Photoluminescence properties of RE-activated Na3GdP2O8 (RE = Tb, Dy, Eu, Sm) under VUV excitation

RE³⁺-activated monoclinic Na₃GdP₂O₈ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na₃GdP₂O₈:RE³⁺ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) were assigned and corroborated. For the sample Na₃GdP₂O₈:5%Tb³⁺, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb³⁺. For Na₃GdP₂O₈:5%Dy³⁺, the broad band at 176 nm could be related to the f-d transitions of Dy³⁺ and the O²⁻ → Dy³⁺ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu³⁺ doped sample, the O²⁻ → Eu³⁺ CTB is observed to be at 245 nm. For the Sm³⁺ doped sample, the O²⁻ → Sm³⁺ CTB is not distinguished obviously and is overlapped with the host-related absorption band.     

Preparation and characterization of NaSm9(SiO4)6O2 powders with infrared absorptive properties

NaSm₉(SiO₄)₆O₂ powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm^− 1 (10.6 μm). The band at 938 cm^− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q¹ species and the band at 989 cm^− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q⁰ species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

Superconductivity at 103 K in CdBa2(Ca0.7Y0.3)Cu2Oy

A cadmium analogue of the mercury system with nominal composition CdBa₂(Ca_1–xY_x)Cu₂O_y has been synthesized. Thex=0 samples contain about 12 vol.% of the 1212 phase but are not superconducting. Thex=0.3 samples are superconducting atT _on = 103 K. The EDX analysis of 18 microcrystals shows a broad cationic distribution of the different components. The observed broad superconducting transition is attributed to the variousT _c of the different microcrystals.     

Radioluminescence of SrAl2O4:Ln (Ln = Eu, Sm, Dy) phosphor ceramic

Phosphors for radiation detection require efficient energy transfer from the ionization track to the luminescent centers. In this work, the radioluminescence (RL) spectra of SrAl₂O₄ phosphor ceramics doped with individual trivalent rare earth element (REE) ions (Sm, Eu and Dy) are reported at the room temperature. Although there is some intrinsic UV/blue emission from the host lattice, the dominant signals are from the rare-earth sites, with signals characteristic of the REE²⁺ and REE³⁺ states. The shapes of the emission bands are different for each dopant. The sharp emission properties show that the SrAl₂O₄ is a suitable host for rare-earth ion doped phosphor material.     

Sol-gel synthesis of yellow-emitting La4Ca(SiO4)3O:Ce phosphors for white-light emitting diodes

Ce³⁺ doped La₄Ca(SiO₄)₃O phosphors with silicate oxyapatite structure were synthesized by the sol-gel process. The X-ray diffraction (XRD) patterns showed that a pure phase was formed when sintering temperature was higher than 1300°C. The optical properties of La₄Ca(SiO₄)₃O:Ce³⁺ phosphors with varying sintering temperature and concentration were investigated by examining their excitation and emission spectroscopy. The phosphors exhibited a broad emission band centered at 550nm which could be attributed to the 5d-4f transition of Ce³⁺ and a stronger excitation peak around 467nm as well as several shoulder bands, nicely matching with the widely applied blue LED chips. Higher emission intensity was observed when firing temperature above 1300°C, due to increasing crystallinity of the powders. When Ce³⁺ concentration was equal to 5 at%, the sample exhibited the optimum excitation and emission efficiency. The results indicate that La₄Ca(SiO₄)₃O:Ce³⁺ is a promising candidate in the application of blue chip excited white light emitting diodes (LEDs).     

Luminescence properties of Ce and/or Mn activated Ca10K(PO4)7 under ultraviolet and vacuum ultraviolet excitation

New Ce³⁺ and/or Mn²⁺ activated Ca₁₀K(PO₄)₇ phosphors were prepared by solid-state reaction, and their photoluminescence properties upon ultraviolet and vacuum ultraviolet excitation were investigated. Under 254 nm excitation, a series of Ca₁₀K(PO₄)₇:xMn²⁺ samples exhibit two emission bands at 463 and 650 nm, which could be attributed to oxygen defects and ⁴T₁–⁶A₁ transition of Mn²⁺, respectively. And an energy transfer from defects to Mn²⁺ has been observed. With the Mn²⁺ content increased, the emitting hues of Ca₁₀K(PO₄)₇:Mn²⁺ can range from blue to red. By co-doping Ce³⁺ to Ca₁₀K(PO₄)₇:Mn²⁺, the emission intensity of Mn²⁺ is strongly enhanced due to an efficient energy transfer by [Ce³⁺ → Mn²⁺] and [defects → Ce³⁺ → Mn²⁺]. But under 147 nm excitation, the emission intensity of Mn²⁺ in Ca₁₀K(PO₄)₇:0.25Mn²⁺ decreases slightly compared with that in Ca₁₀K(PO₄)₇:025Mn²⁺, 0.1Ce³⁺, 0.1K⁺ due to the host sensitization competition between Ce³⁺ and Mn²⁺.     

Infrared emission properties of RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn co-doped Co0.6Zn0.4Fe2O4 ferrites

The RE (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) and Mn ions co-doped Co-Zn ferrites were prepared by solid-state reaction method. X-ray diffraction, infrared spectra, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and infrared emission measurement (IRE-2) were employed to investigate the effect of the substitution RE³⁺ and Mn ions for Fe³⁺ ones on the spinel structure, the chemical homogeneity, and the infrared emission properties of the Co-Zn ferrites. The substitution leads to non-monotonous change of the lattice parameters and infrared emissivity properties, which is mainly attributed to the partial cation exchange among the spinel structure of Co-Zn ferrites. The infrared emission properties of Co-Zn ferrites seem to be greatly influenced by the co-doped of RE³⁺ and Mn ions—maxima values were 0.96-0.97, found for LaF, NdF and GdF, respectively.     

Luminescence of SrGdGa3O7:RE(RE = Eu, Tb) phosphors and energy transfer from Gd to RE

Eu³⁺- and Tb³⁺-activated SrGdGa₃O₇ phosphors were synthesized by the solid-state reaction and their luminescence properties were investigated. Sr(Gd_1 − xEu_x)Ga₃O₇ and Sr(Gd_1 − xTb_x)Ga₃O₇ formed continuous solid solution in the range of x = 0-1.0. Unactivated SrGdGa₃O₇ exhibited a typical characteristic excitation and emission of Gd ion. The SrGdGa₃O₇:xEu³⁺ and SrGdGa₃O₇:xTb³⁺ phosphors also showed the well-known Eu³⁺ and Tb³⁺ excitation and emission. The energy transfer from Gd³⁺ to Eu³⁺ and Tb³⁺ were verified by photoluminescence spectra. The dependence of photoluminescence intensity on Eu³⁺ and Tb³⁺ concentration were also studied in detail and the photoluminescence (PL) intensity of SrGdGa₃O₇:Eu and SrGdGa₃O₇:Tb were compared with commercial phosphors, Y₂O₃:Eu and LaPO₄:Ce,Tb. The luminescence decay measurements showed that the lifetimes of Eu³⁺ and Tb³⁺ were in the range of microsecond. The energy transfer from Gd³⁺ to Tb³⁺ was also observed in decay curve.     

Near UV-based LED fabricated with Ba5SiO4(F,Cl)6:Eu as blue- and green-emitting phosphor

A series of halosilicate phosphor, Ba₅SiO₄(F,Cl)₆:Eu²⁺, were synthesized by a solid state reaction. Excited by 370-nm light, Ba₅SiO₄Cl₆:Eu²⁺ exhibits a broad emission band peaking at 440 nm. Partial substitution of Cl⁻ with F⁻ in the host lattice leads to red-shift in the emission band with centering wavelength from 440 nm to 503 nm. The possible mechanism for the luminescence change was discussed based on the XRD patterns. Blue and green LEDs were fabricated by combination of a 370 nm-emitting near UV chip and the optimal Ba₅SiO₄Cl₆:Eu²⁺ and Ba₅SiO₄(F₃Cl₃):Eu²⁺, respectively. This series of phosphors is considered as a promising blue and green component used in fabrication of near UV-based white LEDs.     

Up-conversion emission in KGd(WO4)2 single crystals triply-doped with Er/Yb/Tm, Tb/Yb/Tm and Pr/Yb/Tm ions

Triply-doped single crystals KGd(WO₄)₂:Er³⁺/Yb³⁺/Tm³⁺, KGd(WO₄)₂:Tb³⁺/Yb³⁺/Tm³⁺ and KGd(WO₄)₂:Pr³⁺/Yb³⁺/Tm³⁺ were grown by the Top Seeded Solution Growth (TSSG) method, with an aim of getting efficient up-converted multicolored luminescence, which subsequently can be used for generation of white light. Such an aim determined the choice of the triply doped compounds: excitation of the Yb³⁺ ions in the infrared spectral region is followed by red, green and blue emission from other dopants. It was shown that all these systems exhibit multicolor up-conversion fluorescence under 980 nm laser irradiation. Detailed spectroscopic studies of their absorption and luminescence spectra were performed. From the analysis of the dependence of the intensity of fluorescence on the excitation power the conclusion was made about significant role played by the host’s conduction band and other possible defects of the KGd(WO₄)₂ crystal lattice in the up-conversion processes.     

Study on structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O crystals

The structural phase transitions and relaxation processes of Cs₂Co(SO₄)₂·6H₂O and Cs₂Zn(SO₄)₂·6H₂O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T₁, of the ¹³³Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, T_C, and these changes coincide with the changes in the splitting of the ¹³³Cs resonance lines. The variations in the temperature dependence for the splitting of the ¹³³Cs resonance lines and T₁ near T_C are related to changes in the symmetry of surrounding Cs⁺. In addition, the ¹³³Cs T₁ of Cs₂Co(SO₄)₂·6H₂O, which contains paramagnetic ions, was found to be shorter than that of Cs₂Zn(SO₄)₂·6H₂O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the ¹³³Cs T₁ of these compounds are probably due to the differences between the electronic structures of their metal ions.     

Polarized spectral properties of Tm:K5Bi(MoO4)4 crystal

Trivalent thulium-doped K₅Bi(MoO₄)₄ single crystals were grown by the Czochralski method. Its polarized absorption and fluorescence spectra and fluorescence decay curves were recorded at room temperature. On the basis of the Judd-Ofelt theory, the spectral parameters of the Tm³⁺:K₅Bi(MoO₄)₄ crystal were calculated. The cross relaxations between Tm³⁺ ions were analyzed. The emission cross sections of the ³F₄ → ³H₆ transition were obtained by the Fuchtbauer-Ladenburg formula and then the gain cross sections around 1.9 μm were calculated. The peak emission cross section and width of emission band around 1.9 μm are comparable to those for Tm³⁺:YAG and the tunable range is about 280 nm for the potential ∼1.9 μm laser operation via the ³F₄ → ³H₆ transition.     

Synthesis and characterization of novel nanostructured fishbone-like Cu(OH)2 and CuO from Cu4SO4(OH)6

The Cu₄SO₄(OH)₆ was synthesized by a simple hydrothermal reaction with a yield of ~ 90%. Using Cu₄SO₄(OH)₆ as the starting material, novel fishbone-like Cu(OH)₂ was produced by a direct reaction of Cu₄SO₄(OH)₆ with NaOH solution. The Cu(OH)₂ consists of many needle-like nanorods parallel to each other and perpendicular to the direction of backbone, forming fishbone-like structure. Using the fishbone-like Cu(OH)₂ as the sacrificial precursor, CuO with similar size and morphology was obtained through a simple heat treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, X-ray photoelectron spectroscopy, BET nitrogen adsorption, and UV-Vis absorption spectroscopy were employed to characterize the as-prepared samples. The conversion of the Cu₄SO₄(OH)₆ to the fishbone-like Cu(OH)₂ was visualized by time-dependent SEM images. A mechanism was also proposed based on the observed results.     

Luminescence and afterglow in Sr2SiO4:Eu, RE [RE = Ce, Nd, Sm and Dy] phosphors—Role of co-dopants in search for afterglow

Luminescence of Eu²⁺ in Sr₂SiO₄:Eu²⁺, RE³⁺ [RE = Ce, Nd, Sm and Dy] phosphors was studied with a view to obtain an afterglow phosphor. The synthesized phosphors were characterized by powder X-ray diffraction (XRD), diffuse reflectance, photo- and thermoluminescence spectroscopic techniques. Afterglow was observed only with Dy³⁺ co-doped phosphor. The observed afterglow with Dy³⁺ co-doping originated from the formation of suitable traps which was supported by thermoluminescence results.     

Thermoluminescence properties of Ce-doped LiSr4(BO3)3 phosphor

Borates LiSr₄(BO₃)₃ were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce³⁺-activated LiSr₄(BO₃)₃ were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce³⁺ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr₄(BO₃)₃:0.01Ce³⁺ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce³⁺.     

Photoluminescence properties of emission-tunable Ca9Y(PO4)7: Tm,Dy phosphor for white light emitting diodes

A white-emitting Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor has been successfully prepared by conventional high-temperature solid-state reaction. X-ray diffraction (XRD) and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The excitation and emission spectra show that all the Tm³⁺ and Dy³⁺ co-doped Ca₉Y(PO₄)₇ samples can be effectively excited by UV light and then emit blue and yellow light simultaneously. Furthermore, the emission and color coordinate of as-obtained samples pumped by 365 nm are able to be adjusted around white light by varying the doping concentrations of Tm³⁺ and Dy³⁺. So, the as-fabricated single-composition Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor will have a promising application in the area of white light emitting diodes.     

Luminescence enhancement of Y2O3:Eu and Y2SiO5:Ce,Tb core particles with SiO2 shells

This paper reports on the luminescence and microstructural features of oxide nano-crystalline (Y₂O₃:Eu³⁺) and submicron-sized (Y₂SiO₅:Ce³⁺,Tb³⁺) phosphor cores, produced by two different synthesis techniques, and subsequently coated by an inert shell of SiO₂ using a sol-gel process. The shells mitigate the detrimental effect of the phosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20-90%, depending on the core composition and shell thickness. For Y₂O₃:Eu³⁺, uniformly shaped, narrow particle size distribution core/shell particles were successfully fabricated. The photoluminescence emission intensity of core nanoparticles increased with increasing Eu³⁺ activator concentration and the luminescence emission intensity of the core/shell particles was 20-50% higher than that of the core particles alone. For Y₂SiO₅:Ce³⁺,Tb³⁺, the core/shell particles showed enhancement of the luminescence emission intensity of 35-90% that of the core particles, depending on the SiO₂ shell thickness.     

Vacuum ultraviolet optical properties of (La,Gd)PO4:RE (RE=Eu, Tb)

Vacuum ultraviolet excitation spectra of phosphors (La,Gd)PO₄:RE³⁺ (RE=Eu or Tb) and X-ray photoelectron spectra of LaPO₄ and GdPO₄ are investigated. The vacuum ultraviolet excitation intensity of (La,Gd)PO₄:RE³⁺ is enhanced with the increasing of Gd³⁺ content, which implies that Gd³⁺ plays an intermediate role in energy transfer from host absorption band to RE³⁺. When Gd³⁺ is doped into LaPO₄:Eu³⁺, charge transfer band (CT band) begins to shift to higher energy region and the overlap degree of CT band and the host absorption band gets greater with more Gd³⁺ doped into LaPO₄. These results suggest that the dopant (Gd³⁺) gives an important influence on energy transfer efficiency. The top of LaPO₄ valance band is formed by the 2p level of O²⁻, whereas that of GdPO₄ valance band is formed by the 2p level of O²⁻ and the 4f level of Gd³⁺, showing the differences in band structures between LaPO₄ and GdPO₄.