Nanocrystalline SrS:Ce3+ system for the generation of white light‐emitting diodes

Nanocrystalline SrS phosphors doped with Ce³⁺ ions at different concentrations (0.5, 1, 1.5 and 2 mol%) are synthesized via the solid‐state diffusion method (SSDM), which is suitable for the large‐scale production of phosphors in industrial applications. The as‐prepared samples are characterized using an X‐ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), high‐resolution transmission electron microscopy (HRTEM) and energy‐dispersive X‐ray (EDX) analysis. The optical properties of these phosphors are analyzed using reflectance spectra, photoluminescence spectra and afterglow decay curves. The cubic structure of the SrS phosphor is confirmed by XRD analysis and the crystallite size calculated by Scherer's formula using XRD data shows the nanocrystalline nature of the phosphors. No phase change is observed with increasing concentrations of Ce³⁺ ions. The surface morphology of the prepared phosphors is determined by FESEM, which shows a sphere‐like structure and good connectivity of the grains. The authenticity of the formation of nanocrystalline phosphors is examined by HRTEM analysis. Elemental compositional information for the prepared phosphors is gathered by EDX analysis. Photoluminescence studies reveal that the emission spectra of the prepared phosphor shows broad band emission centered at 458 and 550 nm due to the transition of electrons from the 5d → 4f energy levels. The afterglow decay characteristics of different as‐synthesized SrS:Ce³⁺ nanophosphors are conceptually described. Copyright © 2016 John Wiley & Sons, Ltd.     

Structural,optical, and luminescence properties of Dy3+-activated potassium calcium silicate phosphor for white light-emitting diodes

A dysprosium (Dy³⁺)-activated potassium calcium silicate (K₄CaSi₃O₉) phosphor was prepared using a solid-state synthesis route. The phosphor had a cubic structure with the space group Pa $\overline{3}$ as confirmed using X-ray diffraction (XRD) measurements. Details of surface morphology and elemental composition of the as-synthesized undoped KCS phosphor was obtained using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The chemical structure as well as the vibrational modes present in the as-prepared KCS phosphor was analyzed using Fourier transform infrared (FT-IR) spectroscopy. Diffuse reflectance spectra (DRS) were used to determine the optical bandgap of the phosphors and were found to be in the optical range 3.52–3.71 eV. Photoluminescence (PL) spectra showed intense yellow emission corresponding to the ⁴F_9/2→⁶H_13/2 transition under 350 nm excitation. Commission International de l′Eclairage colour chromaticity coordinates were evaluated using the PL spectral data lie within the white region. Dexter theory and the Inokuti–Hirayama (I–H) model were applied to study the nature of the energy transfer mechanism in the as-prepared phosphors. The relatively high activation energy of the phosphors was evaluated using temperature-dependent PL (TDPL) data and confirmed the high thermal stability of the titled phosphor. The abovementioned results indicated that the as-prepared KCS:Dy³⁺ phosphor was a promising candidate for n-UV-based white light-emitting diodes.     

Luminescence investigation of a cerium‐doped yttrium vanadate phosphor

Cerium (Ce³⁺)‐doped (1, 3, and 7 mol%) yttrium vanadate phosphors were prepared using a co‐precipitation technique. The structural and optical properties of the synthesized samples were studied using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HR‐TEM), optical absorption, and photoluminescence (PL) spectroscopy techniques. The tetragonal structure and the formation of the nanosized crystallites in the YVO₄:Ce phosphor were confirmed using XRD analysis. HR‐TEM morphology showed rod‐like nanoparticles of different sizes. Optical absorption spectra demonstrated strong absorption bands at 268 and 276 nm. PL spectra showed strong peaks at 546, 574, and 691 nm following excitation at 300 nm. The calculated CIE chromaticity coordinates demonstrated that YVO₄:Ce could be used as a novel phosphor for the development of light‐emitting diode lamps.     

Photoluminescence characteristics of novel Sm3+ ions-doped La1.4Al22.6O36 phosphor for n-UV w-LED

The combustion procedure was used to synthesize La_1.4Al_22.6O₃₆:Sm³⁺ phosphors. The X-ray diffraction (XRD) patterns and morphological and photoluminescence properties were investigated. The XRD patterns consisted of a hexagonal crystal structure. At 405 nm, the maximum excitation intensity was obtained. Following 405 nm excitation, three different emission peaks at 573, 604, and 651 nm were seen. Concentration quenching occurred at 1.5 mol% Sm³⁺ ions. The Commission Internationale de l'éclairage coordinates for the La_1.4Al_22.6O₃₆ phosphor with Sm³⁺ doping were 604 nm (x = 0.644, y = 0.355) falling in the red region. The findings implied that the prepared phosphor may be used to develop w-light-emitting diodes.     

Intense green light emission and thermoluminescence glow curve analysis of Tb3+-activated CaY2O4 phosphor

Here, the synthesis and luminescence analysis of the Tb³⁺-activated phosphor were reported. The CaY₂O₄ phosphors were synthesized using a modified solid-state reaction method with a variable doping concentration of Tb³⁺ ion (0.1–2.5 mol%). As synthesized, the phosphor was characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis techniques for the optimized concentration of doping ions. The prepared phosphor showed a cubic structure, and FTIR analysis confirmed functional group analysis. It was discovered that the intensity of 1.5 mol% was higher than at other concentrations after the photoluminescence (PL) excitation and emission spectra were recorded for different concentrations of doping ions. The excitation was monitored at 542 nm, and the emission was monitored at 237 nm. At 237 nm excitation, the emission peaks were found at 620 nm (⁵D₄→⁷F₃), 582 nm (⁵D₄→⁷F₄), 542 nm (⁵D₄→⁷F₅), and 484 nm (⁵D₄→⁷F₆). The 1931 CIE (x, y) chromaticity coordinates showed the distribution of the spectral region calculated from the PL emission spectra. The values of (x = 0.34 and y = 0.60) were very close to dark green emission. Therefore, the produced phosphor would be very useful for light-emitting diode (green component) applications. Thermoluminescence glow curve analysis for various concentrations of doping ions and various ultraviolet (UV) exposure times was carried out, and a single broad peak was found at 252°C. The computerized glow curve deconvolution method was used to obtain the related kinetic parameters. The prepared phosphor exhibited an excellent response to UV dose and could be useful for UV ray dosimetry.     

ZnAl2O4:Eu novel phosphor: SEM and mechanoluminescence characterization synthesized by solution combustion technique

Eu doped ZnAl₂O₄ phosphors were synthesized by the solution combustion technique using carbohydrazide as a fuel. Mechanoluminescence (ML) was excited impulsively by dropping a piston of 0.7 kg onto the phosphors. Two distinct peaks were observed in the ML glow curve of the γ‐ray irradiated ZnAl₂O₄:Eu phosphors. Dependence of ML on various parameters as impact velocity of the piston dropped on to it, mass of the sample, gamma ray doses given to the sample and ML spectra have been studied. ML emission spectrum showed the characteristic emission of Eu³⁺ ion in this system. ML is observed to be optimum for the sample having 0.2 mol% of Eu in the ZnAl₂O₄ phosphor. XRD result confirms formation of the phosphors. SEM characterization shows its surface morphology. This novel phosphor may be a potential candidate for dosimetric use due to its linear dose response. Copyright © 2014 John Wiley & Sons, Ltd.     

Novel red colour emitting Ca0.995Mg2(SO4)3:0.5Eu2+ phosphor under ultraviolet,blue, and green excitation for plant growth LEDs

In the recent few years, Eu²⁺- and Mn⁴⁺-activated phosphors are widely used as potential colour converters for indoor plant cultivation lighting application due to their marvellous luminescence characteristics as well as low cost. In this investigation, we synthesized novel red colour-emitting Ca_(2−x)Mg₂(SO₄)₃:xmol% Eu²⁺ (x = 0–1.0 mol%) phosphors via a solid-state reaction method in a reducing atmosphere. The photoluminescence (PL) excitation spectra of synthesized phosphors exhibited a broad excitation band with three excitation bands peaking at 349 nm, 494 nm, and 554 nm. Under these excitations, emission spectra exhibited a broad band in the red colour region at ~634 nm. The PL emission intensity was measured for different concentrations of Eu²⁺. The maximum Eu²⁺ doping concentration in the Ca₂Mg₂(SO₄)₃ host was observed for 0.5 mol%. According to Dexter theory, it was determined that dipole–dipole interaction was responsible for the concentration quenching. The luminous red colour emission of the sample was confirmed using Commission international de l'eclairage colour coordinates. The results of PL excitation and emission spectra of the prepared phosphors were well matched with excitation and emission wavelengths of phytochrome P_R. Therefore, from the entire investigation and obtained results it was concluded that the synthesized Ca_0.995Mg₂(SO₄)₃:0.5mol%Eu²⁺ phosphor has huge potential for plant cultivation application.     

Synthesis and characterization of Ba3Si6O12N2:Eu2+ phosphor

Eu²⁺‐doped Ba₃Si₆O₁₂N₂ phosphors were prepared successfully via a modified solid‐state diffusion method. The phosphors were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence measurements. These phosphors were effectively excited at 355 nm and an intense emission peaking in the range 480 nm to 525 nm in the blue region was observed. The optimized dopant concentration was determined to be 1 mol% of Eu²⁺ ion. The colour coordinates for phosphor were found to be (0.196, 0.326) in the blue region. This phosphor may find application for near‐ultraviolet (NUV) excited lamp phosphors. The thermoluminescence study shows the complex glow curve. Trapping parameters (activation energy and frequency factor) were calculated for individual deconvoluted peaks by Chen's peak shape method, the initial rise method and the whole glow peak method. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescence investigation of CaY2Al4SiO12:Dy3+ phosphor synthesized by sol–gel method

Dy³⁺-doped CaY₂Al₄SiO₁₂ phosphors were prepared using the sol–gel method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy analyses (EDS) were used to analyse the crystal structure, morphology, and elemental composition of the prepared samples. The luminescence behaviour of the sample was investigated using photoluminescence (PL) and thermoluminescence (TL) techniques. The prepared CaY₂Al₄SiO₁₂:xDy³⁺ phosphor showed a characteristic blue and yellow emission at ~480 and 583 nm, respectively, with an excitation wavelength of 350 nm. The most intense PL emission was found for a 4 mol% doping concentration of Dy³⁺ ions. The CIE diagram of the phosphor showed bluish-white colour emission. For TL studies, the prepared phosphors were irradiated with a ⁶⁰Co γ (gamma) source and the TL glow curve of the CaY₂Al₄SiO₁₂:0.04Dy³⁺ phosphor showed three overlapped peaks. For the Gaussian peaks, Chen's peak shape method was applied to determine the kinetic parameters of the samples.     

Characterization and luminescence properties of CaMgSi2O6:Eu2+ blue phosphor

A blue CaMgSi₂O₆:Eu²⁺ phosphor was prepared by the solid‐state reaction method and the phosphor characterized in terms of crystal structure, particle size, photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) properties using X‐ray diffraction (XRD), transmission electron microscopy (TEM), PL spectroscopy, TLD reader and ML impact technique. The XRD result shows that phosphor is formed in a single phase and has a monoclinic structure with the space group C2/c. Furthermore, the PL excitation spectra of Eu²⁺‐doped CaMgSi₂O₆ phosphor showed a strong band peak at 356 nm and the PL emission spectrum has a peak at 450 nm. The depths and frequency factors of trap centers were calculated using the TL glow curve by deconvolution method in which the trap depths were found to be 0.48 and 0.61 eV. The formation of CaMgSi₂O₆:Eu²⁺ phosphor was confirmed by Fourier transform infrared spectroscopy. The ML intensity increased linearly with the impact velocity of the piston used to deform the phosphor. It was shown that the local piezoelectricity‐induced electron bombardment model is responsible for the ML emission. Finally, the optical properties of CaMgSi₂O₆:Eu²⁺ phosphors are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Infrared and visible emissions of rare‐earth‐doped CeO2 phosphor

This paper reports the synthesis and characterization of Er³⁺‐doped CeO₂ phosphor with variable concentrations of erbium. The sample was synthesized using a solid‐state reaction method, which is useful for the large‐scale production of phosphors and is also eco‐friendly. The prepared sample was characterized using an X‐ray diffraction (XRD) technique. The XRD pattern confirmed that sample has the pure cubic fluorite crystal structure of CeO₂. The crystallite size of the prepared phosphor was determined by Scherer's formula and the crystallite size giving an intense XRD peak is 40.06 nm. The surface morphology of the phosphor was determined by field emission gun scanning electron microscopy (FEGSEM). From the FEGSEM image, good surface morphology with some agglomerates was found. The functional group in the prepared sample was analysed by Fourier transform infrared (FTIR) spectroscopy. All samples prepared with variable concentrations of Er³⁺ (0.1–2 mol%) were studied by photoluminescence analysis and it was found that the excitation spectra of the prepared phosphor shows broad excitation centred at 251 nm. Emission spectra at different concentrations of Er³⁺ show strong peaks at 413 and 470 nm and a weaker peak at 594 nm. The dominant peaks at 413 and 470 nm are caused by the allowed electronic transition ⁴S_3/2 → ⁴I_15/2 and the weaker transition at 594 nm is due to the transition ⁴ F_9/2 → ⁴I_15/2. Spectrophotometric determinations of peaks were evaluated using the Commission Internationale de I'Eclairage (CIE) technique. The emission spectra were also observed using an infrared (IR) laser 980 nm source, and three distinct peaks were found in the IR region at 848, 870 and 980 nm. The prepared phosphor has utility for application in display devices. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,PL characterizations and concentration quenching effect in Dy3+ and Eu3+ activated LiCaBO3 phosphor

LiCaBO₃:Dy³⁺/Eu³⁺ phosphors were synthesized by a solid‐state reaction. The synthesized materials were characterized using powder X‐ray diffraction pattern (XRD) for confirmation. All the structural parameters were calculated from the XRD data. Scanning electron microscopy (SEM) images showed rod‐like morphology. Photoluminescence (PL) emission spectra showed two emissions (484 and 577 nm) in Dy³⁺‐doped LiCaBO₃:Dy³⁺phosphors with the concentration quenching effect and the critical distance was calculated to be about 22.76 Å. LiCaBO₃:Eu³⁺ phosphor was effectively excited by a near‐UV light of 392 nm. The emission spectra exhibited the transition from ⁵D₀ level to ⁷F_J (J = 0–2) with main emission at 614 nm, which comes from the electrodipole transition because of the asymmetric point group. The quenching concentration of Eu³⁺ is about 0.2 mol%, and the critical distance was calculated to be about 38.93 Å. Copyright © 2014 John Wiley & Sons, Ltd.     

Eu2+ luminescence in SrCaP2O7 pyrophosphate phosphor

A series of Eu²⁺ activated SrCaP₂O₇ pyrophosphate phosphors were synthesized by the modified solid‐state reaction method. The X‐ray diffraction (XRD) and photoluminescence (PL) properties of these phosphors were investigated at room temperature. The excitation spectra indicate that these phosphors can be effectively excited by Hg‐free excitation. The emission spectra exhibit strong blue performance, which is due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The Fourier transform infrared spectrum at room temperature was investigated and surface morphology has been studied by scanning electron microscope. The prepared phosphor exhibited intense blue emission at the 427 nm owing to Eu²⁺ ion by Hg‐free excitation at 330 nm, that is, solid‐state lighting excitation. Hence, the availability of such a phosphor will significantly help in the growth of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural characterization and optical properties of Ca2MgSi2O7:Eu2+,Dy3+ phosphor by solid‐state reaction method

Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was prepared by the solid‐state reaction method under a weak reducing atmosphere. The obtained phosphor was characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared (FT‐IR) techniques. The phase structure of the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was akermanite type, which is a member of the melilite group. The surface morphology of the sintered phosphor was not uniform and phosphors aggregated tightly. EDX and FT‐IR spectra confirm the elements present in the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor. Under UV excitation, a broadband emission spectrum was found. The emission spectra observed in the green region centered at 535 nm, which is due to the 4f–5d transition. The mechanoluminescence (ML) intensity of the prepared phosphor increased linearly with increases in the mechanical load. The ML spectra were similar to the photoluminescence (PL), which indicates that ML is emitted from the same emitting center of Eu²⁺ ions as PL. Copyright © 2014 John Wiley & Sons, Ltd.     

Europium doped Sr2YNbO6 double perovskite phosphor for photoluminescence and thermoluminescence properties

A luminescent double perovskite phosphor Sr₂YNbO₆ doped with Eu³⁺ crystallized to the monoclinic phase and was synthesized successfully via a conventional high-temperature combustion method. The formation of the crystal structure, phase purity, and surface morphology were studied using X-ray diffraction patterns and scanning electron microscopy. The characteristic vibrations between the atoms of the functional groups present in phosphor were studied using Fourier transform infrared spectra analysis. The luminescence properties of the prepared phosphors were investigated in terms of photoluminescence (PL) and thermoluminescence (TL). PL excitation spectra exhibited charge transfer bands and the characteristic 4f⁶ transitions of Eu³⁺. A prominent PL emission was obtained for the phosphor doped with 4 mol% Eu³⁺ under the 396 nm excitation wavelength. PL emission quenching was observed for the higher doping concentrations due to a multipole–multipole interaction. A highly intense PL emission arose due to the hypersensitive ⁵D₀–⁷F₂ electric dipole transition of Eu³⁺ that dominated the emission spectra. The thermal stability of the phosphor was examined through temperature-dependent PL. The TL properties of the Sr₂YNbO₆ double perovskites irradiated with a ⁹⁰Sr beta source at different doses were measured. The double perovskite phosphors under study showed a linear dose–response with increasing beta dose, ranging from 1 Gy to 10 Gy. Trapping parameters of the TL glow curves were determined using Chen's peak shape method and computerized glow curve deconvolution (CGCD). CGCD fitting of the TL glow curves revealed that it was consisted of three major peaks and followed second-order kinetics. The estimated activation energies were determined using different methods and were comparable and significant.     

Synthesis and characterization of erbium‐doped YAlO3 phosphor

In the yttrium aluminium system, the YAlO₃ phosphor is a prominent host because of the yttrium aluminium ratio (1:1). Phosphor was synthesized by the solid‐state reaction method at variable concentrations of erbium (0.1–2.5 mol%). This method is suitable for large‐scale production and is a less time‐consuming method when compared with the soft synthesis method. The prepared sample was characterized by X‐ray diffraction technique and the crystallite size was calculated by Scherer's formula. Vibrational and bending analysis of prepared phosphor for optimized concentration of erbium ion is described based on the Fourier transform infrared spectroscopic technique. The photoluminescence (PL) emission spectra of prepared phosphor for variable concentrations of erbium ion were recorded and the excitation spectrum was found to be at 291 nm with three shoulder peaks at 305, 270 and 242 nm. For 291 nm excitation, the emission spectrum was found at 546 nm and 552 nm. PL intensity increased with increasing concentrations of erbium and after 2 mol% emission intensity decreased due to concentration quenching. Spectrophotometric determination of YAlO₃:Er³⁺ is described by CIE co‐ordinates and shows an intense emission in the green region such that the prepared phosphor can act as a single host for green light emission. Thermoluminescence glow curve analysis of the YAlO₃:Er³⁺ phosphor was recorded for different ultraviolet (UV) light exposures and gamma exposure. Different gamma doses 0.5–2 kGy show a linear response. Kinetic parameters were calculated by the peak shape method. Copyright © 2015 John Wiley & Sons, Ltd.     

Orange‐red emitting europium doped strontium ortho‐silicate phosphor prepared by a solid state reaction method

In the present article we report europium‐doped strontium ortho‐silicates, namely Sr₂SiO₄:xEu³⁺ (x = 1.0, 1.5, 2.0, 2.5 or 3.0 mol%) phosphors, prepared by solid state reaction method. The crystal structures of the sintered phosphors were consistent with orthorhombic crystallography with a Pmna space group. The chemical compositions of the sintered phosphors were confirmed by energy dispersive X‐ray spectroscopy (EDS). Thermoluminescence (TL) kinetic parameters such as activation energy, order of kinetics and frequency factors were calculated by the peak shape method. Orange‐red emission originating from the ⁵D₀–⁷F_J (J = 0, 1, 2, 3) transitions of Eu³⁺ ions could clearly be observed after samples were excited at 395 nm. The combination of these emissions constituted orange‐red light as indicated on the Commission Internationale de l'Eclairage (CIE) chromaticity diagram. Mechanoluminescence (ML) intensity of the prepared phosphor increased linearly with increasing impact velocity of the moving piston that suggests that these phosphors can also be used as sensors to detect the stress of an object. Thus, the present investigation indicates that the piezo‐electricity was responsible for producing ML in the prepared phosphor.     

Ultrasound assisted synthesis of CaF2:Eu3+ phosphor nanoparticles

In this work, the optical and structural properties of ultrasonically prepared CaF₂:Eu³⁺ nanoparticles have been reported. Ultrasonically prepared CaF₂:Eu³⁺ phosphor shows orange, red emission bands at 591 nm and 612 nm, respectively, when it is excited by 394 light‐emitting diode (LED) excitation wavelengths. Further phosphor materials are well characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) techniques to confirm the phase purity, metal oxygen (MO) bonding and crystallites size of the materials. Here synthesized materials show a tube‐like structure under 100 nm resolution and 0.1 mol% is the best doping value of the europium ion (Eu³⁺) in calcium fluoride (CaF₂) that shows highest intensity when prepared with an ultrasound assisted method.     

Combustion synthesis of Na2Sr(PO4)F:Dy3+ white light emitting phosphor

The synthesis, X‐ray diffraction, photoluminescence, TGA/DTA and FTIR techniques in Dy³⁺ activated Na₂Sr(PO₄)F phosphor are reported in this paper. The prepared phosphor gave blue, yellow and red emission in the visible region of the spectrum at 348 nm excitation. CIE color co‐ordinates of Na₂Sr(PO₄)F:Dy³⁺ are suitable as white light‐emitting phosphors. Copyright © 2009 John Wiley & Sons, Ltd.