Experimental and theoretical study of mechanoluminescence and lyoluminescence of Li3PO4: RE (RE=Dy and Tb) phosphors

Li₃PO₄ phosphors prepared by solid‐state diffusion technique and lyoluminescence (LL) as well as mechanoluminescence (ML) studies are reported. Dy‐ and Tb‐activated phosphors show dosimetric characteristics using LL and ML techniques. The energy levels and hence trapping and detrapping of charge carriers in the material can be studied using ML. Li₃PO₄ phosphor can be used in the dosimetric applications for ionizing radiation. By using the LL technique, the LL characteristics of Li₃PO₄ may be useful for high radiation doses. We also report a more detailed theoretical understanding of the mechanism of LL and ML. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescence in Li3Al2(PO4)3:Eu2+

A series of efficient Li₃Al₂(PO₄)₃:Eu²⁺ novel phosphors were synthesized by the facile combustion method. The effects of dopant on the luminescence behavior of Li₃Al₂(PO₄)₃ phosphor were also investigated. The phosphors were characterized by X‐ray diffraction, field emission scanning electron microscope and photoluminescence techniques. The result shows that all samples can be excited efficiently by near‐ultraviolet excitation under 310 nm. The emission was observed for Li₃Al₂(PO₄)₃:Eu²⁺ phosphor at 425 nm, which corresponded to the d → f transition. The concentration quenching of Eu²⁺ was observed in Li₃Al₂(PO₄)₃:Eu²⁺ when the Eu concentration was at 0.5 mol%. The prepared powders exhibited intense blue emission at the 425 nm owing to the Eu²⁺ ion by Hg‐free excitation at 310 nm (i.e., solid‐state lighting excitation). Consequently, the availability of such a phosphor will significantly help in the development of blue‐emitting solid‐state lighting applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence properties of Eu3+‐activated Ba2Mg(PO4)2 phosphor

In this paper, we have reported the photoluminescence (PL) properties of the Ba₂Mg(PO₄)₂:Eu³⁺ phosphor synthesized using a wet chemical method. The preliminary scanning electron microscopy (SEM) investigation of the sample revealed irregular surface morphology with particle sizes in the 10–50 μm range. The strongest PL excitation peak was observed at 396 nm. The emission spectra indicated that this phosphor can be effectively excited by the 396 nm wavelength. Upon 396 nm excitation, the emission spectrum showed characteristics peaks located at 592 nm and 615 nm. These intense orange‐red emission peaks were obtained due to f→f transitions of Eu³⁺ ions. The emission peak at 592 nm is referred to as the magnetic dipole ⁵D₀→⁷F₁ transition and the emission peak at 615 nm corresponded to the electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺. The Commission Internationale de l’Eclairage (CIE) coordinates of the Ba₂Mg(PO₄)₂:Eu³⁺ phosphor were found to be (0.586, 0.412) for wavelength 592 nm and (0.680, 0.319) for wavelength 615 nm situated at the edge of the CIE diagram, indicating high colour purity of phosphors. Due to the high emission intensity and a good excitation profile, Eu³⁺‐doped Ba₂Mg(PO₄)₂ phosphor may be a promising orange‐red phosphor candidate for solid‐state lighting applications.     

Thermoluminescence and photoluminescence studies on γ‐ray‐irradiated Ce3+,Tb3+‐doped potassium chloride single crystals

Single crystals of KCl doped with Ce³⁺,Tb³⁺ were grown using the Bridgeman–Stockbarger technique. Thermoluminescence (TL), optical absorption, photoluminescence (PL), photo‐stimulated luminescence (PSL), and thermal‐stimulated luminescence (TSL) properties were studied after γ‐ray irradiation at room temperature. The glow curve of the γ‐ray‐irradiated crystal exhibits three peaks at 420, 470 and 525 K. F‐Light bleaching (560 nm) leads to a drastic change in the TL glow curve. The optical absorption measurements indicate that F‐ and V‐centres are formed in the crystal during γ‐ray irradiation. It was attempted to incorporate a broad band of cerium activator into the narrow band of terbium in the KCl host without a reduction in the emission intensity. Cerium co‐doped KCl:Tb crystals showed broad band emission due to the d–f transition of cerium and a reduction in the intensity of the emission peak due to ⁵D₃–⁷F_j (j = 3, 4) transition of terbium, when excited at 330 nm. These results support that energy transfer occurs from cerium to terbium in the KCl host. Co‐doping Ce³⁺ ions greatly intensified the excitation peak at 339 nm for the emission at 400 nm of Tb³⁺. The emission due to Tb³⁺ ions was confirmed by PSL and TSL spectra. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhancement of the luminescence properties of Sr3(PO4)2:Dy3+,Li+ white‐light‐emitting phosphors by charge compensator Li+ co‐doping

Sr₃(PO₄)₂:Dy³⁺,Li⁺ phosphors were prepared using a simple high temperature solid method for luminescence enhancement. The structures of the as‐prepared samples agreed well with the standard phase of Sr₃(PO₄)₂, even when Dy³⁺ and Li⁺ were introduced. Under ultraviolet excitation at 350 nm, the Sr₃(PO₄)₂:Dy³⁺ sample exhibited two emission peaks at 483 nm and 580 nm, which were due to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions, respectively. A white light was fabricated using these two emissions from the Sr₃(PO₄)₂:Dy³⁺ phosphors. The luminescence properties of Sr₃(PO₄)₂:Dy³⁺,Li⁺ phosphors, including emission intensity and decay time, were improved remarkably with the addition of Li⁺ as the charge compensator, which would promote their application in near‐ultraviolet excited white‐light‐emitting diodes.     

Enhancement of the photoluminescence and long afterglow properties of Sr2MgSi2O7:Eu2+ phosphor by Dy3+ co‐doping

Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ long afterglow phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by powder X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX), and photo‐, thermo‐ and mechanoluminescence spectroscopic techniques. The phase structure of the sintered phosphor was an akermanite type structure, which belongs to tetragonal crystallography. The thermoluminescence properties of these phosphors were investigated and compared. Under ultraviolet light excitation, the emission spectra of both prepared phosphors were composed of a broad emission band peaking at 470 nm. When the Sr₂MgSi₂O₇:Eu²⁺ phosphor was co‐doped with Dy³⁺, the photoluminescence (PL), afterglow and mechanoluminescence (ML) intensity were strongly enhanced. The decay graph indicated that both the sintered phosphors contained fast decay and slow decay processes. The ML intensities of Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphors were increased proportionally with increasing impact velocity, a finding that suggests that these phosphors could be used as sensors to detect the stress of an object. Copyright © 2015 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.     

Lyoluminescence,thermoluminescence and mechanoluminescence studies in γ‐ray irradiated Dy3+ activated potassium chloride phosphor for accidental radiation dosimetry

The lyoluminescence (LL), thermoluminescence (TL) and mechanoluminescence (ML) of γ‐ray‐irradiated coloured powder of KCl:Dy (0.05–0.5 mol%) phosphors are reported in this paper. To understand the mechanism of LL and ML, the LL and ML spectra are compared with TL studies. The variation of intensity of respective luminescence with different γ‐ray doses and with different concentrations of Dy³⁺ ion doped in KCl is found to be similar in nature. The intensities differ from each other, but their nature is found to be similar with γ‐ray exposures. The ML glow peak intensity is linear up to high 1 kGy exposure as compared to LL (up to 0.5 kGy) and TL (up to 0.75 kGy) techniques. Therefore, according to our results, the recommendation is that KCl:Dy (0.1 mol%) phosphor prepared by wet chemical technique is useful for high‐dose measurements using the ML technique for accidental radiation dosimetry. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanoluminescence of Ba2MgSi2O7 doped with Eu2+ and Dy3+ phosphor by impulsive deformation

Di‐barium magnesium silicate phosphor doped with Eu²⁺ and Dy³⁺ was prepared using a solid‐state reaction technique under a reducing atmosphere. The sample underwent impulsive deformation by impact from a piston for mechanoluminescence (ML) investigations. The temporal ML characteristics of the phosphor were observed, which expressed a single sharp peak with a long decaying period. To investigate the luminescence centre responsible for the ML peak, the ML spectrum of the phosphor was also observed. The recorded ML spectrum was similar in shape and peak wavelength to the photoluminescence (PL) spectrum, which verifies the existence of a single emission centre due to the transition of Eu²⁺ ions, i.e. transitions from any of the sublevels of the 4f⁶5d¹ configuration to the ⁸S_7/2 level of the 4f⁷ configuration. Decay rates for different impact velocities were also calculated using curve‐fitting techniques. The time of the ML peak and the rate of decay did not change significantly with respect to increasing impact velocity of the load and peak ML intensity varied linearly. The mechanism of the ML emission was also discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel red‐emitting phosphor,KAl1‐xPO4Cl:Eux3+ (0.1 ≤ x ≤ 1.0)

A series of phosphors KAl_1‐xPO₄Cl:Eu_x³⁺ (0.1 ≤ x ≤ 1.0) was synthesized using a facile combustion method using urea as a fuel and their structural, morphological and photoluminescence properties were investigated. It was found that the particle size was in the range of 1–2 µm with an irregular shape. The f–f transitions of Eu³⁺ in the host lattice were assigned and discussed. The excitation and emission spectra indicated that this phosphor can be efficiently excited by ultraviolet (395 nm), and exhibit reddish orange emission corresponding to the ⁵D₀→⁷F_J (J = 0, 1, 2) transitions of Eu³⁺. The impact of the Eu³⁺ concentration on the relative emission intensity was investigated, and the best doping concentration is 0.5. The present study suggests that the KAl_0.5PO₄Cl: Eu_0.5³⁺ phosphor is a strong candidate as a red component for phosphor‐ converted white light‐emitting diodes (LEDs). Copyright © 2015 John Wiley & Sons, Ltd.     

Fracto‐mechanoluminescence and thermoluminescence properties of UV and γ‐irradiated Ca2Al2SiO7:Ce3+ phosphor

Ce³⁺‐doped calcium aluminosilicate phosphor was prepared by a combustion‐assisted method at an initiating temperature of 600°C. Structural characterization was carried out using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The absorption spectra of Ca₂Al₂SiO₇:Ce³⁺ showed an absorption edge at 230 nm. The optical characterization of Ca₂Al₂SiO₇:Ce³⁺ phosphor was investigated in a fracto‐mechanoluminescence (FML) and thermoluminescence (TL) study. The peak of ML intensity increased as the height of impact of the moving piston increased. The TL intensity of Ca₂Al₂SiO₇:Ce³⁺ was recorded for different exposure times of UV and γ‐irradiation and it was observed that TL intensity was maximum for a UV irradiation time of 30 min and for a γ‐dose of 1180 Gy. The TL intensity had three peaks for UV irradiation at temperatures 82°C, 125°C and 203°C. Also the TL intensity had a single peak at 152°C for γ‐irradiation. The TL and ML emission spectra of Ca₂Al₂SiO₇:Ce³⁺ phosphor showed maximum emission at 400 nm. The possible mechanisms involved in the TL and ML processes of the Ca₂Al₂SiO₇:Ce³⁺ phosphor are also explained. Copyright © 2015 John Wiley & Sons, Ltd.     

Intense green‐, red‐emitting Tb3+, Tb3+/Bi3+‐doped and Sm3+, Sm3+/La3+‐doped Ca2Al2SiO7 phosphors

This paper focuses on an optical study of a Tb³⁺/Bi³⁺‐doped and Sm³⁺/La³⁺‐ doped Ca₂Al₂SiO₇ phosphor synthesized using combustion methods. Here, Ca₂Al₂SiO₇:Sm³⁺ showed a red emission band under visible light excitation but, when it co‐doped with La³⁺ ions, the emission intensity was further enhanced. Ca₂Al₂SiO₇:Tb³⁺ shows the characteristic green emission band under near‐ultraviolet light excitation wavelengths, co‐doping with Bi³⁺ ions produced enhanced photoluminescence intensity with better colour tunable properties. The phosphor exhibited better phase purity and crystallinity, confirmed by X‐ray diffraction. Binding energies of Ca(2p), Al(2p), Si(2p), O(1s) were studied using X‐ray photoelectron spectroscopy. The reported phosphor may be a promising visible light excited red phosphor for light‐emitting diodes and energy conversion devices.     

Structural characterization of Er3+,Yb3+‐doped Gd2O3 phosphor,synthesized using the solid‐state reaction method,and its luminescence behavior

We report the synthesis and structural characterization of Er³⁺,Yb³⁺‐doped Gd₂O₃ phosphor. The sample was prepared using the conventional solid‐state reaction method, which is the most suitable method for large‐scale production. The prepared phosphor sample was characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermoluminescence (TL), photoluminescence (PL) and CIE techniques. For PL studies, the excitation and emission spectra of Gd₂O₃ phosphor doped with Er³⁺ and Yb³⁺ were recorded. The excitation spectrum was recorded at a wavelength of 551 nm and showed an intense peak at 276 nm. The emission spectrum was recorded at 276 nm excitation and showed peaks in all blue, green and red regions, which indicate that the prepared phosphor may act as a single host for white light‐emitting diode (WLED) applications, as verified by International de I'Eclairage (CIE) techniques. From the XRD data, the calculated average crystallite size of Er³⁺ and Yb³⁺‐doped Gd₂O₃ phosphor is ~ 38 nm. A TL study was carried out for the phosphor using UV irradiation. The TL glow curve was recorded for UV, beta and gamma irradiations, and the kinetic parameters were also calculated. In addition, the trap parameters of the prepared phosphor were also studied using computerized glow curve deconvolution (CGCD). Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Thermal quenching of luminescence of LiSr4(BO3)3:Eu2+ orange‐emitting phosphor

An orange‐emitting phosphor, Eu²⁺‐activated LiSr₄(BO₃)₃, was synthesized using the conventional solid‐state reaction. The photoluminescence excitation and emission spectra, and temperature dependence of the luminescence intensity of the phosphor were investigated. The results showed that LiSr₄(BO₃)₃:Eu²⁺ could be efficiently excited by incident light of 250–450 nm, and emits a strong orange light. With increasing temperature, the emission bands of LiSr₄(BO₃)₃:Eu²⁺ show an abnormal blue‐shift with broadening bandwidth and decreasing emission intensity. Copyright © 2013 John Wiley & Sons, Ltd.     

A new Pr3+‐activated molybdate‐based phosphor for application to white LEDs with blue excitation

The novel red‐emitting phosphors K_xSr_1?2xMoO₄:Pr³⁺_x (0.00 ≤ x ≤ 0.04) were prepared by solid‐state reaction. The crystallization and particle sizes of samples were investigated by powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). TEM images were in good agreement with the theoretical calculation data from the XRD patterns. Photoluminescence analysis indicated that there were three excitation peaks under 430–500 nm, and all samples showed the intensely red emission at 648 nm corresponding to the ³P₀ → ³F₂ transition of Pr³⁺. The concentrations of doping ions, temperature and polyethylene glycol in the phosphor system can significantly influence the intensity of the red emission. The photoluminescence spectral intensity reached its maximum at x = 0.02. The results showed that the investigated phosphor is a potential red phosphor for white light‐emitting diodes. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigations on luminescence behaviour of Ce‐activated BaMgAl10O17 phosphor

The present paper describes the synthesis of cerium‐doped barium magnesium aluminate phosphor by combustion method. The crystal structure of synthesized phosphor belongs to the P6₃/mmc space group and is related to the β‐alumina structure. The photoluminescence emission spectra exhibited a broad peak centered at 440 nm showing the Ce³⁺ emission. The thermoluminescence properties of phosphors under ultraviolet irradiation were investigated. The activation energy was calculated by Chen's empirical method. Fracto‐mechanoluminescence properties were also investigated. The phosphor showed mechanoluminescence (ML) properties without irradiation and the ML intensity increased linearly with the impact height of the moving piston. Therefore this compound may have a use as a damage sensor. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and characterization of pure and Li+ activated Alq3 complexes for green and blue organic light emitting diodes and display devices

Pure and Li⁺‐doped Alq₃ complexes were synthesized by simple precipitation method at room temperature, maintaining the stoichiometric ratio. These complexes were characterized by X‐ray diffraction, ultraviolet‐visible absorption and Fourier transform infrared and photoluminescence (PL) spectra. X‐ray diffraction analysis reveals the crystalline nature of the synthesized complexes, while Fourier transform infrared spectroscopy confirm the molecular structure, the completion of quinoline ring formation and presence of quinoline structure in the metal complex. Ultraviolet‐visible and PL spectra revealed that Li⁺ activated Alq₃ complexes exhibit the highest intensity in comparison to pure Alq₃ phosphor. Thus, Li⁺ enhances PL emission intensity when doped into Alq₃ phosphor. The excitation spectra lie in the range of 383–456 nm. All the synthesized complexes other than Liq give green emission, while Liq gives blue emission with enhanced intensity. Thus, he synthesized phosphors are the best suitable candidates for green‐ and blue‐emitting organic light emitting diode, PL liquid‐crystal display and solid‐state lighting applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Zn‐doped CaTiO3:Eu3+ red phosphors for enhanced photoluminescence in white LEDs by solid‐state reaction

Zn‐doped CaTiO₃:Eu³⁺ red phosphors for enhanced photoluminescence in white light‐emitting diodes (LEDs) were synthesized by a solid‐state method. The structure and morphology of the obtained phosphor samples were observed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM), and the impact of Ca, Zn and Eu content on their photoluminescence properties was studied. The results indicated that Zn not only participates in the formation of defects in suitable lattice matrices but also has a role in flux in the transformation from ZnO to Zn₂TiO₄, which is beneficial for the enhancement of photoluminescence properties. Photoluminescence test data showed that the Zn‐doped phosphor is excited efficiently by near‐ultraviolet (NUV) light at wavelengths around 398 nm and emits an intense red light with a broad peak around 616 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺. The intensity of this phosphor emission is three times stronger than that without Zn‐doping. Furthermore, this phosphor has very good thermal stability, high color purity and a low sintered temperature, all of which suggest its potential as a promising red phosphor for white LEDs. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescence study and dosimetry approach of Ce on an α‐Sr2P2O7 phosphor synthesized by a high‐temperature combustion method

We report synthesis of a cerium‐activated strontium pyrophosphate (Sr₂P₂O₇) phosphor using a high‐temperature combustion method. Samples were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), photoluminescence (PL) and thermoluminescence (TL). The XRD pattern reveals that Sr₂P₂O₇ has an α‐phase with crystallization in the orthorhombic space group of Pnam. The IR spectrum of α‐Sr₂P₂O₇ displays characteristic bands at 746 and 1190 cm^‐1 corresponding to the absorption of (P₂O₇)^‐4. PL emission spectra exhibit a broad emission band around 376 nm in the near‐UV region due to the allowed 5d–4f transition of cerium and suggest its applications in a UV light‐emitting diode (LED) source. PL also reveals that the emission originates from 5d–4f transition of Ce³⁺ and intensity increases with doping concentration. TL measurements made after X‐ray irradiation, manifest a single intense glow peak at around 192°C, which suggests that this is an outstanding candidate for dosimetry applications. The kinetic parameters, activation energy and frequency factor of the glow curve were calculated using different analysis methods. Copyright © 2014 John Wiley & Sons, Ltd.