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.     

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.     

Blue excitable green emitting Ce3+ doped CaS phosphor for w‐LEDs

CaS:Ce³⁺ is an efficient green‐emitting (535 nm) phosphor, excitable with blue light (450–470 nm) and was synthesized via a solid‐state reaction method by heating under a reducing atmosphere. The luminescent properties, photoluminescent (PL) excitation and emission of the phosphor were analyzed by spectrofluorophotometry. The excitation and emission peaks of the CaS:Ce³⁺ phosphor lay in the visible region, which made them relevant for light‐emitting diode (LED) application for the generation of white light. Judd‐Oflet parameters were calculated and revealed that green light emitted upon blue illumination. The prepared phosphor had strong blue absorption at 470 nm and a broad green emission band range from 490–590 nm with the peak at 537 nm. The characteristics of the CaS:Ce³⁺ phosphor make it suitable for use as a wavelength tunable green emitting phosphor for three band white LEDs pumped by a blue LED (470 nm). The Commission International de l'Eclairage co‐ordinates were calculated by a spectrophotometric method using the spectral energy distribution (0.304, 0.526) and confirm the green emission. The potential application of this phosphor is as a phosphor‐converted white light‐emitting diode. Copyright © 2015 John Wiley & Sons, Ltd.     

Crystal structure and luminescence properties of the blue‐green‐emitting Ba9(Lu,Y)2Si6O24:Ce3+ phosphor

Samples of the Ba₉(Lu_2‐xY_x)Si₆O₂₄:Ce³⁺ (x = 0–2) blue‐green phosphors were synthesized by solid‐state reactions. All the samples exhibited a rhombohedral crystal structure. As the Y³⁺ concentration increased, the diffraction peaks shifted to the small angle region and the lattice parameters increased due to the larger ionic radius of Y³⁺ (r = 0.900 Å) compared with that of Lu³⁺ (r = 0.861 Å). Under 400 nm excitation, samples exhibited strong blue‐green emissions around 490 nm. The emission bands had a slight blue shift that resulted from weak crystal‐field splitting with increasing Y³⁺ concentration. Luminescence intensity and quantum efficiency (QE) decreased with increasing Y³⁺ concentration. The internal QE decreased from 74 to 50% and the external QE decreased from 50 to 34% as x increased from 0 to 2. The thermal stability of the Lu series was better than that of the Y‐series. The excitation band peak around 400 nm matched well with the emission light from the efficient near‐ultraviolet (NUV) chip. These results indicate promising applications for these NUV‐based white light‐emitting diodes.     

Luminescence and energy‐transfer properties of color‐tunable Ca2Mg0.25Al1.5Si1.25O7:Ce3+/Eu2+/Tb3+ phosphors for ultraviolet light‐emitting diodes

A series of Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺/Eu²⁺/Tb³⁺ phosphors was been prepared via a conventional high temperature solid‐state reaction and their luminescence properties were studied. The emission spectra of Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Eu²⁺ and Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Tb³⁺ phosphors show not only a band due to Ce³⁺ ions (409 nm) but also as a band due to Eu²⁺ (520 nm) and Tb³⁺ (542 nm) ions. More importantly, the effective energy transfer from Ce³⁺ to Eu²⁺ and Tb³⁺ ions was confirmed and investigated by emission/excitation spectra and luminescent decay behaviors. Furthermore, the energy level scheme and energy transfer mechanism were investigated and were demonstrated to be of resonant type via dipole–dipole (Ce³⁺ to Eu²⁺) and dipole–quadrupole (Ce³⁺ to Tb³⁺) reactions, respectively. Under excitation at 350 nm, the emitting color could be changed from blue to green by adjusting the relative doping concentration of Ce³⁺ and Eu²⁺ ions as well as Ce³⁺ and Tb³⁺ ions. The above results indicate that Ca₂Mg_0.25Al_1.5Si_1.25O₇:Ce³⁺,Eu²⁺/Tb³⁺ are promising single‐phase blue‐to‐green phosphors for application in phosphor conversion white‐light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Optical characterization and the energy level scheme for Ce3+‐doped BaY2Si3O10 blue‐emitting phosphor

A series of Ce³⁺‐activated blue‐emitting phosphors BaY₂Si₃O₁₀ (BYSO) was designed and synthesized by a conventional solid‐state method. Upon ultraviolet light (250–370 nm) excitation, the obtained phosphors showed an intense blue emission band centered at 400–427 nm depending on doping concentration, and corresponding to the 5d→4f transition of Ce³⁺. The effects of doping concentration on crystal structure, emitting color, photoluminescence and photoluminescence excitation spectra, as well as the concentration quenching mechanism were studied in detail. The optimal doping concentration of Ce³⁺ in this phosphor was demonstrated to be about 0.75% and the concentration quenching mechanism can be ascribed to electric dipole–dipole interactions with a critical distance of ~38 Å. These fine luminescence properties indicate that BYSO:Ce³⁺ may be a potential blue phosphor for full‐color ultra‐violet (UV) white light emitting diodes (WLEDs).     

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.     

Effect of Dy3+ or Eu2+ co‐activator on a BaCa(SO4)2:Ce3+ mixed alkaline earth sulfate phosphor

The individual emission and energy transfer between Ce³⁺ and Eu²⁺ or Dy³⁺ in BaCa(SO₄)₂ mixed alkaline earth sulfate phosphor prepared using a co‐precipitation method is described. The phosphor was characterized by X‐ray diffraction (XRD) and photoluminescence (PL) studies and doped by Ce;Eu and Dy rare earths. All phosphors showed excellent blue–orange emission on excitation with UV light. PL measurements reveal that the emission intensity of Eu²⁺ or Dy³⁺ dopants is greater than when they are co‐doped with Ce³⁺. An efficient Ce³⁺ → Eu²⁺ [²T_2g(4f⁶5d) → ⁸S_7/2(4f₇)] and Ce³⁺ → Dy³⁺ (⁴ F_9/2 → ⁶H_15/2 and ⁴ F_9/2 → ⁶H_13/2) energy transfer takes place in the BaCa(SO₄)₂ host. A strong blue emission peak was observed at 462 nm for Eu²⁺ ions and an orange emission peak at 574 nm for Dy³⁺ ions. Hence, this phosphor may be used as a lamp phosphor. Copyright © 2015 John Wiley & Sons, Ltd.     

5d–4f transition in new phosphate‐based phosphors

The preparation of Ce³⁺‐doped Sr₆AlP₅O₂₀ and Ba₆AlP₅O₂₀ by a combustion method is described. Formation of compounds was confirmed by X‐ray diffraction (XRD) analysis. The photoluminescence (PL) emission spectra were observed at 355 nm when excited at 307 nm for the various concentrations. The PL emission spectra of phosphors showed strong Ce³⁺ emission due to the 5 d → 4f transition of Ce³⁺ ions. The Ce³⁺ emission intensity in Sr₆AlP₅O₂₀:Ce phosphor was higher than that in Ba₆AlP₅O₂₀:Ce and it may be useful for scintillation applications. Copyright © 2011 John Wiley & Sons, Ltd.     

The luminescent properties and crystal structure of Sr(1.5‐x)‐(1.5y)Mg0.5SiO4:xEu2+,yCe3+ blue phosphor synthesized by co‐precipitation method

In order to improve the luminescent performance of silicate blue phosphors, Sr_{(1.5‐x)‐(1.5y)}Mg_0.5SiO₄:xEu²⁺,yCe³⁺ phosphors were synthesized using one‐step calcination of a precursor prepared by chemical co‐precipitation. The crystal structure and luminescent properties of the phosphors were analyzed using X‐ray diffraction and fluorescence spectrophotometry, respectively. Because the activated ions (Eu²⁺) can occupy two different types of sites (Sr₁ and Sr₂), the emission spectrum of Eu²⁺ excited at 350 nm contains two single bands (EM₁ and EM₂) in the wavelength range 400–550 nm, centered at 463 nm, and the emission intensity first increases and then decreases with increasing concentrations of Eu²⁺ ions. Co‐doping of Ce³⁺ ions can greatly enhance the emission intensity of Eu²⁺ by transferring its excitation energy to Eu²⁺. Because of concentration quenching, a higher substitution concentration of Ce³⁺ can lead to a decrease in the intensity. Meanwhile, the quantum efficiency of the phosphor is improved after doping with Ce³⁺, and a blue shift phenomenon is observed in the CIE chromaticity diagram. The results indicate that Sr_{(1.5‐x)‐(1.5y)}Mg_0.5SiO₄:xEu²⁺,yCe³⁺ can be used as a potential new blue phosphor for white light‐emitting diodes.     

Optical properties and energy transfer of Eu2+/Ce3+ co‐activated Na3Ca6(PO4)5 phosphor

Ce³⁺/Eu²⁺ co‐doped Na₃Ca₆(PO₄)₅ phosphors were prepared using a combustion‐assisted synthesis method. X‐Ray powder diffraction (XRD) analysis confirmed the formation of a Na₃Ca₆(PO₄)₅ crystal phase. Na₃Ca₆(PO₄)₅:Eu²⁺ phosphors have an efficient bluish‐green emission band that peaks at 489 nm, whereas Ce³⁺‐doped Na₃Ca₆(PO₄)₅ showed a bright emission band at 391 nm. Analysis of the experimental results suggests that enhancement of the Eu²⁺ emission intensity in co‐doped Na₃Ca₆(PO₄)₅:Eu²⁺,Ce³⁺ phosphors is due to a resonance‐type energy transfer from Ce³⁺ to Eu²⁺ ions, which is predominantly governed by an exchange interaction mechanism. These results indicate that Ce³⁺/Eu²⁺ co‐doped Na₃Ca₆(PO₄)₅ is potentially useful as a highly efficient, bluish‐green emitting, UV‐convertible phosphor for white‐light‐emitting diodes. Copyright © 2014 John Wiley & Sons, Ltd.     

Design,synthesis and luminescence properties of Ba2YB2O6Cl‐ and Ba2YB2O6F‐based phosphors

Using a high‐temperature solid‐state reaction, the chlorine in Ba₂YB₂O₆Cl is gradually replaced by F, and a new compound with the nominal chemical formula Ba₂YB₂O₆F and two phosphors doped with Ce³⁺ and Eu³⁺, respectively, are obtained. X‐Ray diffraction and photoluminescence spectroscopy are used to characterize the as‐synthesized samples. The as‐synthesized Ba₂YB₂O₆Cl exhibits bright blue emission in the spectral range ~ 330–410 nm with a maximum around 363 nm under X‐ray or UV excitation. Ba₂YB₂O₆F:0.01Ce³⁺ exhibits blue emission in the range ~ 340–570 nm with a maximum around 383 nm. Ba₂YB₂O₆F:0.01Eu³⁺ exhibits a predominantly ⁵D₀–⁷ F₂ emission (~610 nm) and the relative intensities of the ⁵D₀–⁷ F_0,1,2 emissions are tunable under different wavelength UV excitation. The luminescence behaviors of the two phosphors are explained simply in terms of the host composition and site occupancy probability of Ce³⁺ and Eu³⁺, respectively. The results indicate that these phosphors have potential application as a blue phosphor or as a red phosphor. Copyright © 2014 John Wiley & Sons, Ltd.     

Energy transfer between Ce3+ → Gd3+ or Tb3+ in KNaSO4 microphosphor

KNaSO₄ microphosphor doped with Ce,Gd and Ce,Tb and prepared by a wet chemical method was studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) characterization. KNaSO₄ has a 5‐µm particle size detected by SEM. KNaSO₄:Ce³⁺,Tb³⁺ showed blue and green emission (at 494 nm, 557 nm, 590 nm) of Tb³⁺ due to ⁵D₄ → ⁷F_J (J = 4, 5, 6) transitions. KNaSO₄:Ce³⁺,Gd³⁺ showed luminescence in the ultraviolet (UV) light region at 314 nm for an excitation at 271 nm wavelength. It was observed that efficient energy transfer took place from Ce³⁺ → Gd³⁺ and Ce³⁺ → Tb³⁺ sublattices indicating that Ce³⁺ could effectively sensitize Gd³⁺ or Tb³⁺ (green emission). Ce³⁺ emission weakened and Gd³⁺ or Tb³⁺ enhanced the emission significantly in KNaSO₄. This paper discusses the development and understanding of photoluminescence and the effect of Tb³⁺ and Gd³⁺ on KNaSO₄:Ce³⁺. Copyright © 2015 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.     

Studies on the luminescence properties of cerium co‐doping on Ca2MgSi2O7:Eu2+ phosphor by solid‐state reaction method

Ca₂MgSi₂O₇:Ce³⁺, Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺,Ce³⁺ phosphors were prepared using the solid‐state reaction method. The crystal structures of the sintered phosphors were of melilite type, which has a tetragonal crystallography. The chemical compositions of the sintered phosphors was confirmed by energy dispersive X‐ray spectroscopy. The different thermoluminescence kinetic parameters [activation energy (E), frequency factor (s) and order of the kinetics (b)] of these phosphors were evaluated and compared using the peak shape method. Under ultraviolet excitation, the emission spectra of both Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺,Ce³⁺ phosphors were composed of a broad emission band peaking at 530 nm. When the Ca₂MgSi₂O₇:Eu²⁺ phosphor is co‐doped with Ce³⁺ ions, photoluminescence, afterglow and mechanoluminescence intensity was strongly enhanced. Ca₂MgSi₂O₇:Eu²⁺ showed some afterglow with a short persist time. On incorporation of Ce³⁺, efficient energy transfer from Ce³⁺ to Eu²⁺ was found and the emission intensity of Eu²⁺ was enhanced. The mechanoluminescence intensities of Ca₂MgSi₂O₇:Ce³⁺, Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺,Ce³⁺ phosphors increased proportionally increased with the increase in impact velocity, which suggests that these phosphors can be used as sensors to detect stress in an object.     

Luminescent properties of Ca3SiO4Cl2 co‐doped with Ce3+ and Eu2+ for near‐ultraviolet light‐emitting diodes

Ca₃SiO₄Cl₂ co‐doped with Ce³⁺,Eu²⁺ was prepared by high temperature reaction. The structure, luminescent properties and the energy transfer process of Ca₃SiO₄Cl₂: Ce³⁺,Eu²⁺ were investigated. Eu²⁺ ions can give enhanced green emission through Ce³⁺ → Eu²⁺ energy transfer in these phosphors. The green phosphor Ca_2.9775SiO₄Cl₂:0.0045Ce³⁺,0.018Eu²⁺ showed intense green emission with broader excitation in the near‐ultraviolet light range. A green light‐emitting diode (LED) based on this phosphor was made, and bright green light from this green LED could be observed by the naked eye under 20 mA current excitation. Hence it is considered to be a good candidate for the green component of a three‐band white LED. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and photoluminescence characteristics of (Y,Gd)BO3:RE (RE = Eu3+, Ce3+, Dy3+ and Tb3+) phosphors for blue chip and near‐UV white LEDs

A series of Eu³⁺‐, Ce³⁺‐, Dy³⁺‐ and Tb³⁺‐doped (Y,Gd)BO₃ phosphors was synthesized by a solid‐state diffusion method. X‐Ray diffraction confirmed their hexagonal structure and the scanning electron microscopy results showed crystalline particles. The excitation spectra revealed that (Y,Gd)BO₃ phosphors doped with Eu³⁺, Ce³⁺ , Dy³⁺ and Tb³⁺ are effectively excited with near UV‐light of 395 nm/blue light, 364, 351 and 314 nm, respectively. Photoluminescence spectra of Eu³⁺‐, Ce³⁺‐ and Tb³⁺/Dy³⁺‐doped phosphor showed intense emission of reddish orange, blue and white light, respectively. The phosphor Y_0.60Gd_0.38BO₃:Ce_0.02 showed CIE 1931 color coordinates of (0.158, 0.031) and better color purity compared with commercially available blue BAM:Eu²⁺ phosphor. The phosphor (Y,Gd)BO₃ doped with Eu³⁺, Dy³⁺ and Tb³⁺ showed CIE 1931 color coordinates of (0.667, 0.332), (0.251, 0.299) and (0.333, 0.391) respectively. Significant photoluminescence characteristics of the prepared phosphors indicate that they might serve as potential candidates for blue chip and near‐UV white light‐emitting diode applications. Copyright © 2015 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.     

Luminescence and energy transfer in Ce3+, Mn2+‐doped K2AEP2O7 (AE = Ca,Sr) phosphor

Pyrophosphates K₂AEP₂O₇ (AE = Ca, Sr) prepared by the classical solid‐state technique and activated with Ce³⁺ are described. Intense emission was observed in K₂AEP₂O₇ (AE = Ca, Sr). The effect of Mn²⁺ co‐doping was studied. The broad emission peak of Mn²⁺ was observed at 534 nm in K₂SrP₂O₇:Ce³⁺ and at 539 nm in K₂CaP₂O₇:Ce³⁺, Mn²⁺. Mn²⁺ emission was greatly enhanced by addition of the sensitizer Ce³⁺ due to efficient energy transfer from Ce³⁺ to Mn²⁺. Copyright © 2015 John Wiley & Sons, Ltd.