Thermoluminescence Spectra Research Articles

Defect characterization in Bi12GeO20 single crystals by thermoluminescence

Bi12GeO20 single crystal grown by Czochralski method was investigated in terms of thermoluminescence (TL) properties. TL experiments were performed for various heating rates between 1 and 6 K/s in the temperature region of 300–675 K. One TL peak with peak maximum temperature of 557 K was observed in the TL spectrum as constant heating rate of 1 K/s was employed. Curve fitting, initial rise and variable heating rate methods were applied to calculate the activation energy of trap level corresponding to this TL peak. Analyses resulted in a presence of one trap center having mean activation energy of 0.78 eV. Heating rate characteristics of revealed trap center was also explored and theoretically well-known behavior that TL intensity decreases and peak maximum temperature increases with heating rates was observed for the trap level. Distribution of trapping levels was studied by thermally cleaning process for different Tstop between 425 and 525 K. Quasi-continuously distributed trapping levels were revealed with mean activation energies ranging from 0.78 to 1.26 eV. Moreover, absorption analysis revealed an optical transition taking place between a defect level and conduction band with an energy difference of 2.51 eV. These results are in good agreement for the presence of intrinsic defects above valence band in Bi12GeO20 crystals.

Sol-Jel Tekniği ile Sentezlenmiş Sr0,5Ca0,5WO4 Fosforunda Eu3+ İyonunun Lüminesans, TL Kinetik Parametreler ve Elektrokimyasal Davranışındaki Rolü

The Eu3+doped Sr0,5Ca0,5WO4 has been synthesized by the sol-gel method for the first time. The phosphors were analyzed by XRD, SEM, DTA/TG optical absorption spectra, radioluminescence (RL), photoluminescence (PL), and thermoluminescence (TL) spectra. The energy transfer mechanism was determined on Eu3+ doped Sr0,5Ca0,5WO4 phosphor. The XRD results reveal that the samples exhibit a tetragonal scheelite structure. FT-IR spectra provide the proof of scheelite structure with W-O anti-symmetric stretching vibration in [WO4]2- tetrahedrons at 750-910 cm-1. The Sr0,5Ca0,5WO4 phosphor showed a broad emission between 350-750 nm with a maximum of 506 nm. Sr0,5Ca0,5WO4:0.5Eu3+ phosphor exhibit characteristic emissions of Eu+3 (545, 592, 614, 650, and 700 nm) in the RL spectrum. The host material has excellent energy transfer efficiency for lanthanide ions. The kinetic parameters were calculated by the computerized glow curve deconvolution (CGCD) analysis method. As a result of CGCD, three peaks (Etrap:0.74-1.46 eV) for un-doped Sr0,5Ca0,5WO4 and five peaks (Etrap:0.75-1.28 eV) for Sr0,5Ca0,5WO4: Eu3+ were determined under main TL glow curve. In the cyclic voltammogram of the doped sample, an oxidation peak of about -0.4 eV, which is thought to be derived from Eu3+, was observed. Based on the results, the Sr0,5Ca0,5WO4:Eu+3 phosphors may be potential applicants for LEDs.

Luminescence spectra and energy transfer of Tm<sup>3+</sup> and Tb<sup>3+</sup> doped in LiMgPO<sub>4</sub> phosphors

<sec> LiMgPO<sub>4</sub> (LMP) phosphor doped with rare earth is a promising radiation dosimeter material. Thermoluminescence (TL) spectroscopy is an effective method to study the carrier traps and luminescence centers in materials. To study the luminescent mechanism of rare-earth-doped LMP phosphors, LMP phosphors doped with Tm and Tb (LMP:Tm, LMP:Tb and LMP:Tm, Tb) are prepared by high temperature solid state reaction. The TL glow curve and TL spectrum of the phosphors are measured by the linear heating method, and compared with the photoluminescence (PL) spectrum. </sec><sec> The shape of the TL glow curve of LMP phosphor varies with the doping active impurities, but the TL glow curves can be fitted by seven TL peaks. Double-doping Tm<sup>3+</sup> and Tb<sup>3+</sup> in LMP phosphor can enhance the TL intensity of the fifth peak (<i>E</i> ~ 1.39 eV) and weaken the seventh TL peak (<i>E</i> ~ 1.70 eV). </sec><sec> By comparing the PL spectra with TL spectra of the phosphors, it can be seen that the TL spectra are more complex than the PL spectra excited by ultraviolet light (λ = 352 nm). In the TL process, the electrons which are excited to the conduction band release the energy to recombination centers, and the released energy can more effectively excite the rare earth ions from the ground state to excited states, resulting in the more TL emitting peaks than in the the PL process. </sec><sec> Although Tm<sup>3+</sup> and Tb<sup>3+</sup> can be the luminescent centers in LMP phosphors when Tm<sup>3+</sup> and Tb<sup>3+</sup> are doped in LMP simultaneously, Tb<sup>3+</sup> ions are likely to act as sensitizers in LMP:Tm and LMP:Tb phosphor, and Tb<sup>3+</sup> ions transfer energy to the low-energy Tm<sup>3+</sup> ions, which makes the luminescent centers, Tm<sup>3+</sup> ions, excited to the high-energy state and then de-excited with emitting light. This result is also proved by the fact that the luminescence decay of Tb<sup>3+</sup> in phosphors increases with Tm<sup>3+</sup> concentration increasing. The energy transfer through non-radiative transition is more significant at higher temperature. </sec>

In-situ Insights into trap attributions in Fe3+-activated long persistent phosphors

Here, a novel NIR afterglow center of Fe3+ is proposed, and a long persistent phosphor of SrAl12O19: Fe3+ is successfully fabricated. Some in-situ characterizations, including temperature-dependent electron paramagnetic resonance (EPR) spectra and thermoluminescence (TL) spectra of Al2O3 and SrCO3 raw materials, support the fact that the substitution of Fe3+ to Al3+ creates a trap with the negative effective charge by binding an electron around [AlFe]. Further, the existence of isoelectronic trap-cluster (AlFe-VO) endows a bright emission band that appeared in the range of 750–1000 nm with an afterglow duration of >2 h. Notably, these analyses in the aspect from the influence of raw materials on afterglow properties are very rarely found in the searchable reports. This top-down investigation route reveals the possibility of perfecting the research skills on the afterglow mechanism from the fountainhead and may offer a wide-range understanding of the trapping and de-trapping process of long persistent phosphors.

Novel UV and X-ray irradiated white-emitting persistent luminescence and traps distribution of Ca5Ga6O14: Pr3+ phosphors

In the current study, we synthesized a new white-emitting long persistent luminescence (LPL) phosphor Ca5Ga6O14: Pr3+ by the solid-state reaction, and investigated its LPL properties for the first time. Ca5Ga6O14: Pr3+ is a multi-stimulus phosphor that can be activated by X-ray and 254 nm ultraviolet (UV) lamp. Under the excitation of 254 nm UV lamp and X-ray, Ca5Ga6O14: Pr3+ provides white light consisting of green-bluish and red ingredients. The phenomenon stems from 3P0 and 1D2 multiplets electrons transition in 4f level of Pr3+. Following the removal of UV excitation, a fantastic white luminescent LPL can be detected in Ca5Ga6O14: Pr3+ for 10.3 h. Moreover, the distribution of traps in Ca5Ga6O14: Pr3+ was also discussed by thermoluminescence (TL) spectra, which contained large shallow and deep traps, that were critical for exceptional LPL properties for UV and X-ray irradiation, respectively. Our results indicated that Ca5Ga6O14: Pr3+ could be used as multi-stimulus LPL phosphors in different fields.

Boosted UV emission on the optically and thermally stimulated luminescence of CaB6O10:Gd,Ag phosphors excited by X-rays

The luminescent properties of X-ray phosphors based on optically stimulated luminescence (OSL) are quite fortuitous, since it demands the existence of both trapping and recombination (luminescent) centers. Nevertheless, lanthanide-doped materials have changed this paradigm by two main reasons: lanthanide doping provides the development of high efficient phosphors and allows for a relatively easy prediction of the energy-levels of the trapping centers involved in OSL phenomena. In view of that, this work reveals some luminescent and dosimetric properties of a phosphor never reported before, i.e., gadolinium and silver doped CaB6O10 polycrystalline samples. The phosphor synthesis followed a solid state reaction method and was optimized regarding the concentration of dopants for a better OSL response. Comparing to non-doped samples, the OSL showed an enhancement of ∼ 140x when doped with gadolinium and silver. The phosphor exhibited a high UV emission under blue stimulation (475 nm), with a linear dose-response for the range analyzed (1 mGy up to 2 Gy) and a minimum detectable dose of ∼ 40 μGy. The material exhibited a fading of ∼ 30% within the first 24 h after irradiation, which is attributed to shallow traps created by Ag+ incorporation. Wavelength-resolved thermoluminescence (TL) and OSL spectra revealed a sharp 317 nm emission, which is ascribed to 6PJ → 8S7/2 transition of Gd3+ centers, indicating that the Gd3+ has a crucial role in the luminescence mechanisms. In addition, the OSL spectrum exhibited also a broad emission at 350 nm attributed to 3DJ,1D2 → 1S0 transitions of Ag+ centers. Insights on the luminescent processes are given, including the role of Gd3+ and Ag+ centers in the trapping and recombination processes responsible for the TL and OSL. New mechanisms of luminescent enhancement by silver incorporation are suggested.

Long persistent luminescence and traps distribution of Tb3+ doped calcium gallium germanate

A new type of long persistent green luminescent phosphor Ca2Ga2GeO7: Tb3+ was prepared by high temperature solid-state reaction technique. In this paper, the crystal structure, luminescence properties and decay curves of phosphors were mainly studied. The long persistent luminescence (LPL) properties of these phosphors were characterized by LPL spectra, LPL decay curves and thermoluminescence (TL) spectra. When the ultraviolet (UV) light source was turned off, Ca2Ga2GeO7: Tb3+ phosphor exhibit typical LPL behavior for approximately 1.2 h. The green-emitting LPL was originated form the typical 5D4→7F5 transition of Tb3+ ions, and the green LPL is similar to PL. Based on the experimental results, the LPL mechanism and traps distribution of the Ca2Ga2GeO7: Tb3+ was described via TL analysis in detail.

Self‐activated persistent luminescence from Ba2Zr2Si3O12for information storage

AbstractTill now, many doped persistent luminescence (PersL) phosphors have been investigated and found various applications in such as bioimaging, photocatalysis and information storage, but introducing PersL emitters into a proper host is mostly complex. In this research, a self‐activated PersL phosphor Ba2Zr2Si3O12(BZSO) is prepared by solid state reaction. By adding NH4Cl, the self‐activated PersL intensity is evidently enhanced. The trap depths and concentrations are examined by thermoluminescence spectra. Meanwhile, Bi3+ions are introduced into BZSO and show wide band photoluminescence (PL) from 300 to 600 nm. Moreover, the PL of Bi3+is tunable under excitation by 265‐350 nm lights. Furthermore, as a proof‐of‐concept design, we designed a patterned quick response (QR) code based on the self‐activated PersL of BZSO, and the information of “South China University of Technology (SCUT)” can be read out by the code scanning technology. Bi3+‐doped BZSO phosphors are suggested to provide potential applications in information storage by its self‐activated PersL, and to excite researchers to study the tunable PL in Bi3+‐doped phosphor.

Optically stimulated luminescence and spectral emission features of radioluminescence and thermoluminescence of natural kunzite

Features of luminescence optically stimulated from natural kunzite using 470 nm blue light are reported. Preparatory measurements of its X-ray excited radioluminescence and thermoluminescence show that the sample has two main bands centered at 360 nm and 600 nm. The optically stimulated luminescence discussed in this report was monitored in the UV region and is presumed to be the same 360 nm emission that appears in the radioluminescence and thermoluminescence spectra. The glow curve shows at least three peaks at 74, 202, 432 oC for heating at 1 oC and the third one is a composite of two. Only the first two peaks are deduced to contribute most of the optically stimulated luminescence.

Cation sites modification enhanced luminescence and thermal quenching characteristic in the blue light-emitting Na3Sc2-xZnx(PO4)3:0.03Eu2+ phosphors

Eu2+ luminescence in the host of Na3Sc2(PO4)3 have attracted increasing attention due to its zero-thermal quenching phenomenon. In this paper, we have investigated a site modification strategy, in which Zn2+ is substituted for partial Sc3+ of the host lattice, and find such a strategy benefits great deal to Eu2+ luminescence. Through the solid-state reaction, a series of modified Na3Sc2-xZnx(PO4)3:0.03Eu2+ phosphors was synthesized. Phase purity of the synthesized phosphors was identified by powder X-ray diffraction and their luminescence properties were studied through excitation and emission spectra, fluorescence lifetime, quantum efficiency, temperature-dependent emission spectra and thermoluminescence spectra. With the nonequivalent substitution, the modified Na3Sc2-xZnx(PO4)3:0.03Eu2+ phosphors exhibit higher luminescence intensity. In the meantime, thermal performance of Eu2+ photoluminescence has been further optimized. Finally, the white light-emitting diodes (WLEDs) application is examined by combining 340 nm near ultraviolet (n-UV) LED chip and phosphors (Blue: Na3Sc1.92Zn0.08(PO4)3: 0.03Eu2+, Yellow: Y3Al5O12: Ce3+, Red: K2SiF6: Mn4+). The fabricated WLED device has excellent properties with CIE color coordinate x = 0.3844, y = 0.4206, correlated color temperature (CCT) = 4161 K and color rendering index (Ra) = 93.8, indicating the potential application in WLED fields.

Design and characterization of Eu2+-doped Ba4Si6O16 photostimulated phosphor for optical information storage

Novel persistent luminescence (PersL) phosphors are emerging as potential candidates for up-to-data information storage devices owing to its large memory capacity, low cost, and rewritable capability. In this study, a novel photostimulated luminescence (PSL) phosphor was successfully developed through co-doping Eu2+ and La3+ ions in Ba4Si6O16 (BSO) host. Firstly, the crystal structure, photoluminescence (PL), and PL excitation (PLE) of BSO:xEu2+ were studied systematically. Under the UV light source irradiation, the as-prepared BSO:0.02Eu2+ sample exhibits the best PersL decay property. Secondly, by applying the strategy of trap depth engineering, outstanding PersL performance is observed when La3+ ions were introduced into BSO:0.02Eu2+ as well. Moreover, the trap distribution and dynamics of electron motion in BSO: Eu2+, La3+ are characterized using methods of thermoluminescence spectra. Finally, verified by 980/808 nm photostimulation, BSO: Eu2+, La3+ shows promising application in optical information systems with a good optical storage capacity. In addition, based on the analysis of experiment and theoretical calculation results, a tentative energy level schematic is proposed to illustrate the mechanism of PersL and PSL in BSO:0.02Eu2+, La3+.

An insight into indium effect on the crystal structure and thermoluminescence of LiMgPO4: Combined experiment and ab initio calculations

In this work, indium doped LiMgPO4 is first considered as a dosimetric material. We present studies of the structural properties and thermally stimulated luminescence (TSL), as well as electronic structure of pure and indium doped LiMgPO4. We observed a nonmonotonic shift in the TSL peak with increasing indium concentration (x), which was associated with two different indium sites. We demonstrated that In3+ predominantly replaces Mg2+, but at indium concentration of less than 1%, it occupies the Li+ positions. The variation in indium substitution site affects also the depth of electron traps. Doping of LiMgPO4 with indium changes not only the TSL glow curves, but also the spectra of thermoluminescence. The spectrum of undoped LiMgPO4 consists of two broad bands located in the UV region (λ = 350 nm) and in the red region (λ = 640 nm), while there is only one line (λ = 630 nm) in the TSL spectra of LiMgPO4:In3+. The mechanism of thermoluminescence in pure and indium doped LiMgPO4 is discussed.

Electron transport in Tradescantia leaves acclimated to high and low light: thermoluminescence, PAM-fluorometry, and EPR studies.

Using thermoluminescence, PAM-fluorometry, and electron paramagnetic resonance (EPR) for assaying electron transport processes in chloroplasts in situ, we have compared photosynthetic characteristics in Tradescantia fluminensis leaves grown under low light (LL, 50-125µmol photons m-2 s-1) or high light (HL, 875-1000µmol photons m-2 s-1) condition. We found differences in the thermoluminescence (TL) spectra of LL- and HL-acclimated leaves. The LL and HL leaves show different proportions of the Q (~ 0°C) and B (~ 25-30°C) bands in their TL spectra; the ratios of the "light sums" of the Q and B bands being SQ/SB ≈ 1/1 (LL) and SQ/SB ≈ 1/3 (HL). This suggests the existence of different redox states of electron carriers on the acceptor side of PSII in LL and HL leaves, which may be affected, in particular, by different capacities of their photo-reducible PQ pools. Enhanced content of PQ in chloroplasts of LL leaves may be the reason for an efficient performance of photosynthesis at low irradiance. Kinetic studies of slow induction of Chl a fluorescence and measurements of P700 photooxidation by EPR demonstrate that HL leaves have faster (about 2 times) response to switching on actinic light as compared to LL leaves grown at moderate irradiation. HL leaves also show higher non-photochemical quenching (NPQ) of Chl a fluorescence. These properties of HL leaves (faster response to light and generation of enhanced NPQ) reflect the flexibility of their photosynthetic apparatus, providing sustainability and rapid response to fluctuations of environmental light intensity and solar stress resistance. Analysis of time-courses of the EPR signals of [Formula: see text] induced by far-red (λmax = 707nm), exciting predominantly PSI, and white light, exciting both PSI and PSII, suggests that there is a contribution of cyclic electron flow around PSI to electron flow through PSI in HL leaves. The data obtained are discussed in terms of photosynthetic apparatus sustainability of HL and LL leaves under variable irradiation conditions.

Insights into the relationship between luminescence and ESR dating signals from Spanish sedimentary quartz samples of different geologic origins

Trapped charge dating of optically bleached quartz deposits that lie beyond the dose-saturation limits of conventional optically stimulated luminescence (OSL) has typically focused on two main techniques over the last decade: electron spin resonance (ESR) and thermally transferred optically stimulated luminescence (TT-OSL). In spite of a clear association between these two dating techniques through their shared dose rate terms, the exact relationships between the various ESR centre (i.e., Al and Ti) and TT-OSL dating signals remain largely unexplored. In this study we undertake ESR and luminescence signal comparisons on paired sedimentary quartz samples from two Middle Pleistocene Spanish archaeological sites (Porto Maior in northwest Spain and Cuesta de la Bajada in northeast Spain) to examine the empirical relationships between quartz dating signals across different geological provinces. For this purpose we undertake 3-dimensional (3D) thermoluminescence (TL) spectral measurements, single-grain TT-OSL dating and signal analyses, normalised multiple centre (MC) ESR signal characterisation (ESR intensities, signal composition, dose-response curve properties), MC ESR De evaluation, and ICP-OES analysis of quartz extracts to evaluate potential correlations between elemental impurity concentrations and Al, Li–Ti and Li–H centre signals. The ESR samples from Cuesta de la Bajada and Porto Maior display similar Al centre signal intensities and dose-response behaviour, but they exhibit major differences in their Ti centre properties. Geochemical analysis reveals that the Cuesta de la Bajada quartz extracts contain higher concentrations of Al and Ti impurities (15 and 21% higher, respectively) when compared with the Porto Maior quartz extracts. These compositional differences appear correlated with the relative Ti–H signal intensities for the two sample datasets but not with the relative Al and Ti–Li signal intensities. The luminescence characterisation comparisons reveal a higher proportion of TT-OSL-producing grains in the Cuesta de la Bajada samples (6.2% versus ~1.6% for Porto Maior), and single-grain TT-OSL signal intensities that are almost an order of magnitude higher than for the Porto Maior samples. The 3D TL spectra for the Cuesta de la Bajada quartz are dominated by two major TL peaks in the red emission band (620 nm) at 265–310 °C and 365 °C (when using a heating rate of 1 °C/s), which are up to seven times more intense than the corresponding signals observed for the Porto Maior quartz. However, no major inter-sample differences were observed in the blue and UV-blue bands of the 3D TL spectra. These contrasting luminescence characteristics may be indicative of variable signal sensitisation histories related to dissimilar sedimentary recycling or geological origins between the two sites. Our results provide a useful baseline dataset for future comparative ESR and luminescence characterisation studies, and indicate a potentially close relationship between the quartz ESR Ti centre and single-grain TT-OSL signals. There is significant potential to refine understanding of these signal relationships in the future by expanding the number, and geographic coverage, of paired ESR–luminescence comparison studies, and by incorporating comparative 3D TL spectral investigations that focus exclusively on TT-OSL-producing grains (as opposed to bulk grain populations) to better elucidate luminescence trapping and recombination characteristics.

Luminescence of Bi3+ and Bi2+ ions in novel Bi-doped SrAl4O7 phosphor

Bismuth-doped SrAl4O7 powders were synthesized via modified Pechini process and their photoluminescence, radioluminescence and thermoluminescence properties were studied and discussed. Obtained results showed that in studied materials bismuth is present in two valence states, Bi3+ and Bi2+. Upon UV excitation SrAl4O7:Bi powders yield broad multicomponent luminescence in the 350–670 nm range, associated with the 3P0,1 → 1S0 transition of Bi3+ ions, and the most intense component located in green (λmax = 515 nm) part of spectrum. It was found that the emission spectral distribution is excitation wavelength-dependent. By changing the excitation wavelength in the 270–340 nm range the emission colour can be modulated from blue, through bluish-cyan to green. The studied phosphors also showed broad-band 2P3/2 → 2P1/2 Bi2+ emission in deep red region centered at around 710 nm. This luminescence was found predominant in radioluminescence and thermoluminescence spectra, which is deemed unique for bismuth-doped materials. The Bi2+ 630–830 nm emission might be attractive for bioimaging as it appears in the Ist biological window and may be utilized for deep red scintillation.

Enhancing the blue luminescence behaviour of the Li co-doped novel phosphor ZnB2O4: Tm3+

Abstract Here we report a detailed structural analysis, and properties of the cathodoluminescence (CL), photoluminescence (PL) and 3D thermoluminescence spectra of the Tm3+ incorporated ZnB2O4 phosphor successfully synthesized through wet-chemical synthesis. The formation of a single-phase compound is verified through X-ray diffraction (XRD) studies. The phosphor shows an efficient blue emission located at 458 nm corresponding to 1D2→3F4 under both a low voltage electron beam and UV excitation. The optimal concentration of the doped Tm3+ is 0.5 mol% in CL and PL measurements. The corresponding concentration quenching mechanism is confirmed to be a multipole-multipole interaction, and the critical distance between Tm3+ ions is estimated to be 34 A. Incorporating Li+ remarkably enhances the luminescence intensity probably because of the charge compensation effect. Li ions are speculated to fill the defects in the ZnB2O4 host and then the excitation energy transfers from the host to Tm3+. Surprisingly, the thermoluminescence spectra of ZnB2O4:Tm3+ and Li+ co-doped ZnB2O4:Tm3+ recorded in the temperature range 30–400 °C follow a different pattern compared with PL and CL data. The dominant signals come from Tm3+ sites. Above room temperature, the Tm3+ ions do not show the peak temperature movement, but do exhibit a different pattern with the addition of co-doped Li+ ions. These results indicate that these phosphors are promising candidates for luminescence-based optoelectronic devices.

Thermoluminescence of β-particle induced Bern-4M muscovite

Bern-4M muscovite from Switzerland was investigated via X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and thermoluminescence (TL). Muscovite has the theoretical formula KAl2(AlSi3O10)(FOH)2, or (KF)2(Al2O3)3(SiO2)6(H2O). Chemical analysis of the muscovite sample was carried out using EDS for major oxides. The results indicate that muscovite includes oxygen (59.1%), silicon (18.86%), and aluminum (15.22%) as major elements and contains low concentrations of potassium, magnesium, and sodium. In standard muscovites potassium use to be 10% and oxygen 47%, probably the sample was strongly lixiviated before the analysis. The thermoluminescence spectrum exhibits a wide glow peak located at 250 °C with a shoulder peak at high temperature region. Trap depth and frequency factor were calculated using Hoogenstraaten's method and found to be 1.16 eV and 1.4 × 1010 s−1, respectively. Reproducibility test indicated that the values within ±5% were obtained after 15 cycles. The storage time experiments were performed for different time periods up to 1 week for dark fading.

Detailed luminescence (RL, PL, CL, TL) behaviors of Tb3+ and Dy3+ doped LiMgPO4 synthesized by sol-gel method

The un-doped, Tb3+ and, Dy3+ doped LiMgPO4 phosphors were successfully synthesized by the sol-gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the light-emitting phosphors. The XRD spectra verify the phase formation of samples. The luminescence properties were analyzed by radioluminescence (RL), photoluminescence (PL), cathodoluminescence (CL) and, thermoluminescence (TL) spectra. Also, the effect of Tb3+, Dy3+ ions in LiMgPO4 was determined on the luminescence intensity in detail.The RL spectrum of un-doped LiMgPO4 consists of two broad emission bands in the 310–450 nm and 575–850 nm range. The maximum intensities of these bands were observed at 360 nm and 655 nm. The emission spectrum of Dy3+ doped LiMgPO4 under X-ray excitation show characteristic emissions of Dy3+ corresponds to 4F9/2→6Hj transitions. In addition to the 5D4→7Fj (j:6–1) transitions of Tb3+ doped LiMgPO4 phosphor, strong emissions derived from 5D3→7Fj (j:6–3) transitions were observed in the blue region. Also, these blue emissions were seen at RL, PL and, CL spectra. The optical absorption spectra were recorded and the energy band gaps were calculated 3.62 eV, 3.30 eV and, 4,01 eV for un-doped, Dy3+ and, Tb3+ doped LiMgPO4 phosphors, respectively. The phosphors irradiated with UV (254 nm) light. The main TL glow peak was observed at 288 °C for the Dy3+ doped phosphor, and the peaks at 198, 283 °C were observed for the Tb3+ doped phosphor.

CaSiO3:Eu2+, Er3+, BaSiO3:Eu2+, Er3+ and SrSiO3:Eu2+, Er3+ phosphors: molten salt synthesis, optical and thermal studies

In this study, thermal and optical behaviors of CaSiO3:Eu2+, Er3+, BaSiO3:Eu2+, Er3+ and SrSiO3:Eu2+, Er3+ phosphors synthesized by molten salt synthesis technique are investigated. The doped phosphors activated with Eu2+ and Er3+ ions with varying doping concentrations of 0 mol% to 1 mol% were subjected to structural, optical, and thermal analyses. The powder X-ray diffraction analysis confirms the triclinic structure of CaSiO3: Eu2+, Er3+, orthorhombic structure of BaSiO3: Eu2+, Er3+, and monoclinic structure of SrSiO3: Eu2+, Er3+ phosphors with good homogeneity and phase purity. The morphological and topographical traits are studied via field emission scanning electron microscopy and transmission electron microscopy analyses. These analyses indicate the irregular shape and size of particles along with agglomeration that occurred as a result of prolonged heat treatment processes. The thermal behavior studied by thermogravimetric (TG) analysis confirms the thermal stability of these phosphors with less weight loss occurring while heating the phosphors from room temperature to 700 °C. The study of thermoluminescent spectra of ultraviolet (UV) and gamma-irradiated phosphors confirms deep trapping that occurred in the synthesized phosphors along with second-order kinetics. The trap depth analysis indicates the trapping of electrons in deep trap centers and hence high activation energy (~ 3 eV) is required to vacate the trapped electrons. Doping of conjugate rare earth pair Eu2+ and Er3+ in the host lattice leads to formation of more defects and hence enhances the trapping mechanism. The gamma-irradiated phosphors exhibit increased TL intensity, efficient trapping in much deeper trap centers, and improved fading characteristics in comparison to the UV-irradiated phosphors.

F- and F+-band radioluminescence and the influence of annealing on its emission spectra in Al2O3:C,Mg

Radioluminescence spectra of Al2O3:C,Mg monitored at temperatures up to 400 °C is reported. Measurements were made on samples either as received or on ones annealed at 1200 °C. Radioluminescence is observed at 410 nm for the unannealed sample but principally at 330 and 410 nm in the annealed sample with the emission at 330 nm dominant. Both bands are subject to thermal quenching but the change for the F+ band is atypical. Temperature induced effects on these and other bands are discussed, as are complementary measurements of thermoluminescence spectra.