Microwave Sol–Gel Synthesis of CaGd2(MoO4)4:Er3+/Yb3+ Phosphors and Their Upconversion Photoluminescence Properties

CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ phosphors with the doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2, and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by the microwave sol–gel method, and the crystal structure refinement and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after heat‐treatment at 900°C for 16 h, showed a well‐crystallized morphology. Under the excitation at 980 nm, CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited strong 525 and 550‐nm emission bands in the green region and a weak 655‐nm emission band in the red region. The Raman spectrum of undoped CaGd₂(MoO₄)₄ revealed about 15 narrow lines. The strongest band observed at 903 cm^?1 was assigned to the ν₁ symmetric stretching vibration of MoO₄ tetrahedrons. The spectra of the samples doped with Er and Yb obtained under 514.5 nm excitation were dominated by Er³⁺ luminescence preventing the recording Raman spectra of these samples. Concentration quenching of the erbium luminescence at ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions in the CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ crystal structure was established to be approximately at the 10 at.% doping level.     

Intense upconversion luminescence and energy‐transfer mechanism of Ho3+/Yb3+ co‐doped SrLu2O4 phosphor

A series of novel SrLu₂O₄: x Ho³⁺, y Yb³⁺ phosphors (x=0.005‐0.05, y=0.1‐0.6) were synthesized by a simple solid‐state reaction method. The phase purity, morphology, and upconversion luminescence were measured by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The doping concentrations and sintering temperature were optimized to be x=0.01, y=0.5 and T=1400°C to obtain the strongest emission intensity. Under 980 nm laser diode excitation, the SrLu₂O₄:Ho³⁺, Yb³⁺ phosphors exhibit intense green upconversion (UC) emission band centered at 541 nm (⁵F₄,⁵S₂→⁵I₈) and weak red emission peaked at 673 nm (⁵F₅→⁵I₈). Under different pump‐power excitation, the UC luminescence can be finely tuned from yellow‐green to green light region to some extent. Based on energy level diagram, the energy‐transfer mechanisms are investigated in detail according to the analysis of pump‐power dependence and luminescence decay curves. The energy‐transfer mechanisms for green and red UC emissions can be determined to be two‐photon absorption processes. Compared with commercial NaYF₄:Er³⁺, Yb³⁺ and common Y₂O₃:Ho³⁺, Yb³⁺ phosphors, the SrLu_1.49Ho_0.01Yb_0.5O₄ sample shows good color monochromaticity and relatively high UC luminescence intensity. The results imply that SrLu₂O₄:Ho³⁺, Yb³⁺ can be a good candidate for green UC material in display fields.     

Synthesis,structural characterization,and photoluminescence properties of Eu3+‐doped Mg3‐xEux(BO3)2 phosphor

Eu³⁺‐doped Mg_3‐xEu_x(BO₃)₂ (x = 0.000, 0.005, 0.010, 0.020, 0.050, and 0.100) phosphors were synthesized for the first time by solution combustion synthesis method, which is a fast synthesis method for obtaining nano‐sized borate powders. The optimization of the synthesis conditions of phosphor materials was performed by TG/DTA method. These phosphors were characterized by XRD, FTIR, SEM‐EDX, and photoluminescence, PL analysis. The XRD analysis exhibited that all of the prepared ceramic compounds have been crystallized in orthorhombic structure with space group Pnnm. Also, the influence of europium dopant ions on unit cell parameters of host material was analyzed using Jana2006 program and the crystalline size was determined by Debye‐Scherrer's formula. The luminescence properties of all Eu³⁺‐doped samples were investigated by excitation and emission spectra. The excitation spectra of Mg_3‐xEu_x(BO₃)₂ phosphors show characteristic peak at 420 nm in addition to other characteristic peaks of Eu³⁺ under emission at 613 nm. The emission spectra of Eu³⁺‐doped samples indicated most intensive red emission band dominated at 630 nm belonging to ⁵D₀→⁷F₂ magnetic dipole transition. Furthermore, the optimum or quenching concentration of Eu³⁺ ion has been determined as x = 0.010 showed the maximum emission intensity when it was excited at 394 nm.     

Tailorable Multicolor Up‐conversion Emissions in Tm3+/Ho3+/Yb3+ Co‐Doped LiLa(MoO4)2

Using a modified sol–gel method, LiLa(MoO₄)₂: Tm³⁺/Ho³⁺/Yb³⁺ phosphors with tailorable up‐conversion (UC) emission colors were prepared. Under the excitation of a 980 nm laser diode, up‐conversion red and green emissions in Ho³⁺/Yb³⁺ co‐doped and blue emission in Tm³⁺/Yb³⁺ co‐doped LiLa(MoO₄)₂ were observed, respectively. The intensities of the RGB (red, green, and blue) emissions could be controlled by varying concentrations of Tm³⁺ or Ho³⁺, and the optimal composition was also determined. In Tm³⁺/Ho³⁺/Yb³⁺ co‐doped LiLa(MoO₄)₂, the UC emission colors could be tuned from blue through white to yellow by adjusting the concentrations of Tm³⁺ or Ho³⁺. The UC excitation mechanisms were also investigated based on the power dependence of UC luminescence intensity.     

Upconversion Luminescence and Energy‐Transfer Mechanism of NaGd(MoO4)2: Yb3+/Er3+ Microcrystals

Uniform and well‐crystallized NaGd(MoO₄)₂: Yb³⁺/Er^{3 +} microcrystals with tetragonal plate morphology were synthesized by a facile hydrothermal method. The structure and phase purity of the samples were identified by powder XRD analysis. The steady‐state and transient luminescence spectra were measured and analyzed. Under 980 nm excitation, intense green luminescence at 531 and 553 nm, and red luminescence at 657 and 670 nm were observed. The optimum doping concentrations for Yb³⁺ and Er³⁺ are determined to be 20% and 1% in NaGd(MoO₄)₂ tetragonal plate microcrystals. With increasing Yb³⁺ doping concentrations, the total integral emission intensities increase first and then decrease. The red/green intensity ratio of NaGd(MoO₄)₂: Yb³⁺/Er³⁺ microcrystals increases from 0.4 to 1.0 with the increase in Yb³⁺ concentrations. Based on the energy level diagram, the energy‐transfer mechanisms are investigated in detail according to the double logarithmic plot of upconversion intensities versus pump powers. The energy‐transfer mechanisms for green and red upconversion luminescence are ascribed to two‐photon processes at lower Yb³⁺ concentrations, and involve high‐Yb³⁺‐induced one‐photon processes at higher Yb³⁺ concentrations. For the red upconversion luminescence, energy back‐transfer process, that is, ⁴S_3/2 (Er³⁺) + ²F_7/2 (Yb³⁺) → ⁴I_13/2 (Er³⁺) + ²F_5/2 (Yb³⁺), is dominant at higher Yb³⁺ concentrations. Theoretical model of the energy‐transfer mechanisms based on rate equations is established, which agrees well with the experimental results.     

Pr3+/Yb3+:PLZT ferroelectric ceramics for near‐infrared radiation at 1340 nm

The near‐infrared luminescence properties of Pr³⁺/Yb³⁺:PLZT ferroelectric ceramics have been examined for the first time. Independently, upon either 450 nm (Pr³⁺) or 980 nm (Yb³⁺) excitation, luminescence centered at 1340 nm was observed, which corresponds to the ¹G₄→³H₅ transition of Pr³⁺. Several spectroscopic parameters for the ¹G₄→³H₅ transition of Pr³⁺ ions were determined. The average product of emission cross section and radiative lifetime were relatively large for all x/65/35 PLZT samples (x=6‐10) studied, with values close to 105±2 (×10^?26 cm²·s). These spectroscopic investigations indicate that Pr³⁺/Yb³⁺:PLZT ferroelectric ceramics are promising candidate for efficient sources emitting near‐infrared radiation at 1340 nm.     

Synthesis and photoluminescence properties of CaGd2(MoO4)4:Eu3+ red phosphors

The novel red-emitting Eu³⁺ ions activated CaGd₂(MoO₄)₄ phosphors were prepared by a citrate sol–gel method. The X-ray diffraction patterns confirmed their tetragonal structure when the samples were annealed above 600 °C. The photoluminescence excitation spectra of CaGd₂(MoO₄)₄:Eu³⁺ phosphors exhibited the charge transfer band (CTB) and intense f–f transitions of Eu³⁺ ion. The optimized annealing temperature and Eu³⁺ ion concentration were analyzed for CaGd₂(MoO₄)₄:Eu³⁺ phosphors based on the dominant red (⁵D₀→⁷F₂) emission intensity under NUV (394 nm) excitation. All decay curves were well fitted by the single exponential function. These luminescent powders are expected to find potential applications such as WLEDs and optical display systems.     

Synthesis and luminescence properties of single‐component Ca5(PO4)3F:Dy3+, Eu3+ white‐emitting phosphors

A series of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors was synthesized by a solid‐state reaction method. The XRD results show that all as‐prepared Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ samples match well with the standard Ca₅(PO₄)₃F structure and the doped Dy³⁺ and Eu³⁺ ions have no effect on the crystal structure. Under near‐ultraviolet excitation, Dy³⁺ doped Ca₅(PO₄)₃F phosphor shows blue (486 nm) and yellow (579 nm) emissions, which correspond to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions respectively. Eu³⁺ co‐doped Ca₅(PO₄)₃F:Dy³⁺ phosphor shows the additional red emission of Eu³⁺ at 631 nm, and an improved color rendering index. The chromaticity coordinates of Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors also indicate the excellent warm white emission characteristics and low correlated color temperature. Overall, these results suggest that the Ca₅(PO₄)₃F:Dy³⁺, Eu³⁺ phosphors have potential applications in warm white light‐emitting diodes as single‐component phosphor.     

Fabrication and Characterization of Transparent (Y0.98−xTb0.02Eux)2O3 Ceramics with Color‐Tailorable Emission

Transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ (x = 0–0.04) ceramics with color‐tailorable emission have been successfully fabricated by vacuum sintering at the relatively low temperature of 1700°C for 4 h. These ceramics have the in‐line transmittances of ~73%–76% at 613 nm, the wavelength of Eu³⁺ emission (the ⁵D₀→⁷F₂ transition). Thermodynamic calculation indicates that the Tb⁴⁺ ions in the starting oxide powder can essentially be reduced to Tb³⁺ under ~10^?3 Pa (the pressure for vacuum sintering) when the temperature is above ~394°C. The photoluminescence excitation (PLE) spectra of the transparent (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics exhibit one spin‐forbidden (high‐spin, HS) band at ~323 nm and two spin‐allowed (low‐spin, LS) bands at ~303 and 281 nm. Improved emissions were observed for both Eu³⁺ and Tb³⁺ by varying the excitation wavelength from 270 to 323 nm, without notably changing the color coordinates of the whole emission. The transparent (Y_0.98Tb_0.02)₂O₃ ceramic exhibits the typical green emission of Tb³⁺ at 544 nm (the ⁵D₄→⁷F₅ transition). With increasing Eu³⁺ incorporation, the emission color of the (Y_0.98?xTb_0.02Eu_x)₂O₃ ceramics can be precisely tailored from yellowish‐green to reddish‐orange via the effective energy transfer from Tb³⁺ to Eu³⁺ under the excitation with the peak wavelength of the HS band. At the maximum Eu³⁺ emission intensity (x = 0.02), the ceramic shows a high energy‐transfer efficiency of ~85.3%. The fluorescence lifetimes of both the 544 nm Tb³⁺ and 613 nm Eu³⁺ emissions were found to decrease with increasing Eu³⁺ concentration.     

Molecular‐Like Ag Clusters and Eu3+ Co‐Sensitized Efficient Broadband Spectral Modification with Enhanced Yb3+ Emission

AgNO₃/EuF₃/YbF₃ tri‐doped oxyfluoride glass was prepared by a melt‐quenching method, in which a high‐efficient broadband spectral modification can be realized due to the simultaneous energy‐transfer processes of Eu³⁺→Yb³⁺, molecular‐like Ag (ML‐Ag) clusters→Yb³⁺, and ML‐Ag clusters→Eu³⁺→Yb³⁺. The spectral measurements indicated that besides the F‐center brought by the fluorides, the formation of the ML‐Ag clusters and the evolution of silver species within the glass matrix were also closely related to the introduction of Eu³⁺ and Yb³⁺ ions and which in return greatly affected the luminescence properties of these rare‐earth ions. As the UV‐visible irradiation in the wavelength region of 250–600 nm can be efficiently converted into near‐infrared emission around 1000 nm in the AgNO₃/EuF₃/YbF₃ tri‐doped glass, which thus has promising application in enhancing the photovoltaic conversion efficiency of the silicon solar cell.     

Broadband Near‐Infrared Down‐Shifting by Yb–O Charge‐Transfer Band in Yb3+ Singly Doped Tellurite Glasses

Yb³⁺ singly doped tellurite as‐prepared glasses and glass ceramics were synthesized by high‐temperature melt‐quenching method. The excitation and emission spectra have shown that there is an efficient near‐infrared (NIR) down‐shifting due to the sensitization of a novel Yb³⁺–O^2? charge‐transfer (CT) band. The CT band in the present host is located at around 320 nm at room temperature, which is much lower than that in other oxide hosts reported before. The possible energy‐transfer mechanism from the Yb³⁺–O^2? CT band to the ²F_5/2 multiplet of Yb³⁺ ions is discussed in detail. The concentration quenching is not observed even when the Yb³⁺‐doped concentration is increased up to 40 mol%. The excitation of this strong broad CT band causes intense NIR emission of Yb³⁺:²F_5/2→²F_7/2 from 920 to 1120 nm, making the tellurite glasses suitable for efficient photovoltaic (PV) application as a spectral conversion material for the crystalline Si (c‐Si) solar cells.     

Structural and emission properties of Eu3+‐doped alkaline earth zinc‐phosphate glasses for white LED applications

Quaternary alkaline earth zinc‐phosphate glasses in molar composition (40 ? x)ZnO – 35P₂O₅ – 20RO – 5TiO₂ – xEu₂O₃ (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (T_g) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT‐IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (⁵D₀→⁷F₂) under excitation of 392 nm, which matches well with excitation of commercial n‐UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 ? x)ZnO – 35P₂O₅ – 20BaO – 5TiO₂ – xEu₂O₃ (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu₂O₃. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu₂O₃. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid‐state lighting devices.     

Up-conversion emission color tuning in NaLa(MoO4)2: Nd3+/Yb3+/Ho3+ excited at 808 nm

As alternatives to Yb³⁺-sensitized up-conversion (UC) materials excited at 980 nm, Nd³⁺-sensitized UC phosphors irradiated by 808 nm have been used to decrease the absorption of water and alleviate the overheating effect in vivo biological application. Intense red and green UC emissions from ⁵F₅→⁵I₈ and ⁵F₄/⁵S₂→⁵I₈ transitions of Ho³⁺ appeared in Nd³⁺/Yb³⁺/Ho³⁺ tri-doped NaLa(MoO₄)₂ through successive energy transfer Nd³⁺→Yb³⁺→Ho³⁺ under 808 nm excitation, in which Yb³⁺ ions were proven to be the energy transfer bridge between Nd³⁺ and Ho³⁺ by lifetime measurement. The variable emission color and intensity ratios of red to green emissions were realized by adjusting the doping concentration of Yb³⁺, pulse width of the excitation laser and the addition of Ce³⁺ ion, which depends on the different population pathways to the green and red emitting states of Ho³⁺. The chromaticity modulation mechanisms of these approaches were proposed, which provides a feasible strategy to tune the UC emission color.     

Near-IR Emission and upconversion luminescent properties of Tb3+/Yb3+ Co-doped HfO2/SiO2 nanoparticles

The luminescent characteristics of spherical hafnia/silica (HfO₂/SiO₂) nanoparticles (NP?s) co-doped with Tb³⁺/Yb³⁺ were analysed. These NP?s were synthesized using the spray pyrolysis technique. The addition of SiO₂ and Tb³⁺/Yb³⁺ was found to induce a cubic phase in HfO₂. The luminescent spectra presented the characteristic emission peaks for inter-electronic energy levels transitions of the Tb³⁺ and Yb³⁺ ions, with an excitation band centred at 270 nm. Under solid-state laser excitation at 980 nm an upconversion emission related to the Tb³⁺ ion was observed. The maximum emission peak in the visible region was at 543 nm, associated with ⁵D₄ → ⁷F₅ transitions of the Tb³⁺ ions and an IR emission peak at 970 nm (²F_5/2 → ²F_7/2) pertaining to Yb³⁺, with irradiation at 270 nm (UV). The energy transfer mechanism from Tb³⁺→Yb³⁺ (excitation at 270 nm), is discussed based on the time decay of the luminescence intensity analysis and the energy transfer efficiency (η_ET) and was determined to be in the range of 29.2% to40.8%.     

Precipitation Synthesis and Color‐Tailorable Luminescence of α‐Zr(HPO4)2: RE3+(RE = Eu,Tb) Nanosheet Phosphors

The rare earth (RE = Eu and Tb) ions‐doped α‐Zr(HPO₄)₂ (ZrP) nanosheet phosphors were synthesized by direct precipitation method, and their structures and photoluminescence properties were investigated. The results of X‐ray diffraction and scanning electron microscopy indicated that the systems of ZrP:RE³⁺ had similar nanosheet structure except with relatively larger interlayer spacing as compared with pure α‐ZrP. Under the excitation of UV light, the ZrP:RE³⁺ nanosheet phosphors showed red and green emission peaks corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ and the ⁵D₄→⁷F₅ transition of Tb³⁺, respectively. After Eu³⁺ and Tb³⁺ were co‐doped in ZrP host, not only the red and green emission peaks were simultaneously observed, but also the luminescent intensity and fluorescence lifetimes of Tb³⁺ were gradually decreased with the increase in Eu³⁺‐doping concentration, which implied the energy transfer from Tb³⁺ to Eu³⁺ happened. It was deduced that the energy transfer from Tb³⁺ to Eu³⁺ occurred via exchange interaction. Through optimization to the samples, a nearly white‐light emission with the color coordinate (0.322, 0.263) was achieved under 377 nm excitation. The ZrP:RE³⁺ nanosheet phosphors may be a potential color‐tailorable candidate for fabricating optoelectronic devices such as electroluminescence panels.     

Spectral management and energy‐transfer mechanism of Eu3+‐doped β‐NaGdF4:Yb3+,Er3+ microcrystals

β‐NaGdF₄:Yb³⁺,Er³⁺ upconversion (UC) microcrystals were prepared by a facile hydrothermal process with the assistance of ethylene diamine tertraacetic acid (EDTA). The β‐NaGdF₄ UC microcrystal morphology was controlled by changing the doses of EDTA and NaF. Uniform hexagonal structure can be obtained at the 2 mmol EDTA and 9‐10 mmol NaF. The UC emissions of β‐NaGdF₄:Yb³⁺,Er³⁺ microcrystals were tuned by the variation of Eu³⁺ doping level (0%‐5%), where the red/green intensity ratio decreased with the Eu³⁺ concentration increase. It was found on the base of rate equations that with the Eu³⁺ doping, the energy back transfer process ²H_11/2/⁴S_3/2 (Er³⁺) → ⁴I_13/2 (Er³⁺) decreased. In addition, an energy‐transfer process from ⁴F_7/2 (Er³⁺) to ⁵D₁ (Eu³⁺) and a cross relaxation process of ⁷H_9/2 (Er³⁺) + ⁵D₀ (Eu³⁺) → ⁴F_7/2 (Er³⁺) + ⁵D₂ (Eu³⁺) were proposed and verified by rate equations, which dominated the energy‐transfer mechanism between Er³⁺ and Eu³⁺, resulted in the spectra tuning of β‐NaGdF₄:Yb³⁺,Er³⁺. The results suggested that the color tuning of β‐NaGdF₄:Yb³⁺,Er³⁺,Eu³⁺ UC microcrystals would have potential applications in such fields as flat‐panel displays, solid‐state lasers, and photovoltaics.     

Optical Temperature Sensing Behavior of High‐Efficiency Upconversion: Er3+–Yb3+ Co‐Doped NaY(MoO4)2 Phosphor

A class of Yb³⁺/Er³⁺ co‐doped NaY(MoO₄)₂ upconversion (UC) phosphors have been successfully synthesized by a facile hydrothermal route with further calcination. The structural properties and the phase composition of the samples were characterized by X‐ray diffraction (XRD). The UC luminescence properties of Yb³⁺/Er³⁺ co‐doped NaY(MoO₄)₂ were investigated in detail. Concentration‐dependent studies revealed that the optimal composition was realized for a 2% Er³⁺ and 10% Yb³⁺‐doping concentration. Two‐photon excitation UC mechanism further illustrated that the green enhancement arised from a novel energy‐transfer (ET) pathway which entailed a strong ground‐state absorption of Yb³⁺ ions and the excited state absorption of Yb³⁺–MoO₄^2? dimers, followed by an effective energy transfer to the high‐energy state of Er³⁺ ions. We have also studied the thermal properties of UC emissions between 303 and 523 K for the optical thermometry behavior under a 980 nm laser diode excitation for the first time. The higher sensitivity for temperature measurement could be obtained compared to the previous reported rare‐earth ions fluorescence based optical temperature sensors. These results indicated that the present sample was a promising candidate for optical temperature sensors with high sensitivity.     

Preparation and photoluminescence enhancement of Au nanoparticles embedded LaPO4:Eu3+ inverse opals

In this work, we present a facile preparation approach of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opal photonic crystals. In the typical preparation process, the transparent LaPO₄:Eu³⁺ sol including HAuCI₄ was infiltrated into the opal templates. After the sintering, the 10‐20 nm Au nanoparticles were formed in the interior of nano‐sized wall of LaPO₄:Eu³⁺ inverse opal and the Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opals were obtained. The luminescence of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opal was investigated. The emission peaks located at the 593 (⁵D₀→⁷F₁), 618 (⁵D₀→⁷F₂) and 698 nm (⁵D₀→⁷F₄) from Eu³⁺ ions were observed. The 593, 618, and 698 nm emissions of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opals were enhanced in contrast to these of LaPO₄:Eu³⁺ inverse opal without the Au nanoparticles, which is from the excitation field enhancement caused by the localized surface plasmon resonance of Au nanoparticles.     

Novel Broadband Excited and Linear Red‐Emitting Ba2Y(BO3)2Cl: Ce3+, Tb3+, Eu3+ Phosphor: Luminescence and Energy Transfer

A series of Ce³⁺, Tb³⁺, Eu³⁺ tri‐doped Ba₂Y(BO₃)₂Cl red‐emitting phosphor have been synthesized by solid‐state method. The Ce³⁺→Tb³⁺→Eu³⁺ energy‐transfer scheme has been proposed to realize the sensitization of Eu³⁺ ion emission by Ce³⁺ ions. Following this energy‐transfer model, near‐UV convertible Eu³⁺‐activated red phosphors have been obtained in Ba₂Y(BO₃)₂Cl: Ce³⁺, Tb³⁺, Eu³⁺ phosphors. Energy transfers from Ce³⁺ to Tb³⁺, and Tb³⁺ to Eu³⁺, as well as corresponding energy‐transfer efficiencies are investigated. The combination of narrow‐line red emission and near‐UV broadband excitation makes Ba₂Y(BO₃)₂Cl: Ce³⁺, Tb³⁺, Eu³⁺ as a novel and efficient red phosphor for NUV LED applications.     

EDTA-assisted hydrothermal synthesis of KLa(MoO4)2:Eu3+ microcrystals and their luminescence properties

Monoclinic KLa(MoO₄)₂:Eu³⁺ microarchitectures with different morphologies were synthesized by an EDTA-assisted hydrothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR) and photoluminescence (PL) spectrometer. It was found that the amounts of EDTA and the pH values of precursor solution have crucial influences on the structure, morphology and size of the obtained samples, respectively. Under 270 nm excitation, Eu³⁺ doped KLa(MoO₄)₂ samples showed red emission centered at 618 nm which attributed to ⁵D₀→⁷F₂ transition of Eu³⁺. The dependence of luminescence intensity on different morphologies were discussed in detailed. With further annealing treatment, the emission intensities of peanut-like samples increased amazingly. Moreover, the lifetime of the annealed samples were calculated. The significantly enhanced photoluminescence performances indicate that the as-annealed samples are promising phosphors which can be used for white light-emitting diodes (WLEDs).