A novel red-emitting phosphor Ca9Bi(PO4)7:Eu3+ for near ultraviolet white light-emitting diodes

Red phosphors Ca₉Bi_1-x(PO₄)₇:xEu³⁺ (x = 0.06, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 1.00) were synthesized by a conventional solid-state reaction (SSR) route. The X-ray diffraction patterns, photoluminescence spectra, ultraviolet–visible reflection spectroscopy, decay time and the International Commission on Illumination (CIE) chromaticity coordinates of these compounds were characterized and analyzed. The Eu-doped Ca₉Bi(PO₄)₇ phosphors exhibited strong red luminescence which peaks located at 615 nm due to the ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺ ions after excitation at 393 nm. Ultraviolet–visible spectra indicated that the band-gap of Ca₉Bi_0.30(PO₄)₇:0.70Eu³⁺ is larger than that of Ca₉Bi(PO₄)₇. The results indicate that the phosphor Ca₉Bi_0.30(PO₄)₇:0.70Eu³⁺ can be a suitable red-emitting phosphor candidate for LEDs.     

Luminescence spectroscopy and electronic structure of ZrP2O7 and KZr2(PO4)3 crystals

The photoluminescence (PL) of ZrP₂O₇ and KZr₂(PO₄)₃ phosphate crystalline micro-powders grown by spontaneous crystallization method is studied under vacuum ultra-violet (VUV) synchrotron radiation excitations (4–20 eV region of excitation photon energies) in 8–300 K temperature region. The electronic structures (partial densities of states) and optical absorbance spectra of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. Both phosphate crystals reveal PL emission band in the UV spectral region peaking near 300 and 295 nm for ZrP₂O₇ and KZr₂(PO₄)₃ respectively. The spectral profile of the band weakly depends on temperature. The excitation spectra of the UV emission in each crystal contain intensive excitation band peaking at 189 and 182 nm for ZrP₂O₇ and KZr₂(PO₄)₃ respectively. The excitation band of the UV emission is related to band-to-band electronic transitions with charge transfer from O 2p to Zr 4d states. The energy band gaps E_g of ZrP₂O₇ and KZr₂(PO₄)₃ are estimated as 6.7 and 6.6 eV respectively.     

Synthesis and photoluminescence properties of MZr2(PO4)3:Eu3+; Bi3+ (M=Na; K) phosphors

A series of new red phosphors, MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K), were synthesized using the solidstate reaction method, and their photoluminescence spectra were measured. The MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors were efficiently excited by an ultraviolet (UV; 395 nm) source, and showed intense orange-red emission at 595 nm. Further investigation of the concentration-dependent emission spectra indicated that the MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors exhibit the strongest luminescence intensity when y = 0.01 in NaZr_2(0:95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ and y = 0.09 in NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺, whereas the relative PL intensity decreases with increasing Bi³⁺ concentration due to concentration quenching. The addition of Bi³⁺ widens the excitation band of NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ around 320 nm, which provides the useful idea of broadening the excitation band around 300–350 nm to fit the ultraviolet chip.     

Luminescence spectroscopy of the Bi single and dimer centers in Y3Al5O12:Bi single crystalline films

Luminescence of the Bi³⁺ single and dimer centers in UV and visible ranges is studied in YAG:Bi (0.13 and 0.27 at% of Bi, respectively) single crystalline films (SCFs), grown by liquid phase epitaxy from a Bi₂O₃ flux. The cathodoluminescence spectra, photoluminescence decays, and time-resolved spectra are measured under the excitation by accelerated electrons and synchrotron radiation with energies of 3.7 and 12 eV, respectively. The energy level structure of the Bi³⁺ single and dimer centers was determined. The UV luminescence of YAG:Bi SCF in the bands that peaked at 4.045 and 3.995 eV at 300 K is caused by radiative transitions of Bi³⁺ single and dimer centers, respectively. The excitation spectra of UV luminescence of Bi³⁺ single and dimer centers consist of two dominant bands, peaked at 4.7/4.315 and 5.7/6.15 eV, related to the ¹S₀→³P₁ (A band) and ¹S₀→ ¹P₁ (C-band) transitions of Bi³⁺ ions, respectively. The excitation bands that peaked at 7.0 and 7.09 eV are ascribed to excitons bound with the Bi³⁺ single and dimer centers, respectively. The visible luminescence of YAG:Bi SCF presents superposition of several wide emission bands peaking within the 3.125-2.57 eV range and is ascribed to different types of excitons localized around the Bi³⁺ single and dimer centers. Apart from the above mentioned A and C bands the excitation spectra of visible luminescence contain wide bands at 5.25, 5.93, and 6.85 eV ascribed to the O²⁻→Bi³⁺ and Bi³⁺→Bi⁴⁺ + e charge transfer transition (CTT) in Bi³⁺ single and dimer centers. The observed significant differences in the decay kinetics of visible luminescence under excitation in A and C bands of Bi³⁺ ions, CTT bands, and in the exciton and interband transitions confirm the radiative decay of different types of excitons localized around Bi³⁺ ions in the single and dimer centers.     

Photoluminescence and thermoluminescence characterization of Eu- and Dy -activated Ca3(PO4)2 phosphor

Rare-earth-doped polycrystalline Ca₃(PO₄)₂:Eu, Ca₃(PO₄)₂:Dy and Ca₃(PO₄)₂:Eu,Dy phosphors prepared by a modified solid-state synthesis has been studied for its X-ray diffraction, thermoluminescence (TL) and photoluminescence (PL) characteristics. The PL emission spectra of the phosphor suggest the presence of Eu³⁺ ion in Ca₃(PO₄)₂:Eu and Dy³⁺ ion in Ca₃(PO₄)₂:Dy lattice sites. The TL glow curve of the Ca₃(PO₄)₂:Eu compounds has a simple structure with a prominent peak at 228 °C, while Ca₃(PO₄)₂:Dy peaking at 146 and 230 °C. TL sensitivity of phosphors are compared with CaSO₄: Dy and found 1.52 and 1.20 times less in Ca₃(PO₄)₂:Eu and Ca₃(PO₄)₂:Dy phosphors, respectively. The Ca₃(PO₄)₂:Eu,Dy phosphors shows switching behavior under two different excitation wavelengths and enhancement in PL intensity of Dy³⁺ ions were reported. The paper discusses the photoluminescence and thermoluminescence behavior of Eu³⁺ and Dy³⁺ ion in Ca₃(PO₄)₂ hosts, it may be applicable to solid-state lighting as well as thermoluminescence dosimetry applications.     

A time-resolved luminescence spectroscopy study of non-linear optical crystals K2Al2B2O7

We report the results of complex study of luminescence and dynamics of electronic excitations in K₂Al₂B₂O₇ (KABO) crystals obtained using low-temperature luminescence-optical vacuum ultraviolet spectroscopy with sub-nanosecond time resolution under selective photoexcitation with synchrotron radiation. The paper discusses the decay kinetics of photoluminescence (PL), the time-resolved PL emission spectra (1.2–6.2 eV), the time-resolved PL excitation spectra and the reflection spectra (3.7–21 eV) measured at 7 K. On the basis of the obtained results three absorption peaks at 4.7, 5.8 and 6.5 eV were detected and assigned to charge-transfer absorption from O^2? to Fe³⁺ ions; the intrinsic PL band at 3.28 eV was revealed and attributed to radiative annihilation of self-trapped excitons, the defect luminescence bands at 2.68 and 3.54 eV were separated; the strong PL band at 1.72 eV was revealed and attributed to a radiative transition in Fe³⁺ ion.     

掺Bi钨酸镉单晶体发光特性的研究

用坩埚下降法(Bridgman)生长出了Bi离子掺杂的CdWO₄单晶.测定了晶体不同部位的吸收光谱、发射光谱和X射线电子能谱(XPS).Bi离子的掺入引起CdWO₄晶体的吸收边从345 nm红移到399 nm.在311 nm, 373 nm,808 nm和980 nm光的激发下,分别观测到中心波长为470 nm,528 nm,1078 nm和较弱的1504 nm四个不同发射带.Bi:CdWO₄单晶的XPS谱分别与Bi₂ 关键词： Bi离子 荧光光谱 X射线电子能谱 4单晶')" href="#">CdWO₄单晶     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Bi(PO4)3 phosphors

A series of orange reddish emitting phosphors Eu³⁺-doped Sr₃Bi(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence (PL) properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Bi(PO₄)₃:Eu³⁺ phosphors invariably exhibit five peaks assigned to the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The luminescence intensity was enhanced with increasing Eu³⁺ content and the emission reached the maximum intensity at x=0.05 in Sr₃Bi(PO₄)₃:xEu³⁺. The energy transfer behavior in the phosphors was discussed. The Commission Internationale de lEclairage (CIE) chromaticity coordinates, the quantum efficiencies, and the decay curves of the entitled phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Bi(PO₄)₃ phosphors are promising orange reddish-emitting phosphors pumped by near-UV light.     

Photoluminescence and excited state structure in Bi3+-doped Y2SiO5 single crystalline films

Single crystalline films of Bi-doped Y₂SiO₅ are studied at 4.2–350 K by the time-resolved luminescence methods under excitation in the 3.8–6.2 eV energy range. Ultraviolet luminescence of Y₂SiO₅:Bi (≈3.6 eV) is shown to arise from the radiative decay of the metastable and radiative minima of the triplet relaxed excited state (RES) of Bi³⁺ centers which are related to the ³P₀ and ³P₁ levels of a free Bi³⁺ ion, respectively. The lowest-energy excitation band of this emission, located at ≈4.5 eV, is assigned to the ¹S₀ → ³P₁ transitions of a free Bi³⁺ ion. The phenomenological model is proposed to describe the excited-state dynamics of Bi³⁺ centers in Y₂SiO₅:Bi, and parameters of the triplet RES are determined.     

Luminescence of LiTb(PO3)4:Sm3+ and energy transfer from Tb3+ to Sm3+ under vacuum ultraviolet–ultraviolet excitation

The photoluminescence (PL) of LiTb(PO₃)₄, LiGd_0.97Sm_0.03(PO₃)₄, and LiTb_0.97Sm_0.03(PO₃)₄ under vacuum ultraviolet (VUV)/ultraviolet (UV) excitation were studied. We observed the VUV–UV sensitization of Sm³⁺ emission (561 nm, 601 nm, 649 nm, and 710 nm) by Tb³⁺ in LiTb(PO₃)₄:Sm³⁺, which leads to the yellow light emission (486 nm, 546 nm, 561 nm, 587 nm, 601 nm, 621 nm, 649 nm, and 710 nm) of LiTb(PO₃)₄:Sm³⁺ phosphor under UV and VUV excitation. The emission is a result of partial energy transfer from Tb³⁺ to Sm³⁺, which is discussed in detail in terms of the excitation and emission spectra and decay curves.     

Eu and Ce emission in sulphate based phosphors

Polycrystalline KMgSO₄Cl:Eu and Na₅(PO₄)SO₄:Ce phosphors prepared by a wet chemical method have been studied for its photoluminescence (PL) and thermoluminescence (TL) characteristics. The TL glow curve of the compound has a prominent peak at 200 °C and may be useful for TL study. TL sensitivity of the KMgSO₄Cl:Eu phosphor is found to be 1.7 times less than that of TLD—CaSO₄:Dy. The presence of bands at around 420, 435 and 445 nm in the PL emission spectra of the phosphor suggests the presence of Eu²⁺ in the host compound. Moreover a TL glow curve of the Na₅(PO₄)SO₄:Ce gives a better understanding of the TL mechanism (peaks at 271 and 310 °C) involved in the concerned phosphor. The PL emission spectra are observed at 382 nm for the various concentrations. In this paper we report PL and TL characteristics of KMgSO₄Cl:Eu halosulphate and Na₅(PO₄)SO₄:Ce phosphate sulphate phosphors first time.     

Crystal growth and optical properties of Cr3+, Er3+, RE3+: Gd3Ga5O12 (RE=Tm,Ho, Eu) for mid-IR laser applications

In this paper we report on the optical properties of triply Cr³⁺, Er³⁺, and RE³⁺ (RE=Tm, Ho, Eu) doped Gd₃Ga₅O₁₂ crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr³⁺ ion highly increases the absorption pump power and the three kinds of co-doped RE³⁺ ions depopulate the Er:⁴I_13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ～3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others.     

Time-resolved luminescence spectroscopy of pure and doped with Ce3+ ions SrAlF5 crystals

The results of a study of time-resolved photoluminescence (PL) and energy transfer in both pure and doped with Ce³⁺ ions SrAlF₅ (SAF) single crystals are presented. The time-resolved and steady-state PL spectra in the energy range of 1.5–6.0 eV, the PL excitation spectra and the reflectivity in the energy range of 3.7–21 eV, as well as the PL decay kinetics were measured at 8.8 and 295 K. The lattice defects were revealed in the low temperature PL spectra (emission bands at 2.9 and 4.5 eV) in the undoped SAF crystals. The luminescence spectra of the doped Ce³⁺:SAF crystals demonstrate a new selective emission bands in the range of 3.7–4.5 eV with the exponential decay kinetics (τ ≈ 60 ns at X-ray excitation). These bands correspond to the d-f transitions in Ce³⁺ ions, which occupy nonequivalent sites in the crystal lattice.     

Synthesis and optical properties of Er and Eu doped SrAl2O4 phosphor ceramic

We report, for the first time on luminescence from a Er³⁺ doped SrAl₂O₄ phosphor. Effects of Eu³⁺ doping were also studied. The influence of rare-earth doping in crystal structure and its optical properties were analysed by means of X-ray diffraction (XRD), Raman scattering, optical absorption, excitation and emission (PL) spectroscopy, thermally stimulated luminescence (TSL) and scanning electron microscope (SEM). Luminescence spectra and luminescence decay curves for Er³⁺ transitions in the near infrared region were recorded. The PL maximum for Eu doped SrAl₂O₄ is obtained at 620 nm and corresponds to the orange region of the spectrum. Diffraction patterns reveal a dominant phase, characteristic of the monoclinic SrAl₂O₄ compound and the presence of dopants has no effect on the basic crystal structure of SrAl₂O₄. The shapes of the glow curves are different for each dopant irradiated with either a ⁹⁰Sr-⁹⁰Y beta source, or UV light at 311 nm, and in detail the TL signals differ somewhat between Er and Eu dopants.     

Luminescence properties of Eu3+ and Sm3+ coactivated Gd(III) tungstate phosphor for light-emitting diodes

Rare-earth ions coactivated red phosphors Gd_0.2RE_1.8(WO₄)₃ (RE=Eu³⁺ and Sm³⁺) were synthesized by conventional solid-state reaction using boric acid as a flux agent. The samples were characterized by X-ray diffractometer (XRD), energy-dispersive X-ray spectrometer (EDS) and luminescence spectrometer (LS). The results showed that the Eu–Sm system exhibits higher emission intensity than those of the Eu single-doped system and Sm separate-doped system under ultraviolet (UV) radiation. Samarium(III) ions are effective in broadening and strengthened absorptions around 400 nm. Furthermore, it exhibits enhanced luminescence emission. when the mole ratio of boric acid is about 0.16, the luminescence capability is optimum. Two strongest lines at ultraviolet (394 nm) and blue (465 nm) in excitation spectra of these phosphors match well with the output wavelengths of UV and blue GaN-based light-emitting diodes (LEDs) chips.     

Luminescence and electronic excitations in crystals K<Subscript>2</Subscript>Al<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>7</Subscript> with defects

This paper reports on the results of the comprehensive study of the dynamics of electronic excitations in K₂Al₂B₂O₇ (KABO) crystals, obtained by low-temperature luminescence vacuum ultraviolet spectroscopy with nanosecond time resolution upon photoexcitation by synchrotron radiation. For the first time, the data have been obtained on the photoluminescence (PL) decay kinetics, PL spectra with time resolution, PL excitation spectra with time resolution, and reflection spectra at 7 K; the intrinsic nature of PL at 3.28 eV has been established; luminescence bands of defects have been separated in the visible and ultraviolet spectral regions; an intense long-wavelength PL band has been detected at 1.72 eV; channels of the formation and decay of electronic excitations in K₂Al₂B₂O₇ crystals have been discussed.     

Photoluminescence of AgGaS2 and CuGaS2 doped with rare-earth impurities

Photoluminescence (PL) related to rare-earth (RE) impurities (Ho, Er and Eu) in AgGaS₂ and CuGaS₂ crystals has been studied. In Ho-doped AgGaS₂ and CuGaS₂, two series of PL lines are observed in 1.86–1.92 eV region and 2.24 eV region, and they are assigned to ⁵F₃–⁵I₇ and ⁵S₂–⁵I₈ transitions of the Ho³⁺ ion, respectively. Similarly, in Er-doped AgGaS₂ and CuGaS₂, Er³⁺-related two PL series are observed: 1.83–1.88 eV region (⁴F_9/2–⁴I_15/2) and 2.22–2.26 eV region (⁴S_3/2–⁴I_15/2). For both Ho and Er impurities, the profile of the PL spectrum in AgGaS₂ is complex, and PL exhibited large number of lines compared with that in CuGaS₂. The differences in PL spectra between this two compounds are related to the crystal field at the cation site and the local atomic arrangement of the RE impurities. This work also refers to the PL band at 2.28 eV observed for the Eu-doped AgGaS₂ crystal.     

Luminescence of Bismuth‐Activated Ceramics of Yttrium and Scandium Oxides

The luminescence spectra of Y₂O₃:Bi and Sc₂O₃:Bi ceramics have been investigated. The spectra have been resolved into elementary components by the Alentsev–Fock method. It has been established that the luminescence is attributed to emission centers of three types, two of which are due to the replacement of Y³⁺ (or Sc³⁺) by Bi³⁺ at the nodes of the crystal lattice of Y₂O₃ (or Sc₂O₃) with the point symmetry C ₂ and C _3i . The emission center Bi³⁺ in the position C_3i leads to the appearance of blue luminescence with maxima at 3.03 eV for Y₂O₃:Bi and at 3.05 eV for Sc₂O₃:Bi; this luminescence is attributed to the transition ³ P ₁–¹ S ₀. The emission center Bi³⁺ in the position C ₂ initiates green luminescence (which is also related to the ³ P ₁–¹ S ₀ transition in Bi³⁺) with a maximum in the region of 2.40 eV in Y₂O₃:Bi and in the region of 2.46 eV in Sc₂O₃:Bi. The red luminescence band with maxima at 1.85 eV in Y₂O₃:Bi and at 1.95 eV in Sc₂O₃:Bi is related to the presence of structural defects.     

Effect of solid-phase amorphization on the spectral characteristics of europium-doped gadolinium molybdate

A method is proposed for detecting spectral characteristics of optically inactive molybdates of rare-earth elements by their doping with rare-earth ions whose luminescence lies in the transparency region of all structural modifications of the sample. Gadolinium molybdate is chosen as the object of investigations, while europium ions are used as an optically active and structurally sensitive admixture. It is shown that after the action of a high pressure under which gadolinium molybdate passes to the amorphous state, the spectral characteristics of Gd_1.99Eu_0.01(MoO₄)₃ (GMO:Eu) change radically; namely, considerable line broadening is observed in the luminescence spectra and the luminescence excitation spectra, while the long-wave threshold of optical absorption is shifted considerably (by approximately 1.1 eV) towards lower energies. It is found that by changing the structural state of GMO:Eu by solid-state amorphization followed by annealing, the spectral characteristics of the sample can be purposefully changed. This is extremely important for solving the urgent problem of designing high-efficiency light-emitting diodes producing “white” light.     

Violet-blue-shift of emission and enhanced luminescent properties of Ca3(PO4)2:Ce3+ phosphor induced by substitution of Gd3+ ions

Ca₃(PO₄)₂:1mol%Ce³⁺/xGd³⁺ (where x = 0.5, 1.0, 3.0 and 5.0 mol%) phosphors were synthesized by the conventional combustion synthesis method. The X-ray diffraction patterns showed their rhombohedral structure with space group of R3c. The optical properties including reflectance, excitation and emission were investigated. The band gaps of the phosphors were calculated from diffuse reflectance spectra data using the Kubelka–Munk function. The photoluminescence (PL) excitation spectra exhibited the broadband 4f–5d transition of Ce³⁺ ions centered at ~265 nm. The PL emission properties of the Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphors were studied as a function of the Gd³⁺ ion concentration. The Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor had a wide emission band ranging from 320 to 400 nm, and peaking at 365 nm. This emission is ascribed to the transition from the higher 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. The 365 nm peak shifted to longer wavelengths with increasing concentration of the Gd³⁺ ion. The CIE chromaticity diagram of Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor showed tunable emission colour from violet to violet-blue, suggesting that this phosphor can act as a source of violet-blue colour for application in information displays, phototherapy and photoluminescent liquid crystal displays.