Mechanoluminescence of SrAl2O4:Eu,Dy nanophosphors induced by low impact velocity

The present paper reports the impulsive excitation of mechanoluminescence (ML) in Sr_0.97Al₂O₄:Eu_0.01,Dy_0.02 nanophosphors prepared using a combustion technique. The phosphors are characterized using X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). The XRD results show that the samples exhibit a monoclinic α‐phase in the crystal structure. The space group of SrAl₂O₄:Eu,Dy nanophosphors is monoclinic P2₁. The PL and ML spectra of SrAl₂O₄:Eu,Dy nanophosphors are excited using light with a wavelength of 365 nm and emission is found at 516 nm. The prepared nanophosphors exhibits an intense ML that can be seen in daylight with the naked eye. When a sample powder is deformed impulsively by the impact of a moving piston, the ML intensity initially increases linearly with time, attains a peak value, I_m, at time t_m, and then decreases with time. The peak ML intensity, I_m, and total ML intensity, I_T, increase linearly with applied pressure and impact velocity. The ML intensity decreases with successive impacts of load onto the phosphors, and the diminished ML intensity can be approximately recovered by UV irradiation. The activation energy using thermoluminescence is found to be 0.57 eV for SrAl₂O₄:Eu,Dy nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Thermoluminescence properties of Eu‐doped and Eu/Dy‐codoped Sr2Al2SiO7 phosphors

We report the thermoluminescence properties of Sr_1.96Al₂SiO₇:Eu_0.04 and Sr_1.92Al₂SiO₇:Eu_0.04Dy_0.04 phosphors. These phosphors were prepared by a high‐temperature solid‐state reaction method. The prepared phosphors were characterized by X‐ray diffraction. A 254 nm source was used for ultraviolet (UV) irradiation and a ⁶⁰Co source was used for γ‐irradiation. The effect of heating rate and UV‐exposure were examined. The thermoluminescence temperature shifts to higher values with increasing heating rate and thermoluminescence intensity increases with increasing UV exposure time. The trapping parameters such as activation energy (E), order of kinetics and frequency factor (s) were calculated by peak shape method. The effect of γ‐ and UV‐irradiation on thermoluminescence studies was also examined.     

Photoluminescence and thermoluminescence properties of Eu2+ doped and Eu2+,Dy3+ co‐doped Ba2MgSi2O7 phosphors

In this work, we report the preparation, characterization, comparison and luminescence mechanisms of Eu²⁺‐doped and Eu²⁺,Dy³⁺‐co‐doped Ba₂MgSi₂O₇ (BMSO) phosphors. Prepared phosphors were synthesized via a high temperature solid‐state reaction method. All prepared phosphors appeared white. The phase structure, particle size, and elemental analysis were analyzed using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and energy‐dispersive X‐ray (EDX) analysis. The luminescence properties of the phosphors were investigated by thermoluminescence (TL) and photoluminescence (PL). The PL excitation and emission spectra of Ba₂MgSi₂O₇:Eu²⁺ showed the peak to be around 381 nm and 490 nm respectively. The PL excitation spectrum of Ba₂MgSi₂O₇:Eu²⁺Dy³⁺ showed the peak to be around 341 nm and 388 nm, and the emission spectrum had a broad band around 488 nm. These emissions originated from the 4f⁶ 5d¹ to 4f⁷ transition of Eu²⁺. TL analysis revealed that the maximum TL intensity was found at 5 mol% of Eu²⁺ doping in Ba₂MgSi₂O₇ phosphors after 15 min of ultraviolet (UV) light exposure. TL intensity was increased when Dy³⁺ ions were co‐doped in Ba₂MgSi₂O₇:Eu²⁺ and maximum TL intensity was observed for 2 mol% of Dy³⁺. TL emission spectra of Ba_1.95MgSi₂O₇:0.05Eu²⁺ and Ba_1.93MgSi₂O₇:0.05Eu²⁺,0.02Dy³⁺ phosphors were found at 500 nm. TL intensity increased with UV exposure time up to 15 min, then decreased for the higher UV radiation dose for both Eu doping and Eu,Dy co‐doping. The trap depths were calculated to be 0.54 eV for Ba_1.95MgSi₂O₇:0.05Eu²⁺ and 0.54 eV and 0.75 eV for Ba_1.93MgSi₂O₇:0.05Eu²⁺,0.02Dy³⁺ phosphors. It was observed that co‐doping with small amounts of Dy³⁺ enhanced the thermoluminescence properties of Ba₂MgSi₂O₇ phosphor. Copyright © 2016 John Wiley & Sons, Ltd. [Correction added on 5 April 2016, after first online publication: The following parts of the abstract have been edited for consistency. '4f65d1' has been corrected to '4f⁶ 5d¹', '4f7' has been corrected to '4f⁷', 'Ba1.95' has been corrected to 'Ba_1.95' and 'Ba1.93' has been corrected to 'Ba_1.93' respectively.]     

Sol–gel synthesis and luminescence property of Sr4Al2O7:Re3+,R+ (Re = Eu and Dy; R = Li,Na and K) phosphors for white LEDs

Sr₄Al₂O₇:Eu³⁺ and Sr₄Al₂O₇:Dy³⁺ phosphors with alkali metal substitution were prepared using a sol–gel method. The effects of a charge compensator R on the structure and luminescence of Sr₄Al₂O₇:Re³⁺,R⁺ (Re = Eu and Dy; R = Li, Na and K) phosphors were investigated in detail. Upon heating to 1400°C, the structure of the prepared samples was that of the standard phase of Sr₄Al₂O₇. Under ultraviolet excitation, all Sr₄Al₂O₇:Eu³⁺,R⁺ samples exhibited several narrow emission peaks ranging from 550 to 700 nm due to the 4f → 4f transition of Eu³⁺ ions. All Sr₄Al₂O₇:Dy³⁺,R⁺ phosphors showed two emission peaks at 492 and 582 nm, due to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions, respectively. The luminescence intensity of Sr₄Al₂O₇:Re³⁺,R⁺ (Re = Eu and Dy; R = Li, Na and K) phosphors improved markedly upon the addition of charge compensators, promoting their application in white light‐emitting diodes with a near‐ultraviolet chip.     

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.     

Tunable white light emission from single‐phased Li2SrSiO4:Dy3+ phosphors by co‐doping with Eu3+

A series of single‐phase full‐color emitting Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ phosphors were synthesized by solid‐state reaction and characterized by X‐ray diffraction and photoluminescence analyses. The samples showed emission peaks at 488 nm (blue), 572 nm (yellow), 592 nm (orange) and 617 nm (red) under 393 nm excitation. The photoluminescence excitation spectra, comprising the Eu–O charge transfer band and 4f–4f transition bands of Dy³⁺ and Eu³⁺, range from 200 to 500 nm. The Commission Internationale de I'Eclairage chromaticity coordinates for Li₂Sr_0.98−xSiO₄:0.02Dy³⁺,xEu³⁺ phosphors were simulated. By manipulating Eu³⁺ and Dy³⁺ concentrations, the color points of Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ were tuned from the greenish‐white region to white light and eventually to reddish‐white region, demonstrating that a tunable white light can be obtained by Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ phosphors. Li₂Sr_0.98−xSiO₄:0.02Dy³⁺, xEu³⁺ can serve as a white‐light‐emitting phosphor for phosphor‐converted light‐emitting diode. Copyright © 2014 John Wiley & Sons, Ltd.     

Ca2Al2SiO7:Ce3+ phosphors for mechanoluminescence dosimetry

A series of Ce³⁺ ion single‐doped Ca₂Al₂SiO₇ phosphors was synthesized by a combustion‐assisted method at an initiating temperature of 600 °C. The samples were annealed at 1100 °C for 3 h and their X‐ray diffraction patterns confirmed a tetragonal structure. The phase structure, particle size, surface morphology and elemental analysis were analyzed using X‐ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) spectroscopy techniques. Thermoluminescence (TL) intensity increased with increase in ultraviolet (UV) light exposure time up to 15 min. With further increase in the UV irradiation time the TL intensity decreases. The increase in TL intensity indicates that trap concentration increased with UV exposure time. A broad peak at 121 °C suggested the existence of a trapping level. The peak of mechanoluminescence (ML) intensity versus time curve increased linearly with increasing impact velocity of the moving piston. Mechanoluminescence intensity increased with increase in UV irradiation time up to 15 min. Under UV‐irradiation excitation, the TL and ML emission spectra of Ca₂Al₂SiO₇:Ce³⁺ phosphor showed the characteristic emission of Ce³⁺ peaking at 400 nm (UV–violet) and originating from the Ce³⁺ transitions of 5d‐4f (²F_5/2 and ²F_7/2). The photoluminescence (PL) emission spectra for Ca₂Al₂SiO₇:Ce³⁺ were similar to the ML/TL emission spectra. The mechanism of ML excitation and the suitability of the Ca₂Al₂SiO₇:Ce³⁺phosphor for radiation dosimetry are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanoluminescence,thermoluminescence, photoluminescence studies on Ca3Y2Si3O12:RE3+ (RE3+ = Dy3+and Eu3+) phosphors

Dy³⁺ and Eu³⁺ activated Ca₃Y₂Si₃O₁₂ phosphors were synthesized by the solid‐state synthesis method. The phosphors were characterized by X‐ray diffraction (XRD), mechanoluminescence (ML), thermoluminescence (TL) and photoluminescence (PL) to determine structure and luminescence. For ML glow curves, only one peak was observed, as only one type of luminescence centre was formed during irradiation. The Ca₃Y₂Si₃O₁₂:Dy³⁺ TL glow curve showed a single peak at 151.55°C and the Ca₃Y₂Si₃O₁₂:Eu³⁺ TL glow curve peaked at 323°C with a small peak at 192°C, indicating that two types of traps were activated. The trapping parameters for both the samples were calculated using Chen's peak shape method. Dy³⁺‐activated Ca₃Y₂Si₃O₁₂ showed emission at 482 and 574 nm when excited by a 351 nm excitation wavelength, whereas the Eu³⁺‐activated Ca₃Y₂Si₃O₁₂ phosphor PL emission spectra showed emission peaks at 613 nm, 591 nm, 580 nm when excited at 395 nm wavelength. When excited at 466 nm, prominent emission peaks were observed at their respective positions with very slight shifts. Copyright © 2015 John Wiley & Sons, Ltd.     

The luminescence properties of Sr2–1.5x−1.5yP2O7:xDy3+,yCe3+ phosphor for near‐UV‐based white LEDs synthesized by a chemical co‐precipitation method

A series of Sr₂P₂O₇:Dy³⁺, Sr₂P₂O₇:Ce³⁺ and Sr₂P₂O₇:Dy³⁺,Ce³⁺ phosphors was synthesized via the one‐step calcination process for the precursors prepared by co‐precipitation methods. The phases, morphology, quantum efficiency and photoluminescence properties of the obtained phosphors were characterized systematically. These results show that the near‐spherical particles prepared through calcining the precursors by means of ammonium dibasic phosphate co‐precipitation (method 3) have the smallest particle size and strongest emission intensity among the three methods in the paper. With Dy³⁺ concentration increasing in Sr₂P₂O₇:Dy³⁺ phosphors, the luminescence intensity first increases, reaches maximum, and then decreases. A similar trend was followed by Sr₂P₂O₇:Ce³⁺ with Ce³⁺concentration increasing. A successful attempt was made to initiate the energy transfer mechanism from Ce³⁺ to Dy³⁺ in the host lattice and an overlap between the emission band of Ce³⁺ and the excitation band of Dy³⁺ indicated that the Ce³⁺ → Dy³⁺ energy transfer may indeed exist. It is clear that the photoluminescence intensity of Dy³⁺ as well as the quantum efficiency of the phosphor can be enhanced markedly by co‐doping Ce³⁺. Sr₂P₂O₇:Dy³⁺,Ce³⁺ has its (CIE) chromaticity coordinates in the bluish‐white‐light region, near the standard illuminant D₆₅. The CIE 1913 chromaticity coordinates of Sr₂P₂O₇:Dy³⁺ phosphors fall in the white‐light region, and are adjacent to the ideal white‐light coordinates. In addition, the colour temperature and colour tone of Sr₂P₂O₇:Dy³⁺ could be adjusted by changing the relative concentration of Dy³⁺. In short, Sr₂P₂O₇:Dy³⁺ can be a promising single‐phased white‐light emitting phosphor for near‐UV (NUV) w‐LEDs.     

Photoluminescence properties and energy transfer in Ce3+/Dy3+ co‐doped Sr3MgSi2O8 phosphors for potential application in ultraviolet white light‐emitting diodes

Sr₃MgSi₂O₈:Ce³⁺, Dy³⁺ phosphors were prepared by a solid‐state reaction technique and the photoluminescence properties were investigated. The emission spectra show not only a band due to Ce³⁺ ions (403 nm) but also as a band due to Dy³⁺ ions (480, 575 nm) (UV light excitation). The photoluminescence properties reveal that effective energy transfer occurs in Ce³⁺/Dy³⁺ co‐doped Sr₃MgSi₂O₈ phosphors, and the co‐doping of Ce³⁺ could enhance the emission intensity of Dy³⁺ to a certain extent by transferring its energy to Dy³⁺. The Ce³⁺/Dy³⁺ energy transfer was investigated by emission/excitation spectra, and photoluminescence decay behaviors. In Sr_2.94MgSi₂O₈:0.01Ce³⁺, 0.05Dy³⁺ phosphors, the fluorescence lifetime of Dy³⁺ (from 3.35 to 27.59 ns) is increased whereas that of Ce³⁺ is greatly decreased (from 43.59 to 13.55 ns), and this provides indirect evidence of the Ce³⁺ to Dy³⁺ energy transfer. The varied emitted color of Sr₃MgSi₂O₈:Ce³⁺, Dy³⁺ phosphors from blue to white were achieved by altering the concentration ratio of Ce³⁺ and Dy³⁺. These results indicate Sr₃MgSi₂O₈:Ce³⁺, Dy³⁺ may be as a candidate phosphor for white light‐emitting diodes. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and characterization of blue long‐lasting BaCa2Al8O15:Eu2+, Dy3+ phosphor

We have synthesized and characterized a new BaCa₂Al₈O₁₅:Eu²⁺,Dy³⁺ phosphor prepared by the combustion method. X‐ray diffraction, thermoluminescence, scanning electron microscope, time decay and optical spectral analysis photoluminescence excitation, emission spectra were used to characterize the phosphors. Broadband ultraviolet excited luminescence of the BaCa₂Al₈O₁₅:Eu²⁺,Dy³⁺ was observed in the blue region (λ_max = 435 nm) due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. Scanning electron microscopy has been used for exploring the morphological properties of the prepared phosphors. The BaCa₂Al₈O₁₅:Eu²⁺ phosphor has a blue afterglow when Dy³⁺ ions were co‐doped. The thermoluminescence spectra show that the Dy³⁺ ion induces a proper trap in the phosphor with a depth of 0.67 eV and results in a long afterglow phosphorescence. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Composition and Impurities on the Phosphorescence of Green-Emitting Alkaline Earth Aluminate Phosphor

Recent improvements to SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors have enabled the use of luminescent hosts with a stable crystal structure and high physical and chemical stability, thus overcoming the bottleneck in the applicability of ZnS:Cu phosphors. However, enhancement of afterglow lifetime and brightness in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors remains a challenging task. Here, we have improved the afterglow characteristics in terms of persistence time and brightness by a systematic investigation of the composition of Eu-doped alkaline earth aluminate SrAl₂O₄:Eu²⁺, Dy³⁺ crystals. We found that a Dy³⁺/Eu²⁺ ratio of ~2.4 and ~0.935 mol Eu²⁺ (per mol of SrAl₂O₄) gave the brightest and longest emissions (11% and 9% increase for each). Doping with Si⁴⁺ also resulted in a slight increase in brightness up to ~15%. Doping with alkali metal or alkaline earth metal significantly enhanced the phosphorescence intensity. In particular, doping with 0.005 mol Li⁺ (per mol of SrAl₂O₄) alone boosted the phosphorescence intensity to 239% of the initial value, as compared to that observed for the non-doped crystal, while doping with 0.01 mol Mg²⁺ and 0.005 mol Li⁺ (per 1 mol SrAl₂O₄) boosted the phosphorescence intensity up to 313% of the initial value. The results of this investigation are expected to act as a guideline for the synthesis of bright and long persistent phosphors, and facilitate the development of persistent phosphors with afterglow characteristics superior to those of conventional phosphors.     

Persistent luminescence of CaMgSi2O6:Eu2+,Dy3+ and CaMgSi2O6:Eu2+,Ce3+ phosphors prepared using the solid‐state reaction method

CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors were synthesized using the solid‐state reaction method. X‐Ray diffraction (XRD) and photoluminescence (PL) analyses were used to characterize the phosphors. The XRD results revealed that the synthesized CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors were crystalline and are assigned to the monoclinic structure with a space group C2/c. The calculated crystal sizes of CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors with a main (221) diffraction peak were 44.87 and 53.51 nm, respectively. Energy‐dispersive X‐ray spectroscopy (EDX) confirmed the proper preparation of the sample. The PL emission spectra of CaMgSi₂O₆:Eu²⁺,Dy³⁺ and CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphors have a broad band peak at 444.5 and 466 nm, respectively, which is due to electronic transition from 4f⁶5d¹ to 4f⁷. The afterglow results indicate that the CaMgSi₂O₆:Eu²⁺,Dy³⁺ phosphor has better persistence luminescence than the CaMgSi₂O₆:Eu²⁺,Ce³⁺ phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoluminescence properties of Ca2Al2O5:RE3+ (RE = Eu,Dy and Tb) phosphors for solid state lighting

Ca₂Al₂O₅:Eu³⁺, Ca₂Al₂O₅:Dy³⁺ and Ca₂Al₂O₅:Tb³⁺ phosphors were synthesized using a combustion synthesis method. The prepared phosphors were characterized by X‐ray powder diffraction for phase purity, by scanning electron microscopy for morphology, and by photoluminescence for emission and excitation measurements. The Ca₂Al₂O₅:Eu³⁺ phosphors could be efficiently excited at 396 nm and showed red emission at 594 nm and 616 nm due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions. Dy³⁺‐doped phosphors showed blue emission at 482 nm and yellow emission at 573 nm. Ca₂Al₂O₅:Tb³⁺ phosphors showed emission at 545 nm when excited at 352 nm. Concentration quenching occurred in both Eu³⁺ and Dy³⁺phosphors at 0.5 mol%. Photoluminescence results suggested that the aluminate‐based phosphor could be a potential candidate for application in environmentally friendly based lighting technologies.     

Sol–gel preparation and luminescent properties of red‐emitting phosphor Sr‐Ba‐Mo‐W‐O‐(Eu3+,Sm3+)

Two series of red‐emitting phosphors Sr‐Ba‐Mo‐W‐O:Eu,Sm and Sr‐Ba‐Mo‐W‐O:Eu have been synthesized by a sol–gel method. The effects of the chemical composition, concentrations of Sm³⁺ and Eu³⁺, the Sr²⁺/Ba²⁺ ratio, and the W⁶⁺/Mo⁶⁺ ratio on the luminescent properties were investigated. The as‐prepared phosphors were characterized by X‐ray diffraction and Raman spectra. Results showed that single phases of the two series were prepared. The compositions of Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 and Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10 had the strongest luminescent intensity. The excitation spectra of Sm³⁺, Eu³⁺ co‐doped phosphors were broader and the strongest peak moved to 404 nm when compared with that of Eu³⁺ single‐doped phosphors. The luminescent intensity of the Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 at 618 nm were 2.8 times greater than that of Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10. The luminescent intensity of Sr_0.6Ba_0.13Mo_0.8 W_0.2O₄:Eu_0.10Sm_0.08 and Sr_0.75Ba_0.1Mo_0.8 W_0.2O₄:Eu_0.10 at 150 °C decreased to 56.8% and 50.3% of the initial value at room temperature, respectively. 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.     

Thermoluminescence studies of zinc borate (ZnB2O4) phosphor doped with rare earths for dosimetric aspects

A series of ZnB₂O₄ phosphors doped with different concentrations of Eu and Dy (0.05 0.1, 0.2, 0.5, 1.0 mol%) and co-doped with Ce (1, 2, 5, 7, 10 mol%) respectively was prepared via the solid-state reaction technique and the thermoluminescence (TL) behaviour of gamma ray-irradiated samples was studied. The synthesized samples were irradiated with γ-rays for the dose range 0.03–1.20 kGy. The TL intensity variations with dose, dopant concentration, and the effect of co-doping were studied. The TL response curves for ZnB₂O₄:Eu³⁺ and ZnB₂O₄:Dy³⁺, ZnB₂O₄:Eu³,Ce³⁺ and ZnB₂O₄:Dy³⁺,Ce³⁺ phosphor were observed. It was revealed that ZnB₂O₄:Eu³⁺ showed a linear TL behaviour for the dose 0.03–1.20 kGy and ZnB₂O₄:Dy³⁺ showed linearity for the gamma dose range 0.03–0.10 kGy. Furthermore, fading for all the samples was observed to be less than 10% for a storage period of 30 days. In addition to this, the trapping parameters, especially activation energies were evaluated using the Ilich method and the initial rise method. The activation energy values obtained from both methods were in complete agreement with each other.     

Combustion synthesis of blue‐emitting submicron CaAl4O7:Eu2+, Dy3+ persistence phosphor

Long persistence phosphor CaAl₄O₇: Eu²⁺, Dy³⁺ were prepared by a combustion method. The phosphors were characterized by means of X‐ray diffraction (XRD), scanning electron microscopy (SEM), decay time measurement techniques and photoluminescence spectra (PL). The CaAl₄O₇: Eu²⁺, Dy³⁺ phosphor showed a broad blue emission, peaking at 445 nm when excited at 341 nm. Such a blue emission can be attributed to the intrinsic 4f → 5d transitions of Eu²⁺ in the host lattices. The lifetime decay curve of the Dy³⁺ co‐doped CaAl₄O₇: Eu²⁺ phosphor contains a fast decay component and another slow decay one. Surface morphology also has been studied by SEM. The calculated CIE colour chromaticity coordinates was (0.227, 043). We have also discussed a possible long‐persistent mechanism of CaAl₄O₇:Eu²⁺, Dy³⁺ phosphor. All the results indicate that this phosphor has promising potential for practical applications in the field of long‐lasting phosphors for the purposes of sign boards and defence. Copyright © 2011 John Wiley & Sons, Ltd.     

The high thermal stability of white emitting phosphor Mg2Y2Al2Si2O12:Dy3+,Eu3+,La3+/Lu3+ for white light emitting diodes

A series of Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ was prepared using a solid-state method, and the phosphor emitted white light by tuning the ratio of Dy³⁺/Eu³⁺. The effects of La³⁺/Lu³⁺ on the structure and luminescence properties of Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺ were explored. Under the influence of bond length and twist, the luminescence intensity of the materials increased first and then decreased under excitation with ultraviolet light. The lattice distortion of the trivalent cation La³⁺-substituted Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺ and Eu³⁺ phosphors was reduced, the symmetry of polyhedron occupied by the luminescence centre improved, and the thermal stability of the luminescence centre improved to a certain extent. White light emitting diodes (LEDs) were fabricated by combining a 370 nm LED chip and the Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺,La³⁺ (Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺,Lu³⁺) phosphor. The results showed that Mg₂Y₂Al₂Si₂O₁₂:Dy³⁺,Eu³⁺,La³⁺/Lu³⁺ may have potential application in the area of white LEDs.