Luminescence properties of a novel greenish-blue emission long persistent phosphor Sr3TaAl3Si2O14:Pr3+

Pr³⁺exhibits prominent red emission in most oxide phosphors, which derives from the ¹D₂→³H₄ transition, and green or blue emission from ³P₀→³H_{4, 5} transitions are normally less intense in most cases. However, a greenish-blue emission was observed from Sr₃TaAl₃Si₂O₁₄:Pr³⁺prepared via solid state reaction. All as-prepared phosphors were studied systematically by X-ray diffraction (XRD), photoluminescence spectra, decay curves, long afterglow (LAG) spectra and thermoluminescence (TL) glow curves. Based on the excitation and emission spectra, the Sr₃TaAl₃Si₂O₁₄ (STAS) host is proved to be a self-activated luminescent host lattice. In the emission spectra for Pr³⁺doped STAS, the predominant greenish-blue emission locating at ~489 nm and ~507 nm coming from ³P_0,1→³H₄ transitions were observed. And the different mechanisms for concentration quenching in both cases were discussed. At last, a model was proposed on the basis of experimental results to discuss the LAG mechanism of STAS:Pr³⁺in detail.     

Red-emitting enhancement of Bi4Si3O12:Sm3+ phosphor by Pr3+ co-doping for White LEDs application

In this account, Bi₄Si₃O₁₂:Sm³⁺ and (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) red phosphors were prepared by solution combustion method fueled by citric acid at 900 °C for 1 h. The effects of co-doping Pr³⁺ ions on red emission properties of Bi₄Si₃O₁₂:Sm³⁺ phosphors, as well as the mechanism of interaction between Sm³⁺ and Pr³⁺ ions were investigated by various methods. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) revealed that smaller amounts of doped rare earth ions did not change the crystal structure and particle morphology of the phosphors. The photoluminescence spectroscopy (PL) indicated that shape and position of the emission peaks of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at λ_ex=403 nm were similar to those of Bi₄Si₃O₁₂:Sm³⁺ phosphors. The strongest emission peak was recorded at 607 nm, which was attributed to the ⁴G_5/2→⁶H_7/2 transition of the Sm³⁺ ion. The photoluminescence intensities of Bi₄Si₃O₁₂:Sm³⁺ phosphors were significantly improved by co-doping with Pr³⁺ ions and were maximized at Sm³⁺ and Pr³⁺ ions doping concentrations of 4 mol% and 0.1 mol%, respectively. The characteristic peaks of Sm³⁺ ions were displayed in the emission spectra of (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors excited at respectively λ_ex=443 nm and λ_ex=481 nm (Pr:³H₄→³P₂, ³H₄→³P₀). This indicated the existence of Pr³⁺→Sm³⁺ energy transfer in (Bi₄Si₃O₁₂:Sm³⁺, Pr³⁺) phosphors.     

Persistent photoluminescence emission from SrTa2O6:Pr3+ phosphor prepared at different temperatures

Phosphors with persistent emission are of interest for security and emergency signage, and medical diagnosis. Three SrTa₂O₆:Pr³⁺phosphor samples with persistent emission were prepared by solid state reaction at 1200, 1400 and 1500 °C. Structural crystallization was shown to improve with an increase in temperature as identified by X-ray diffraction. The scanning electron microscopy images showed that the particles of the phosphor were agglomerated and co-melting was induced by increasing the synthesis temperature. The ion distribution in the phosphors was determined using the time of flight secondary ion mass spectroscopy. The red emission was obtained from the D₂→³H₄ and the ³P₀→³H₆ transitions at 608 and 619 nm, respectively. The main absorption occurred at 225 nm (5.5 eV), and the band gap (E_g) calculations confirmed that it corresponds to band-to-band excitation. Another excitation due to charge transfer at 300 nm was also obtained which makes the phosphor suitable to be used in red light emitting diodes. The persistent emission time parameters (260–296 s) were calculated from the phosphorescence decay curves using the second order exponential decay equation. The corresponding electron trapping centers were determined using the thermoluminescence spectroscopy, and the activation energy was determined using the initial rise method.     

Photoluminescence properties of Pr3+ ion-doped YInGe2O7 phosphor under an ultraviolet irradiation

Pr³⁺ ion-doped YinGe₂O₇ phosphors are synthesized by a vibrating milled solid state reaction. There is a red shift for the excitation peak for the charge transfer transition between In³⁺ and O^2- ion because the numbers of oxygen vacancies change the structure, which leads to a change in the crystal field. The results indicate that the emission spectra for the YinGe₂O₇:Pr samples under an excitation of 263 nm exhibit two dominant peaks at 486 and 604 nm, which are respectively assigned to the ³P₀→³H₄ and ¹D₂→³H₄ transitions. The chromaticity coordinate for (Y_1?xPr_x)InGe₂O₇ phosphors varies with the Pr³⁺ doping concentration, from white, to greenish, to blueish. This has a potential application as a white light emitting phosphor for ultraviolet light-emitting diodes.     

Fatigue-resistant,temperature-insensitive strain behavior and strong red photoluminescence in Pr-modified 0.92(Bi0.5Na0.5)TiO3–0.08(Ba0.90Ca0.10)(Ti0.92Sn0.08)O3 lead-free ceramics

An electric-field-induced large strain and strong photoluminescence was achieved by introducing trivalent Pr³⁺ as the activator into 0.92(Bi_0.5Na_0.5)TiO₃ − 0.08(Ba_0.90Ca_0.10)(Ti_0.92Sn_0.08)O₃ (BNT−8BCST) ceramics. Around a critical composition of 0.4 mol% Pr³⁺, a large strain of ∼0.39% with a relatively small hysteresis compared with existing lead-free Bi-perovskite ceramics was obtained. In particular, the strain is very resistant to field cycling and thermal shock, giving the materials attractive for its exceptionally good fatigue resistance and high temperature stability. Besides the excellent electrical properties, Pr³⁺-modified BNT−8BCST host exhibits a strong photoluminescence with a bright red emission at 610 nm assigned to ¹D₂ → ³H₄ transitions of the Pr³⁺ ions upon a blue light excitation of 400–500 nm. The photoluminescence can be enhanced through poling treatment of the samples. Moreover, samples have a superior water resistance property which almost maintaining the same photoluminescence intensity after 40 h water immersion time. These results suggest the material may have potential application as a multifunctional device such as “on-off” actuator and electric field-controlled photoluminescence devices by integrating its excellent luminescence and electrical properties.     

Efficient near-infrared to visible and ultraviolet upconversion in polycrystalline BiOCl:Er3+/Yb3+ synthesized at low temperature

Er³⁺/Yb³⁺ co-doped BiOCl poly-crystals were synthesized by the conventional solid state method at 500 °C, which exhibited good crystalline and low phonon energy. Under 980 nm excitation, the samples showed intense red upconversion (UC) luminescence (Er³⁺: ⁴F_9/2→⁴I_15/2) as well as other four UC emission bands, including ultraviolet (UV) emission at 380 nm, violet emission at 411 nm, green UC emissions at 525 and 545 nm and near-infrared (NIR) emission between 800 and 850 nm, corresponding to the transitions of ⁴G_11/2, ²H_9/2, ²H_11/2, ⁴S_3/2 and ⁴I_9/2→⁴I_15/2 of Er³⁺, respectively. Interestingly, including the violet and green UC emissions, the red one originated a nearly three-photon process in this system, and a possible UC mechanism was proposed for the enhanced red emission.     

Fabrication and characterizations of (Lu,Gd)2O3:Eu scintillation ceramics

In this paper, (Lu,Gd)₂O₃:Eu ceramics were consolidated by the solid-state reaction method combined with vacuum sintering at 1820 °C for 10 h. It is found that the Gd₂O₃ incorporates well into the Lu₂O₃ lattices and forms a solid solution. Particularly, strong red emission of ⁵D₀→⁷F₂ transition of Eu³⁺ at 611 nm, matched well to the spectral sensitivity of typical CCD arrays, was observed in the photoluminescence and radioluminescence spectra. What's more, radioluminescence intensity of the 4f→4f transitions of Eu³⁺ reaches up to 10 times of bismuth germanium oxide (BGO) single crystal reference scintillator. Intensities of the radioluminescence and the integrated thermoluminescence versus temperatures, as well as the influence of annealing treatment on the thermoluminescence intensity, were also studied. We think that (Lu,Gd)₂O₃:Eu ceramic scintillators may have great potential in medical X-ray computed tomography (CT) due to their excellent properties.     

Photoluminescence properties of a double perovskite tungstate based red-emitting phosphor NaLaMgWO6:Sm3+

In this work, the conventional solid-state method was applied to synthesize a series of red-emitting NaLaMgWO₆:Sm³⁺ phosphors. The crystal structure, phase purity, morphology, particle size distribution as well as elemental composition of the as-prepared phosphors were investigated carefully with the aid of XRD, SEM, EDS, FT-IR analyses, indicating the high-purity and micron-sized NaLaMgWO₆:Sm³⁺ phosphors with monoclinic structure were prepared successfully. The spectroscopic properties of Sm³⁺ in NaLaMgWO₆ host including UV–vis diffuse reflection spectrum, photoluminescence excitation and emission spectra, decay curves, chromaticity coordinates and internal quantum efficiency were investigated in detail. Upon excitation with UV (290 nm) and n-UV (406 nm), NaLaMgWO₆:Sm³⁺ phosphor presented red emission corresponding to the ⁴G_5/2→⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺, in which the hypersensitive electronic dipole transition ⁴G_5/2→⁶H_9/2 (645 nm) was with the strongest emission intensity because Sm³⁺ ions were located at a lattice site with anti-inversion symmetry. The optimal concentration of Sm³⁺ was different for the given excitation wavelength such as 290 nm and 406 nm, which was interpreted by the extra effect of the energy transfer from W⁶⁺-O^2- group to Sm³⁺. The decay lifetime for ⁴G_5/2→⁶H_9/2 transition of Sm³⁺ was very short (< 1 ms) and decreased with the increasing Sm³⁺ concentration. The present investigation indicates that NaLaMgWO₆:Sm³⁺ phosphor could be a potential red component for application in w-LEDs.     

Efficient sensitization of Tb3+ emission by Dy3+ in CaMoO4 phosphors: Energy transfer,tunable emission and optical thermometry

Dy³⁺/Tb³⁺ codoped CaMoO₄ phosphors were synthesized by a simple sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The energy transfer process of Dy³⁺→Tb³⁺ was confirmed by excitation and emission spectra and luminescence decay curves, and the energy transfer efficiency was also estimated. The results verified that the efficient emission of Tb³⁺ was sensitized by Dy³⁺ under the excitation of 354 nm, realizing tunable emission in CaMoO₄ phosphors. Furthermore, optical thermometry was achieved by the fluorescence intensity ratio between Tb³⁺: ⁵D₄→⁷F₅ (~546 nm) and Dy³⁺: ⁴F_9/2→⁶H_13/2 (~575 nm). It is expected that the investigated CaMoO₄ nanograins doped with Dy³⁺/Tb³⁺ have prospective applications in display technology and optical thermometry.     

Synthesis and photoluminescence properties of Sr3(PO4)2:Re3+, Li+ (Re = Eu,Sm) red phosphors for white light-emitting diodes

Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) red phosphors were prepared via a high temperature solid state reaction, and their structure and luminescence properties were investigated. X-ray diffraction patterns indicate that the phase of as-prepared samples is in good agreement with standard Sr₃(PO₄)₂ structure. Under 395 nm excitation, the emission of Sr₃(PO₄)₂:Eu³⁺ consists of a strong peak centered at 622 nm and two weak peaks centered at 598 nm and 660 nm, which correspond to ⁵D₀→⁷F₂, ⁵D₀→⁷F₁ and ⁵D₀→⁷F₃ transitions, respectively. Also, the emission spectrum of Sr₃(PO₄)₂:Sm³⁺ shows three main peaks at 568 nm, 603 nm and 651 nm, which are attributed to ⁴G_5/2→⁶H_I/2 (I = 5, 7, 9) transitions of Sm³⁺. Furthermore, luminescence properties of Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) samples are enhanced significantly by Li⁺ ions doping as charge compensator. Results indicate that as-prepared Sr₃(PO₄)₂:Re³⁺, Li⁺ (Re = Eu, Sm) could be the potential red phosphors used in white light-emitting diodes.     

1.53 µm luminescence properties of Er3+-doped K–Sr–Al phosphate glasses

Trivalent erbium (Er³⁺)-doped K–Sr–Al phosphate glasses were prepared and studied their spectroscopic properties as a function of Er₂O₃ concentration. Judd–Ofelt analysis has been carried out for 1.0 mol% Er₂O₃-doped phosphate glass and in turn radiative properties have been evaluated for the excited levels of Er³⁺ ion. The radiative lifetime for the ⁴I_13/2 level was found to be higher for the present glass when compared to other Er³⁺-doped glasses. The Er³⁺-doped glasses exhibit intense near infrared emission at 1.53 µm corresponds to ⁴I_13/2→⁴I_15/2 transition as well as green emission at 546 nm corresponding to ⁴S_3/2→⁴I_15/2 under 980 nm and 488 nm excitations, respectively. The emission cross-section spectrum for 1.0 mol% of Er₂O₃-doped glass has been evaluated using McCumber theory. The gain cross-section has been evaluated as a function of population inversion, which revealed that the lasing action would be achieved at 1.53 µm for a population inversion about 40%. Decay curves for the ⁴I_13/2 level were measured and lifetimes have been determined for the studied glasses. The results indicate that the present glasses could be useful for laser as well as optical amplifiers at 1.53 µm.     

Photochemical reductive elimination of [PtIV(NH3)4(NH2)Cl]2 +: Photogeneration of hydrazine

When [Pt^IV(NH₃)₅Cl]^3 + is deprotonated the complex [Pt^IV(NH₃)₄(NH₂)Cl]^2 + is formed. Upon NH₂⁻ → Pt^IV LMCT excitation (λ_irr > 250 nm) a reductive elimination takes place: [Pt^IV(NH₃)₄(NH₂)Cl]^2 + → [Pt^II(NH₃)₃Cl]⁺ + N₂H₄ + H⁺. Since Pt(II) ammine complexes can be reoxidized to Pt(IV) by H₂O₂ it is suggested that in a cyclic process the overall reaction could proceed according to the equation: 2 NH₃ + H₂O₂ → N₂H₄ + 2 H₂O.     

Upconverting luminescence based dual-modal temperature sensing for Yb3+/Er3+/Tm3+: YF3 nanocrystals embedded glass ceramic

Yb³⁺/Er³⁺/Tm³⁺ doped transparent glass ceramic containing orthorhombic YF₃ nanoparticles was successfully synthesized by a melt-quenching method. After glass crystallization, tremendously enhanced (about 5000 times) upconversion luminescence, obvious Start-splitting of emission bands as well as long upconversion lifetimes of Er³⁺/Tm³⁺ confirmed the incorporation of lanthanide activators into precipitated YF₃ crystalline environment with low phonon energy. Furthermore, temperature-dependent upconversion luminescence behaviors of glass ceramic were systematically investigated to explore its possible application as optical thermometric medium. Impressively, both fluorescence intensity ratio of Er³⁺: ²H_11/2 → ⁴I_15/2 transition to Er³⁺: ⁴S_3/2 → ⁴I_15/2 one and fluorescence intensity ratio of Tm³⁺: ³F_2,3 → ³H₆ transition to the combined Tm³⁺: ¹G₄ → ³F₄/Er³⁺: ⁴F_9/2 → ⁴I_15/2 ones were demonstrated to be applicable as temperature probes, enabling dual-modal temperature sensing. Finally, the thermal effect induced by the irradiation of 980 nm laser was found to be negligible in the glass ceramic sample, being beneficial to gain intense and precise probing signal and detect temperature accurately.     

Spectroscopic and energy transfer mechanism of Er3+, Pr3+-codoped ZBYA glass

Absorption spectra, emission spectra and the rate parameters of the energy-exchange processes relevant to the ⁴I_11/2→⁴I_13/2 laser transition in Er³⁺/Pr³⁺- codoped ZBYA(ZrF₄–BaF₂–AlF₃–YF₃) glass were presented. Intensive 2.7 μm emission was obtained in the codoped glass and the optimized concentration ratio of Pr³⁺ to Er³⁺ was found to be 0.1:1. With the presence of Pr³⁺ ions, the intensities of the green and near-infrared emission were dramatically reduced to 1/15 and 1/21, respectively. The Er³⁺/Pr³⁺-codoped sample was found to have higher predicted spontaneous transition probability (16.57%) along with larger calculated emission cross section (14.6×10⁻²¹ cm²). These results suggest that the 2.7 μm emission of Er³⁺ ions could be achieved in ZBYA glass and codoping with Pr³⁺ could greatly improve the mid-infrared emission performance.     

New LiNi0.5PrxFe2−xO4 nanocrystallites: Synthesis via low cost route for fabrication of smart advanced technological devices

Praseodymium substituted nano-crystalline Li-Ni spinel ferrites with different Pr³⁺ contents were synthesized by micro-emulsion method. X-ray diffraction (XRD), scanning electron spectroscopy (SEM) and vibrating sample magnetometery (VSM) techniques were employed to study the impact of substitution of the Pr³⁺ on the structure, surface morphology and magnetic parameters. XRD confirmed the formation of the single phase spinel ferrites of all compositions of LiNi_0.5Pr_xFe_2−xO₄ nanocrystallites. The crystallite size determined from XRD data by Scherrer formula was calculated in range from 40 nm to 70 nm. However the nanoparticles size estimated by SEM was found 35–115 nm. The room temperature VSM measurements were carried out in the applied field range from “−10,000 Oe” to “10000” Oe. Saturation magnetization (M_S) (41 emu/g) and coercivity (H_C) values (156.9 Oe) of LiNi_0.5Fe₂O₄ were improved by the addition of rare earth Pr³⁺ cations. The value of Hc is low, which is a strong indication of soft ferrites. The synthesized LiNi_0.5Pr_xFe_2−xO₄ ferrites may be utilized for low core losses on transformers.     

Gd-based oxyfluoride glass ceramics: Phase transformation,optical spectroscopy and upconverting temperature sensing

A series of precursor glasses with compositions of SiO₂-Al₂O₃-AlF₃-Na₂O- NaF-Gd₂O₃/GdF₃-YbF₃-ErF₃ were prepared and their crystallization behaviors were investigated. For the samples with high F content, meta-stable hexagonal GdF₃ nanocrystals were preferentially precipitated from glass matrix and decreasing F/O ratio induced phase transformation to cubic NaGdF₄ and finally to hexagonal NaGdF₄. Benefited from its multiple active sites, significant enhanced upconversion luminescence was achieved for Yb/Er co-doped glass ceramic containing hexagonal NaGdF₄ nanocrystals. Importantly, significant temperature-sensitive upconversion fluorescence intensity ratio between Er³⁺: ²H_11/2 → ⁴I_15/2 transition (520 nm) and ⁴S_3/2 → ⁴I_15/2 one (540 nm) was detected owing to the competitive radiation transitions from these two thermally coupled emitting-states. Furthermore, linear temperature-dependent fluorescence intensity ratio between Er³⁺: ⁴F_9/2 → ⁴I_15/2 transition (650 nm) to ⁴S_3/2 → ⁴I_15/2 one (540 nm) was achieved, showing the advantages of high sensitivity, superior signal discriminability as well as excellent thermal stability for temperature determination.     

Synthesis and characterization of Eu3+-doped C12H18Ca3O18 phosphor

A series of Eu³⁺-doped C₁₂H₁₈Ca₃O₁₈ phosphors were synthesized through a facile hydrothermal method and the properties of as-prepared phosphors were explored by X-ray diffractometer (XRD), scanning electron microscope (SEM), and photoluminescence (PL) spectrometer. The exploration results indicated that the C₁₂H₁₈Ca₃O_18:Eu³⁺ had been successfully synthesized. The morphology of C₁₂H₁₈Ca₃O_18:Eu³⁺ was a strip with the size of 100–4000 nm × 50–400 nm × 50–200 nm and the ratio of length to width of 2–80. The strongest emission peak of C₁₂H₁₈Ca₃O_18:Eu³⁺ around 620 nm was ascribed to ⁵D_o→⁷F₂ transition of Eu³⁺, and the peaks centered at 590, 653 and 694 nm respectively corresponded to ⁵D_o →⁷F₁, ⁷F₃, and ⁷F₄ transitions. C₁₂H₁₈Ca₃O_18: Eu³⁺ gave the red light emission, as indicated by color coordinate analysis. The photoluminescence intensity of the phosphors prepared under the Eu³⁺ concentration of 6% was the highest. The crystal structure of C₁₂H₁₈Ca₃O_18:Eu³⁺ was changed after europium ions occupied the lattice position of calcium ions. Europium ion could displace calcium arbitrarily. As a new kind of matrix, calcium citrate possesses the properties of both organic and inorganic compounds and the luminescent C₁₂H₁₈Ca₃O₁₈: x Eu³⁺ particles may be applied in biological fluorescent tags and luminescent materials.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Y(PO4)3 red phosphors

A series of red-emitting phosphors Eu³⁺-doped Sr₃Y(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence 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 Sr₃Y(PO₄)₃:Eu³⁺ phosphors exhibit peaks associated with 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 integral intensity of the emission spectra of Sr₃Y_0.94(PO₄)₃:0.06Eu³⁺ phosphors excited at 392 nm is about 3.4 times higher than that of Y₂O₃:Eu³⁺ commercial red phosphor. The Commission Internationale de l’Eclairage chromaticity coordinates, the quantum efficiencies and decay times of the phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Y(PO₄)₃ phosphors are promising red-emitting phosphors pumped by near-UV light.     

Investigation on the preparation and luminescence property of (Gd1−xDyx)2O3 (x=0.01–0.10) spherical phosphors

Uniform spheres of (Gd_1−xDy_x)₂O₃ (x=0.01–0.10) have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The synthesis, particle size control, luminescent properties and energy transfer of the (Gd_1-xDy_x)₂O₃ were systematically studied by the combined techniques of fourier transform infrared (FT-IR) spectroscopy, x-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence excitation/ photoluminescence (PLE/PL) spectroscopy, and fluorescence decay analysis. The precursor exhibit mono-dispersed spherical morphology and its size can be efficiently controlled by adjusting the urea content. The phase pure (Gd_1−xDy_x)₂O₃ oxides can be obtained by calcining precursor at 600 °C, and the spherical morphology remained at even high temperature of 1000 °C. The (Gd_1−xDy_x)₂O₃ phosphors display strong yellow emission at 575 nm (⁴F_9/2→⁶H_13/2 transition of Dy³⁺) and weak blue emission at 486 nm (⁴F_9/2→⁶H_15/2 transition of Dy³⁺) upon ultraviolet (UV) excitation of Gd³⁺ at 275 nm (⁸S_7/2→⁶I_J transition of Gd³⁺). The optimal content of Dy³⁺ was found to be ~2 at% (x=0.02) due to the concentration quenching. Owing to the efficient Gd³⁺→Dy³⁺energy transfer, the fluorescent property of the phosphor was significantly improved. The emission intensity of (Gd_1−xDy_x)₂O₃ increased with calcination temperature and particle size increasing, while the lifetime for the 575 nm emission gradually decreased. The (Gd_1−xDy_x)₂O₃ spheres developed in the present work is expected to be a promising yellow phosphor widely used in the lighting and display areas.     

Broad band down conversion from ultra violet light to near infrared emission in YVO4:Bi3+, Yb3+ as spectral conversion phosphor for c-Si solar cells

Vanadate based down conversion phosphors have been synthesized by a novel co-precipitation technique. The effect of pH on crystal structure, particle size, morphology and luminescence properties were investigated by XRD, SEM-EDAX, FT-IR and PL measurements. As different from other reports (blue, green emission) the produced phosphors have shown greenish–yellow emission, owing to their fine particle size. A broad band excitation (280–370 nm), ascribed to ¹S₀→³P₁ and an intense greenish–yellow band emission (410–700 nm) attributed to ³P₁→¹S₀ transition of Bi³⁺ were observed. A strong greenish–yellow emission was measured with 3 mol. % of Bi³⁺ ions, as an optimum dopant concentration. The characteristic NIR emission of Yb³⁺, owing to ²F_5/2→²F_7/2 was recorded at 1039 nm, as a result of efficient energy transfer from Bi³⁺ to Yb³⁺, ions. The phosphors with chemical composition as Y_0.96VO₄: Bi_0.03³⁺, Yb_0.01³⁺ and Y_0.87VO₄: Bi_0.03³⁺,Yb_0.1³⁺ are suggested to be the novel candidates for the efficient down conversion of broad band ultra violet (UV) light into visible/near infrared (NIR) emission, as DC layers on c-Si solar cells for better harvesting the solar spectrum via spectral matching phenomena.