Kinetics and TL glow curve study of europium-activated strontium aluminate

The present paper reports the thermoluminescence (TL) glow curve of Eu²⁺-activated SrAl₂O₄ phosphor with different UV exposure times. Evaluation of kinetic parameters was done by the peak shape method. The recorded glow curve shifts towards lower temperatures with respect to increasing UV exposure time. The peaks were found at 146.76, 141.34 and 140.37 °C, respectively, for 5, 10 and 15 min of UV exposure using the heating rate of 3°C s^?1. The glow peak shows the second-order kinetics. Different kinetic parameters, i.e. trap depth, order of kinetics, activation energy, and frequency factor are also calculated. The XRD pattern of the sample is compared with reported XRD using the software match.     

Thermoluminescence studies of UV-irradiated Y2O3:Eu3+ doped phosphor

The present paper reports thermoluminescence (TL) glow curves of Eu³⁺-doped Y₂O₃ phosphor with different ultraviolet (UV) exposure times. The glow peak shows second-order kinetics of Eu³⁺-doped Y₂O₃, and corresponding kinetic parameters were evaluated using the peak shape method. Calculations of trap depth were carried out using different methods. The kinetics order, activation energy, and frequency factor were calculated. The recorded glow curve shifts towards higher intensity with longer UV exposure. The heating rate used for recording TL was 3.0 °C s^?1. Particle size and structure were verified by X-ray diffraction (XRD) pattern and morphology by scanning electron microscopy (SEM) imaging.     

Thermoluminescence study of ZnS:Cu nanoparticles

In this paper, we report on the TL glow curves and kinetic parameters, activation energy, order of kinetics, and the frequency factor of copper-doped zinc sulfide nanophosphor under UV irradiations. The sample was prepared by the chemical precipitation method; thereafter, the TL glow curves were recorded for different doses of UV exposure at a heating rate of 10 °C/s. The synthesized nanophosphor exhibited TL glow peaks at 241, 255, and 281 °C for the heating rate 10 °C/s at different doses of 5, 10, and 15 min of UV exposure. The kinetic parameters activation energy E, the order of kinetics b, and the frequency factor S of synthesized nanophosphor of ZnS:Cu have been calculated by using a peak shape method while the trap depth was determined using different formulae. The sample was characterized by XRD (X-ray diffraction) and SEM (scanning electron microscope).     

Characterization and luminescence properties of Gd2O3 phosphor

Gd₂O₃ phosphor was synthesized by combustion synthesis using gadolinium nitrate hexahydrate as precursor and urea as fuel. Structural and surface morphology were studied by X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Chemical composition analysis of the phosphor was performed by Fourier-transform infrared spectroscopy, and tts optical properties were characterized by use of photoluminescence (PL) and thermoluminescence (TL) techniques. In PL spectra, feeble emission at 490 nm (blue) and intense emission at approximately 545 nm (green) are observed after excitation at 300 nm. TL measurement was performed on the Gd₂O₃ phosphor by irradiating it with γ-rays (1 kGy). A well resolved glow peak at 226.4 °C was observed. Kinetic data were estimated from the TL glow curve by use of Chen’s peak-shape method; the results are discussed in detail. The average particle size of the Gd₂O₃ phosphor was 41 nm; a monoclinic phase was formed at a firing temperature of 500 °C. This was in agreement with SEM and TEM results.     

Red phosphors in MgAl2Si2O8 doping with Mn4+, Gd3+ and Lu3+ and host-sensitized luminescence properties

Mn⁴⁺ doped and Gd³⁺, Lu³⁺ co-doped MgAl₂Si₂O₈-based phosphors were first of all synthesized by solid state reaction at about 1300.0 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors which showed broad red emission bands in the range of 610–715 nm and had a different maximum intensity when activated by UV illumination was discussed. Such a red emission can be attributed to the intrinsic ²E → ⁴A₂ transitions of Mn⁴⁺.     

Thermal annealing of LaF3:Eu3+ nanocrystals synthesized by a solvothermal method and their luminescence properties

In this work, we used a low temperature solvothermal method to synthesize Eu³⁺-doped LaF₃ (LaF₃:Eu³⁺) nanocrystals. The effect of thermal annealing on their phase structures and luminescence properties was studied. Transformation from LaF₃ to LaOF was observed after the annealing, and the initial transformation process was studied using a rapid thermal annealing technique. It was found that a sufficiently high annealing temperature is required for the transformation of LaF₃ to LaOF. LaOF phase started to be formed after annealing at 500 °C for as short as 5 min, and higher annealing temperatures and longer annealing time led to a larger amount of LaOF formed. With the increase of the formation of LaOF, the luminescence was greatly enhanced. Strong O^2? → Eu³⁺ charge transfer band was present in these samples annealed at 500 °C and higher temperatures, and greatly enhanced ⁷F₀ → ⁵D₂ transition of Eu³⁺ was also observed.     

Mn4+-, Tb3+,4+-, and Er3+-activated red phosphors in the MgAl2Si2O8 system

Mn⁴⁺ doped and Tb^3+,4+, Er³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid-state synthesis at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had different maximum intensities when activated by UV illumination, was discussed. Such a red emission can be attributed to the intrinsic ²E → ⁴A₂ transitions of Mn⁴⁺.     

Effect of Sr2+ doping on the luminescence properties of YVO4:Eu3+,Sr2+ particles prepared by a solvothermal method

Well-dispersed Eu³⁺ and Sr²⁺ co-doped YVO₄ luminescent particles (YVO₄:Eu³⁺,Sr²⁺) on the submicron scale were prepared by a facile solvothermal method at low temperature. The effect of Sr²⁺ doping on the luminescence of YVO₄:Eu³⁺,Sr²⁺ particles was investigated by fixing the Eu³⁺ doping concentration at 7 mol%. It was found that the luminescence intensity of the as-prepared YVO₄:Eu³⁺,Sr²⁺ particles increased with the Sr²⁺ doping concentration x to reach a two-fold enhancement when x = 5 %, and then decreased for higher x. We also investigated the effect of thermal annealing on the luminescence properties of the YVO₄:Eu³⁺ and YVO₄:Eu³⁺,Sr²⁺ particles. A remarkable enhancement in their luminescence properties was observed after annealing at 900 °C in air for 30 min. It was showed that the annealed YVO₄:Eu³⁺,Sr²⁺ particles exhibited a two-fold stronger emission than the annealed YVO₄:Eu³⁺. This work indicates that Sr²⁺ doping is beneficial to the luminescence enhancement for both the as-prepared and annealed YVO₄:Eu³⁺,Sr²⁺ particles.     

Luminescence enhancement and potential application of sky-blue sulfide phosphor doped with promoter

The luminescence of the ZnS:Tm phosphor was enhanced by the addition of a KCl promoter, and a white phosphor was prepared for potential white-light applications. It was found that a high synthesis temperature and high TmF₃ concentration promoted the substitution of Tm³⁺ ions for Zn²⁺ ions. KCl doping facilitated the growth of the hexagonal phase and decreased the phase transformation temperature of ZnS. In addition, the luminescence center concentration, excitation energy absorption, effective energy transfer, charge balance, and luminescence intensity of the phosphor were improved by the addition of the KCl promoter. The emission pattern and peaks of the ZnS:Tm,KCl phosphor were similar to those of the ZnS:Tm phosphor, indicating that the ligand field variation of Tm³⁺ caused by KCl doping was small. When the sky-blue ZnS:Tm,KCl phosphor was blended with a yellow ZnS:Mn,KCl phosphor in 1:1 weight ratio, white-light emission was observed under excitation from a 6-W ultraviolet lamp (1,350 μW/cm², λ?=?254 nm). The Commission Internationale de l’Eclairage coordinates were (0.36, 0.35), and the luminance intensity was 28.1 cd/m².     

A new evaluation technique for analyzing the thermoluminescence glow curve and calculating the trap parameters

A step-fitting simulation technique was developed for the thermoluminescence (TL) glow-curve analysis and the kinetic trap parameters determination. These parameters include the order of kinetics b, the activation energy E (eV) and the pre-exponential factor S″ (s⁻¹). A general equation was developed to estimate the order of kinetics b. The characteristics point of this equation is that any set of three data points in a TL glow curve can yield the kinetics order. Using this characteristic, an improved procedure was suggested to separate a composite glow curve, which includes several overlapping peaks, into its individual components and to obtain the trap parameters of the glow peaks. The program was used to analyze the TL glow curve of the UV dosimetric material pure zirconium oxide (ZrO₂).     

Effects of Pb2+ ions concentration on the structure and PL intensity of Pb-doped ZnAl2O4 nanocrystals synthesized using sol–gel process

Undoped and Pb²⁺-doped ultrafine cubic zinc aluminate (ZnAl₂O₄) hosts were successfully prepared at a relatively low temperature (~80 °C) using the sol–gel method. The concentration of Pb²⁺ was varied from 0 to 5 mol%. The TGA showed that the minimum annealing temperature required to obtain single phase ZnAl₂O₄ must be above 400 °C. The XRD data revealed that all the annealed samples were single phase crystalline structures and the estimated crystallites size were in the range of 21–30 nm in diameter. The FTIR results suggest that heat-treating can destroy some of the bonds. The surface morphology of the phosphors was influenced by the Pb²⁺ mol%. Undoped and Pb²⁺-doped ZnAl₂O₄ nanoparticles exhibit the violet emission at slightly different positions. The slight peak shifts suggests the possibilities that the luminescence centre can either be due to the defects level in the host or Pb²⁺ ions. The emission peaks at 390 and 399 nm are ascribed to the typical UV transitions ³P_0,1 → ¹S₀ in Pb²⁺ ion. At the higher Pb²⁺ mol%, the luminescence quenching behaviour occurs, which suggests that doping with Pb²⁺ ions is accompanied by the introduction of new defect sites that enhance non-radiative recombination of the excited electrons.     

Synthesis of CaWO4:Er3+@SiO2 and CaWO4:Tm3+@SiO2 nano-particles via a combustion pathway and study of their optical properties

Use of citric acid as a chelating agent and fuel, ammonium nitrate as fuel, boric acid as flux material and silica as supports, CaWO₄:Ln³⁺@SiO₂ (Ln = Er and Tm) nanoparticles were synthesized via a combustion reaction at 800 °C. Characterization of the samples was performed by X-ray diffractometer (XRD), reflectance UV–Vis spectrophotometer, fluorescence spectrophotometer (PL) and transmission electron microscope (TEM). XRD patterns showed that tetragonal crystalline structure of scheelite and silica supports were formed, and that the formation of a silica support could enhance the luminescence intensity of CaWO₄:Ln³⁺. The reflectance UV–Vis and PL spectra indicated the broad absorption band of WO₄ ^2? groups about 240 nm, the WO₄ ^2? wide excitation band with maximum at 240 nm, a broad emission band of WO₄ ^2? with maximum about 420 nm, and characteristic emissions of Ln³⁺ ions. According to the TEM analysis, CaWO₄:Er³⁺@SiO₂ and CaWO₄:Tm³⁺@SiO₂ nanoparticles have almost the same morphology with average particle sizes about 50 nm.     

TL characteristics of Ce3+-doped NaLi2PO4 TLD phosphor

Ce³⁺-doped NaLi₂PO₄ orthophosphate (with different impurity concentrations, i.e., 0.01–0.3 mol%) was prepared by a solid state reaction method. Formation of the material was confirmed using powder X-ray diffraction analysis. TL intensity was found to be the highest for the material having impurity concentration 0.2 mol% after annealing it at around 600 K for 1 h and subsequently quenching to room temperature. A typical glow curve consists of three peaks at around 454, 493 and 570 K (dosimetry peak). Good sensitivity (~8 times more than that of TLD-100), low fading (~15 % in 2 months), low-Z material (Z _eff ≈ 10.8), very wide dose response (i.e., 0.1 Gy–1.0 kGy of γ rays) make the material a ‘good’ thermoluminescent dosimeter (TLD) phosphor suitable for personnel, medical and environmental dosimetry of high-energy radiation using TL. It could also be used during cancer therapy and sterilization of food where high doses are needed to be monitored.     

Characterizations of white-light ZnWO4 phosphor prepared by blending complementary phosphor

In the preparation of ZnWO₄ phosphor, crystalline ZnWO₄ was created, even though the concentration of WO₃ was only 10 mol%. ZnWO₄ was the dominant crystallization phase when the concentration of WO₃ exceeded 40 mol%. The optimal crystallization of ZnWO₄ phosphor was obtained when the composition molar ratio of ZnO to WO₃ was 1:1, and sintering was carried out at 1,100°C for 3 h. In this condition, a bluish-green emission with a peak at 460 nm was observed. For Y₂O₃:Eu³⁺,Li⁺, the complementary phosphor of ZnWO₄, the Li flux improved phosphor crystallization. The red emission peak of the Y₂O₃:Eu³⁺,Li⁺ phosphor was measured at about 612 nm. The optimal photoluminescence intensity of the Y₂O₃:Eu³⁺,Li⁺ phosphor was obtained when it was sintered at 1,200°C for 5 h and was mixed with 11 mol% Eu₂O₃ and 70 mol% Li₂CO₃. When the weight ratio of Y₂O₃:Eu³⁺,Li⁺ to ZnWO₄ was 1:4, the Y₂O₃:Eu³⁺,Li⁺-blended ZnWO₄ phosphor showed white-light emission with Commission Internationale de l’Eclairage coordinates at (0.34, 0.30). The luminance of the white-light phosphor excited by a 6-W UV lamp was around 160 cd/m².     

Optical and kinetic studies of CdS:Cu nanoparticles

CdS:Cu nanoparticles were successfully synthesized by a coprecipitation method using mercaptoethanol as a capping agent. Thermoluminescence (TL) spectra of CdS:Cu nanoparticles were studied for different exposure time. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectrometry. XRD and SEM measurements showed that the size of the crystallites was in the range 8–17 nm. Optical measurements indicated a blue-shift in the absorption band edge upon Cu doping. The direct allowed bandgap of undoped and Cu-doped CdS nanoparticles was 2.53 and 2.64 eV, respectively. We also calculated the kinetic parameters for Cu-doped CdS nanoparticles from the TL glow curves measured at 254, 249, and 244 °C with variation of the ultra-violet (UV) exposure time. The glow curve shows general order kinetics, and its kinetic parameters are calculated.     

Thermoluminescence of irradiated polystyrene

Thermoluminescence of irradiated polystyrene has been studied in the temperature range 100 to 440°K. Three glow peaks with maximum at 160, 221, and 378°K have been observed. These peaks are analyzed by different methods and the activation energies which were obtained are compared. The activation energies are found to be 0.22, 0.48, and 1.45 eV for the peaks with maxima at 160, 221, and 378°K, respectively. Second-order kinetics is appropriate to all these cases. The glow peaks are attributed to the decay of the free radicals formed on irradiation and subsequent thermal stimulation. The peak with the maximum at 160°K is attributed to electron trapping by the carbonyl groups or peroxy radicals formed on irradiation. The curve with the peak at 221°K is attributed to the cyclohexadienyl radical, and the curve with the peak at 378°K is attributed to the chain radical ? CH₂? C (C₆H₅)? CH₂? . The centers responsible for the observed thermoluminescence are identified by correlation with electron spin resonance (ESR) data obtained on the same samples.     

Synthesis and characterization of novel blue emitting Na2CaSiO4:Ce3+ phosphor

The blue phosphors Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ were synthesized by the sol–gel method and their luminescence characteristics were investigated for the first time. Structural information about prepared samples is obtained by analyzing the XRD patterns and SEM micrographs. The photoluminescence (PL) excitation spectra indicate that the Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors can be effectively excited by ultraviolet (360 nm) light. The PL emission spectra exhibit tunable blue broadband emission with the dominant wavelength of 427–447 nm under excitation of 360 nm by controlling the doping concentration of Ce³⁺. The concentration quenching effect for Ce³⁺ was found at the optimum doping concentration of 4 mol%. The Commission Internationale de l’Eclairage 1931 chromaticity coordinates of Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ are (0.1447, 0.0787), which are better color purity compared to the commercial Eu²⁺-doped BaMgAl₁₀O₁₇ phosphor. Na_1.96Ca_0.96SiO₄:0.04Ce³⁺ composition shows intense blue emission (peak wavelength, 439 nm) with relative intensity versus commercial BaMgAl₁₀O₁₇:Eu²⁺ blue phosphor (Nichia) 65 and 158 % under 254 and 365 nm excitation, respectively. All the results indicate that Na_(2?x)Ca_(1?x)SiO₄:xCe³⁺ phosphors are potential candidate as a blue emitting phosphor for UV-converting white light-emitting diodes.     

K3Eu5(PO4)6: hydrothermal synthesis,crystal structure and photoluminescence properties

An anhydrous orthophosphate, K₃Eu₅(PO₄)₆ (tripotassium pentaeuropium hexaphosphate), has been prepared by a high‐temperature solid‐state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single‐crystal X‐ray diffraction analysis (SC‐XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three‐dimensional framework of [Eu₅(PO₄)₆]_∞, with the tunnel filled by K⁺ ions. The IR spectrum, UV–Vis spectrum and luminescence properties of polycrystalline samples of K₃Eu₅(PO₄)₆, annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu³⁺ concentration (9.96 × 10²¹ ions cm^?3), the self‐activated phosphor K₃Eu₅(PO₄)₆ shows s strong luminescence emission intensity with a quantum yield of 37%. Under near‐UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu³⁺ ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.     

Ba3P5N10Br:Eu2+: A Natural‐White‐Light Single Emitter with a Zeolite Structure Type

Illumination sources based on phosphor‐converted light emitting diode (pcLED) technology are nowadays of great relevance. In particular, illumination‐grade pcLEDs are attracting increasing attention. Regarding this, the application of a single warm‐white‐emitting phosphor could be of great advantage. Herein, we report the synthesis of a novel nitridophosphate zeolite Ba₃P₅N₁₀Br:Eu²⁺. Upon excitation by near‐UV light, natural‐white‐light luminescence was detected. The synthesis of Ba₃P₅N₁₀Br:Eu²⁺ was carried out using the multianvil technique. The crystal structure of Ba₃P₅N₁₀Br:Eu²⁺ was solved and refined by single‐crystal X‐ray diffraction analysis and confirmed by Rietveld refinement and FTIR spectroscopy. Furthermore, spectroscopic luminescence measurements were performed. Through the synthesis of Ba₃P₅N₁₀Br:Eu²⁺, we have shown the great potential of nitridophosphate zeolites to serve as high‐performance luminescence materials.     

A new promising phosphor, Na3La2(BO3)3:Ln (Ln=Eu, Tb)

We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na₃La₂(BO₃)₃ (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb³⁺ and Eu³⁺)-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb³⁺, Eu³⁺) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu³⁺ ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613 nm, which is attributed to ⁵D₀-⁷F₂ transition of Eu³⁺. The luminescence indicates that the local symmetry of Eu³⁺ in NLBO crystal lattice has no inversion center. Optimum Eu³⁺ concentration of NLBO:Eu³⁺ under UV excitation with 395 nm wavelength is about 30 mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252 nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb³⁺ in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb³⁺ and Eu³⁺) was analyzed. The relative high quenching concentration was also discussed.