Sm³⁺ in the afterglow and the type of trap are clarified. BaZrSi₃O₉:Eu²⁺, Sm³⁺ is found to produce Sm²⁺ during the excitation by X-ray absorption near-edge structure (XANES), etc., and it is thus proved that Sm³⁺ exists as an electron trap in the afterglow process. In the field of persistent phosphors activated by Eu²⁺ and Re³⁺ such as Sm³⁺ or Dy³⁺ having been widely utilized as emergency guide lights, clock faces, etc. for > 25 years, for the first time it is successfully observed that after excitation Re²⁺ is formed, transferring its electron to 5d band of Eu²⁺, returning to Re³⁺ by itself, where the decrease in Sm²⁺ coincides with the increase in Sm³⁺, and the two decay time τ₁ and τ₂ of PL (⁵D₀→⁷F₀) of Sm²⁺ coincides with the two evolution time of PL (5d→4f) of Eu²⁺. The behavior of electron transfer from Sm²⁺ to Eu²⁺ as a key of afterglow is detected. The detailed afterglow mechanism is proposed by analysis of thermoluminescence and defect reaction, which is very important for the in-depth investigation of the long afterglow material and the further improvement of the mechanism.     

The optical properties of Tm3+ doped Na5Lu9F32 single crystal

Tm3+ doped Na5Lu9F32 single crystal with high optical quality was grown by an improved Bridgman method. The Judd-Ofelt intensity parameters Ωt (t=2, 4, 6) were calculated according to the measured absorption spectra and physical-chemical properties of the obtained Na5Lu9F32 single crystal. The stimulated emission cross-section of the 3F4→3H6 transition (~1.8 μm) is 0.35×10-20 cm2 for Tm3+ doped Na5Lu9F32 single crystal. The emission spectra under the excitation of 790 nm laser diode (LD) and fluorescence lifetime at 1.8 μm were measured to reveal the fluorescence properties of Tm3+ doped Na5Lu9F32 single crystal. The research results show that the Tm3+ doped Na5Lu9F32 single crystal has larger stimulated emission cross-section compared with other crystals. All these spectral properties suggest that this kind of Tm3+doped Na5Lu9F32 crystal with high physical-chemical stability and high-efficiency emission at 1.8 μm may be used as potential laser materials for optical devices.     

Photoelectric and luminescent properties of dysprosium-doped silver chloride

The influence of dysprosium doping on the photoelectric and luminescent properties of AgCl crystals is studied by methods of microwave photoconductivity and photoluminescence. Doping affects both the loss kinetics of photogenerated electrons and luminescence spectra and parameters of photostimulated burst of luminescence. It is shown that the charged [Dy_Ag^·· · V′_Ag]^· or neutral [Dy_Ag^·· · 2V′_Ag] ^x complexes are responsible for a new luminescence band peaked at 470 nm, which manifests itself at weight concentrations of the doping additive >10⁻⁶%. The long-wavelength shoulder at 570 nm in the photoluminescence spectra is attributed to intracenter transitions in the Dy³⁺ ions. The rate constant of the reaction of electron capture into the traps forming upon introduction of the dopant, k _t = (3–5) × 10⁻⁸ cm³ s⁻¹, is evaluated. It is assumed that the traps are Dy³⁺ dysprosium ions.