White luminescence of Tm-Dy ions co-doped aluminoborosilicate glasses under UV light excitation

Tm³⁺ and Dy³⁺ ions co-doped aluminoborosilicate glasses were prepared in this study. The luminescence properties of the glasses were analyzed. A combination of blue, green, yellow, and red emission bands was shown for these glasses, and white light emission could be observed under UV light excitation. White light luminescence color could be changed by varying the excitation wavelength. Concentration quenching effect was investigated in this paper. Furthermore, the dependence of luminescence properties on glass compositions was studied. Results showed that the luminescence intensity changed with different network modifier oxides, while the white color luminescence was not affected significantly.     

Luminescent properties of SrBPO5:Dy3+ and effect of Co-doping with Tm3+

A series of phosphors SrBPO₅:Dy³⁺ and SrBPO₅:Dy³⁺,Tm³⁺ was synthesized by traditional solid-state high-temperature method and was characterized by X-ray diffraction (XRD) and fluorescence spectrophotometry. For SrBPO₅:Dy³⁺ material, the f-f transitions of Dy³⁺ ions were assigned and discussed, and the optimal doping concentration of Dy³⁺ was found. As a result of co-doping SrBPO₅:Dy³⁺ with Tm³⁺, the phosphors SrBPO₅:Dy³⁺,Tm³⁺ can be effectively excited by 360 nm ultraviolet (UV), and exhibit color-tunable emission from blue to yellowish-white region with different doping concentration. The present study can pave the way for the creation of efficient UV phosphors using Dy³⁺,Tm³⁺ co-doped systems for near-UV InGaN-based light emitting diodes (LEDs).     

Solvent directed morphologies and enhanced luminescent properties of BaWO4:Tm3+,Dy3+ for white light emitting diodes

A series of Tm³⁺ and Dy³⁺ codoped BaWO₄ phosphors with tunable shapes were controllably synthesized by a facile solvothermal method. The effects of ratio of ethylene glycol (EG) and water on the morphologies of BaWO₄ structures are systematically studied. It was discovered that the reason for these morphological changes is based on the reaction speed of the kinetic control, which relates to the strong chelating abilities of ethylene glycol. And when the solvent is pure ethylene glycol, the peanut-like BaWO₄:Dy³⁺ has the strongest emission intensity. Moreover, the emission color of the phosphors varied from blue (0.232, 0.180) to white (0.268, 0.250) by controlling Dy³⁺ ions content with a fixed Tm³⁺ concentration. The energy transfer mechanism was investigated in detail. With increasing the doped concentration of Dy³⁺ ions, the energy transfer efficiency of BaWO₄:0.005Tm³⁺,yDy³⁺ increased gradually and reached as high as 63% when the Dy³⁺ doped concentration is 0.03. The critical distance R_C calculated by the spectral overlap method is about 19.93 Å, and it is in good agreement with that obtained using the concentration quenching method (19.70 Å), indicating that the electric dipole-dipole interaction is the main energy transfer mechanism for BaWO₄:Tm³⁺,Dy³⁺ phosphors.     

Green and red upconversion luminescence in CeO2:Er powders produced by 785 nm laser

CeO₂:Er³⁺ powders were prepared by Pechini type sol-gel method. The structural properties of CeO₂:Er³⁺ were studied by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra. The results show that CeO₂:Er³⁺ has low phonon cutoff energy, which indicate that CeO₂:Er³⁺ may have high luminescent efficiency. The green and red upconverted luminescence spectra of Er³⁺ were investigated under excitation into the ⁴I_9/2 level by 785 nm laser. The upconversion mechanisms were studied in detail through laser power dependence and Er³⁺ ions concentration dependence of upconverted emissions, and results show that excited state absorption and energy transfer process are the possible mechanisms for the upconversion. The upconversion properties indicate that CeO₂:Er³⁺ may be used in upconversion phosphors.     

UV-VUV-excited photoluminescence of RE-activated CaLaP3O10 (RE=Eu,Tb)

Monazite-type polyphosphate CaLaP₃O₁₀ was synthesized by solid-state reaction at 1000 °C and their photoluminescence of Eu³⁺ and Tb³⁺ in CaLaP₃O₁₀ under ultraviolet (UV) and vacuum-ultraviolet (VUV) excitation were evaluated for the first time. The emission spectra of CaLaP₃O₁₀:Eu³⁺showed that Eu³⁺ are in a site with inversion symmetry because the magnetic dipole transition ⁵D₀-⁷F₁ was the strongest both upon 254 and 147 nm excitation. Monitored at 621 nm the excitation spectra consisted of host absorption bands, charge transfer band of Eu-O and the intraconfiguration 4f⁶ transition of Eu³⁺. Green phosphor CaLaP₃O₁₀:Tb³⁺exhibited better color purity when excited by 147 nm than that excited by 254 nm. With monitored at 542 nm the host absorption bands of CaLaP₃O₁₀:Tb³⁺ were also observed. Besides the host absorption bands there were strong f-d and weak f-f transitions of Tb³⁺.     

Rare-earth-doped glasses for fiber amplifiers in broadband telecommunication

Rare-earth-doped optical amplifiers have a great potential for broadband Wavelength-Division-Multiplexed (WDM) telecommunication by tailoring host glass compositions. In order to design the emission spectra of doped rare-earth ions, it is important to understand the relationship between the local ligand field and various optical properties of specific 4f-levels, such as the radiative transition probability, the nonradiative decay probability, which dominate the spectral line width and quantum efficiency of amplification transitions. For the Er³⁺:1.55 μm transition, the role of the Judd–Ofelt Ω₆ parameters is presented, which is correlated to the Er–ligand bond covalency in glasses. The Tm³⁺: 1.46-μm transition shows quantum efficiency over 90% high enough for the S-band application, in heavy metal oxide glasses with moderate phonon energy and wider spectra than fluorides. A way to improve population inversion by selective energy transfer with codoped lanthanide ions is presented. Finally, the energy level structures and resultant spectral properties of Pr³⁺, Nd³⁺ and Dy³⁺ ions, 1.3-μm-active ions, are compared. The hypersensitivity of Dy³⁺ transitions appears especially in chalcogenide glasses, where the nonradiative loss due to multiphonon decay is also minimized. In conclusion, glass materials have opportunities to vary the radiative cross section, quantum efficiency, and gain flatness, which are important for novel amplifiers in the future DWDM system.     

Enhanced quantum yield of yellow photoluminescence of Dy ions in nonlinear optical Ba2TiSi2O8 nanocrystals formed in glass

Transparent crystallized glasses consisting of nonlinear optical Ba₂TiSi₂O₈ nanocrystals (diameter: ∼100 nm) are prepared through the crystallization of 40BaO-20TiO₂-40SiO₂-0.5Dy₂O₃ glass (in the molar ratio), and photoluminescence quantum yields of Dy³⁺ ions in the visible region are evaluated directly by using a photoluminescence spectrometer with an integrating sphere. The incorporation of Dy³⁺ ions into Ba₂TiSi₂O₈ nanocrystals is confirmed from the X-ray diffraction analyses. The total quantum yields of the emissions at the bands of ⁴F_9/2→⁶H_15/2 (blue: 484 nm), ⁴F_9/2→⁶H_13/2 (yellow: 575 nm), and ⁴F_9/2→⁶H_11/2 (red: 669 nm) in the crystallized glasses are ∼15%, being about four times larger compared with the precursor glass. It is found that the intensity of yellow (575 nm) emissions and the branching ratio of the yellow (575 nm)/blue (484 nm) intensity ratio increase largely due to the crystallization. It is suggested from Judd-Ofelt analyses that the site symmetry of Dy³⁺ ions in the crystallized glasses is largely distorted, giving a large increase in the yellow emissions. It is proposed that Dy³⁺ ions substitute Ba²⁺ sites in Ba₂TiSi₂O₈ nanocrystals.     

Colour tuneability and white light generation in Yb<Superscript>3+</Superscript>–Ho<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript> co-doped SiO<Subscript>2</Subscript>–LaF<Subscript>3</Subscript> nano-glass-ceramics prepared by sol–gel method

Nanostructured transparent glass-ceramics with composition of 95SiO₂–5LaF₃ co-doped with 0.3Yb³⁺, 0.1Ho³⁺ and 0.1Tm³⁺ (mol%) were synthesized by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and transmission electron microscopy analysis point out the precipitation of hexagonal LaF₃ nanocrystals with diameter ranging from 11 to 20 nm in these nano-glass-ceramics. White light generation by means of efficient blue, green and red up-conversion luminescence under infrared excitation at 980 nm was observed and involved mechanisms were analyzed. Colour tuneability is achieved by varying the up-conversion emission ratios as a function of pump power.     

Y(P,V)O4:Dy phosphors for white light generation: Emission dynamics and host effect

The structural characteristics and optical spectra of Y(P,V)O₄:Dy³⁺phosphors obtained by solid state reaction, sol-gel and hydrothermal routes have been investigated and compared. The luminescence features of these materials show a complicate dependence on the composition, synthetic method and excitation conditions. The emission performance depends on different effects: host luminescence, energy transfer to the doping ions and host dependence of the Dy³⁺ emission properties. These effects have been rationalized in order to provide useful information for the development of a suitable material for the white light emitting phosphors technology.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

Single red up-conversion luminescence of Er sensitized layered Y2Ti2O7 phosphor

High color purity red emission with single band successfully achieved in a new Er³⁺, Tm³⁺ co-doped Y₂Ti₂O₇ system under 1550 nm excitation, value of red to green emission ratio of the samples is more than 10³. Efficient up-conversion luminescence can be obtained while the ⁴I_13/2 level of Er³⁺ pumped by 1500 nm directly based on the large absorption section and long luminescence lifetime, and red emission composition will greatly enhanced by co-doping with Tm³⁺ ions, color purity of red emission under 1550 nm excitation is much higher than that of 980 nm. The quenching concentration of Er³⁺ ions is up to 28 mol% in Y₂Ti₂O₇ rely on the layer distribution of cations, which can further improve the red emission color purity.     

White-light-emitting long-lasting phosphorescence in Dy-doped SrSiO3

We report on a luminescent phenomenon in Dy³⁺-doped SrSiO₃ long-lasting phosphor. After irradiation by a 254-nm UV lamp for 5 min, the Dy³⁺-doped SrSiO₃ phosphor emits white light-emitting long-lasting phosphorescence for more than 1 h even after the irradiation source has been removed. Photoluminescence, long-lasting phosphorescence and thermoluminescence (TL) spectra are used to explain this phenomenon. Photoluminescence spectra reveal that the white light-emitting long-lasting phosphorescence originated from the two mixtures of Dy³⁺ characteristic luminescence, the 480-nm blue emission (⁴F_9/2→⁶H_15/2) and the 572-nm yellow emission (⁴F_9/2→⁶H_13/2). TL spectra shows that the introduction of Dy³⁺ ions into the SrSiO₃ host produces a highly dense trapping level at 377 K (0.59 eV), which is responsible for the long-lasting phosphorescence at room temperature. A possible mechanism of the long-lasting phosphorescence based on the experimental results is proposed. It is considered that the long-lasting phosphorescence is due to persistent energy transfer from the electron traps to the Dy³⁺ ions, which creates the persistent luminescence of Dy³⁺ to produce the white light-emitting long-lasting phosphorescence.     

Judd-Ofelt analysis and multiphonon relaxations of rare earth ions in fluorohafnate glasses

The optical properties of fluorohafnate glasses doped with Pr³⁺, Nd³⁺, Sm³⁺, Dy³⁺, Ho³⁺, Er³⁺, and Tm³⁺ have been studied. From optical absorption measurements and using Judd-Ofelt theory, JO parameters Ω₂, Ω₄, and Ω₆ have been obtained. The Ω₂ values indicate that fluorohafnate glasses present a less ionic character than fluorozirconates. Multiphonon emission probabilities for several levels of Er³⁺ and Ho³⁺ ions were determined by the difference between the measured rates and the calculated radiative transition probabilities. The results are almost the same as those found in fluorozirconates. Multiphonon emission probabilities are in agreement with the energy-gap law followed by rare-earth ions in crystals and glasses.     

颜色可调Sr3Y（BO3）3∶Tm3+，Dy3+荧光粉的发光性能及能量传递

采用高温固相法制备了Sr_3Y(BO_3)_3:xTm~(3+),yDy~(3+)荧光粉,并通过XRD、SEM和荧光光谱仪对样品的物相、微观形貌、发光性能、能量传递机制和CIE色坐标进行了分析。结果表明:Sr_3Y(BO_3)_3:xTm~(3+)荧光粉在监测波长为359 nm时发射蓝光,Tm~(3+)的浓度淬灭点为x=0.08;在Sr_3Y(BO_3)_3:0.08Tm~(3+),yDy~(3+)荧光粉中,随着Dy~(3+)掺杂浓度的增加,Tm~(3+)的发光强度降低而Dy~(3+)发光强度却先增加后降低,Dy~(3+)的浓度淬灭点为y=0.1;通过改变Dy~(3+)掺杂浓度或改变激发光的波长,均可实现发射光的颜色可调;在Tm~(3+)-Dy~(3+)离子之间存在能量传递。当Dy~(3+)掺杂浓度(物质的量分数)为0.15时能量传递效率达75.14%,能量传递机制为电偶极-电偶极相互作用。     

Luminescence properties of Dy3+ or/and Sm3+ doped LiLa(WO4)2 phosphors and energy transfer from Dy3+ to Sm3+

The Dy³⁺ or/and Sm³⁺ doped LiLa(WO₄)₂ phosphors are synthesized by a facile solid state reaction method. The phase and luminescence properties of the phosphors are investigated. The powder X-ray diffraction (XRD) results show that the phosphor has a tetragonal phase crystal structure. The quenching concentration of single doped Dy³⁺ and Sm³⁺ in the LiLa(WO₄)₂ are determined to be 6% and 3%, respectively. Under the excitation of 404 nm, warm white light is obtained in the co-doped phosphors. With the concentration of Sm³⁺ increasing, the correlated color temperature (CCT) gradually decreases from 3090 to 2453 K. Two kinds of energy transfer may exist at the same time. The overlap between the emission spectrum of Dy³⁺ and the excitation spectrum of Sm³⁺ reveals that the energy of Dy³⁺ can transfer to Sm³⁺ via radiation. Another way of energy transfer, that is non-radiative energy transfer, is attributed to the excited state of Dy³⁺ (⁴F_9/2) slightly higher than that of Sm³⁺ (⁴I_19/2). The calculation results show that non-radiative energy transfer process from Dy³⁺ to Sm³⁺ ions is predominated by quadrupole–quadrupole interaction.     

Photoluminescence properties of rare earths (Eu3+, Tb3+, Dy3+ and Tm3+) activated NaInW2O8 wolframite host lattice

The photoluminescence (PL) studies on NaIn_1?xRE_xW₂O₈, with RE=Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ phases have shown that the relative contribution of the host lattice and of the intra-f–f emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy³⁺ and Tm³⁺ activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu³⁺, with intense red emission, the host absorption is less pronounced and the intra-f–f transitions of the Eu³⁺ ions play a major role, whereas for Tb³⁺ intra-f–f transitions are only observed, giving rise to green emission.     

Synthesis and VUV-UV spectroscopic properties of rare earth borosilicate oxyapatite: RE5Si2BO13:Ln (RE=La, Gd, Y; Ln=Eu, Tb)

Three rare earth borosilicate oxyapatites, RE₅Si₂BO₁₃ (RE=La, Gd, Y), were synthesized via wet chemical method, of which RE₅Si₂BO₁₃ (RE=Gd, Y) were first reported in this work. In the three oxyapatites, [BO₄] and [SiO₄] share the [TO₄] tetrahedral oxyanion site, and RE³⁺ ions occupy all metal sites. The differential scanning calorimetry-thermo gravimetry measurements and high temperature powder X-ray diffraction pattern revealed a vitrification process within 300-1200 °C, which was due to the glass-forming nature of borosilicates. From the VUV excitation spectra of Eu³⁺ and Tb³⁺ in RE₅Si₂BO₁₃, the optical band gaps were found to be 6.31, 6.54 and 6.72 eV for RE₅Si₂BO₁₃ (RE=La, Gd, Y), respectively. The emission and excitation bands of Eu³⁺ and Tb³⁺ are discussed relating with their coordination environments. Among the three hosts, Y₅Si₂BO₁₃ would be the best for Eu³⁺ and Tb³⁺-doped phosphors.     

Novel rare earth ions-doped oxyfluoride nano-composite with efficient upconversion white-light emission

Transparent SiO₂-Al₂O₃-NaF-YF₃ bulk nano-composites triply doped with Ho³⁺, Tm³⁺ and Yb³⁺ were fabricated by melt-quenching and subsequent heating. X-ray diffraction and transmission electron microscopy measurements demonstrated the homogeneous precipitation of the β-YF₃ crystals with mean size of 20 nm among the glass matrix, and rare earth ions were found to partition into these nano-crystals. Under single 976 nm laser excitation, intense red, green and blue upconversion emissions were simultaneously observed owing to the successive energy transfer from Yb³⁺ to Ho³⁺ or Tm³⁺. Various colors of luminescence, including bright perfect white light, can be easily tuned by adjusting the concentrations of the rare earth ions in the material. The overall energy efficiency of the white-light upconversion was estimated to be about 0.2%.     

Luminescence in La3TaO4Cl6

The luminescence properties of La₃TaO₄Cl₆ are reported and discussed. The rare earth ions Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, and Tm³⁺ show characteristic absorption and emission lines. For Sm³⁺ and Eu³⁺, broad absorption bands are also observed and are attributed to charge-transfer transitions. The line emissions of Tb³⁺ are only from ⁵D₄, even at low (1 at.%) concentration. Broad excitation and emission bands were observed with In³⁺. These bands are attributed to In³⁺Ta⁵⁺ → In⁴⁺Ta⁴⁺ charge-transfer transitions. An additional broad absorption at 250 and 280 nm leading to broad emission at 410 nm is ascribed to OH⁻ impurities.     

Thermal and structural analysis of germanate glass and thin films co-doped with silver nanoparticles and rare earth ions with insights from visible and Raman spectroscopy

This paper reports on the thermal and optical properties of germanate glasses GeO₂–PbO co-doped with silver nanoparticles and rare earth ions (Tm³⁺, Er³⁺ and Yb³⁺) with a focus on the thermal diffusivity (D). The presence of rare earth ions and nanoparticles is evidenced by absorption spectra and TEM images, respectively. Additionally, a structural comparison between thin films and bulk glass with the same nominal composition is given. It is found that D increases up to 20% in samples where nanoparticles are present, although their quantity corresponds only to a volume fraction of 1.7%. Therefore, such enhancement could be associated with the nanoparticles. Nevertheless, a Raman analysis revealed a structural change after the thermal treatment used for the nucleation of the nanoparticles. A decrease in the intensity of the band at 534 cm⁻¹ in the Raman spectra is interpreted as the disruption of the 3-membered rings of the GeO₄ tetrahedra. The Raman analysis also revealed the formation of small crystals of α-GeO₂ type quartz and the adsorption of carbon dioxide on the surface of the silver nanoparticles inserted in the germanate thin film.