Investigation on photoluminescence properties and defect chemistry of GdAlO3:Dy3+ Ba2+ phosphors

GdAlO₃:Dy³⁺ Ba²⁺ phosphors are synthesized by citrate-based sol-gel method. Photoluminescence and positron annihilation studies are used to investigate the emission and defect chemistry of the phosphors respectively. The strong yellow (Dy³⁺) emission properties of phosphors are discussed for various concentrations of Dy³⁺ ions. Upon the addition of Ba²⁺ ion, an enhancement in emission intensity is observed due to the lattice distortions around Dy³⁺ ion. The positron studies indicate the presence of defects at crystallite boundaries, vacancy clusters and large voids in the materials. The influence of Ba²⁺ ion on the photoluminescence and lattice distortion around Dy³⁺ is also explored.     

Color-tunable emission and energy transfer studies in GdOBr:Ce3+ Dy3+ phosphor

Color-tunable blue to bluish white-emitting Ce³⁺/Dy³⁺ co-doped GdOBr phosphors have been synthesized by the conventional solid-state method. The phase structures, luminescent properties and energy transfer process were discussed in detail. Broad-band absorption originating from the f-d transition of Ce³⁺ can be found for the as-prepared GdOBr:Ce³⁺,Dy³⁺ phosphor, and color-tunable blue to bluish white emission can be realized owing to the energy transfer between Ce³⁺ and Dy³⁺. The energy transfer mechanism is demonstrated to be the dipole–dipole process. The energy transfer efficiency increases with increasing Dy³⁺ concentrations. The results indicate that Ce³⁺/Dy³⁺-activated GdOBr phosphors may be potential for phosphor-converted white-light UV-LEDs.     

Porous MAl2O4:Eu (Eu), Dy (M = Sr, Ca, Ba) phosphors prepared by Pechini-type sol-gel method: The effect of solvents

In this work, a series of porous Eu²⁺-doped alkaline earth aluminates phosphors including MAl₂O₄:Eu²⁺ (Eu³⁺), Dy³⁺ (M = Sr, Ca, Ba) have been prepared by Pechini-type sol-gel approach, using citric acid as chelating ligand and ethylene glycol (or H₂O) as solvent. The as-obtained samples were characterized by means of XRPD, FESEM and PL techniques. MAl₂O₄:Eu²⁺, Dy³⁺ (M = Sr, Ca, Ba) phosphors were prepared in a reducing atmosphere (H₂/Ar, 20 + 80%) while MAl₂O₄:Eu³⁺, Dy³⁺ (M = Sr, Ca, Ba) phosphors were obtained in air. Upon changing the molar ratio of citric acid to total metal cations concentration in ethylene glycol can produce spherical phosphors and the higher molar ratio favors the formation of spherical ones. Otherwise, irregular shaped phosphors occur when conducting the reaction in pure H₂O. The irregular shaped phosphors have higher emission intensity than those spherical ones observed with the help of excitation spectra, emission spectra and decay curves.     

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⁺).     

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.     

Controllable white light emission from Dy<Superscript>3+</Superscript>–Eu<Superscript>3+</Superscript> co-doped KCaBO<Subscript>3</Subscript> phosphor

Potassium calcium borate, KCaBO₃:Eu³⁺ phosphors with various Dy³⁺ concentrations (0–3 wt%) were synthesized by solid state reaction and studied for the first time. Under various UV–violet excitations, the obtained single monoclinic phased Dy³⁺–Eu³⁺ co-doped KCaBO₃ polycrystalline phosphors emit a combination of yellow–blue and red–orange wavelength giving intense white light, which can easily be controlled by varying the concentration of Dy³⁺. The increase in white light emission with the increase of Dy³⁺ concentration indicates the efficient energy inter-ion transfer from Dy³⁺ to Eu³⁺ ions. Furthermore, the observed emission lifetimes and the intense white light emission are suggestive exploration for the present phosphor for potential optoelectronic applications such as white light-emitting phosphor for blue LEDs chips.     

Single-component and white light-emitting phosphor BaAl2Si2O8: Dy3+, Eu3+ synthesis,luminescence, energy transfer,and tunable color

A series of Dy³⁺ - Eu³⁺ co-doped BaAl₂Si₂O₈ phosphors were prepared via the conventional solid-state reaction method. Their crystal structure, luminescent characteristic and lifetime were investigated. The optimum doping concentrations of Dy³⁺and Eu³⁺ are both 0.05 for Dy³⁺ or Eu³⁺ singly doped BaAl₂Si₂O₈. Furthermore, BaAl₂Si₂O₈: 0.05Dy³⁺ and BaAl₂Si₂O₈: 0.05Eu³⁺ emits yellow and red light. The emission color of BaAl₂Si₂O₈: Dy³⁺, Eu³⁺ could be tuned from yellow to white due to the energy transfer. This energy transfer from Dy³⁺ to Eu³⁺ was confirmed and investigated by photoluminescence spectra and the decay time of energy donor Dy³⁺ ions. With constantly increasing Eu³⁺ concentration, the energy transfer efficiency from Dy³⁺ to Eu³⁺ in BaAl₂Si₂O₈ host increased gradually and reached as high as 81%, the quantum yield was about 47.43%. BaAl₂Si₂O₈: Dy³⁺, Eu³⁺ phosphors can be effectively excited by UV (about 348 nm) light and emit visible light from yellow to white by altering the concentration ratio of Dy³⁺ and Eu³⁺, indicating that the phosphors have potential applications as a white light-emitting phosphor for display and lighting.     

Luminescence and Optical-Memory model of SrAl2O4:Eu2+,Dy3+ and Sr4Al14O25:Eu2+,Dy3+

The photoluminescence, luminescence excitation, and phosphorescence spectra of SrAl²O⁴:Eu²⁺,Dy³⁺ and Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ powder phosphors have been studied in detail at 80 and 300 K. A conceptual model is proposed for strontium-aluminate-based optical memory.     

Conversion of green emission into white light in Gd2O3 nanophosphors

Gd₂O₃ nanophosphors were prepared by combustion synthesis with and without doping of Dy³⁺ ions. The X-ray powder diffraction patterns indicate that as-prepared Gd₂O₃ and 0.1 mol% Dy₂O₃ doped Gd₂O₃ nanophosphors have monoclinic structures. The transmission electron microscope (TEM) studies revealed that the as-prepared phosphors had an average crystallite sizes around 37 nm. The excitation and emission properties have been investigated for Dy³⁺ doped and undoped Gd₂O₃ nanophosphors. New emission bands were observed in the visible region for Gd₂O₃ nanophosphors without any rare earth ion doping under different excitations. A tentative mechanism for the origin of luminescence from Gd₂O₃ host was discussed. Emission properties also measured for 0.1 mol% Dy³⁺ doped Gd₂O₃ nanophosphors and found the characteristic Dy³⁺ visible emissions at 489 and 580 nm due to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. The chromaticity coordinates were calculated based on the emission spectra of Dy³⁺ doped and undoped Gd₂O₃ nanophosphors and analyzed with Commission Internationale de l'Eclairage (CIE) chromaticity diagram. These nanophosphors exhibit green color in undoped Gd₂O₃ and white color after adding 0.1 mol% Dy₂O₃ to Gd₂O₃ nanophosphors under UV excitation. These phosphors could be a promising phosphor for applications in flat panel displays.     

Synthesis and luminescent properties of Eu3+ and Dy3+ doped BiPO4 phosphors for near UV-based white LEDs

The phosphors BiPO₄:Eu³⁺ co-doped with Dy³⁺ were synthesized by the conventional solid-state reaction method. XRD and scanning electron microscopy results showed that the crystalline phase of the samples BiPO₄:Eu³⁺ transforms from high-temperature monoclinic phase to low-temperature monoclinic phase with the increase of Dy³⁺ concentration. The photoluminescence properties of the samples showed that the colors shifting from red–orange area to blue–green area are close to those of ideal white light by readjusting the doping concentration ratio of Eu³⁺ and Dy³⁺. The Eu³⁺and Dy³⁺ doped BiPO₄ phosphors may be potential applications in white light near-UV light-emitting diodes.     

Photoluminescence properties of MgAl2O4:Dy powder phosphor

Trivalent dysprosium (Dy³⁺) activated magnesium alluminate phosphors were synthesized by high temperature solid state reaction method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting phosphors. The results show that the obtained MgAl₂O₄:Dy³⁺ phosphors have good crystallinity, spherical morphology with sizes ranged from 120 to 140 nm and strong blue emission under an excitation of 258 nm. The emission spectrum of this phosphor consists of two emission bands: blue band and yellow band, and the emission intensity of the former is stronger than that of the later. Luminescence quenching is explained and the corresponding luminescence mechanisms have been proposed.     

Effect of Particle Size on Magnetic and Dielectric Properties of Nanoscale Dy-Doped BiFeO3

In the present report, influence of Dy-substitution and size on the structural, magnetic and dielectric properties of BiFeO₃ nanoparticles has been investigated. The synthesis of pure and Dy-doped BiFeO₃ nanoparticles has been done successfully using sol–gel method. Size of Dy-doped BiFeO₃ nanoparticles was tailored by varying the calcination temperature. Structural analysis reveal that substitution of Dy³⁺ leads to a change in structure from rhombohedral (x=0) to orthorhombic (x=0.15). The average crystallite size varies from 6 to 15 nm. Magnetic study reveals the enhancement in magnetization with the doping of Dy³⁺. Further, this value decreases as the particle size increases. Dielectric property improves with the Dy³⁺ substitution. All the nanoparticles display Debye-type relaxation. The low dielectric loss values observed are attributed to the nanosized grains. Remarkably, enhanced saturation magnetization value (13.8 emu/g) and dielectric constant value (95.8) were observed for Dy-doped BiFeO₃ nanoparticles having the smallest particle size. Thereby, the study indicates strong correlation between size and multiferroism.     

Polyspectral white light emission from Eu3+, Tb3+, Dy3+, Tm3+ co-doped GdAl3(BO3)4 phosphors obtained by combustion synthesis

Polycrystalline sub-micron-sized GdAl₃(BO₃)₄ phosphors co-doped with Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ have been prepared by combustion synthesis with urea. The phosphors have been characterised by X-ray diffraction, scanning electron microscopy, excitation and emission spectroscopy. The chromaticity co-ordinates and the colour temperatures of the fluorescence of the materials presented have been calculated and analysed with Commission Internationale l’Eclairage (CIE) programs and diagrams. Depending on the excitation wavelength, different colour temperatures of the light emitted can be achieved. Due to its polyspectral nature, the emitted light reveals a high colour rendering index.     

Preparation and luminescence properties of yellow long-lasting phosphor Ca2ZnSi2O7:Eu2+, Dy3+

Long-lasting phosphors Ca₂ZnSi₂O₇:Eu²⁺, Dy³⁺ are prepared by solid-state reaction method assisted with different fluxes. Broadband emission, peaked at 580 nm and originating from 4f to 5d transition of Eu²⁺, is observed. The emission intensities of the phosphors can be enhanced by 4.84 and 7.73 times with the introduction of H₃BO₃ and CaF₂, respectively. Moreover, their afterglow times are also respectively prolonged to 11 h and 12 h. The yellow afterglow can be excited by both ultraviolet and visible light, thus permitting its application in both room and outdoor environment. In terms of the crystal structure and trap feature of the phosphors added with different fluxes, the mechanism for the improved luminescence and afterglow properties is discussed.     

Enhanced long persistence of Sr2SnO4:Sm red phosphor by co-doping with Dy

We report the observation of long lasting red phosphorescence in Sr₂SnO₄:Sm³⁺ and Sr₂SnO₄:Sm³⁺, Dy³⁺ phosphors. The decay patterns of afterglow curves demonstrate that the afterglow time of Sr₂SnO₄:Sm³⁺ could be prolonged by the incorporation of Dy³⁺. The remarkable changes in the thermoluminescence glow curve exhibited that the first band responsible for the origin of the afterglow becomes the most prominent feature when Dy³⁺ added. In other words, the enhancement of the red afterglow in Sr₂SnO₄:Sm³⁺, Dy³⁺ compared with Sr₂SnO₄:Sm³⁺ could be ascribed to more appropriate traps (the hole-traps V^″Sr) created by the incorporation of Dy³⁺.     

Synthesis and characterizations of Dy3+ doped Sr3Al2O6:Eu2+ powder phosphors through citric acid precursor

Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors were synthesized by the polymer precursor method. The X-ray powder diffraction patterns show that the samples have a cubic structure with a space group of Pa3. In the excitation spectrum, the phosphors show a wide absorption in the UV region from 250 to 450 nm, which corresponds to the crystal field splitting of the Eu²⁺ d-orbital. All the emission spectrum of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors show the broad band emission peaked at about 518 nm, which can be ascribed to the typical 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺ ions. And the best dopant concentration of Dy³⁺ ions for Sr₃Al₂O₆:2 mol%Eu²⁺, xDy³⁺ phosphors is 2 mol%. The excitation wavelengths have no influences on emission peaks, but have clear influences on emission intensities.     

Luminescent characteristics of LiSrBO3:M (M = Eu, Sm, Tb, Ce, Dy) phosphor for white light-emitting diode

LiSrBO₃:M (M = Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors which have been developed for white light-emitting diodes (LEDs) were synthesized by a normal solid-state reaction. The emission and excitation spectra indicate that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (UVLED), and exhibit satisfactory red, green and blue performances, respectively, nicely fitting in with the widely applied UV chip. Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Luminescence properties of Na3SrB5O10:Dy3+ plate-like microstructures for solid state lighting applications

A series of novel plate-like microstructure Na₃SrB₅O₁₀ doped with various Dy³⁺ ions concentration have been synthesized for the first time by solid-state reaction (SSR) method. X-ray diffraction (XRD) results demonstrated that the prepared Na₃SrB₅O₁₀:Dy³⁺ phosphors are single-phase pentaborates with triclinic structure. The plate-like morphology of the phosphor is examined by Field emission scanning electron microscopy (FE-SEM). The existence of both BO₃ and BO₄ groups in Na₃SrB₅O₁₀:Dy³⁺ phosphors are identified by Fourier transform infrared (FT-IR) spectroscopy. Upon excitation at 385 nm, the PL spectra mainly comprising of two broad bands: one is a blue light emission (∼486 nm) and another is a yellow light emission (∼581 nm), originating from the transitions of ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 in 4f⁹ configuration of Dy³⁺ ions, respectively and the optimized dopant concentration is determined to be 3 at.%. Interestingly, the yellow-to-blue (Y/B) emission integrated intensity ratio is close to unity (0.99) for 3 at.% Dy³⁺ ions, suggesting that the phosphors are favor for white illumination. Moreover, the calculated Commission International de l’Eclairage (CIE) chromaticity coordinates of Na₃SrB₅O₁₀:Dy³⁺ phosphors shows the values lie in white light region and the estimated CCT values are located in cool/day white light region.     

Photoluminescence of nanocrystalline YVO4:TmxDy1−x prepared by a modified Pechini method

This paper reports the luminescence effects of Tm³⁺ doped YVO₄:Dy nanocrystalline synthesized by a modified Pechini method. The structure and morphology were characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The relationship between the ratio of Tm³⁺/Dy³⁺ and the chromaticity is studied, i.e. Tm³⁺ ion doping effectively tunes the emission color of YVO₄:Tm_xDy_1−x phosphors. The best white light emission was observed with YVO₄:1%(Tm_0.6Dy_0.4). These results indicate that thulium doped YVO₄:Dy phosphors are promising white-emitting luminescence materials.     

Hydrothermal synthesis and multi-color photoluminescence of GdVO<Subscript>4</Subscript>: Ln<Superscript>3+</Superscript> (Ln = Sm,Dy, Er) sub-micrometer phosphors

GdVO₄: 5 mol% Ln³⁺ (Ln = Sm, Dy, Er) sub-micrometer phosphors have been synthesized by a facile hydrothermal technology and characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), and FT-IR spectroscopy. These phosphors present fusiform-like polyhedron microcrystals with tetragonal zircon structure and average particle size of about 300 nm. The luminescent properties of the three lanthanide ions activated GdVO₄ submicrometer phosphors are studied, which show the characteristic multicolor luminescence of Sm³⁺ (orange), Dy³⁺ (light yellow) and Er³⁺ (green) ions in visible region.