Tunable luminescence of Dy3+ single-doped and Dy3+/Tm3+ co-doped tungsten borate glasses

RE³⁺ (RE³⁺ = Tm³⁺, Dy³⁺) ion single and co-doped tungsten borate glasses for white light emitting diodes (LEDs) were prepared by melt quenching method. Emission and excitation spectra of the glasses were measured. The color of luminescence can be tuned by changing the composition of glass matrix or the concentrations of Tm³⁺ and Dy³⁺ ions. White light emission can be achieved from 0.5Dy³⁺ single-doped 15WO₃–25La₂O₃–60B₂O₃ and 0.4Tm³⁺/1.5Dy³⁺ co-doped 50WO₃–25La₂O₃–25B₂O₃ glasses. In addition, energy transfers between Tm³⁺ and Dy³⁺ were also analyzed. The Dy³⁺/Tm³⁺ co-doped tungsten borate glasses may be potential candidates for white LED application.     

White light emission of Dy3+-doped and Dy3+:Yb3+-codoped oxyfluoride glass ceramics under 388-nm excitation

Dy³⁺-doped and Dy³⁺:Yb³⁺-codoped oxyfluoride glass ceramics have been prepared by high-temperature solid phase sintering method. The micrographs of scanning electron microscope show that a lot of nanorods are formed on the surface of Dy³⁺:Yb³⁺-codoped sample. The excitation spectra and emission spectra are measured, respectively, and intense photoluminescence peaks at 482 and 575 nm corresponding to the transitions of Dy³⁺ ions are found in single-doped samples under 388-nm excitation. For Dy³⁺:Yb³⁺-codoped oxyfluoride glass ceramics, the intensities at blue and green bands become weaker whereas the intensity at 695 nm gets stronger. The indirect sensitization is detailedly discussed and Commission Internationale de l′E-clairage chromaticity coordinates exhibit that two kinds of oxyfluoride glass ceramics are available candidates for the solid-state white light emission.     

Cold white light generation through the simultaneous emission from Ce3+ and Tb3+ in sodium germanate glass

A spectroscopic investigation of sodium germanate glasses activated with Ce³⁺, Tb³⁺ and Ce³⁺/Tb³⁺ is carried out by analyzing their photoluminescence spectra and decay times. Non-radiative energy transfer from Ce³⁺ to Tb³⁺ is observed upon near-UV excitation at 310 nm (peak emission wavelength of AlGaN-based LEDs). The non-radiative nature of this energy transfer is inferred from the increase in the decay rate of the Ce³⁺ emission when the glass is co-doped with Tb³⁺. From an analysis of the Ce³⁺ emission decay time curve it is inferred that an electric dipole–quadrupole interaction might to be the dominant mechanism for the Tb³⁺ emission sensitized by Ce³⁺. Energy transfer from Ce³⁺ to Tb³⁺ leads to a simultaneous emission of these ions in the blue, green, yellow and red, resulting in white light with CIE1931 chromaticity coordinates, x = 0.30 and y = 0.32, which correspond to cold white light with a colour temperature of 7320 K and very small deviation from the Planckian black-body radiator locus (0.005).     

Structure and optical properties of Dy3+/Tm3+ co-doped oxyfluoride glass ceramics containing β-NaGdF4 nanocrystals

Dy³⁺/Tm³⁺ co-doped oxyfluoride glass ceramics containing hexagonal β-NaGdF₄ nanocrystals were prepared by the melt-quenching method and subsequent heat-treatment procedure. During the crystallization process, the structural evolution of glass network was systematically investigated using XRD, TEM and FTIR spectra. Experimental results provided new evidences that a silica-enriched layer around the precipitated fluoride nanocrystals was formed during the crystallization process. Strong white light emission was obtained in the oxyfluoride glass ceramics by modifying the relative concentration ratio of Tm³⁺ and Dy³⁺ ions.     

White luminescence of Dy3+ ions doped 12CaO 7Al2O3 nanopowders under UV light excitation

12CaO 7Al2O3:Dy3+ nanopowders were successfully synthesized by the chemical co-precipitation method. X-ray diffraction result shows that the single 12CaO 7Al2O3 phase is formed with Dy3+ ions to replace the Ca2+ ions in the host of 12CaO 7Al2O3. The yellow and blue emissions, attributed to the forced electric dipole transition of 4F(9/2) --> 6H(13/2) centered at 571 nm and the magnetic dipole transition of 4F(9/2) --> 6H(15/2) centered at 480 nm, respectively, were observed. The integrated intensity ratios of yellow to blue increase from 1.63 to 1.70 with Dy3+ concentration increasing from 0.8 to 2.0% for the as-prepared 12CaO 7Al2O3:xDy3+ phosphor. The significantly enhanced emission intensities of 12CaO 7Al2O3:1.0% Dy3+ phosphor annealed at 900 degrees C for 2 hours in vacuum ambient could be ascribed to the decrease of OH(-) groups and the change of the surface topography. The thermal stability and the Commission International de l'Eclairage coordinates were also investigated. All the photoluminescence characteristics indicate that Dy3+ ions doped 12CaO 7Al2O3 may be a good candidate for the solid state lighting phosphor as well as white light-emitting diodes.     

White light emission and electrical properties of silicon oxycarbide-based metal-oxide-semiconductor diode

White light emission from silicon oxycarbide-based metal-oxide-semiconductor diode has been realized in this work. Emitted light is visible to the naked eyes as the bias voltage is increased higher than 15 V. Electroluminescence intensity increases linearly with current density. According to the analysis of conduction mechanisms in device, electron-hole radiative recombination at twofold coordinated silicon lone-pair centers, neutral oxygen vacancies, and E_δ′ defect centers in film is responsible for the light emission.     

Synthesis and spectroscopic characterization of Ho3+/Tm3+/Pr3+ doped fluorophosphate glass

Fluorophosphate glass triply doped with Ho³⁺/Tm³⁺/Pr³⁺ has been synthesized. 2.86, 2 and 1.47 μm emissions have been successfully obtained from the present glass pumped by conventional 800 nm LD. The corresponding energy transfer mechanisms and microparameters are discussed and analyzed according to the photoluminescence performance and absorption measurements. Tm³⁺ ions can absorb the pumping energy and transfer it to Ho³⁺ and Pr³⁺ ions. Large energy transfer coefficient from Ho³⁺ to Pr³⁺ ions (8.22 × 10^?39 cm⁶/s) has been obtained based on the Förster-Dexter theory. The results suggest Ho³⁺/Tm³⁺/Pr³⁺ triply doped fluorophosphate glass is a promising candidate for efficient mid-infrared laser.     

White light upconversion of nanocrystalline Er/Tm/Yb doped tetragonal Gd4O3F6

Er³⁺, Tm³⁺ and Yb³⁺ codoped gadolinium oxyfluoride nanoparticles were prepared in aqueous solution by a simple coprecipitation method, under alkaline conditions. After a suitable heat treatment at 500 °C, the nanocrystalline powders were found to be single phase tetragonal Gd₄O₃F₆ after a structural characterization using X-ray powder diffraction. Transmission electron microscopy images showed that the average size of the nanoparticles was approximately 50 nm. Following appropriate lanthanide ion doping, the nanocrystals show bright white light upconversion upon excitation at 980 nm using a diode laser as the excitation source.     

Ag and Dy doped zeolite as a broadband phosphor

Photoluminescence (PL) properties of silver (Ag) and dysprosium (Dy) codoped zeolites were investigated. It was found that PL from the ⁴F_9/2–⁶H_13/2 transition of Dy³⁺ ions at 575 nm is more than 50 times enhanced by the presence of Ag⁺ ions under ultraviolet excitation. The excitation wavelength dependence of the PL intensity coincided well with the absorption spectra of Ag⁺ ions, indicating that Dy³⁺ ions are excited by the energy transfer from Ag⁺ ions. In addition, by carefully optimizing annealing condition and Dy and Ag concentration, white light was realized due to the combination of blue emission of Ag⁺ ions, yellow emission of Dy³⁺ ions and red emission of Ag clusters.     

Tm3+ doped Ga–As–S chalcogenide glasses and fibers

Tm³⁺ doped Ga–As–S chalcogenide glass samples were produced using As₂S₃ pure glass as starting materials. Their photoluminescence properties were characterized and strong emission bands were observed at 1.2 μm (¹H₅ → ³H₆), 1.4 μm (³H₄ → ³F₄) and 1.8 μm (³F₄ → ³H₆) under excitation wavelengths of 698 nm and 800 nm. The thulium and gallium concentrations were optimized to achieve the highest photoluminescence efficiency. From the optimal composition, a Tm³⁺ doped Ga–As–S fiber was drawn and its optical properties were studied.     

Blue up-conversion emission of Yb3+-doped langbeinite salts

Yb³⁺-doped langbeinite salts were prepared by the solid solution method. X-ray diffraction patterns and vibrational spectroscopy confirmed that all obtained phases are highly pure, iso-structural and they crystallize in the cubic system with the space group P2₁3. The emission luminescence comes from the ²F_5/2 → ²F_7/2 transition of Yb³⁺ ions. Moreover, intense blue cooperative emission was observed at 476 nm under excitation in the near infrared at 975 nm.     

Polyspectral white light emission from Eu3+, Tb3+, Dy3+, Tm3+ co-doped GdAl3(BO3)4 phosphors obtained by combustion synthesis

Polycrystalline sub-micron-sized GdAl₃(BO₃)₄ phosphors co-doped with Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ have been prepared by combustion synthesis with urea. The phosphors have been characterised by X-ray diffraction, scanning electron microscopy, excitation and emission spectroscopy. The chromaticity co-ordinates and the colour temperatures of the fluorescence of the materials presented have been calculated and analysed with Commission Internationale l’Eclairage (CIE) programs and diagrams. Depending on the excitation wavelength, different colour temperatures of the light emitted can be achieved. Due to its polyspectral nature, the emitted light reveals a high colour rendering index.     

Efficient generation of blue light in oligothiophene chromophores doped in polymer films and fiber

A conjugated oligothiophene chromophore with large linear and nonlinear absorption cross-sections that emits light in the blue region is studied. Here measurements of the one- and two-photon absorption and fluorescence of an oligothiophene chromophore doped in polymethyl-methacrylate (PMMA) polymer is presented. It was observed that oligothiophene/PMMA fluoresces strongly and through amplified spontaneous emission (ASE), is an efficient source of blue light around 460 nm. Using these materials, a polymer fiber-based blue ASE light source is demonstrated. Blue emitting molecules (mainly in PMMA) are tabulated for comparison.     

Multicolor up conversion emission and color tunability in Yb/Tm/Ho triply doped heavy metal oxide glasses

Multicolor and white light emissions have been achieved in Yb³⁺, Tm³⁺ and Ho³⁺ triply doped heavy metal oxide glasses upon laser excitation at 980 nm. The red (660 nm), green (547 nm) and blue (478 nm) up conversion emissions of the rare earth (RE) ions triply doped TeO₂–GeO₂–Bi₂O₃–K₂O glass (TGBK) have been investigated as a function of the RE concentration and excitation power of the 980 nm laser diode. The most appropriate combination of RE in the TGBK glass host (1.6 wt% Yb₂O₃, 0.6 wt% Tm₂O₃ and 0.1 wt% Ho₂O₃) has been determined with the purpose to tune the primary colors (RGB) respective emissions and generate white light emission by varying the pump power. The involved infrared to visible up conversion mechanisms mainly consist in a three-photon blue up conversion of Tm³⁺ ions and a two-photon green and red up conversions of Ho³⁺ ions. The resulting multicolor emissions have been described according to the CIE-1931 standards.     

Dy~(3+)/Tb~(3+)掺杂高钆镥闪烁玻璃光谱性能

用高温熔融法制备了Dy3+/Tb3+掺杂的高钆镥氟氧化物闪烁玻璃样品,测试分析了其吸收光谱、激发与发射光谱及衰减曲线等。研究了Dy3+和Tb3+离子浓度增加对Tb3+离子发光的影响以及Dy3+离子的浓度猝灭效应;通过IH理论模型分析了Dy3+和Tb3+离子的能量传递方式和能量传递效率。结果表明Dy3+离子对Tb3+离子发光具有敏化作用,随着Dy3+离子浓度增加敏化作用增强,但是当Dy3+离子的浓度达到2%(摩尔分数)以上时,随着Dy3+离子浓度的增加,Tb3+离子的发光强度降低;Dy3+和Tb3+离子的能量传递方式为无辐射能量传递方式,且能量传递效率可以达到60%以上。     

Ag nanoparticles enhanced near-IR emission from Er3+ ions doped glasses

Vitreous materials containing rare-earth (RE) ions and metallic nanoparticles (NPs) attract considerable interest because the presence of the NPs may lead to an intensification of luminescence. In this work, the characteristics of 1.54 μm luminescence for the Er³⁺ ions doped bismuthate glasses containing Ag NPs were studied under 980 nm excitation. The surface plasmon resonance (SPR) band of Ag NPs appears from 500 to 1500 nm. Transmission electron microscopic (TEM) image reveals that the Ag NPs are dispersed homogeneously with the size from 2 to 7 nm. The strength parameters Ω_t(t = 2, 4, 6), spontaneous emission probability (A), radiative lifetime (τ) and stimulated emission section (σ_em) of Er³⁺ ions were calculated by the Judd–Ofelt theory. When the glass contains 0.2 wt% AgCl, the 1.54 μm fluorescence intensity of Er³⁺ reaches a maximum value, which is 7.2 times higher than that of glass without Ag NPs. The Ag NPs embedded glasses show significantly fluorescence enhancement of Er³⁺ ions by local field enhancement from SPR.     

Preparation and luminescence characteristics of LiYF4: Tm3+/Dy3+ single crystals for white-light LEDs

Tm³⁺ /Dy³⁺ co-doped LiYF₄ single crystals were synthesized by using vertical Bridgman method in sealed Pt crucibles. When excited by a proper UV-light, the crystals show blue emission band centered at 485 nm, which overlaps between the transition of Tm³⁺ (¹G₄ → ³H₆) and Dy³⁺ (⁴F_9/2 → ⁶H_15/2) ions, and yellow band of 573 nm ascribed to Dy³⁺ (⁴F_9/2 → ⁶H_13/2) ions. Both chromaticity coordinates and photoluminescence intensity vary with the excitation wavelengths and the concentration of rare earth dopants. A white light can be achieved from Tm³⁺ (0.6 mol%), Dy³⁺ (2.25 mol%) co-doped LiYF₄ crystal with chromaticity coordinates of x ≈ 0.2836, y ≈ 0.3229, and color temperature T _c = 8419 K by the excitation of a 350 nm light. It indicates that this crystal can be a potential candidate for the UV-light excited white-light emitting diodes.     

Visible to near-infrared down-shifting in Tm3+ doped fluoride glasses for solar cells efficiency enhancement

In this paper, down-conversion of Tm³⁺ doped fluoride ZLAG glasses with composition of 70.2ZrF₄–(23.4−x)LaF₃–0.6AlF₃–5.8GaF₃–xTmF₃ (x = 0.25, 0.5, 0.75, 1, 2, 3 and 5 mol%) were tested as encapsulation materials for solar cells. The current density – voltage (J-V) characterizations were performed under solar simulator irradiation. The influence of Tm³⁺ concentration on the mono crystalline silicon solar cells performances was investigated. A slight increase of the solar cell efficiency was observed in the case of fluoride ZLAG for Tm³⁺ doping concentrations up to 1 mol% Tm³⁺. Further increase of the Tm³⁺ concentration leads to a decrease of solar cell conversion efficiency as a result of concentration quenching.