Lattice site dependent cathodoluminescence behavior and surface chemical changes in a Sr5(PO4)3F host

Eu activated Sr₅(PO₄)₃F phosphor powders have been subjected to the electron bombardment at 2 keV (10 μA) at an oxygen pressure of 1×10⁻⁶ Torr. The synthesized Sr₅(PO₄)₃F phosphor was identical to the hexagonal apatite structure, with the Sr present at two different sites C_s (S1) and C₃ (S2) in the Sr₅(PO₄)₃F host, as inferred from the crystallographic study. Cathodoluminescence (CL) and Auger electron spectroscopy of the phosphor excited by the same electron beam were used to monitor changes in the surface state during prolonged electron bombardment. A direct correlation between the surface reactions and the degradation of the CL brightness was observed. Both C and F were depleted from the surface during electron bombardment. The postulated mechanism for the electron stimulated chemical reactions on the phosphor surface is electron beam dissociation of molecular species to atomic species, which subsequently react with C to form volatile compounds CO₂, CH₄, etc. and with Sr₅(PO₄)₃F to form a non luminescence layer of metal oxides of Sr and P.     

Synthesis and photoluminescent characteristics of Sr2CeO4 phosphors prepared via a microwave-assisted solvothermal process

Blue-light emitting Sr₂CeO₄ phosphors were successfully prepared via a microwave-assisted solvothermal method employing ethylene glycol as a solvent. The formation of Sr₂CeO₄ phase began when the solvothermally derived precursors were heated at 800 °C. With increase in heating temperatures, significantly enhanced excitation and emission intensities were observed because of an increase in the amount of Sr₂CeO₄. Heating at 1200 °C led to a substantial decrease in mission intensity due to thermal decomposition of Sr₂CeO₄ at elevated temperatures. The solvothermally derived Sr₂CeO₄ was found to exhibit higher emission intensity than the solid-state-reaction-derived phosphors. According to the deconvoluted emission spectra, two emission peaks are attributed to two metal-to-ligand charge-transfer states. Based on the deconvoluted results, a qualitative energy-level diagram of Sr₂CeO₄ was proposed. VUV-excited luminescence studies for Sr₂CeO₄ indicate that one peak at 193 nm is assigned to the charge-transfer transition between Sr²⁺ and O²⁻.     

Exploring the electronic structure and optical properties of new inorganic luminescent materials Ba(Si,Al)5(O,N)8 compounds for light-emitting diodes devices

Due to growing demand on discovering new materials for light-emitting diodes devices, many efforts were made to discover and characterize new inorganic materials such as phosphors. Using the full potential method within density functional theory the electronic and optical properties of BaAl₂Si₃O₄N₄ and BaAlSi₄O₃N₅ semiconductors have been investigated. The electronic structure and the optical properties of these phosphors were calculated through a reliable approach of modified Beck-Johnson (mBJ) approach. We found that BaAl₂Si₃O₄N₄ and BaAlSi₄O₃N₅ have wide direct band gaps positioned at Γ about 5.846 and 4.96 eV respectively. The optical properties, namely the dielectric function, optical reflectivity, refractive index and electron energy loss, are reported for radiation up to 15 eV. Our study suggests that BaAl₂Si₃O₄N₄ and BaAlSi₄O₃N₅ could be promising materials for applications in the LEDs devices and optoelectronics areas of research.     

The Synthesis,Structure, and Tunable Emission Spectra of A New Phosphor Sm(IO3)3·2H2O

A new phosphor Sm(IO₃)₃ · 2H₂O was synthesized under mild hydrothermal conditions. The structure was confirmed by single‐crystal X‐ray powder diffraction analysis. It crystallizes in the triclinic system with space group P$\bar{1}$ (No.2), a = 7.1570Å, b = 7.4306Å, c = 10.6367Å, α = 95.205°, β = 104.844°, γ = 109.958°. Some characterizations were performed such as Fourier transform infrared spectroscopy (FTIR), powder X‐ray diffraction (PXRD), thermogravimetric and differential thermal analysis (TG‐DTA), and luminescence spectroscopy. The overall structure of the title compound is two‐dimensional. The adjacent iodate layers are further linked with each other by hydrogen bonds to form a three‐dimensional supramolecular network. The luminescent properties of Sm(IO₃)₃ · 2H₂O were studied, the exhibit tunable emission spectra by means of heating treatment.     

Luminescence properties and mechanism of Zn1.92−xBaxSi1−yTiyO4:0.08Mn phosphors in VUV region

The present commercial phosphor Zn₂SiO₄:Mn²⁺ requires further improvement because of its long decay time. In this work, the co-doping effects of Ba²⁺ and Ti⁴⁺ upon emission intensity and decay time were investigated. Ba²⁺ and Ti⁴⁺ cations have favorable influences on the photoluminescent properties. When doped with appropriate amount of Ba²⁺, the intensity of green emission was increased 12% and the decay time was shortened 18%. When doped with appropriate amount of Ti⁴⁺, the luminescence intensity was enhanced a little, and the decay time was shortened 14%. Ba²⁺ and Ti⁴⁺ were co-doped in Zn₂SiO₄:Mn²⁺ system, the luminescence intensity was enhanced 18%, and the decay time was shortened sharply (about 31%).     

Excitation of thermoluminescence in Eu doped Ba0.12Sr0.88SO4 nanophosphor by low energy argon ions

In the present paper thermoluminescence properties of argon ions irradiated barium strontium mixed sulphate phosphor are reported. The Ba_0.12Sr_0.88SO₄ phosphor was prepared by chemical co-precipitation method. The X-ray diffraction study of prepared sample suggests orthorhombic structure with average grain size of 37 nm. The samples were irradiated with 1.2 MeV Argon ions at fluences varying between 10¹¹-10¹⁵ ions/cm². The argon ions penetrate to the depth of 1.89 μm and lose their energy mainly via electronic stopping. Due to ion irradiation, a large number of defects in the sample are formed. Thermoluminescence (TL) glow curves were recorded for each of the ion fluence. These curves exhibit one broad peak with maximum intensity at 498 K composed of three overlapping peaks. This indicates that different sets of traps are being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The peaks were observed due to formation of trap levels by ion irradiation and subsequently activation of traps on thermal stimulation. The TL response of the nanophosphor is linear in the dose range 59 kGy-590 MGy. Kinetic parameters associated with the prominent peaks were calculated using glow curve deconvolution (GCD) and verified by different glow curve shape and sample heating rate methods.     

EPR and photoluminescence properties of Mn-activated zinc gallate phosphor prepared by urea combustion route and post heat treatment

Mn²⁺ activated ZnGa₂O₄ powder phosphors have been prepared by urea combustion route. Powder X-ray diffraction and scanning electron microscopy (SEM) techniques have been used to characterize the as-prepared and post-treated (900 °C, 3 h) phosphors. The morphology shows small particles, voids and pores, with non-uniform shapes and sizes. The EPR spectrum exhibits an intense resonance signal at g≈1.985 with a sextet hyperfine structure (hfs) besides a weak broad signal at g≈4.05 and a hump near g≈2.27. The g≈1.985 resonance is due to Mn²⁺ ions in an environment close to tetrahedral symmetry. The resonances at g≈4.05 and 2.27 are attributed to the rhombic surroundings of the Mn²⁺ ions. The spin concentration (N) and the paramagnetic susceptibility (χ) are evaluated and discussed. It is observed that the intensity of the resonance signal at g≈1.985 increases with decrease in temperature obeying the Boltzmann law. Upon post treatment the intensity of the green emission (λ_em=528 nm,⁴T₁→⁶A₁ transition of Mn²⁺ ions) has been increased to 3.35 times and a red shift has been observed.     

Luminescence of Ce in hydrated rare earth bromides

Intense photoluminescence is reported for hydrated bromides of Gd, La and Y (LaBr₃·7H₂O, CeBr₃·7H₂O, YBr₃·8H₂O and GdBr₃·n H₂O) prepared by the wet chemical method and activated with Ce³⁺. Intensities are comparable to that for a commercial phosphor (SrB₄O₇:Eu²⁺—Sylvania 2052). Luminescence in hydrated salt is usually quenched. The observation of intense luminescence in hydrated bromides is remarkable.     

Structural study of sol-gel silicate glasses by IR and Raman spectroscopies

A study of the structure and bonding configuration of sol-gel silicate glasses by Raman and infrared spectroscopies is presented. Moreover, a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon-oxygen groups and the ring structures are also demonstrated. The evolution of the changes of the bonding configuration in the composition and the stabilization temperature of the bioactive glasses is discussed in terms of the structural and textural characteristics of the glasses. Raman and infrared analyses contribute to the improvement in understanding of the local symmetry for sol-gel silicate glasses. infrared spectroscopy has allowed to identify the vibration bands of the hydroxyl groups associated with various configurations of the terminal silanol bonds on the glass surface and the free molecular water in the glass matrix. Raman analysis has provided an alternative method of quantifying the network connectivity grade and predicting the textural properties of the sol-gel silicate glasses.     

Luminescence property improvement of Ba2LaSbO6:Mn4+ phosphor by using Dy3+ or H3BO3

Ba₂LaSbO₆:Mn⁴⁺, Ba₂LaSbO₆:Mn⁴⁺, Dy³⁺, and Ba₂LaSbO₆:Mn⁴⁺, H₃BO₃ phosphors are synthesized in the air by high temperature solid state reaction method. The particle sizes and sintering degree of Ba₂LaSbO₆:Mn⁴⁺ phosphor may be changed by doping Dy³⁺ ion and H₃BO₃. When the small amount of Dy³⁺ ion and H₃BO₃ are codoped, the emission intensity of Ba₂LaSbO₆:Mn⁴⁺ phosphor can be enhanced 1.2–1.3 times and the quantum efficiency of Ba₂LaSbO₆:Mn⁴⁺ phosphor can be improved. The lifetime of Ba₂LaSbO₆:Mn⁴⁺ phosphor may be changed by doping Dy³⁺ ion and H₃BO₃. The experimental results are valuable in research of luminescence property of Mn⁴⁺-doped luminescence materials.