Luminescence of BaSiO<Subscript>3</Subscript> crystals doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript>

The Stokes and anti-Stokes luminescence of undoped and rare-earth-doped (Er³⁺ and Yb³⁺) BaSiO₃ has been studied in the temperature range 78–450 K under excitation at 10–1000 mV. The results indicate that the emission mechanism in BaSiO₃ crystals is hole recombination and that the anti-Stokes luminescence is due to consecutive sensitization; that is, the Yb³⁺ ions in the BaSiO₃ compound act as luminescence sensitizers, and the Er³⁺ ions, as activators.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

The comparison: photoluminescence and afterglow behavior in CaSnO<Subscript>3</Subscript>:Dy<Superscript>3+</Superscript> and Ca<Subscript>2</Subscript>SnO<Subscript>4</Subscript>:Dy<Superscript>3+</Superscript> phosphors

This paper reports the comparison of photoluminescence and afterglow behavior of Dy³⁺ in CaSnO₃ and Ca₂SnO₄ phosphors. The samples containing CaSnO₃ and Ca₂SnO₄ were prepared via solid-state reaction. The properties have been characterized and analyzed by utilizing X-ray diffraction (XRD), photoluminescence spectroscope (PLS), X-ray photoelectron spectroscopy (XPS), afterglow spectroscopy (AS) and thermal luminescence spectroscope (TLS). The emission spectra revealed that CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors showed different photoluminescence. The Ca₂SnO₄:Dy³⁺ phosphor showed a typical ⁴F_9/2 to ⁶H_j energy transition of Dy³⁺ ions, with three significant emissions centering around 482, 572 and 670 nm. However, the CaSnO₃:Dy³⁺ phosphor revealed a broad T₁ → S₀ transitions of Sn²⁺ ions. The XPS demonstrate the existence of Sn²⁺ ions in CaSnO₃ phosphor caused by the doping of Dy³⁺ ions. Both the CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors showed a typical triple-exponential afterglow when the UV source switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO₃:Dy³⁺ and Ca₂SnO₄:Dy³⁺ phosphors was generated by the suitable electron or hole traps which were resulted from the doping the calcium stannate host with rare-earth ions (Dy³⁺).     

Electrical Conductivity of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> Crystals Doped with Ca<Superscript>2+</Superscript>, Pb<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, and Ba<Superscript>2+</Superscript>

Single crystals of Bi₂WO₆ (a layered perovskite-like compound) doped with Ca²⁺, Pb²⁺, Sr²⁺, and Ba²⁺ on the Bi³⁺ site are grown, and their oxygen ionic conductivity is measured along the polar axis. The intrinsic conductivity of the doped crystals differs insignificantly from the conductivity of undoped Bi₂WO₆, indicating that the oxygen ions in the Bi₂O₂ layers contribute little to the oxygen ionic conductivity of the crystals. The sharp change in the activation energy for conduction at 600°C attests to a transition from one conduction mechanism to another in going from low to high temperatures.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 863–865.Original Russian Text Copyright © 2005 by Kharitonova, Voronkova, Yanovskii.     

The influence of activation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> polycrystalline matrices by Bi<Superscript>3+</Superscript> ions on the luminescence of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

The influence of activation of the Y₂O₃ matrix of the Y₂O₃:Eu³⁺ phosphor by Bi³⁺ ions on the luminescence of Eu³⁺ and Bi³⁺ ions in it and on conditions of the excitation energy transfer to luminescence centers is studied. It is shown that the presence of Bi³⁺ ions leads to the appearance of recombination luminescence with participation of bismuth ions at low concentrations (up to 6–8 at %) of the dominant activator europium and to an increase in the threshold of intrinsic concentration quenching of its luminescence.     

Pulsed cathodoluminescence of single-crystalline and pressed CaF<Subscript>2</Subscript>:Yb<Superscript>2+</Superscript>,Yb<Superscript>3+</Superscript>

We have studied the pulsed cathodoluminescence spectra and kinetics of CaF₂:Yb²⁺,Yb³⁺ (3 mol % YbF₃) single crystals and pressed samples under excitation with nanosecond electron pulses and determined the characteristic times and intensities of nanosecond and microsecond emission decay components at temperatures from 15 to 300 K. The results demonstrate that deformation pressing in vacuum at 1150°C followed by annealing in a CF₄ atmosphere at 1180°C has an insignificant effect on the emissive properties of CaF₂:Yb²⁺,Yb³⁺.     

Electron traps in Gd<Subscript>3</Subscript>Ga<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>12</Subscript>:Ce garnets doped with rare-earth ions

The curves of thermally stimulated luminescence of Gd₃Ga₃Al₂O₁₂:Ce³⁺ ceramics (a nominally pure sample and samples doped with rare-earth ions) are measured in the temperature range of 80–550 K. The depth and the frequency factor of electron traps established by Eu and Yb impurities are determined. An energy-level diagram of rare-earth ions in the bandgap of Gd₃Ga₃Al₂O₁₂ is presented.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, RE<Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and RE³⁺ co-doped strontium aluminates SrAl₂O₄:Eu²⁺, RE³⁺ were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence of the SrAl₂O₄:Eu²⁺, RE³⁺ phosphors with different composition and doping ions were studied and compared. The results showed that the doped Eu²⁺ ion in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy³⁺ ion can hardly yield any luminescence under UV-excitation, but can form a electron trap with appropriate depth and greatly enhance the persistent luminescence and thermo-luminescence of SrAl₂O₄:Eu²⁺. Different co-doping RE³⁺ ions showed different effects on persistent luminescence. Only the RE³⁺ ion (e.g. Dy³⁺, Nd³⁺), which has a suitable optical electro-negativity, can form the appropriate electron trap and greatly improve the persistent luminescence of SrAl₂O₄:Eu²⁺. Based on above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.     

Synthesis and luminescence properties of a novel Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> co-doped Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> whiskers by a gel nano-coating method

Al₁₈B₄O₃₃:Eu³⁺, Tb³⁺ whiskers have been successfully prepared by a simple gel nano-coating method using aluminum isopropoxide as the starting materials. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL), and thermogravimetric analysis (TGA) were used characterize the samples. The results show coexistence of the crystal phase Al₁₈B₄O₃₃, amorphous phase, and Eu³⁺, Tb³⁺ ions of the samples with initial addition Al/B ratios from 3 to 1 are incorporated into the amorphous phase. The Al₁₈B₄O₃₃:Eu³⁺, Tb³⁺ whiskers are very straight with an average diameter of 600 nm and lengths ranging from 5 to 10 μm. Under ultraviolet excitation at 365 nm, samples show mainly exhibit the characteristic emission of Eu³⁺ corresponding to \( ^{ 5} {\text{D}}_{ 0} \to {\text{F}}_{ 1 , 2} \) transitions due to an efficient energy transfer occurs from Tb³⁺ to Eu³⁺.     

Upconversion Luminescence of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocrystals Doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> Ions

The upconversion luminescence (UCL) of nanocrystalline gadolinium oxide (Gd₂O₃) doped with Er³⁺ and Yb³⁺ ions has been studied in the temperature range of 90–400 K. The nanocrystals were synthesized by chemical vapor deposition and possessed a cubic crystalline structure with an average particle size within 48–57 nm. It is established that the USL intensity in the red (⁴F_9/2 → ⁴I_15/2 transition in Er3+ ion) and green (⁴S_3/2 → ⁴I_15/2 transition) spectral regions depends on the sample temperature and concentration of dopant ions, as well as on the additional structural defects (anion vacancies) created in the crystal lattice by the introduction of Zn²⁺ ions or irradiation with high-energy (10 MeV) electrons. The luminescence efficiency and spectrum of the upconversion phosphor are determined by energy transfer processes.     

X-ray diffraction,optical absorption and emission studies on Er<Superscript>3+</Superscript>- and Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped Li<Subscript>3</Subscript>NbO<Subscript>4</Subscript> powder

Er³⁺(/Yb³⁺)-doped Li₃NbO₄ powder were prepared by thermally sintering mixtures of Er₂O₃ (0.5, 1.0 mol%), Yb₂O₃ (0, 0.5, 1.0 mol%), Li₂CO₃ (48–49 mol%) and Nb₂O₅ (50 mol%) at 1125, 1150 and 1450 °C over the durations of 8–22 h. The crystalline phases contained in these samples were determined by using X-ray diffraction and discussed in comparison with a vapor-transport-equilibration-treated (VTE-treated) Er(2.0 mol%):LiNbO₃ single crystal and ErNbO₄ powder previously reported. The results show that the X-ray patterns of the rare-earth-doped samples reveal little difference each other, but large differences with those of the VTE crystal and ErNbO₄ powder. The doped rare-earth ions Er³⁺ (and Yb³⁺) present in the powder as the ErNbO₄ (and YbNbO₄) phase(s). The possibility that the highly Er-doped LiNbO₃ crystal contains Li₃NbO₄ precipitates is small. Optical absorption and emission studies show that the only Er-doped Li₃NbO₄ powder shows similar absorption and emission characteristics with the pure ErNbO₄. The codopant Yb³⁺ ion enhances the 980-nm-upconversion emissions of Er³⁺ ions, results in remarkable spectral alterations at 0.98 μm region, and causes the alterations of relative absorbance and relative emission intensity of individual peaks or bands at 1.5 μm region. On the other hand, the Yb-codoping hardly affects the Er³⁺ energy structure and the lifetime of Er³⁺ ion at 1.5 μm. The measured lifetimes at 1.5 μm of Er³⁺ ions in the singly Er³⁺- and doubly Er³⁺/Yb³⁺-doped mixtures have a nearly same value of ∼ 1.5 ms. For the pure ErNbO₄ powder, the lifetime is prolonged to ∼2 ms perhaps due to radiation trapping effect.     

Large enhancement of upconversion luminescence in Er<Superscript>3+</Superscript>/In<Superscript>3+</Superscript>:Ba<Subscript>0.85</Subscript>Ca<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript> lead-free piezoelectric ceramics

A series of In³⁺-doped Ba_0.85Ca_0.15TiO₃:0.75%Er³⁺/xIn³⁺ (BCT:Er/xIn) lead-free piezoelectric ceramics with excellent upconversion luminescence were synthesized by the solid state reaction method. The effects of In³⁺ content on the crystal structure, ferroelectric, dielectric, piezoelectric, and upconversion luminescence properties were systematically studied. Under 980 nm excitation, a giant enhancement of the green emission (550 nm) by 10 times is achieved upon 2.5% mol In³⁺ doping, which is rarely observed in rare-earth ions-doped perovskite ferroelectric materials. The ultraviolet-visible-near infrared absorption measurements show that the In³⁺ doping may improve the dissolution of Er³⁺ ions and modify the isolate-/clustered-Er³⁺ ratio for x?≤?2.5%, resulting in the enhancement of the absorption cross-section, thereby contributing to the enhancement of green luminescence. Unfortunately, the In³⁺ doping suppresses the ferroelectric and piezoelectric properties of the BCT:Er/xIn ceramics. This problem can be resolved by adding a small amount (1 mol%) of Yb³⁺ to the BCT:Er/xIn ceramics to restore their good ferroelectric and piezoelectric properties. Such In³⁺ and rare-earth ions co-doped ceramics with greatly enhanced upconversion luminescence and good ferroelectricity and piezoelectricity may have potential applications in electro-optical devices.     

Tunable luminescence and energy transfer properties in YVO<Subscript>4</Subscript>:Bi<Superscript>3+</Superscript>,Ln<Superscript>3+</Superscript> (Ln = Dy,Sm, Eu) phosphors prepared by microwave sintering method

YVO₄:Bi³⁺,Ln³⁺ (Ln?=?Dy, Sm, Eu) phosphors were successful synthesized by microwave sintering method, and characterized by X-ray powder diffraction, scanning electron microscope, photoluminescence spectra, lifetime, quantum efficiency and general structure analysis system structure refinement. Refinement results indicated that the introduced ions occupy the sites of Y³⁺. Under 275 nm excitation, the luminescent intensity of YVO₄:Bi³⁺ samples reach the maximum when Bi³⁺ concentration is 0.02, the broad excitation spectrum of YVO₄:Bi³⁺ has a strongest peak at near 343 nm. Doped Bi³⁺ can effectively improve the emission intensity of YVO₄:Ln³⁺. The energy transfer mechanism of Bi³⁺?→?Ln³⁺ was dipole-quadrupole mechanism of electric multipole interaction. The critical distance (R_c) between Ln³⁺ and Bi³⁺ were calculated by concentration quenching method. Emitting color of YVO₄:Bi³⁺,Ln³⁺ phosphors were tunable by adjusting Ln³⁺ content. In a word, the material has a good application prospects on light emitting diodes.     

X-ray Diffraction Study of the Structure and Defect System of Nominally Pure and Er<Superscript>3+</Superscript>- and Ce<Superscript>3+</Superscript>-Activated (Na<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>)MoO<Subscript>4</Subscript> Crystals

Nominally pure and activated (Er³⁺ and Er³⁺ + Ce³⁺) sodium lanthanum molybdate single crystals grown by the Czochralski technique from the (Na_0.5La_0.5)MoO₄ melt in different environments and then oxidized in air at 100°C are characterized in detail by x-ray diffraction (lattice parameters and structure refinement by the Rietveld method and single-crystal techniques). The results confirm that (Na_0.5La_0.5)MoO₄ crystallizes in a tetragonal scheelite structure (sp. gr. I₁/a). The crystals (especially unannealed crystals grown in neutral atmosphere) are shown to contain oxygen vacancies. In addition, some of the samples contain Mo vacancies. The Er³⁺ distribution over some of the activated crystals is highly inhomogeneous. As a result, the crystals contain Er-enriched zones with a distorted scheelite structure.     

Synthesis and luminescence properties of a novel UV-emitting phosphor Sr<Subscript>3</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>:Ce<Superscript>3+</Superscript>

The ultraviolet (UV)-emitting Sr₃P₄O₁₃:Ce³⁺ phosphors were synthesized via the solid-state reaction method, and their structural, morphological and luminescence properties were characterized by X-ray diffraction analysis, scanning electron microscopy, photoluminescence spectroscopy. The obtained results indicate that these phosphors can be effectively excited by short-wavelength ultraviolet (<300 nm), and exhibit long-wavelength ultraviolet (300–380 nm) emission with nanosecond-level fluorescence lifetime corresponding to the parity-allowed 5d–4f transitions of Ce³⁺. The concentration-quenching phenomenon of Ce³⁺ in Sr₃P₄O₁₃ host was also studied, in which the critical energy transfer distance between Ce³⁺ ions and concentration quenching mechanism were determined.     

Synthesis and photoluminescence study of narrow-band UVB-emitting LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Gd<Superscript>3+</Superscript>, Pr<Superscript>3+</Superscript> phosphor

A series of Pr³⁺, Gd³⁺ and Pr³⁺–Gd³⁺-doped inorganic borate phosphors LiSr₄(BO₃)₃ were successfully synthesized by a modified solid-state diffusion method. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. Surface morphology of the sample was studied by scanning electronic microscopy (SEM). The optimal concentrations of dopant Gd³⁺ ions in compound LiSr₄(BO₃)₃ were determined through the measurements of photoluminescence (PL) spectra of phosphors. Gd³⁺-doped phosphors LiSr₄(BO₃)₃ show strong band absorption in UV spectral region and narrow-band UVB emission under the excitation of 276 nm was only due to ⁶P _J → ⁸S_7/2 transition of Gd³⁺ ions. The effect of Pr³⁺ ion on excitation of LiSr₄(BO₃)₃:Gd³⁺ was also studied. The excitation of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ gives a broad-band spectra, which show very good overlap with the Hg 253.7 nm line. The photoluminescence spectra of LiSr₄(BO₃)₃ with different doping concentrations Pr³⁺ and keeping the concentration of Gd³⁺ constant at 0.03 mol have also been studied. The emission intensity of LiSr₄(BO₃)₃:Pr³⁺–Gd³⁺ phosphors increases with increasing Pr³⁺ doping concentration and reaches a maximum at 0.01 mol. From the photoluminescence study of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ we conclude that there was efficient energy transfer from Pr³⁺→ Gd³⁺ ions in LiSr_4?x?y Pr _x Gd _y (BO₃)₃ phosphors.     

Color-tunable luminescence properties of Sm<Superscript>3+</Superscript>/Dy<Superscript>3+</Superscript> co-doped NaLa(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> phosphors and their energy transfer mechanism

The Sm³⁺, Dy³⁺ doped and Sm³⁺/Dy³⁺ co-doped NaLa(MoO₄)₂ spherical phosphors were hydrothermally synthesized by the EDTA-2Na mediated method. Under the excitation of 297 nm, the quenching concentration of Sm³⁺ in NaLa(MoO₄)₂ host was determined to be 13%, and the concentration quenching mechanism was discussed to be the electric quadrupole–quadrupole interaction. After Sm³⁺ and Dy³⁺ ions were co-doped into the NaLa(MoO₄)₂ host, the energy transfer behaviors resulted from Dy³⁺ to Sm³⁺ ions were investigated by the help of the luminescent spectra of the obtained phosphors. By varying co-doping concentrations of Sm³⁺/Dy³⁺ ions, the emission color of NaLa(MoO₄)₂:Sm³⁺/Dy³⁺ can be tuned from reddish-orange, pink and white to bluish-green. The CIE chromaticity coordinate, the correlated color temperature and the quantum efficiency of NaLa_0.87(MoO₄)₂:1%Sm³⁺, 12%Dy³⁺ were calculated to be (0.356, 0.320), 4353 K and 20%, respectively. Furthermore, in the temperature-dependent analysis, it presented good thermal stability, which can become a promising single-phased white-emitting phosphor for white LEDs devices. Based on these results, the possible energy transfer mechanism between Dy³⁺ and Sm³⁺ in NaLa(MoO₄)₂:Sm³⁺/Dy³⁺ was also proposed.     

Preparation and characterization of a new long afterglow phosphor CaSnO<Subscript>3</Subscript>: Yb<Superscript>3+</Superscript>

A new phosphor CaSnO₃: Yb³⁺ was synthesized by a traditional solid-state reaction and the luminescent properties were investigated. The phosphors are well crystallized at 1200?°C. The excitation and the emission spectra show the characteristic broad of the Sn²⁺ ion and the X-ray photoelectron spectroscopy demonstrate the existence of Sn²⁺ ions caused by the doping of Yb³⁺ ions. The CaSnO₃: Yb³⁺ phosphor showed a typical afterglow behavior when the UV source was switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO₃: Yb³⁺ phosphor was generated by the suitable electron or hole traps which were resulted from doping the calcium stannate host with rare-earth ions (Yb³⁺).     

Color tunable luminescence from LaAlO<Subscript>3</Subscript>:Bi<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript> doped phosphors for field emission displays

Bi³⁺-activated LaAlO₃:Ho³⁺ Phosphor, was prepared by Polyol method, and its photoluminescent properties were investigated under (UV) light excitation. Luminescence studies indicated that optimum concentration of Bi³⁺ and Ho³⁺ in LaAlO₃ was found to be 1 and 1.5 at.%. The luminescent intensity of Ho³⁺ emission lines was remarkably enhanced on exciting with 272 nm, which suggested that efficient energy transfer from Bi³⁺ ions to Ho³⁺ ions takes place. There is significant energy overlap between the emission band of Bi³⁺ ions and the excitation band of Ho³⁺ ions.The ET efficiency has been calculated and found to be 69%. The critical ET distance has been calculated by the concentration–quenching method. The enhanced intensity and tuned luminous color of LaAlO₃: Bi³⁺/Ho³⁺ phosphors from blue to cyan provides a promising material for field emission display devices.     

Luminescent properties of Pb<Superscript>2+</Superscript>- and Mn<Superscript>2+</Superscript>-activated CdI<Subscript>2</Subscript> crystals

The luminescent properties of CdI₂, CdI₂:Pb²⁺, CdI₂:Mn²⁺, and CdI₂:Pb²⁺,Mn²⁺) crystals have been studied at temperatures from 85 to 295 K under optical and x-ray excitation. Analysis of new and earlier spectroscopic data suggests that the 560-nm luminescence of CdI₂:Pb²⁺ and CdI₂:(Pb²⁺,Mn²⁺) crystals under excitation on the long-wavelength component of the A absorption band of Pb²⁺ centers is due to Pb²⁺-bound anion excitons. The 640-to 660-nm emission of these crystals is attributable to α centers. The manganese luminescence in the codoped material originates from both intracenter Mn²⁺ excitations and a sensitized process due to energy transfer from the host and Pb²⁺-related centers. The mechanisms of recombination and energy transfer processes in cadmium iodide crystals codoped with Pb²⁺ and Mn²⁺ are discussed.