Lithium solubility limit in ZnGa2O4:Bi0.0013+,Li+ phosphor

The lithium solubility limit, photoluminescence (PL) and photoluminescence excitation (PLE) properties of lithium ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor have been investigated. A LiGaO₂ second phase began to appear from 3 mol% Li⁺ ion co-activated ZnGa₂O₄:Bi³⁺,Li⁺ phosphor. The enhanced brightness of blue (λ_ex = 254 nm) and white (λ_ex = 315 nm) colors of bismuth ions doped ZnGa₂O₄:Bi³⁺,Li⁺ phosphor was assigned to the formation of LiGaO₂. Bi³⁺ activated lithium zinc gallate phosphor showed a more enhanced PLE peak around 315 nm than that of lithium zinc gallate phosphor when λ_em = 520 nm. Thus, we observed that the PL intensity of ZnGa₂O₄:Bi³⁺,Li⁺ phosphor with λ_em = 520 nm was much greater than that of ZnGa₂O₄:Li⁺ phosphor. Also, ZnGa₂O₄:Bi³⁺,Li⁺ phosphor exhibited a shorter decay time than that of ZnGa₂O₄:Li⁺ phosphor by about a factor of about 2.     

Effects of co-doped Li+ ions on luminescence of CaWO4:Sm3+ nanoparticles

CaWO₄, CaWO₄:Sm³⁺ and CaWO₄:(Sm³⁺, Li⁺) nanoparticles were synthesized by the precipitation method with addition of PEG 200. The X-ray diffraction patterns show that the obtained samples have a pure tetragonal phase. The CaWO₄ sample shows an emission peak at 418 nm originating from the charge-transfer transitions within the WO₄ ^2? complex. CaWO₄:Sm³⁺ and CaWO₄:(Sm³⁺, Li⁺) samples show emission peaks originating from the f–f forbidden transitions of the 4f electrons of Sm³⁺ ions. The charge compensator of Li⁺ can enhance the emission intensity effectively. It is found that the emission intensity of CaWO₄:(3 mol% Sm³⁺, 4 mol% Li⁺) phosphor is about double that of CaWO₄:3 mol% Sm³⁺ phosphor.     

Thermoluminescence characteristics of Sm<Superscript>3+</Superscript> doped NaYF<Subscript>4</Subscript> crystals

Thermoluminescence (TL) characteristics of NaYF₄ crystals doped with Sm³⁺ have been studied after γ-ray irradiation. Dependence of luminescence efficiency on Sm³⁺ concentration and radiation dose has been measured and possible applications of NaYF₄: Sm³⁺ as a novel phosphor for TL dosimetry have been investigated. The efficiency of 0·3 mole% Sm³⁺ doped NaYF₄ crystal has been found to be maximum and comparable with commercial thermoluminescence dosimetric (TLD) materials.     

Electrospinning preparation and luminescence properties of one-dimensional SrWO4: Sm3+ nanofibers

One-dimensional Sm³⁺ doped SrWO₄ with or without different charge compensation approaches (co-doping Li⁺, Na⁺ and K⁺) nanofibers were prepared by electrospinning. The structure, morphology and luminescence properties of the obtained nanofiber phosphors were investigated. The X-ray diffraction, Fourier transformation infrared and thermogravimetric results show that the Sr_(1?x)WO₄: Sm _x ³⁺ samples crystallize at 700 °C. Scanning electron microscope results indicate that as prepared nanofibers before/after calcination present uniform fiberlike morphology. The luminescence results show that Sr_(1?x)WO₄: Sm _x ³⁺ phosphors can be excited efficiently by ultraviolet (UV) and near-UV light. The emission spectrum consists of three emission peaks at 561, 596 and 643 nm, corresponding to ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 transitions of Sm³⁺, respectively. The optimal doping concentration of Sm³⁺ in SrWO₄ is experimentally ascertained to be 4 mol%. The introduction of charge compensator R⁺ (R = Li, Na and K) can enhance the emission intensity of phosphors significantly. The co-doping of Li⁺ has the best compensation effect. The present investigation indicates that Sm³⁺ doped SrWO₄ is a promising orange phosphor for light-emitting diode based on UV chip technology.     

Antiquenching effect of modifying cations on samarium clustering: Physical,structural and luminescent behavior of heavy metal borate glass systems

In this paper an attempt has been made to correlate the structural modifications and luminescence efficiencies by changing the environment of the glass network by modifying oxides. Sm³⁺ doped lead borate (SPB) and lead cadmium alumino borate (SCPB) glasses have been fabricated by melt quench technique at high temperature. The glass samples are characterized by XRD, FTIR, optical absorptions, fluorescence and density measurements. The effect of Sm³⁺ ion and glass host interaction on the emission spectra has been discussed in the view of the ionicity and covalency of hosts. The ratio of the intensities of electric to magnetic dipole emissions are calculated by varying both the concentration of the Sm³⁺ ion and the composition of the glass matrix. The XRD profile of all the glasses confirms their amorphous nature and FTIR spectrum shows the presence of BO₃ and BO₄ groups. These glasses have shown strong absorption bands in the visible (VIS and NIR) region and emit strong orange red wavelengths when excited by ultraviolet light. The concentration quenching has been noticed and ascribed to energy transfer through cross-relaxation between Sm³⁺ ions. Shifting of UV absorption edge towards longer wavelength with addition of Sm₂O₃ concentration has been observed. Incorporation of Al₂O₃ and CdO in 2nd glass system is responsible for strong effect on luminescence of the present glass system. Based on these results, an attempt has been made to throw some light on the relationship between the structural modifications and luminescence efficiencies in two different glass hosts as a laser active medium in the visible region. Moreover the optical basicity values were theoretically determined along with covalent behavior of two glass systems.     

Band gap and trapping parameters of color tunable Yb3+/Er3+ codoped Y2O3 upconversion phosphor synthesized by combustion route

This paper reports the structural, optical and luminescence properties of Yb³⁺/Er³⁺ codoped Y₂O₃ phosphor synthesized by combustion method. The prepared phosphor was characterized by X-ray diffraction (XRD). XRD studies confirm the body-centered cubic structure of the phosphor. The optical properties such as diffuse reflectance (DR), photoluminescence and thermoluminescence were studied. DR spectra were used to determine the bandgap of the phosphor. Mechanism of upconversion by two-photon and energy transfer processes are interpreted and explained. The color coordinates were measured and the color tunability was analyzed as a function of the 980 nm excitation source power. Different trapping parameters associated with the glow peak were calculated by various glow curve methods.     

Luminescence properties of the single-phase white light emitting phosphors Li0.04Ca0.93−xSiO3:Eu0.01,Bi0.02,Tbx

The single-phase white light emitting Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x (x?=?0.01–0.05) phosphors were successfully synthesized using the sol–gel method. The phase structure, morphology and photoluminescence properties (PL) of phosphors were characterized by X-Ray Diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and absorption spectra. The results show that the Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors only consist of β-CaSiO₃ phase. The diffraction peak of (320) plane shows right-shift caused by Tb³⁺ ions doped into the β-CaSiO₃ host. The Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors exhibit bright white emitting light on the excitation of 228 nm and the luminescence intensity increases with increase of Tb³⁺ ions until the concentration of Tb³⁺ ions is x?=?0.03. Then the luminescence intensity gradually decreases owing to concentration quenching behavior of Tb³⁺ ions. The emission color of phosphors would move from the white light region towards green direction with the increase of concentrations of Tb³⁺ ions. The color correlated temperature (CCT) values decrease from 8964 to 6118 K with the increase in concentration of Tb³⁺. Li_0.04Ca_0.9SiO₃:Eu_0.01,Bi_0.02,Tb_0.03 phosphor has higher band gap energy E_g (5.43 eV) than that of Li_0.04Ca_0.93SiO₃:Eu_0.01,Bi_0.02 phosphor. The addition of Tb³⁺ ions improve the thermal stability of phosphors with the thermal activation energy of 0.28 eV. The experimental result confirms that Tb³⁺ ions show the transfer energy behavior from Tb³⁺ to Eu³⁺ ions in the Li_0.04Ca_0.93?xSiO₃:Eu_0.01,Bi_0.02,Tb_x phosphors.

     

Preparation and luminescent properties of orange reddish emitting phosphor LaMgAl11O19:Sm3+

An orange reddish emitting phosphor, LaMgAl₁₁O₁₉:Sm³⁺, was synthesized by a high temperature solid-state reaction, and the phase formation, crystal structure and luminescence properties were investigated respectively. The LaMgAl₁₁O₁₉:Sm³⁺ phosphor presents a highly intense orange reddish emission peak under the near ultraviolet excitation at 403 nm, which is corresponds to the ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ ions. It was found that the dipole–dipole interactions mainly results in the concentration quenching in the LaMgAl₁₁O₁₉:Sm³⁺ phosphor with a critical quenching concentration at about 5 mol%. The temperature dependence of luminescence properties was studied from 25 to 200 °C and indicated that LaMgAl₁₁O₁₉:0.05Sm³⁺ phosphors had a relatively higher quenching temperature. The chromatic properties of LaMgAl₁₁O₁₉:0.05Sm³⁺ phosphor have been found to have chromaticity coordinate of (0.578, 0.420). All these properties indicate that the orange reddish emitting LaMgAl₁₁O₁₉:Sm³⁺ phosphor has a potential application in w-LEDs.     

Emission features of LiBaBO3:Sm3+ red phosphor for white LED

A novel red phosphor, LiBaBO₃:Sm³⁺, was synthesized by solid state reaction, and its emission properties were studied. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (UV) 345, 373 and 404 nm light, and exhibit a satisfactory red performance (597 nm), nicely, fitting in with the widely applied UV LED chip. The emission intensity of LiBaBO₃:Sm³⁺ phosphor varies with increasing Sm³⁺ concentration, and occurs to concentration quenching, and the concentration self-quenching mechanisms are the d-d interaction by Dexter theory. Emission intensity of LiBaBO₃:Sm³⁺ phosphor was enhanced by doping charge compensation Li⁺, Na⁺, K⁺, and the emission intensity of doping Li⁺ is higher than that of Na⁺ or K⁺.     

Red-emitting α-SrO·3B2O3:Sm2+ phosphor: an innovative application for increasing color quality and luminous flux of remote phosphor white LEDs

Abstract

By adding red-emitting α-SrO·3B₂O₃:Sm²⁺ phosphor and SiO₂ co-doping particles to yellow-emitting YAG:Ce phosphor compound, a novel method for improving lighting performance of white LEDs with remote phosphor structure, which have an average correlated color temperature (CCT) of 5600–8500 K, is proposed and demonstrated. By varying α-SrO·3B₂O₃:Sm²⁺ concentration from 2 to 30% and maintaining 5% SiO₂, the obtained results indicated that color rendering index (CRI), color quality scale (CQS), and luminous flux can be increased significantly. Moreover, the Mie-scattering theory is employed to verify the scattering properties, which have an effect on the enhancement of color quality and luminous flux. The results prove a prospective practical solution for manufacturing remote phosphor white LED (RP-WLED) having higher color quality and luminous flux.     

A novel red emitting phosphor CaIn2O4:Eu, Sm with a broadened near-ultraviolet absorption band for solid-state lighting

Red phosphor of CaIn₂O₄:Eu³⁺, Sm³⁺ is synthesized by solid state reaction. The ⁵D₀ → ⁷F₂ transition of Eu³⁺ is dominantly observed in the photoluminescence spectrum, leading to a red emission of the phosphor. The doped Sm³⁺ is found to be efficient to sensitize the emission of Eu³⁺ and be effective to extend and strengthen the absorption of near-UV light with wavelength of 400-405 nm, and the energy transfer from Sm³⁺ to Eu³⁺ occurs and is discussed. The effect of the molar concentration of Sm³⁺ on the emission intensities of the phosphor CaIn₂O₄:Eu³⁺, Sm³⁺ is investigated. The temperature quenching effect is also measured from room temperature to 425 K, and the emission intensity of the phosphor at 425 K shows about 85% of that at room temperature. Furthermore, the chromaticity coordinates, the emission intensities and the conversion efficiencies of CaIn₂O₄:Eu³⁺, Sm³⁺ are compared to those of the conventional red phosphor of Y₂O₂S:Eu³⁺.     

Investigations on optical and dielectric properties of PVDF/PMMA blend doped with mixed samarium and nickel chlorides

Samarium and nickel ions, singly and in combination, were doped into poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend. Films were prepared by casting technique. The microstructure of the prepared films were studied using X-ray diffraction (XRD), Infrared (FT-IR) and Fluorescence spectroscopy. The complex formation between Sm³⁺ and/or Ni²⁺ ions with the polymeric chain was confirmed by XRD and FT-IR. XRD analysis revealed that the crystallinity of blend improved by doping. The presence of the dopants led to some changes in the vibrational spectrum of the blend. The effect of doping levels on the optical and dielectric properties of PVDF/PMMA blend was investigated. It was observed that the optical band gap E_g, dielectric constant ε`, AC conductivity σ_Ac and loss tangent tanδ increase significantly with increasing Sm³⁺ content. The correlation between optical and dielectric properties and the microstructure of polymeric systems was studied.     

Investigations on the low voltage cathodoluminescence stability and surface chemical behaviour using Auger and X-ray photoelectron spectroscopy on LiSrBO3:Sm phosphor

Orange-red emissive LiSrBO₃:Sm³⁺ phosphors were synthesized through the solid-state reaction method. Under UV radiation (221 nm) and low-voltage electron beam (2 keV, 12 mA/cm²) excitation, the Sm³⁺ doped LiSrBO₃ phosphor shows emission corresponding to the characteristic ⁴G_5/2-⁶H_7/2 transitions of Sm³⁺ with the strongest emission at 601 nm. A high stability of cathodoluminescence (CL) emission during prolong electron bombardment with low-energy electrons was observed. Surface sensitive diagnostic tools such as Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to study the surface chemistry. AES results revealed modifications in the surface concentrations of Li, Sr, B, O and C on the surface of the LiSrBO₃:Sm³⁺ phosphor as indicated by the changes in their Auger peak to peak heights (APPH) as a function of electron dose. Observed changes in the high resolution XPS spectra of the LiSrBO₃:Sm³⁺ surface irradiated with the low energy electron beam provide evidence of compositional and structural changes as a result of the electron beam stimulated surface chemical reactions (ESSCRs). Additional SrO₂ was identified by XPS on the phosphor surface after it received an electron dose of 300 C/cm² together with the increase in the concentrations of chemical species containing the B-C-O bonding. The new surface chemical species formed during electron beam bombardment are possibly responsible for the stability of the CL in the LiSrBO₃:Sm³⁺ phosphor.     

Spectral and trapping parameters of Eu3+ in Gd2O2S nanophosphor

This paper reports the structural, photometric, spectral and trapping parameters of Eu³⁺-doped gadolinium oxysulphide nanophosphor. The X-ray diffraction (XRD) data show the presence of the hexagonal phase of Gd₂O₂S and a crystallite size in nanometre range. Different structural parameters were calculated from XRD data. The Fourier transform infrared (FTIR) spectrum also confirms the formation of a compound. Scanning electron microscope studies reveal the morphology and crystallite size of the prepared phosphor. The band gap of the phosphor was calculated from diffuse reflectance spectra using the Kubelka–Munk function at 4.76 eV. The phosphor was illuminated with ultraviolet light and shows the characteristic red luminescence corresponding to ⁵D₀→⁷F_J transitions of Eu³⁺. The Judd–Ofelt intensity parameters and spectral parameters were estimated from the photoluminescence data. The nanophosphor was irradiated with γ-rays in the dose range 15–50 Gy for thermoluminescence (TL) studies and a shifting of the peak towards lower temperatures was observed with increasing γ-dose. Trapping parameters were calculated from TL data using various glow curve analysis methods.     

Green emission enhancement of Ba2SiO4:Eu2+ phosphor via Gd co-doping and charge compensation

A series of new green-emitting Ba_2?x?2ySiO₄:xEu²⁺, yGd³⁺, yR⁺ (R = Li, Na or K) phosphors were synthesized by the solid-reaction method. X-ray diffraction (XRD) and fluorescence spectrophotometer are utilized to characterize the crystal structure and luminescence properties of the as-synthesized phosphors, respectively. The XRD patterns reveal that the doping of Gd³⁺, Eu²⁺ and R⁺ ions have no significant influence on the Ba₂SiO₄ phase. The green emission of Eu²⁺ ion associated with 4f⁶5d¹ → 4f⁷ can be obtained by 396 nm UV excitation source, which match well with the emission wavelength of UV-LEDs chip (380–420 nm). Moreover, the effect of charge compensator ions (Li⁺, Na⁺ or K⁺) on the luminescence intensity of (Ba, Gd)₂SiO₄:Eu²⁺ phosphors were also investigated. When introducing the Li⁺ ions into the (Ba, Gd)₂SiO₄ host lattices, the as-prepared phosphors show the strongest emission. The emission intensity of Ba_1.95SiO₄:0.04Eu²⁺, 0.005Gd³⁺, 0.005Li⁺ is about 1.39 times than that of Ba_1.96SiO₄:0.04Eu²⁺. Furthermore, the mechanism of energy transfer and concentration quenching of Ba_1.982?xSiO₄:xEu²⁺, 0.009Gd³⁺, 0.009Li⁺ phosphors are also discussed.     

Synthesis of infrared up-conversion material SrS: Eu,Sm

Europium and samarium co-doped strontium sulfide (SrS: Eu, Sm) infrared up-conversion phosphor was synthesized through calcining the precursor, which was prepared by the wet method with strontium carbonate (SrCO₃), sulfur (S), europium oxide (Eu2O₃) and samarium oxide (Sm₂O₃) as the starting materials, and lithium fluoride (LiF), lithium carbonate (Li2CO₃), natrium carbonate (Na₂CO₃) and potassium oxalate (K₂C₂O₄) as the fluxing agents, at 750-1200°C in a carbon-reducing atmosphere. The effects of calcining temperature, calcining time, category and concentration of the fluxing agents and concentration of dopants on the final up-conversion luminescence properties were studied. The SrS crystal structure is formed primarily at 750°C, but the best calcining temperature should be 1100°C. The most suitable calcining time is 1-1.5 h, the up-conversion luminescence intensity increases along with the increase of time within this range and decreases above the range. Excellent up-conversion luminescence was obtained with 10% fluxing agent LiF and 0.2% dopants Eu and Sm. The up-conversion emission spectrum is a continuous broadband spectrum with one peak at 599 nm which resulted from the transitions of Eu²+5d(²T_2g) → 4f(⁸S_11/2).     

Photoluminescence of Bi ions in sol-gel derived Zn2SiO4

The luminescence of sol-gel derived Zn₂SiO₄ powder sample doped with Bi³⁺ ions has been presented in this paper. From the photoluminescence (PL) spectra of the doped sample, it can be concluded that Bi³⁺-doped Zn₂SiO₄ powder is an interesting PL material whose luminescence properties are adjusted by changing the excitation wavelength. The luminescence of Bi³⁺ ions is quite diverse in Zn₂SiO₄ powder sample. The blue and yellow emission bands have been observed from the doped Zn₂SiO₄ powder. This novel luminescence property is attributed to an energy transfer involving Bi³⁺, Zn²⁺, and Si⁴⁺ ligand of Zn₂SiO₄ lattice.     

Synthesis and luminescent properties of spindle-like CaWO4:Sm3+ phosphors

Spindle-like CaWO₄:Sm³⁺ phosphors were prepared via a Polyvinylpyrrolidone (PVP)-assisted sonochemical process, and characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectroscopy (PL). The XRD results suggested that the prepared samples are single-phase. The FE-SEM images indicated that the prepared CaWO₄:Sm³⁺ phosphors are composed of many spindles with maximum average diameter of 150 nm and maximum average length of 500 nm. Under 404 nm excitation, the characteristic emissions corresponding to ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ in CaWO₄ phosphors were observed. The color coordinates for 1 mol% Sm³⁺ doped CaWO₄ phosphor were calculated to be (0.595, 0.404). The fluorescent concentration quenching of Sm³⁺ doped spindle-like phosphors was studied based on the Van Uitert's model, and it was found that the electric dipole–dipole (D–D) interaction is the dominant energy transfer mechanism between Sm³⁺ ions in the CaWO₄:Sm³⁺ phosphors. The critical energy transfer distance was estimated.     

Synthesis and luminescence properties of Na+, Li+ compensated Er3+ doped CaAl4O7 phosphors

Here the green-emitting highly luminescent Er³⁺ doped, Er³⁺-Li⁺ co-doped, Er³⁺-Na⁺ co-doped CaAl₄O₇ is synthesized by Pechini method at 1000^°C. Photoluminescence (PL) of CaAl₄O₇: Er³⁺ studies have been compared with Li⁺ co-doped CaAl₄O₇: Er³⁺ and Na⁺ co-doped CaAl₄O₇: Er³⁺. Na⁺ co-doped CaAl₄O₇:Er³⁺ shows increases in luminescence intensity compared to Li⁺ co-doped CaAl₄O₇: Er³⁺ and Er³⁺ doped CaAl₄O_7. The results suggest that CaAl₄O₇:Er³⁺ phosphor can be used as efficient green-emitting phosphor in white LED. The resultant phosphor emits green color peaking at 549 nm upon 378 nm excitation. Powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques have been studied to characterize the synthesized microparticles. Further, this phosphor has good thermal stability that implies its potential to act as green phosphor in white light-emitting diodes. The effect of activator (Er³⁺), Na⁺ co-doped CaAl₄O₇:Er³⁺, and Li⁺ co-doped CaAl₄O₇:Er³⁺ phosphors luminescence spectra as well as photoluminescence life time studies were studied in detail. The results show that as the concentration of Er³⁺ in CaAl₄O₇ increases, the symmetry around the Er³⁺ ion decreases due to the creation of lattice defects in the crystal. Addition of Na⁺ and Li⁺ ions in CaAl₄O₇: Er³⁺leads to a small distortion in the local symmetry of Er³⁺ ions, thereby significantly enhancing its luminescence property. Analysis of photoluminescence life time studies of the prepared samples shows a smaller concentration quenching of Er³⁺ luminescence in charge compensated Na⁺ and Li⁺ CaAl₄O₇ phosphor.

     

Facile synthesis and luminescent properties of LaPO4: Eu,Sm nanorods via a designed two-step hydrothermal method

LaPO₄: Eu³⁺, Sm³⁺ nanorods have been successfully prepared by a designed two-step hydrothermal method. The whole process was carried out under aqueous conditions without the use of any organic solvent, surfactant, or catalyst. The crystal structure, morphology have been characterized by XRD, FT-IR, SEM and TEM, respectively. The detailed conversion process of the product LaPO₄ nanorods has been investigated on the basis of time-dependent XRD experiments and SEM experiments. Moreover, the LaPO₄ samples doped with Eu³⁺ and Sm³⁺ under ultraviolet excitation showed red emission corresponding to the ⁵D₀–⁷F₁ transition of the Eu³⁺ ions. The doped Sm³⁺ was found to be efficient to sensitize the emission of Eu³⁺ and be effective to extend the absorption of near-UV light with wavelength of 400–405 nm. The effect of the concentration of Sm³⁺ on the emission intensities of the phosphor LaPO₄: Eu³⁺, Sm³⁺ is also investigated. These samples could be potentially used in the fields of near UV-excited white-light-emitting diode and optoelectronic devices.