Synthesis and spectroscopic analysis of Sm3+ doped CeO2 ceramic powders for the application of white LEDs

Orange-red light-emitting Sm³⁺-doped cerium oxide (CeO₂) ceramic powder with various concentrations of Sm³⁺ ions was prepared through a sol-gel process. X-ray diffraction and Rietveld analysis confirmed the formation of a purely cubic structure with a space group of $\mathit{Fm}\stackrel{?}{3}m$. The lattice parameters and unit cell volumes of the CeO₂:Sm³⁺ powder increased with the concentration of Sm³⁺ ions. The energy-dispersive X-ray spectra and corresponding mapping images confirmed the elemental composition and adequate dispersion of all elements in the CeO₂:Sm³⁺ powder. A broad excitation band at approximately 365?nm was observed in the excitation spectra of CeO₂:Sm³⁺ phosphors owing to the charge transfer transition from O 2p to Ce 4f orbitals. The Sm³⁺ doped CeO₂ phosphors emitted sharp luminescence with a main peak at 615?nm under excitation at 360?nm. The spectral analysis revealed that the CeO₂:Sm³⁺ phosphors exhibited strong orange-red emission. Concentration quenching was observed in the CeO₂:Sm³⁺ phosphors with 0.5?mol% of critical concentration of Sm³⁺ ions due to dipole dipole interaction of two nearest Sm³⁺ ions. The quantum efficiency was observed as high as 58%. The thermal stability of the present materials was estimated with the evaluation of activation energy as 0.31?eV. The broad excitation band and sharp orange–red emission indicated the potential use of CeO₂:Sm³⁺ phosphors for white light-emitting diodes.     

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.     

Effects of argon sintering atmosphere on luminescence characteristics of Ca6BaP4O17:Sm3+ phosphors

In this paper, Ca₆BaP₄O₁₇:Sm³⁺ and Li⁺ co-doped Ca₆BaP₄O₁₇:Sm³⁺ phosphors were synthesized in air and argon atmospheres using a solid-state reaction method. The phosphor morphologies and crystal structure were studied using scanning electron microscopy and X-ray diffraction, respectively. The emission and absorption characteristics were investigated using photoluminescence emission spectroscopy and diffuse reflectance spectroscopy. The surface states and composition of phosphor were investigated using X-ray photoelectron spectroscopy. The emission integrated intensities of the phosphors sintered in an argon atmosphere increased 3.5 fold than the ones sintered in air atmosphere, with Li⁺ ions becoming embedded in the lattice of the Ca₆BaP₄O₁₇:Sm³⁺ phosphor. This occurs because there are fewer defect/oxygen vacancies and less of the secondary phase forms, leading to better Sm³⁺ emission. The results suggest that sintering a mixture of the raw materials of a phosphor in an argon atmosphere is a good approach for synthesizing Ca₆BaP₄O₁₇:Sm³⁺ phosphor powders. The color purity and CIE values of an optimized phosphor sample sintered in an argon atmosphere with an Li⁺ ion compensator were calculated to be ~ 99.6% and (0.612,0.386) in the orange–red region under 405-nm excitation, respectively. Moreover, the solid solubility of Sm³⁺ ions in the Ca₆BaP₄O₁₇ host can be enhanced by using an argon atmosphere in the synthesis process.     

X-ray photoelectron spectroscopy and optical analysis of pure white light emitting Dy3+ and Mn2+ codoped Na3Y(PO4)2 phosphors for solid-state lighting

A single-phase and optimized pure white light emitting Dy³⁺-doped and Dy³⁺/Mn²⁺ codoped Na₃Y(PO₄)₂ phosphors (NYPO) were synthesized by traditional solid state reaction process. The as-synthesized phosphors were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectra and photoluminescence studies. The results suggested that the NYPO: Dy, Mn phosphors were crystallized in orthorhombic structures. The presence of dopants Dy and Mn was quantified by XPS analysis. All of the phosphors were effectively excited using a light of wavelength 351?nm and emissions in two regions, blue (~482?nm, ⁴F_9/2→⁶H_15/2) and yellow (~573?nm, ⁴F_9/2→⁶H_13/2), were obtained due to the f-f transitions of Dy³⁺ ions. The maximum intensities of Dy and Mn obtained were 0.07 and 0.05 for NYPO:Dy and NYPO:0.07Dy, Mn, respectively. The chromaticity coordinates, color temperatures, and color rendering indices of NYPO: 0.07Dy ((0.32, 0.33), 6194?K, and 48) and NYPO:0.07Dy, 0.05Mn phosphors ((0.33, 0.33), 5688?K, and 62) were determined. The energy transfer mechanism and oxygen vacancies that arise due to the introduction of Mn²⁺ ions in the NYPO:Dy phosphors, are responsible for the tuning of cool white light to pure day white light. The introduction of Mn in the Dy doped NYPO phosphor enhances the emission intensity in the phosphor.     

Dazzling cool white light emission from Ce3+/Sm3+ activated LBZ glasses for W-LED applications

We synthesized a batch of co-doped (Ce³⁺+Sm³⁺): LBZ glass specimens by melt quenching process and their structural and radiation properties were studied by employing XRD, FE-SEM, optical absorption, photoluminescence and lifetime measurements. UV–Vis–NIR absorption studies of the co-doped (Ce³⁺+Sm³⁺): LBZ glassy matrix displays pertinent bands of both Ce³⁺ and Sm³⁺ ions. Individually doped Sm³⁺: LBZ glass exhibit bright orange emission at 603?nm (⁴G_5/2 → ⁶H_7/2) under the excitation of 403?nm. Nevertheless, the luminescence intensities pertaining to Sm³⁺ were extraordinarily increased by co-doping with Ce³⁺ ions to Sm³⁺: LBZ glassy matrices because of energy transfer from Ce³⁺ to Sm³⁺. The fluorescence spectra of co-doped (Ce³⁺+Sm³⁺): LBZ exhibits characteristic emission bands of Ce³⁺ (441?nm, blue) and Sm³⁺ (603?nm, reddish orange) under the excitation of 362?nm. Decay curves of Ce³⁺ and Sm³⁺ ions in co-doped glass has been fitted to double exponential nature. The decreasing lifetime of donor ion and rising lifetime of acceptor ion in double doped glass could support the energy transfer from Ce³⁺ to Sm³⁺ ions in the host matrix. The CIE coordinates and CCT values were calculated for all the obtained co-doped glassy samples from their luminescence spectra. By adding Ce³⁺ ions to individually doped Sm³⁺: LBZ glass matrix, the emitting color changes from reddish orange to white light which resembles the energy transfer from Ce³⁺ to Sm³⁺ ions. These studies, perhaps implied that attained co-doped (Ce³⁺+Sm³⁺): LBZ glassy samples are potential materials for white lighting appliances.     

Synthesis and photoluminescence properties of novel Ca2LaSbO6:Mn4+ double perovskite phosphor for plant growth LEDs

A novel Mn⁴⁺ activated Ca₂LaSbO₆ (CLS) far-red phosphor was synthesized by high temperature solid state reaction. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence spectra, ultraviolet-visible spectra, luminescence decay times, emission-temperature relationship and internal quantum efficiency (IQE). It is found that CLS:Mn⁴⁺ phosphor has a strong broad excitation band in the range of 200–550?nm. The samples can be excited by ultraviolet and blue light. There is a wide emission band centered at 685?nm between 600?nm and 760?nm. The optimum doping concentration of Mn⁴⁺ is approximately 0.5?mol%. In addition, all the CIE chromaticity coordinates of CLS:0.005Mn⁴⁺ located at far-red region. The concentration quenching mechanism is the dipole-dipole interaction of Mn⁴⁺ activator. Importantly, the CLS:0.005 Mn⁴⁺ sample has an IQE of up to 52.2%. Finally, a 365?nm ultraviolet light emitting diode (LED) chip combined with 0.5?mol% Mn⁴⁺ far-red phosphor was used to fabricate the LED device. All the results indicated that CLS:Mn⁴⁺ phosphors have potential applications in indoor plant cultivation.     

Photoluminescence and optical temperature sensing in Sm3+-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

A series of orange-red emitting Sm³⁺ activated Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCZT: xSm³⁺, x?=?0.001–0.007) are synthesized by a conventional solid-state reaction method. The Sm³⁺ ions composition dependent photoluminescence properties are systematically investigated. Under the excitation of a 407?nm near-ultraviolet light, the ceramics exhibit strong characteristic emission of Sm³⁺ ions with dominant orange-red emission peak at around 595?nm, which is ascribed to the transition of ⁴G_5/2 → ⁶H_7/2. The BCZT: 0.004Sm³⁺ ceramic displays the optimal emission among these Sm³⁺-doped BCZT solid solutions. Moreover, the photoluminescence intensity exhibits extremely sensitive to temperature, suggesting that BCZT: 0.004Sm³⁺ could be applicable for temperature sensing. A maximum relative sensitivity of 1.89%?K^?1 at 453?K is obtained. Furthermore, the existence of ferroelectricity in the BCZT host combined with Sm³⁺ activated photoluminescence properties could be useful for developing optical-electro multifunctional materials and devices.     

Energy transfer and photoluminescent analysis of a novel color-tunable Ba2Y1-xV3O11:xSm3+ nanophosphor for single-phased phosphor-converted white LEDs

Metal nitrates are used to synthesize a series of novel Ba₂Y_1-xV₃O₁₁:xSm³⁺ nanophosphors via urea-assisted solution combustion route. X-ray diffraction (XRD), diffuse reflectance (DR), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were employed to analyse the structure, morphology, photoluminescent behaviour and energy transfer mechanism. Rietveld analysis over Ba₂Y_0.98Sm_0.02V₃O₁₁ showed that Y³⁺ ions can be well-replaced by trivalent samarium ions without resulting any major alteration in the crystal structure of host lattice. Furthermore, the lattice parameters were determined for both the host as well as the doped composition. The Scherrer equation yielded an average particle size of 44?nm, which in turn was further confirmed by TEM micrographs. The optical band-gap of the host (3.92?eV) was calculated from the diffuse reflectance spectra. Moreover, the photoluminescence spectral studies showed that under near ultra-violet (NUV) excitation of 340?nm, our nanophosphor powder exhibits the characteristic emission peaks of trivalent samarium along with the emission of VO₄^3? (501?nm) group. The excitation energy transfer from vanadate group to Sm³⁺ produced a systematic color tunablity in white region itself. The optimum Sm³⁺ concentration for better luminescence was found to be 2?mol%. The critical distance for energy transfer was calculated to be 29.02?Å, which in turn assisted to shortlist the mechanism responsible for luminescence-quenching (dipole-dipole) arising from the over-doping of the activator. The photoluminescence decay curves revealed the decay kinetics of ⁴G_5/2 electronic state. Finally, the calculation of CIE color coordinates from emission spectra in MATLAB program unveiled a somewhat white-light emitter which may find potential applications in phosphor-converted white light emitting diodes (PC-WLED) under near-ultraviolet (NUV) excitation.     

Thermal stability and luminescence of novel garnet-type yafsoanite Ca3Zn3(TeO6)2:Sm3+ phosphors for white LEDs

In this study, novel garnet-type yafsoanite tellurate Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphors are successfully synthesized using the traditional high-temperature solid-state reaction. The phase purity of the obtained phosphors is analyzed by X-ray diffraction and Rietveld refinement studies. Morphological variations are also observed with the different concentrations of Sm³⁺ ions substitution, which is analyzed using Scanning Electron Microscopy (SEM). The photoluminescent properties of the phosphors are systematically investigated. Results show that the samples display the strongest emission peak at 612 nm under the near-ultraviolet (n-UV) 409 nm excitation. This peak can be ascribed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The Ca₃Zn₃(TeO₆)₂:Sm³⁺ phosphor shows a high color purity, exhibits excellent thermal stability and good color drifting resistance. Furthermore, red and white light-emitting diodes have been successfully prepared. The white light-emitting diodes (w-LEDs) demonstrates a high color rendering index (CRI, R_a) and low correlated color temperature (CCT). This study introduces a new orange-red-emitting phosphor and discusses its application in herb-growth w-LEDs.     

Photoluminescence investigation of novel reddish-orange phosphor Li2NaBP2O8:Sm3+ with high CP and low CCT

The exploration of appropriate inorganic phosphors with high color purity (CP) and low correlated color temperature (CCT) has always been a hot issue for solid state light applications. In this work, we have developed series of Sm³⁺ doped Li₂NaBP₂O₈ (abbreviated as: LNBP) phosphors by means of the solid state synthesis route. The crystalline phase compositions, micromorphology, valence state of elements as well as photoluminescence properties were systematically illustrated. Upon the excitation wavelength at 400?nm, emission peaks are located at 561，597，643 and 699?nm, corresponding to the ⁴G_5/2 → ⁶H_5/2, ⁶H_7/2, ⁶H_9/2 and ⁶H_11/2 transitions of Sm³⁺ in the same order. The optimal doping amount of Sm³⁺ ions is 2?mol% for the reddish-orange photoluminescence of the LNBP:Sm³⁺ phosphor system. The critical energy transfer distance, mechanism of concentration quenching, CIE chromaticity coordinate, CP, CCT and internal quantum efficiency were extensively investigated. The title product might be considered as a promising candidate of phosphor in near UV-based warm white LEDs.     

Self-activated persistent luminescence from Ba2Zr2Si3O12 for information storage

Till now, many doped persistent luminescence (PersL) phosphors have been investigated and found various applications in such as bioimaging, photocatalysis and information storage, but introducing PersL emitters into a proper host is mostly complex. In this research, a self-activated PersL phosphor Ba₂Zr₂Si₃O₁₂ (BZSO) is prepared by solid state reaction. By adding NH₄Cl, the self-activated PersL intensity is evidently enhanced. The trap depths and concentrations are examined by thermoluminescence spectra. Meanwhile, Bi³⁺ ions are introduced into BZSO and show wide band photoluminescence (PL) from 300 to 600 nm. Moreover, the PL of Bi³⁺ is tunable under excitation by 265-350 nm lights. Furthermore, as a proof-of-concept design, we designed a patterned quick response (QR) code based on the self-activated PersL of BZSO, and the information of “South China University of Technology (SCUT)” can be read out by the code scanning technology. Bi³⁺-doped BZSO phosphors are suggested to provide potential applications in information storage by its self-activated PersL, and to excite researchers to study the tunable PL in Bi³⁺-doped phosphor.     

Luminescence properties of Ca2GdNbO6: Sm3+, Eu3+ red phosphors with high quantum yield and excellent thermal stability for WLEDs

A series of Ca₂GdNbO₆: xSm³⁺ (0.01 ≤ x ≤ 0.15) and Ca₂GdNbO₆: 0.03Sm³⁺, yEu³⁺ (0.05 ≤ y ≤ 0.3) phosphors were synthesized by the traditional solid-state sintering process. XRD and the corresponding refinement results indicate that both Sm³⁺ and Eu³⁺ ions are doped successfully into the lattice of Ca₂GdNbO₆. The micro-morphology shows that the elements of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor are evenly distributed in the sample, and the particle size is about 2 μm. The optical properties and fluorescence lifetime of Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors were detailedly studied. The emission peak at ⁵D₀→⁷F₂ (614 nm) is the strongest and emits red light under 406 nm excitation. The increase of Eu³⁺ concentration causes the energy transfers from Sm³⁺ to Eu³⁺ ions, and the transfer efficiency reaches 28.6%. Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor has a quantum yield of about 82.7%, and thermal quenching activation energy is of 0.312 eV. The color coordinate (0.646, 0.352) of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphors is located in the red area. The LED device fabricated based on the above phosphor emit bright white light, and CCT = 5400 K, Ra = 92.8. The results present that Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors potentially find use in the future.     

Photoluminescence properties of NUV light excited Ba(Mg1/3Nb2/3)O3:Eu3+ red phosphor with high color purity

In this work, a new red phosphor with high color purity, Eu³⁺ ions doped Ba(Mg_1/3Nb_2/3)O₃ phosphor has been prepared by wet chemical method. The structure analysis suggests BMN:x%Eu phosphors have a hexagonal phase and Ba²⁺ ions are replaced by Eu³⁺ ions in BMN. Upon excitation of NUV light, the BMN:x%Eu phosphors emit strong red light around 615?nm, derived from the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The relationship between luminescent properties and structure of BMN:x%Eu was discussed. The Judd-Ofelt intensity parameters (Ω₂, Ω₄) were calculated to analyze the asymmetry of the Eu³⁺ ions site occupancy further, and the quantum efficiency of BMN:3%Eu was found to be 77.26%. In addition, the decay curve indicates the decay time(τ) of BMN:3%Eu is determined to be 1.34?ms and Eu³⁺ ions occupy only one type of site. The CIE chromaticity coordinate (0.656,0.344) of BMN:3%Eu is quite close to the red phosphors standard value (0.670, 0.330), which indicates BMN:x%Eu can be a suitable red phosphor used in NUV-based white LEDs.     

Synthesis and optical characterization of novel Sr3Ga2O6:Eu phosphor

Alkaline earth metal gallets have been identified as an important ceramic material. The crystal chemistry of many of these gallets is well explored; however, very rare studies regarding optical properties of rare earth (RE) ions doped in such gallets, particularly in Sr₃Ga₂O₆ host, have been carried out. The present study reports on synthesis and characterization of novel Sr₃Ga₂O₆:Eu³⁺ phosphors. The phosphors have been synthesized using a conventional solid state reaction method. Crystal structure, morphology and luminescence properties (excitation, emission and CIE coordinate) of these phosphors have been studied as a function of sintering temperature and Eu³⁺ concentration. X-ray diffraction study reveals that the phosphor sintered at low temperature (900 °C) contains an impurity phase which is removed at higher sintering temperatures and results into cubic crystalline phase of Sr₃Ga₂O₆. Particle size of the phosphor increases with an increase in sintering temperature which results to a red shift in the peak position of excitation band lying in a broad range from 250 to 370 nm. Optimum emission intensity is attained for 0.12 mol% concentration of Eu³⁺ ions; above this concentration, a quenching in emission intensity is observed.     

A high quantum yield red phosphor NaGdSiO4: Eu3+ with intense emissions from the 5D0→7F1,2 transition

Red phosphors with a high quantum yield and a lower thermal quenching are needed to improve the luminescence efficiency and the stability of phosphor-converted white light-emitting diodes (pc-WLEDs). We have designed a high quantum yield NaGdSiO₄ (NGSO) based phosphor with enhanced Eu³⁺ emissions of the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions. This design is based on the Eu³⁺ at both the inversion and non-inversion symmetry sites. In detail, we have studied the structure, morphology, and luminescence properties of NGSO: Eu³⁺ phosphors. Using a 394 nm UV excitation, a series of Eu³⁺ emissions of ⁵D₀→⁷F_J (0–4) transitions has been observed. The internal quantum efficiency (IQE) is 83.42% and the red color purity is 91.4%. These values are much higher than some reported results. The higher IQE and double intense ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ emissions might originate from an unusual structure disorder around Eu³⁺ ions in the NGSO lattice. The lifetime of the optimal phosphor NGSO: 0.5Eu³⁺ is about 2 ms, suitable for solid-state lighting. The intensities of the strong emissions at 595 and 624 nm of NGSO: 0.5Eu³⁺ at 150 °C is about 85% of that at 30 °C, demonstrating its excellent thermal stability. Furthermore, this red NGSO: 0.5Eu³⁺ phosphor was packaged into a warm pc-WLED, exhibiting a lower correlated color temperature (CCT) of 4222 K and a comparable color rendering index (CRI) of 86.7. These results show that this red phosphor could act as a red component of pc-WLEDs excited by the n-UV LED chip.     

White Light Emission from Sr2LiSiO4F:Sm3+,Tb3+ Phosphors Under Near‐UV Light Excitation

The Tb³⁺/Sm³⁺ codoped Sr₂LiSiO₄F white emitting phosphors were synthesized by a solid‐state reaction technique at high temperature. The X‐ray diffraction patterns, photoluminescence properties, and decay behaviors have been investigated. The Tb³⁺ emissions (blue and green) and Sm³⁺ emissions (orange) are both observed in the codoped samples Sr₂LiSiO₄F: 0.05Sm³⁺, xTb³⁺ by near‐UV light (370 nm) exciting. The white emission has been obtained by adjusting Tb³⁺ doping concentration at 5% (x = 0.05). These luminescent powders are expected to be a potential candidate as white emitting phosphor for near‐ultraviolet InGaN‐based white light‐emitting diodes.     

Charge transfer band excitation of La3NbO7:Sm3+ phosphors induced abnormal thermal quenching toward high-sensitivity thermometers

Different luminescent behaviors of La₃NbO₇:Sm³⁺ phosphors under the excitations of charge transfer band (CTB, 250 nm) and featured absorption peak (⁶H_5/2 → ⁴H_7/2, 405 nm) of Sm³⁺ ions were demonstrated. Under the excitation wavelength of 405 nm, the optimal La₃NbO₇:0.1Sm³⁺ phosphor exhibited an orange-red emission while the chromatic coordinate was found to be (0.609, 0.387), which also showed the excellent thermal performance, exhibiting its emission intensity of about 90.67% at 423 K with respect to 303 K. In the case of CTB excitation, the La₃NbO₇:0.1Sm³⁺ phosphor emitted an orange-yellow region with the chromaticity coordinate of (0.540, 0.443), and the emission intensity was stronger than the above one (λ_ex =405 nm) even though the optimized sample would be changed to the La₃NbO₇:0.05Sm³⁺ phosphor. With the increase of temperature, the obtained sample revealed an abnormal thermal quenching phenomenon between the emission peak of the host material and the emission transition of ⁴G_5/2 → ⁶H_9/2 under the excitation wavelength of 250 nm, which could be suggested to turn into a pair of thermal-couple levels. Therefore, the sensing sensitivity of the obtained sample was further investigated based on the fluorescence intensity ratio theory. Eventually, the absolute and relative sensing sensitivities of the La₃NbO₇:0.01Sm³⁺ phosphor were estimated to be as high as 5.379 × 10⁻² K⁻¹ and 1.60% K⁻¹, respectively.     

Tuning of Bi3+-related excitation and emission positions through crystal field modulation in the perovskite-structured La2(Znx, Mg1-x)TiO6 (0 ≤ x ≤ 1):Bi3+ solid solution for white LEDs

In the past year, emission-tunable crystals based on the rare-earth (RE) ions as luminescent center have been frequently reported for use in UV and blue converted white LEDs, but so far tuning the non-RE Bi³⁺ related emissions through the crystal field modulation is still not discovered in the perovskite crystals. In this work, we design and report a type of Bi³⁺ doped La₂(Zn_x,Mg_1-x)TiO₆ (0 ≤ x ≤ 1) perovskite solid solutions, which enable showing the tunable Bi³⁺ excitation and emission positions. The XRD results show that gradual substitution of smaller Mg²⁺ ions with larger Zn²⁺ ions can lead to the blue-shifting of X-ray diffraction (XRD) position, revealing the expansion of cell lattice. Together with structural analysis, our refined XRD and time-resolved spectral results reveal that there is only one type of La site available for Bi³⁺ substitution. With this regular crystal lattice change, the crystal field strength around Bi³⁺ ions is found to vary regularly, allowing to realization of the excitation and emission spectral tuning, i.e., the Bi³⁺ excitation and emission positions as the Mg ions are replaced by the Zn ions can tune from 348?nm to 392?nm and from 405?nm to 433?nm, respectively. This Bi³⁺ spectral tuning peak after calculated by the dielectric chemical bond theory features a linear relationship with the crystal field strength and, thus, is ascribed to the crystal field modulation. On basis of the La₂(Zn_0.4,Mg_0.6)TiO₆ blue, SrGa₂S₄:Eu²⁺ green and Y₂O₃:Eu³⁺ red phosphors, a UV converted warm white LED device with desirable color rendering index (CRI) of 78, correlated color temperature (CCT) of 3650 K and good luminous efficacy of 118.13?lm/W, is fabricated. This work provides new insights into using the crystal-field modulation to discover more Bi³⁺ emission-tunable crystals for white LEDs in the future.     

Spectroscopic investigations on high efficiency deep red-emitting Ca2SiO4:Eu3+ phosphors synthesized from agricultural waste

Europium doped calcium orthosilicate (Ca₂SiO₄) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO₂). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu³⁺ ions luminescent properties in Ca₂SiO₄ phosphors have been studied from the excitation, emission and decay curves analysis. The ⁵D₀ → ⁷F_J transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu³⁺ ion. A charge transfer band (CTB) at around 260?nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu³⁺ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu³⁺ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu³⁺ ions (0.01–0.4?mol%) and the lifetimes varied from 2.67 to 2.78?ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.     

Effect of sintering atmosphere and lithium ion co-doping on photoluminescence properties of NaCaPO4:Eu phosphor

This paper reports on the photoluminescence properties of Na_1−yLi_yCa_1−xPO₄:_xEu²⁺ phosphors synthesized by a solid state reaction method. The prepared phosphors have been thoroughly characterized by means of X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectrum (FTIR), Raman spectrum, Thermo gravimetric and differential thermal analysis (TG–DTA) and photoluminescent spectral measurements. The structure of Na_1−yLi_yCa_1−xPO_4:xEu²⁺ phosphors were found to be orthorhombic in nature with a sphere-like morphology and having the particle size in micrometer range. The excitation spectra of NaCaPO₄:Eu²⁺ phosphors revealed a broad excitation band having its maximum intensity at 373 nm and ranging from 250 m to 450 nm. Incidentally, it matches well with the ultraviolet (UV) radiation of light-emitting diodes (LEDs). Upon 373 nm excitation, these phosphors exhibited intense bluish-green emission band centered at 505 nm. The effect of sintering atmospheres and co-doping of lithium ions on the photoluminescence properties of the NaCaPO₄:Eu²⁺ phosphors were studied and explained suitably. The obtained results indicate that the prepared NaCaPO₄:Eu²⁺ phosphors are promising bluish-green candidates for the phosphor-converted white LED applications.