Luminescent cellulose fibers modified with cerium fluoride doped with terbium particles

This article describes UV‐active cellulose fibers obtained by dry‐wet spinning method. The fibers have been formed from an 8% by weight cellulose solution in N‐methylomorpholine‐N‐oxide (NMMO) modified by Ce_0.85Tb_0.15F₃ nanocrystals. The modifier was synthesized by wet chemical method, coprecipitation approach. The host was chosen as the most promising one for the green emitting Tb³⁺ ions. Photoluminescent nanoparticles were introduced into the polymer matrix during the process of dissolving cellulose in NMMO. The modifier occurred in the form of white paste, consisting of luminescent nanoparticles dispersed in glycerine. The dependencies between the concentration of nanocrystals, emission intensity, and excitation energy of the final cellulosic luminescent products were examined by photoluminescence spectroscopy. The size and structure of Ce_0.85Tb_0.15F₃ nanocrystals were studied by X‐ray powder diffraction analysis. The dispersion of the nanoparticles in the polymer matrix was evaluated using scanning electron microscopy and transmission electron microscopy. The real content of luminescent nanocrystals in the fibers was estimated as well. The influence of different concentrations of modifier particles (in the range from 0.5 to 5% by weight) on the mechanical properties of the fibers was determined. POLYM. COMPOS., 153–160, 2016. © 2014 Society of Plastics Engineers     

Luminescence properties and energy transfer of GdAl3(BO3)4:Ce3+, Tb3+ phosphor

Ce³⁺ and Tb³⁺ singly doped and co-doped GdAl₃(BO₃)₄ phosphors were synthesized by solid state reaction. The crystal structure, the luminescent properties, the lifetimes and the temperature-dependent luminescence characteristic of the phosphors were investigated. Through an effective energy transfer, the emission spectra of GdAl₃(BO₃)₄:Ce³⁺, Tb³⁺ phosphor contains both a broad band in the range of 330–400 nm originated from Ce³⁺ ions and a series of sharp peaks at 484, 541, 583, and 623 nm due to Tb³⁺ ions. The energy transfer from Ce³⁺ to Tb³⁺ in GdAl₃(BO₃)₄ host is demonstrated to be phonon assisted nonradiative energy transfer via a dipole–dipole interaction.     

Tb3+-doped transparent BaGdF5 glass-ceramics scintillator for X-ray detector

Commercial Bi₄Ge₃O₁₂ (BGO) monocrystal scintillator is relatively complicated to produce and too expensive. Therefore, it is desired to look for alternative scintillating materials with simple process, low consumption, large size, and high efficiency. Here, glass-ceramics (GC) with high volume fraction of crystal phase and high density by increasing the proportion of heavy metal fluorides in the composition were designed. And bulk Tb³⁺-doped transparent BaGdF₅ glass-ceramics with 23.3% crystal volume ratio and density of 4.65 g/cm³ have been prepared. The structural, optical, and luminescent properties of precursor glass and GC were systematically explored through series of characterization techniques including X-ray diffraction (XRD), transmittance spectra, transmission electron microscope (TEM), photoluminescence (PL) spectra, and X-ray excited luminescence (XEL). After heat treatment, both PL emission and XEL intensity of GC are enhanced because of the movement of Tb³⁺ ions from the amorphous glass matrix into BaGdF₅ nanocrystals, which possess lower phonon energy and better crystal field. The luminescent quantum efficiency of GC reaches 30.7% and the XEL intensity of GC is around 140% of that of the commercial BGO scintillating crystal. Our results demonstrate that BaGdF₅:Tb³⁺ GC may act as efficient scintillator for X-ray detection.     

The Energy Transfer and Thermal Stability of a Blue‐Green Color Tunable K2CaP2O7:Ce3+,Tb3+ Phosphor

Novel blue‐green emitting Ce³⁺‐ and Tb³⁺‐activated K₂CaP₂O₇ (KCPO) luminescent materials were synthesized via a solid‐state reaction method. X‐ray diffraction, luminescence spectroscopy, decay time, and fluorescent thermal stability tests have been used to characterize the prepared samples. The KCPO:Ce³⁺,Tb³⁺ luminescence spectra show broad band of Ce³⁺ ions and characteristic line of Tb³⁺ ion transition (⁵D₄–⁷F₅). The color variation in the light emitting from blue to green under UV excitation can be obtained by tailoring the Tb³⁺ content in KCPO:Ce³⁺. Besides, Ce³⁺ ions obviously intensify Tb³⁺ ion emission through an effective energy transfer process, which was confirmed from decay curves. The energy transfer efficiency was determined to be 82.51%. A resonant type mechanism via the dipole–quadrupole interaction can be proposed for energy transfer. As a whole, the KCPO:Ce³⁺,Tb³⁺ phosphor exhibits excellent performance in the range from 77 to 673 K, indicating the phosphors are highly potential candidates for solid‐state lighting.     

Luminescence properties and energy transfer investigations of Sr2B2O5:Ce3+,Tb3+ phosphors

Ce³⁺ and Tb³⁺ co-doped Sr₂B₂O₅ phosphors were synthesized by the solid-state method. X-ray diffraction (XRD) was used to characterize the phase structure. The luminescent properties of Ce³⁺ and Tb³⁺ co-doped Sr₂B₂O₅ phosphors were investigated by using the photoluminescence emission, excitation spectra and reflectance spectra, respectively. The excitation spectra indicate that this phosphor can be effectively excited by near ultraviolet (n-UV) light of 317 nm. Under the excitation of 317 nm, Sr₂B₂O₅:Ce³⁺,Tb³⁺ phosphors exhibited blue emission corresponding to the f–d transition of Ce³⁺ ions and green emission bands corresponding to the f–f transition of Tb³⁺ ions, respectively. The Reflectance spectra of the Sr₂B₂O₅:Ce³⁺,Tb³⁺ phosphors are noted that combine with Ce³⁺ and Tb³⁺ ion absorptions. Effective energy transfer occurred from Ce³⁺ to Tb³⁺ in Sr₂B₂O₅ host due to the observed spectra overlap between the emission spectrum of Ce³⁺ ion and the excitation spectrum of Tb³⁺ ion. The energy transfer efficiency from Ce³⁺ ion to Tb³⁺ ion was also calculated to be 90%. The phosphor Sr₂B₂O₅:Ce³⁺,Tb³⁺ could be considered as one of double emission phosphor for n-UV excited white light emitting diodes.     

White‐emitting phosphor Ba2B2O5:Ce3+, Tb3+, Sm3+: Luminescence,energy transfer,and thermal stability

A series of Ba₂B₂O₅: RE (RE=Ce³⁺/Tb³⁺/Sm³⁺) phosphors were synthesized using high‐temperature solid‐state reaction. The X‐ray diffraction (XRD), luminescent properties, and decay lifetimes are utilized to characterize the properties of the phosphors. The obtained phosphors can emit blue, green, and orange‐red light when single‐doped Ce³⁺, Tb³⁺, and Sm³⁺. The energy can transfer from Ce³⁺ to Tb³⁺ and Tb³⁺ to Sm³⁺ in Ba₂B₂O₅, but not from Ce³⁺ to Sm³⁺ in Ce³⁺ and Sm³⁺ codoped in Ba₂B₂O₅. However, the energy can transfer from Ce³⁺ to Sm³⁺ through the bridge role of Tb³⁺. We obtain white emission based on energy transfer of Ce³⁺→Tb³⁺→Sm³⁺ ions. These results reveal that Ce³⁺/Tb³⁺/Sm³⁺ can interact with each other in Ba₂B₂O₅, and Ba₂B₂O₅ may be a potential candidate host for white‐light‐emitting phosphors.     

Na1.5Y2.5F9: Ce3+, Tb3+, Eu3+ glass-ceramics for white light

A simply encapsulated, long-range excitation method for white light generation was proposed. Na_1.5Y_2.5F₉: Ce³⁺, Tb³⁺, Eu³⁺ (NYFCTE) glass-ceramics (GCs) were synthesized by the melt-quenching method. The effect of crystallization temperature on the formation of crystallites was analyzed by X-ray diffraction (XRD). The morphology and size of nanocrystals were investigated by transmission electron microscope (TEM). The unit cell diagram of Na_1.5Y_2.5F₉ nanocrystals was drawn. In addition, the luminescence properties of Ce³⁺, Tb³⁺, Eu³⁺ ions-doped Na_1.5Y_2.5F₉ GCs were tested and analyzed. The sample NYFCTE2 emits bright white light when excited by a 320 nm light source at a distance from the light source. The NYFCTE2 sample obtained white light with Commission Internationale de L'Eclairage (CIE) coordinate of (0.3110, 0.3472), Correlated Color Temperature (CCT) of 6467.72 K, and reliable thermal stability. The above results indicate that the proposed white light generation method and NYFCTE GCs have immense application prospects for illumination.     

Improvement of Luminescence Properties of Blue‐to‐Red Emitting NaCaBO3: Ce3+, Mn2+ Phosphor Prepared by Sol–Gel Method

Color‐tunable phosphors NaCaBO₃: Ce³⁺, Mn²⁺ were synthesized by sol–gel (SG) and solid state (SS) method. SEM observation indicated that the microstructure of phosphor (SG) consisted of regular fine grains with an average size of about 5 μm. NaCaBO₃: Ce³⁺, Mn²⁺ showed two emission bands: one at 425 nm for Ce³⁺ and another at 610 nm for Mn²⁺. NaCaBO₃: Ce³⁺, Mn²⁺ (SG) exhibit higher energy‐transfer efficiency (90%) and higher Mn²⁺ quantum efficiency (80%) than SS samples, due to smooth surface, narrow size distribution, and improved homogeneity of sensitizer/activator ions. NaCaBO₃: Ce³⁺, Mn²⁺ exhibits blue‐to‐red tunable color by changing Ce³⁺/Mn²⁺ ratio.     

Photoluminescence and energy transfer of Lu3Al5O12:Ce3+, Pr3+ phosphors

Ce³⁺ and Pr³⁺ co?doped Lu₃Al₅O₁₂ phosphors were synthesized by the sol–gel process, and their crystal structure, photoluminescence (PL) properties, and energy transfer (ET) from the Ce³⁺ to Pr³⁺ were studied. The Lu_2.94?yAl₅O₁₂:0.06Ce³⁺, yPr³⁺ phosphors (0.002 ≤ y ≤ 0.008) showed the green?yellow emission from the ²D_3/2 → ²F_{5/2, 7/2} transition of Ce³⁺ and the red emission at 610 and 637 nm, which were caused by the ¹D₂→³H₄ and ³P₀→³H₅ transitions of Pr³⁺, respectively. The optimal concentration of Pr³⁺ for efficient ET was found to be x = 0.006. The electric quadrupole?quadrupole interaction was responsible for the concentration quenching in the Lu_2.94?yAl₅O₁₂:0.06Ce³⁺, yPr³⁺ phosphors, based on Dexter's theory. The incorporation of Pr³⁺ for Lu³⁺ enhanced the red PL intensity in the Lu_2.94Al₅O₁₂:0.06Ce³⁺ phosphor.     

Local coordination,electronic structure,and thermal quenching of Ce3+ in isostructural Sr2GdAlO5 and Sr3AlO4F phosphors

Sr₂GdAlO₅:Ce and Sr₃AlO₄F:Ce are isostructural phosphors in which the Ce³⁺ 4f-5d₁ transition can be efficiently excited by a photon with energy lower than 3.1 eV. Herein, we analyze the crystal chemistry of the Ce³⁺ local coordination, compare the thermal quenching behavior and construct the electronic structure of Ce³⁺ in them. The Rietveld refinement on two occupancy models suggests that Gd³⁺ only occupies the 8h site in Sr₂GdAlO₅; this provides a hint on the preferred occupancy of dopant Ce³⁺ in this site. The large crystal filed splitting of Ce_8h is mainly due to the fact that the 8h site is bonded to two oxygen with relatively short d_Sr/Gd-O and forms a quasi-square antiprism which experiences a large distortion. The Ce³⁺ 5d-4f luminescence in Sr₃AlO₄F is much more stable against thermal quenching than that in Sr₂GdAlO₅, as evidenced by the temperature-dependent luminescence intensity and luminescence decay studies. The energy of the O²⁻-Eu^3+/2+ and O²⁻-Ce^4+/3+ charge transfer as well as bandgap were estimated and the electronic structure of Ce³⁺ were constructed. A larger energy barrier ΔE_dC between the Ce³⁺ 5d₁ level and the conduction band bottom in Sr₃AlO₄F is seen from the Vacuum Referred Binding Energy (VRBE) diagrams which explains the higher thermal quenching temperature by thermal ionization model.     

Luminescent properties of a novel afterglow phosphor Sr3Al2O5Cl2:Eu,Ce

A series of Eu²⁺ and Ce³⁺ doped/co-doped Sr₃Al₂O₅Cl₂ afterglow phosphors that presented various bright colors were successfully synthesized via high temperature solid state reaction. The structure and luminescence properties of the obtained samples were characterized by X-ray powder diffraction (XRD), photoluminescence (PL) spectra and decay curves as well as the thermoluminescence (TL) glow curves. The XRD results showed that all the phase could be indexed to the orthorhombic structure with the space group P2₁2₁2₁. After being exposed to a 254 nm or 365 nm mercury lamp, blue/yellow-orange afterglow emissions with broad bands peaking around 620 nm/435 nm, which were ascribed to the characteristic 4f⁶5d–4f⁷/5d¹–4f¹ transitions of Eu²⁺/Ce³⁺, could be observed in phosphors of Sr₃Al₂O₅Cl₂:Eu²⁺/Sr₃Al₂O₅Cl₂:Ce³⁺, respectively. Because of the overlap spectral range between the Sr₃Al₂O₅Cl₂:Eu²⁺ and Sr₃Al₂O₅Cl₂:Ce³⁺ phosphors, the energy transfer (ET) from Ce³⁺ to Eu²⁺ occurred. The related ET process was discussed in detail. Moreover, the incorporation of Ce³⁺ could significantly prolong the afterglow duration of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor, which was due to the increase of trap concentration. Consequently, 6 h of the afterglow duration could be observed in Sr₃Al₂O₅Cl₂:1.0%Eu²⁺, 0.5%Ce³⁺ sample, exhibiting much longer than that of Sr₃Al₂O₅Cl₂: 1.0%Eu²⁺ (3 h). From the afterglow decay curves and the fitting results, the optimal concentration of Ce³⁺ for the enhanced afterglow property was experimentally determined to be 0.5%.     

The influence of concentration on the formation of BaTiO3 by direct reaction of TiCl4 with Ba(OH)2 in aqueous solution

The formation of fine BaTiO₃ particles by reaction between liquid TiCl₄ and Ba(OH)₂ in aqueous solution at 85 °C and pH⩾13 has been studied for 0.062⩽[Ba²⁺]⩽0.51 mol l⁻¹. The concentration of Ba²⁺ ions has a strong influence on reaction kinetics, particle size and crystallite size. When [Ba²⁺]>≈0.12 mol l⁻¹, the precipitate consists of nanosized (≈30 nm) to submicron (100–300 nm) particles of crystalline BaTiO₃. At lower concentrations, the final product is a mixture of crystalline BaTiO₃ and a Ti-rich amorphous phase even for very long reaction times. A two-steps precipitation mechanism is proposed. Initially, a Ti-rich amorphous precipitate is rapidly produced. Reaction between the amorphous phase and the Ba²⁺ ions left in solution then leads to crystallisation of BaTiO₃. In addition to nucleation and growth of nanocrystals, the final size and morphology of BaTiO₃ particles obtained at low concentration can be determined by aggregation of nanocrystals and heterogeneous nucleation on existing crystal surfaces.     

Influence of Ce3+ and Gd3+ co-doping on the structure and upconversion emission in hexagonal Ho3+ doped NaYbF4 phosphors

Hexagonal Ho³⁺ doped NaYbF₄ phosphors are synthesized via a hydrothermal method. The influence of Gd³⁺ and Ce³⁺ content on the phase structure and upconversion (UC) emission of NaYbF₄ phosphors is investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UC spectra. The results of XRD and TEM indicate that the solubility of Ce³⁺ in hexagonal NaYbF₄ is low due to the large difference of ionic radius between Ce³⁺ and Yb³⁺. With help of Gd³⁺ co-doping (15 mol%), pure hexagonal NaYbF₄ phosphors with high doping concentration of Ce³⁺ (15 mol%) and small crystal size are obtained. When excited by a 980 nm laser diode, Ho³⁺ doped hexagonal NaYb_0.85Gd_0.15F₄ phosphors exhibit strong green UC emission at 540 nm and weak red one at 646 nm. UC luminescence tuning from green emission to red emission is observed in hexagonal Ho³⁺ doped NaYb_0.85Gd_0.15F₄ phosphors by co-doping with Ce³⁺ ions. The UC luminescence tuning phenomenon is attributed to two resonant energy transfer processes of ⁵S₂/⁵F₄(Ho³⁺)+²F_5/2(Ce³⁺)→⁵F₅(Ho³⁺)+⁵F_7/2(Ce³⁺) and ⁵I₆(Ho³⁺)+²F_5/2(Ce³⁺)→⁵I₇(Ho³⁺⁾+⁵F_7/2(Ce³⁺) between Ho³⁺ and Ce³⁺, which suppress the green emission at 540 nm, while promote the red one at 646 nm.     

Facile synthesis and luminescence properties of highly uniform YF3:Ln (Ln = Eu, Tb, Ce, Dy) nanocrystals in ionic liquids

Uniform YF₃ nanocrystals were prepared through a facile ethylene glycol (EG)/ionic liquid interfacial synthesis route in a imidazolium ionic liquids (1-octyl-3-methylimidazolium hexafluorophosphate) with the ionic liquids acting as both reagents and templates. The partial hydrolysis of PF₆⁻ was utilized to introduce a fluoride source. X-ray diffraction (XRD), field emission scanning microscopy (FE-SEM) and transmission electron microscopy (TEM) have been used to study the morphologies and crystal structure. The detailed growth mechanism of the YF₃ nanocrystals was researched. Furthermore, under ultraviolet exaltation, the phosphor of YF₃:Eu³⁺ and YF₃:Tb³⁺ shows red and green emission, corresponding to ⁵D₀-⁷F₁ transition of Eu³⁺ and ⁵D₄-⁷F₅ transition of Tb³⁺. The emission spectrum of YF₃:Ce³⁺ phosphor exhibits one dissymmetrical band extending from 350 to 500 nm with a maximum at about 383 nm. A bright fluorescent yellow emission at 574 nm and blue emission at 487 nm were observed in the YF₃:Dy³⁺. These novel nanocrystals could be potentially used in biolabels and light emitting diodes (LEDs).     

Impact of Eu3+ Dopants on Optical Spectroscopy of Ce3+: Y3Al5O12‐Embedded Transparent Glass‐Ceramics

Transparent glass‐ceramics containing Ce³⁺: Y₃Al₅O₁₂ phosphors and Eu³⁺ ions were successfully fabricated by a low‐temperature co‐sintering technique to explore their potential application in white light‐emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X‐ray spectroscopy. The impact of co‐sintering temperature, Ce³⁺: Y₃Al₅O₁₂ crystal content and Eu³⁺ doping content on optical properties of glass‐ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass‐ceramics, where Ce³⁺ ions located in YAG crystalline phase while the Eu³⁺ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce³⁺: 5d→4f transition and red luminescence originating from Eu³⁺: 4f→4f transitions. As a result, the quantum yield of the glass‐ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.     

A comparison study on the substitution of Y3+−Al3+ by M2+−Si4+(M = Ba,Sr, Ca,Mg) in Y3Al5O12: Ce3+ phosphor

Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ (M = Ba, Sr, Ca, Mg) phosphors were successfully prepared through a classic solid-state reaction method. The crystal structures, photoluminescence spectra, quantum yields, and thermal stabilities of the phosphors were investigated in detail. The results indicate that all Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ phosphors maintain the crystal structure of garnets. The emission peaks of Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ (M = Ba, Sr, Ca, Mg) phosphors are located at 537, 538, 554, and 565 nm, respectively. A red-shift trend of emission peak is observed with decreasing M radius, which can be ascribed to the increase in the crystal-field splitting in the Ce³⁺ 5d level owing to the co-doping of M²⁺−Si⁴⁺. Under 460 nm excitation, the luminescence quantum yields and thermal stabilities of the Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ phosphors decreased with the decrease of M radius. The IQE of the Y_1.94BaAl₄SiO₁₂:0.06Ce³⁺ phosphor is 92.89%, and the resistance to thermal quenching is improved to be 93.32% at 150°C. In addition, the color shifts of Y_1.94MAl₄SiO₁₂: 0.06Ce³⁺ phosphors with increasing temperature are all tiny, which also demonstrates good resistance to thermal quenching of luminescence. The linear shrinkage of Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ phosphors is significantly improved compared with that of YAG: Ce³⁺, which is expected to generate Y_1.94MAl₄SiO₁₂:0.06Ce³⁺ transparent/translucent ceramics and fabricate high-powder w-LEDs for high-quality solid-state lighting in the future.     

Synthesis and photoluminescent properties of high-efficient color-tunable Ba3Y2B6O15: Ce3+, Tb3+ phosphors

High-efficient Ce³⁺/Tb³⁺ co-doped Ba₃Y₂B₆O₁₅ phosphors with multi color-emitting were firstly prepared, and their structural and luminescent properties were studied by XRD Rietveld refinement, emission/excitation spectra, fluorescence lifetimes as well as temperature-variable emission spectra. Upon 365?nm excitation, the characteristic blue Ce³⁺ band along with green Tb³⁺ peaks were simultaneously found in the emission spectra. Moreover, by increasing concentration of Tb³⁺, a blue-to-green tunable emitting color could be realized by effective Ce³⁺→Tb³⁺ energy transfer. Furthermore, all Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ phosphors exhibit high internal quantum efficiency of ~?90%, while the temperature-variable emission spectra reveal that the phosphors possess impressive color stability as well as good thermal stability (T₅₀ =?~?120?°C). The results indicate that these efficient color-tuning Ba₃Y₂B₆O₁₅: Ce³⁺, Tb³⁺ might be candidate as converted phosphor for UV-excited light-emitting diodes.     

Effect of codoping Ce3+ on the luminescence properties of Sr9Mg1.5(PO4)7:Eu2+ orange–yellow phosphor

Sr₉Mg_1.5(PO₄)₇:Eu²⁺ has recently been reported as a promising blue light-excited orange–yellow phosphor that can be used in white LED device. Here, Ce³⁺-codoping is found to be an effective strategy to improve the luminescence performance of Sr₉Mg_1.5(PO₄)₇:Eu²⁺ phosphor. The coexistence of Eu²⁺ and Eu³⁺ ions has been verified via photoluminescence spectral analysis. The reduction of Eu³⁺ to Eu²⁺ in Sr₉Mg_1.5(PO₄)₇ lattice cannot be completed in a reducing atmosphere, but can be promoted through codoping with Ce³⁺ ions to a great extent, which finally increase the effective concentration of Eu²⁺ in the crystal lattice. The Eu³⁺−Eu²⁺ reduction mechanism is analyzed using a charge compensation model. This work not only achieves enhanced luminescence of the Sr₉Mg_1.5(PO₄)₇:Eu²⁺ phosphor by codoping with Ce³⁺ ions, but also provides new insights into the design of Ce³⁺/Eu²⁺ codoped luminescent materials.     

Enhanced photoluminescence quantum yield of Ce3+-doped aluminum–silicate glasses for scintillation application

Ce³⁺-doped 20Gd₂O₃–20Al₂O₃–60SiO₂ (GAS:xCe³⁺) glasses (x = 0.3, 0.7, 1.1, 1.5, 1.9 mol%) with Si₃N₄ as a reducing agent were prepared. The density of the glasses is around 4.2 g/cm³. With the increase in the Ce³⁺ concentration, both the photoluminescence (PL) and PL excitation peaks of GAS:xCe³⁺ glasses show a redshift because the 4f–5d energy levels of Ce³⁺ ions are narrowed. PL quantum yield and PL decay time of GAS:xCe³⁺ glasses are 28.32–50.59% and 43–64 ns, respectively. In addition, they both first increases and then decreases with the Ce³⁺ concentration increasing, reached the maximum when x = 1.1 mol%. The integrated X-ray excited luminescence (XEL) intensity of the GAS:1.1Ce³⁺ glass is 23.86% of that of Bi₄Ge₃O₁₂ (BGO) crystal, and the light yield reaches 1200 ph/MeV with an energy resolution of 22.98% at 662 keV when exposed to γ-rays. The PL and XEL thermal activation energies of GAS:xCe³⁺ glasses are independent of Ce³⁺ ions concentration. Scintillating decay time of the glasses exhibits two components consisting of nanosecond and microsecond levels, and the scintillating decay time gradually decreases with the Ce³⁺ concentration increasing. The difference between PL and scintillating decay time is discussed regarding the different luminescent mechanisms.     

MgNb2O6:Dy3+ nanophosphor: A facile preparation,down conversion photoluminescence and UV driven photocatalytic properties

Series of (1–9 mol %) dysprosium (Dy³⁺) ions doped MgNb₂O₆ (MNO) nanophosphors were synthesized by chemical combustion process and their photo luminescent and photocatalytic behaviours were examined. Powder X-ray diffraction (PXRD) reveals the columbite structure and crystal structure parameters were calculated. The average crystallite size was found to be in the range of 20–30 nm as calculated by Scherrer's method. The photoluminescence (PL) of MgNb₂O₆:Dy³⁺ (λ_exc-393 nm) reflects white emission for the prepared samples as confirmed by CIE and CCT. The photocatalytic activities of these nanophosphors were probed for the decolorization of acid red 88 (AR-88) under UV light irradiation. The photocatalyst with MgNb₂O₆:Dy³⁺ (5 mol %) showed enhanced activity of 97%, attributed to effective separation of charge carriers. All the above experimental results confirm that, the optimized phosphor is quite useful for WLEDs, solid-state lighting applications and as a photocatalyst.