Phosphor Samples Research Articles

The novel Sr3LiSbO6:Mn4+, Ca2+ far-red-emitting phosphors with over 95% internal quantum efficiency for indoor plant growth LEDs

Sr3LiSbO6:x%Mn4+, y%Ca2+ (x = 0.1, 0.2, 0.3, 0.4, 0.5, x: y = 1: 1.5) phosphors have been successfully synthesized via conventional high-temperature solid-state reaction method. The phosphor samples were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence spectra, ultraviolet–visible (UV–vis) absorption spectra, Raman spectra and decay curves as well as internal quantum efficiency (IQE). The quantum efficiency of Sr3LiSbO6:Mn4+ phosphor can be as high as 96% by co-doping small amount of Ca2+ ions. The excitation and emission intensities of Sr3LiSbO6:Mn4+, Ca2+ phosphors can be enhanced 1.3–1.6 times. Furthermore, the Sr3LiSbO6:0.3%Mn4+, 0.45%Ca2+ phosphor exhibited good thermal stability and the emission intensity at 423 K maintained 87% compared with its initial value at 298 K. Under the excitation of 365 nm, the phosphor exhibits an intense far-red emission band centered at 693 nm which can match well with the absorption band of phytochrome PFR. Finally, a LED device was fabricated with the Sr3LiSbO6:0.3%Mn4+, 0.45%Ca2+ phosphor, which showed an effective promotion of growth in red beans and pakchoi cabbages. All the results show that the synthesized phosphors may have promising applications for use in plant growth LEDs.

Synthesis and luminescence characterization of Eu3+ -doped Ca7 Mg2 (PO4 )6 phosphor for eco-friendly white light-emitting diodes and thermoluminescence dosimetric applications.

A Eu3+ -activated Ca7 Mg2 (PO4 )6 phosphor was prepared at high temperature (800°C) using a solid-state reaction method. The crystal structure, phase formation of the prepared phosphor was characterized using X-ray diffraction patterns and Fourier transformed infrared analysis. The luminescence properties of the synthesized phosphor were characterized using photoluminescence and thermoluminescence techniques. The prepared phosphor showed two emission peaks at 594 nm with an orange colour due to the 5 D0 →7 F1 transition and at 612 nm a red colour due to the 5 D0 →7 F2 transition under 396 nm near-UV excitation. The prepared phosphors were irradiated with different doses of γ-rays from a 60 Co gamma irradiation source. Thermoluminescence glow curves for this sample phosphor were obtained using a Nucleonix 1009I TL reader. Synthesized phosphor samples were exposed to a 3.6 kGy dose of γ-rays. The thermoluminescence glow curve of the Ca7 Mg2 (PO4 )6 :0.05 mol%Eu3+ phosphor showed maximum intensity at all concentrations of Eu3+ ions. The Ca7 Mg2 (PO4 )6 :0.05 mol%Eu3+ phosphor was irradiated with different doses of 60 Co γ-irradiation and a linear response was observed between 0.6 kGy and 3.6 kGy. Trapping parameters such as activation energy, frequency factor and order of kinetics were calculated. The CIE chromaticity diagram showed the colour coordinates of the synthesized phosphor in the orange and red regions of the visible spectrum; this spectral feature revealed high colour purity and excellent chromaticity coordinate characteristics. Photoluminescence and thermoluminescence properties revealed that the prepared phosphor could be a potential red-emitting phosphor for eco-friendly white light generation and an excellent thermoluminescent dosimeter material for thermoluminescence dosimetric applications.

Morphology modulation and near infrared to visible upconversion luminescence properties of Er3+/Yb3+-doped α-NiMoO4 nanoparticles

In this work, for the first time, the near infrared (NIR) to visible upconversion luminescence (UCL) properties of α-NiMoO4 were explored by doping with Er3+/Yb3+ ions. A microwave hydrothermal method was used to fabricate Er3+ (2 mol%)/Yb3+ (12–20 mol%)-doped α-NiMoO4 phosphors. X-ray diffraction patterns suggest the formation of the Yb2(MoO4)3 phase, which is beneficial for UCL enhancement. Nanorods (α-NiMoO4), bundles of rods (α-NiMoO4: Er3+), and cactus (α-NiMoO4: Er3+/Yb3+)-like morphologies were obtained, and a morphology modulation mechanism has been proposed. TEM elemental mapping, XPS, and UV–Vis DRS measurements confirm the existence of Ni, Mo, O, Er, and Yb elements in the samples. The synthesized samples demonstrate intense green (522 nm: 2H11/2 → 4I15/2 and 546: 4S3/2 → 4I15/2), weak red (660 nm: 4F9/2 → 4I15/2), and NIR (803 nm: 4S3/2 → 4I13/2) emissions under 980 nm excitation. Downshifting emission was also obtained at 1538 nm (Er3+: 4I13/2 → 4I15/2). The highest emission intensity was achieved in the Er3+ (2 mol%)/Yb3+ (15 mol%)-doped α-NiMoO4 sample. An intense green color and strong UCL were observed in the MN/Er2/Yb15 sample based on CIE chromaticity and fluorescence decay curves. A graph of pump power versus intensity for the phosphor samples indicates that the upconversion process occurs by two photonic processes. The proposed energy transfer process is explained based on ground state absorption and excited state absorption. The particles were found to be safe at doses up to 0.125 mg/mL, as assessed by cytotoxicity investigation in bovine skeletal muscle cells. The obtained results open the possibilities of potential applications of Er3+/Yb3+-doped α-NiMoO4 as an efficient luminescent material for bioimaging applications.

Characterization of Ce:CSSO, Pr:CSSO, and co-doped Ce,Pr:CSSO phosphors for aerosol phosphor thermometry

The phosphor Ce:Ca3Sc2Si3O12(Ce:CSSO) was recently investigated for aerosol phosphor thermometry (APT) and shown to be capable of temperature imaging up to at least 1400 K. To date, no thorough characterization of the temperature dependent emission properties of the phosphor has been performed up to 1400 K. Additionally, due to limited sensitivity over certain temperature ranges continuous temperature imaging from 300 to 1400 K was not possible. Here, cerium and praseodymium doped into CSSO are investigated to address these limitations. Singly-doped Ce:CSSO and Pr:CSSO, and co-doped Ce,Pr:CSSO phosphor samples were studied. Emission lifetimes and quenching behavior were characterized in a tube furnace for each phosphor. Results from the singly-doped phosphors were used to interpret the co-doped phosphor results. The phosphor characterization data was used to estimate thermometry performance at temperatures relevant to low-temperature ignition studies in engines. The proposed diagnostic uses a combination of co-doped APT, host-referenced APT, and scattering-referenced APT approaches to increase the range over which high-precision temperature measurements can be made. Characterization results include the first reported measurements of luminescence lifetimes for Ce:CSSO and Pr:CSSO at temperatures up to 1400 K, and the highest reported quenching temperature for a phosphor using 4f5d emission (1230 K for Ce:CSSO). Furnace measurements showed a normalized temperature-sensitivity of % K−1 from room temperature to 1400 K for at least one diagnostic approach using the co-doped Ce,Pr:CSSO phosphor. Estimates suggest that the co-doped Ce,Pr:CSSO phosphor is feasible for APT at temperatures ranging from 300 to 925 K and 1030 to at least 1400 K, with better than 40-K single-shot precision. The performance of Ce:CSSO and Ce,Pr:CSSO are similar throughout the investigated temperature range.

Two steps enhancement of dual mode (UC and DS) behaviour of Ho3+/Yb3+ and Tm3+/Yb3+ co-doped GdVO4 phosphors: Improvement in spectral and color purity

In the present work, the dual mode (Upconversion and Downshifting) emission behavior of Tm3+/Yb3+ and Ho3+/Yb3+ co-doped GdVO4 phosphors synthesized via high temperature solid state reaction technique have been studied. The pure phase formation has been confirmed by X-rays diffraction (XRD) studies. The crystalline nature has been found to improve on calcining the phosphors at 1473 K and also by incorporation of TiO2. The surface particles’ shape and size have been studied by SEM technique. The vibrational behaviour of the vanadate host has been investigated by Fourier Transform Infrared (FTIR) measurements. The UV–vis absorption spectra show the formation of charge transfer band (CTB) in UV region due to (VO4)3 group. The non-linear upconversion (UC) spectra show intense blue and NIR emission in GdVO4: Tm3+/Yb3+ phosphor on excitation with 980 nm radiation, whereas intense green and red UC emissions are observed in GdVO4: Ho3+/Yb3+ phosphor. The downshifting (DS) behaviour has been investigated in both the phosphors which show the self activation behaviour of GdVO4 host along with some sharp peaks in blue and green regions due to f-f transitions in Tm3+ and Ho3+ ions. The dual mode (UC and DS) emission has been further improved on heating the samples at higher temperatures and also by incorporation of TiO2. The color of the phosphor samples in the UC emission spectra has been visualized by CIE diagram. The color purity enhances in both the phosphors by increasing the calcination temperature and also by addition of TiO2. The spectral purity has been also calculated for the UC emission spectra and its also shows the same trend. Such phosphors are applicable for the display devices in blue, green and red regions via dual mode processes.

Site occupancy preference of Bi3+ and Bi3+-Eu3+ codoped yttrium galliate phosphors for white LEDs.

A variety of Bi3+-activated and Bi3+-Eu3+ codoped Y3GaO6 phosphor samples were obtained by solid-state reaction. The phase purity and crystal structure of the specimens were characterized via powder X-ray diffraction (XRD) analysis and Rietveld refinement. For the single Bi3+-doped Y3GaO6 phosphor, two different PL peaks at 410 and 595 nm were obtained, resulting from the two different Bi3+ sites occupied. The site occupation is driven by Bi3+ ion concentration. There is an energy transfer from the Bi3+ to Eu3+ ions in the YGO:Bi3+,Eu3+ phosphors. Besides, the energy transfer mechanism, efficiencies, quantum efficiency and thermal stability have been discussed in detail, demonstrating that the sample possesses high quantum efficiency and good thermal stability. The high color-rendering index Ra (92.9, and 81.6) and low CCT (3286 K, and 3904 K) of the white light-emitting diodes (WLEDs) clearly indicate that these samples are promising candidates for WLEDs.

Gamma dosimetric properties of radiophotoluminescent CaSO4:Eu3+ with novel readout instrument

We report investigations carried out on radiophotoluminescence (RPL) response of Eu3+ doped CaSO4 phosphor using an in-house developed compact system for gamma dosimetry. The system comprises a sample holder to hold 200 mg phosphor powder having particle sizes 90–212 µm in the disc form (15 mm dia, 1 mm thick) and a microcontroller-based reader with Hamamatsu PMT (H10720-110) for collection of emitted luminescence. Conversion of Eu3+ to Eu2+ on gamma irradiation in phosphor samples is studied with 320 nm UVLED (FWHM 10 nm) stimulation. The performance of the system is evaluated in 100 mGy to 10,000 mGy gamma dose range and a linear response is observed. The dosimetric properties of synthesized phosphor in terms of gamma dose response, reproducibility, dose rate response, relative photon energy dependence and fading are reported.

Spectroscopic investigation of rare earth activated potassium calcium pyrophosphate K2Ca1-xRExP2O7 (RE = Tb3+, Dy3+, Sm3+ and Eu3+) phosphors

This study investigates the spectroscopic properties of rare earth activated potassium calcium pyrophosphate K2Ca1-xRExP2O7 (RE = Tb3+, Dy3+, Sm3+ and Eu3+) phosphors synthesized by a solid-state reaction method. The synthesized phosphor samples were characterized by powder X-ray diffraction, Scanning electron microscope, Fourier transform infrared, and Photoluminescence spectroscopy. The phosphors exhibit a strong excitation band in near UV to blue region in the range 350–400 nm showing spectral overlap with the emission band of a UV light emitting diode (LED) chip. Spectroscopic analysis has also been carried out using the Judd-Ofelt theory. The obtained luminescence properties and calculated spectroscopic parameters indicate usefulness of these phosphors in solid-state lighting, white light emitting phosphor for near UV excited LEDs and other displays applications.

Tb3+/Eu3+/Tm3+ co-doped single-phase phosphors emitting close to standard white light

A sequence of Tb3+/Eu3+/Tm3+ co-doped LaAl2.03(B4O10)O0.54 single-phase phosphor samples have been produced using a sol-gel reaction. A number of properties such as phase composition, crystal structure, luminescence performance and lifetime decay curves were tested and discussed. The energy transfer process in Tb3+/Eu3+ co-doped LaAl2.03(B4O10)O0.54 phosphors was testified by luminescence spectra and lifetime decay curves. The transfer mechanism is determined to be a dipole-dipole interaction, and the energy transfer efficiency can reach 74.03%. By adjusting the doping ratio of the three ions of Tb3+, Tm3+ and Eu3+, the light emitting region of the phosphor can be adjusted to white light region. When the composition is LaAl2.03(B4O10)O0.54:0.1 Tb3+,0.06Tm3+,0.04Eu3+, the color coordinate is (0.334, 0.331), which is very close to the standard white light (0.33, 0.33). These results make clearly that Tb3+/Eu3+/Tm3+ co-doped LaAl2.03(B4O10)O0.54 phosphors have potential application value in the field of single-phase white-emitting phosphors.

Synthesis, characterization and spectroscopic properties of some rare earth activated LiAlO2 phosphor

The current paper comprises the synthesis of LiAlO 2 phosphor doped with rare-earth elements Tb 3+ , Eu 3+ , and Dy 3+ by microwave-assisted solution combustion synthesis method (SCS) and the spectroscopic properties were examined. The phosphors samples were identified and characterized by XRD, FT-IR, thermo-gravimetric analysis TG-DTA and SEM. All the prepared phosphors show polycrystalline nature with a grain size of about 49 nm as confirmed from XRD and SEM. Photoluminescence excitation and emission spectrum of Tb 3+ , Eu 3+ , and Dy 3+ doped LiAlO 2 with different sintering temperature and concentration of dopants were investigated. The Dy 3+ shows the strongest blue emission peak at 484 nm corresponding to the transition 4 F 9/2 to 6 H 15/2 under UV excitation of 358 nm. The Eu 3+ doped LiAlO 2 phosphor shows emission peak 591 nm to 615 nm for UV excitation of 238 nm which arise due to 5 D 0 to 7 F 1 electric dipole transitions. The Tb 3+ doped phosphor shows a broad excitation peak centered at 238 nm whereas it exhibits an emission peak at 544 nm corresponding to the peak transition 5 D 4 - 7 F 6 under the UV excitation at 238 nm.

Effect of Tb3+ ion concentration on photoluminescence and thermoluminescence studies of Y4Al2O9 phosphor

Herein Tb3+ (0.1, 0.2, 0.5, 1, 1.5, 2 and 2.5 mol %) doped Y4Al2O9 (monoclinic phase of yttrium aluminium oxide Y/Al 2:1) phosphors have been synthesized by conventional modified solid state reaction method (CMSSRM) using inorganic materials like Yttrium Oxide (Y2O3), Aluminium Oxide (Al2O3), Terbium Oxide (Tb2O3) and boric acid as a flux. The prepared phosphor samples were characterized using X-ray diffraction analysis (XRD), photoluminescence (PL), and thermoluminescence (TL) glow curve. From the XRD data, using the Scherrer formula the calculated average crystallite size of Tb3+ doped Y4Al2O9 phosphor is around 235 nm. Photoluminescence excitation spectra show sharp excitation peak centred at 270 nm and broad excitation peak centred at 300 nm which is due to charge transfer band. Here emission spectra show three distinct peaks centred at 492 nm (5D4 → 7F7), 544 nm (5D4 → 7F6) and 584 nm (5D4 → 7F4). Results indicate that PL intensity increases with increasing the concentration of doping ion i.e. Tb3+ up-to 2 mol % after that due to concentration quenching PL intensity decreases. Commission Internationale de l'Éclairage (CIE) values were calculated as X = 0.24 and Y = 0.56 and it shows intense green emission. TL glow curves were analysed with effect of doping ion concentration and effect of variable UV exposure time. Kinetic parameters were calculated using various methods proposed by Chen and others.

Study of Photoluminescence,Thermoluminescence, and Afterglow properties of Dy3+ doped Ba2ZnSi2O7 phosphor

Barium Zinc Silicate Ba2ZnSi2O7 (BZS) phosphor doped with Dysprosium (Dy3+) was prepared at 1200 °C in the air by a solid-state reaction method. The prepared phosphor shows an efficient blue and yellow emission centered around 480 nm and 580 nm, respectively under UV excitation, which is believed due to incorporation of Dy3+ ion. The optimum concentration for Dy3+ ion is at 2 mol% and concentration quenching is attributed to exchange interaction. The CIE diagram is drawn for the whole series of phosphor samples prepared and it confirms that emission color had, indeed, tuned with the incorporation of Dy3+ ion in the BZS samples. The afterglow properties and Thermoluminescence (TL) have also been studied. TL curve confirms the presence of at least four traps in the phosphor material. The present results suggest BZS:Dy3+phosphor is a promising one for display and dosimetry application.

A three-mode self-referenced optical thermometry based on up-conversion luminescence of Ca2MgWO6:Er3+,Yb3+ phosphors

To develop new up-conversion luminescent materials for optical thermometry, a sequence of Ca2MgWO6:xEr3+,yYb3+ phosphor samples were synthesized via high temperature solid-state reaction method. Their structure, morphology and luminescent performances were completely explored via X-ray diffraction, scanning electron microscopy and photoluminescence. Excited by 980 nm laser, all phosphor samples emit intense up-conversion luminescence of Er3+ at 531, 549 and 661 nm. Besides, these emissions were greatly enhanced with addition of Yb3+ ions. Benefiting from the different temperature dependence of three emission peaks, a dual-mode temperature sensor based on fluorescence intensity ratio (2H11/2/4S3/2 and 2H11/2/4F9/2) is realized by using single luminescent center. Meanwhile, the fluorescence lifetime of 4S3/2 state of Er3+ ions was used as the third temperature detection signal. More importantly, the phosphors exhibit superior thermal stability that will be helpful to obtain high precision temperature measurement. All results show that Ca2MgWO6:Er3+, Yb3+ samples could have potential applications for self-referenced optical thermometry.

The color tunable of Tb3+/Sm3+ co-doped phosphors through Tb3+ → Sm3+ energy transfer

Two sets of LaAl2.03B4O10.54 phosphor samples were prepared by the sol–gel method using citric acid as a complexing agent. One set was a sample doped only with Tb3+ ions, and the other set was a sample co-doped with Tb3+/Sm3+ ions. After related tests, its luminescence performance and energy transfer were analyzed and studied in detail. It can be clearly seen that there are a total of five emission peaks in the emission spectrum of the Tb3+/Sm3+-doped sample, of which the emission at 490 nm and 546 nm belongs to the 5D4 → 7F6 and 5D4 → 7F5 transitions of Tb3+ ions, while the emission at 562 nm, 601 nm and 646 nm belongs to the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions of Sm3+ ions. The energy transfer efficiency from Tb3+ ions to Sm3+ ions is positively correlated with the change of Sm3+ concentration, and its interaction mechanism is determined to be a dipole–dipole interaction. By controlling the ratio of Tb3+ and Sm3+ ions, the emission color of the phosphors can be controlled in the green, yellow, and white regions. All these indicated that Tb3+/Sm3+ co-doped phosphor is a new type of color-tunable phosphor suitable for WLED.

Study of Radiophotoluminescence of Eu Doped CaSO4 Phosphor for Gamma Dosimetric Applications

CaSO4:Eu phosphor is synthesised by acid distillation method with varying synthesis parameters for studying its Radiophotoluminescence (RPL) properties for gamma absorbed dose measurements. Five phosphor samples are prepared by varying quantity of solvent, distillation temperature and reaction time. XRD, SEM, particle size analysis and photoluminescence studies are carried out. The characterisation study shows polycrystalline luminescent particles of average size varying from 35 μm to 55 μm. Characteristic emission of Eu3+ is observed around 590, 615 and 620 nm at 242 nm excitation. Gamma dose response of maximum Eu3+ PL intensity sample is studied in the range 10 cGy to 1000 cGy using Co-60 source. Gamma radiation exposure induces conversion of Eu3+ to Eu2+ giving luminescence at 385 nm with 320 nm excitation. Repetitive measurements of gamma exposed samples are carried out and no significant fading is observed within one week of post-irradiation. The phosphor has the potential to be used for gamma dosimetry.

Upconversion and downshifting emissions of Ho3+-Yb3+ co-doped ATiO3 perovskite phosphors with temperature sensing properties in Ho3+-Yb3+ co-doped BaTiO3 phosphor

In this work, we report a comparative study on upconversion and downshifting properties of Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors for the first time. The phosphor samples are prepared via solid state reaction method in a programmable furnace at 1523 K. The phosphor samples are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The EDS analyses show the presence of the desired elements used in the synthesis. The vibrational structures of the phosphor samples are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to Ho3+ and Yb3+ ions. The optical band gap (Eg) is calculated using Wood and Tauc relation and its values are found to be 3.61, 3.20 and 3.32 eV for the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphor samples, respectively. The upconversion emission spectra are monitored by exciting these phosphor samples at 980 nm. The phosphor samples give intense green emission in all the cases. However, the UC emission intensity is higher for the Ho3+-Yb3+ co-doped CaTiO3 perovskite phosphor. These phosphor samples also give intense green downshifting emission upon 419 and 452 nm excitations. The Ho3+-Yb3+ co-doped BaTiO3 perovskite produces relatively larger emission intensity among these phosphors. The lifetime of green emitting level (5F4) of Ho3+ ion shows temporal behavior of these perovskite phosphors. Furthermore, the temperature versus UC emission intensities of the green thermally coupled levels of Ho3+-Yb3+ co-doped BaTiO3 phosphor gives the fluorescence intensity ratio (FIR) and FIR-based relative (SR) and absolute (SA) temperature sensor sensitivities are obtained as 0.0034 K-1 and 0.0050 K-1, respectively at 305 K. Thus, the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors may be found suitable in display devices, solid state lighting, upconversion based devices and temperature sensing devices.

Structure and Photoluminescence Properties of Rare-Earth (Dy3+, Tb3+, Sm3+)-Doped BaWO4 Phosphors Synthesized via Co-Precipitation for Anti-Counterfeiting.

Barium tungstate (BaWO4) powders with various sintering temperatures, and BaWO4:Dy3+ phosphor samples with concentrations of different rare-earth (RE) activator ions (Dy3+, Sm3+, Tb3+) were prepared through co-precipitation. The structural, morphological, and photoluminescent characteristics of barium tungstate phosphors depend on the concentration of RE ions. The crystallographic characteristics of the synthesized BaWO4 were analyzed using X-ray diffraction (XRD) patterns. The size and shape of the crystalline particles were estimated based on images measured with a field emission scanning electron microscope (FE-SEM). As the sintering temperature of the BaWO4 particles increased from 400 °C to 1000 °C, the size of the particles gradually increased and showed a tendency to clump together. In the sample doped with 7 mol % Dy3+ ions, the intensity of all emission bands reached their maximum. The emission spectra of the RE3+-doped BaWO4 powders by excitation at 325 nm were composed of yellow (Dy3+), red (Sm3+), and green (Tb3+) band at 572, 640, and 544 nm. This indicates that most of the RE3+ ions absorbed the position without reversal symmetry in the BaWO4 lattice. These results propose that strong emission intensity and tunable color for the phosphors can be accomplished by rare-earth doped host with an suitable quantity. In addition, the phosphor thin films, having high transparency from aqueous colloidal solutions, were deposited on banknotes, and it is considered whether it is suitable for anti-counterfeiting applications.

Citrate sol-gel synthesis of BaAl2O4:x% Cu2+ (0 ≤ x ≤ 1) nano-phosphors: Structural, morphological and photoluminescence properties

Abstract This paper reports on the effects of varying the Cu2+ doping concentration on the structure, morphology and optical properties of the BaAl2O4 phosphor. BaAl2O4:x% Cu2+ (0 ≤ x ≤ 1) series were successfully synthesized via citrate sol-gel method. The X-ray diffraction (XRD) results revealed that the prepared phosphor sample consist of a single phase hexagonal structure. The presence of Ba, Al, O and Cu were confirmed by the energy dispersive X-ray spectroscopy (EDS). Scanning electron microscope (SEM) revealed that the morphology of the prepared samples highly depends on the Cu2+ concentration. Transmission electron microscopy (TEM) results revealed the hollow tubular and nano-nature of the crystallite sizes. When the un-doped sample was excited at 283 nm, the photoluminescence (PL) results revealed six emission peaks located at 420, 435, 457, 521, 612 and 722 nm, which were attributed to the intrinsic intra band gap defects within the BaAl2O4 (host). The emission at 425 nm observed for the BaAl2O4:Cu2+ samples was attributed to the 3d84s1 → 3d9 transition in Cu2+ ion. The optimum doping Cu2+ concentration was found to be 0.075% Cu2+. Critical energy transfer distance (Rc) of Cu2+ ions was found to be 12.01 A, which suggested that the multipole-multipole interaction was the main reason for the luminescence quenching. The International Commission on Illumination (CIE) colour showed that the bluish emission colour of the prepared samples depends on the excitation wavelength and Cu2+ concentration. Thermo stimulated luminescence (TSL) of the host material showed the presence of both the swallow and deep traps respectively located at 75 and 240 °C.

Thermoluminescence glow curves of beta irradiated NaBaBO3: Ce3+ phosphor synthesized by combustion method

NaBaBO3 samples incorporated with various concentration of Ce3+ were prepared by combustion method. The influences of rare earth doping in synthesized samples were analyzed by X-ray diffraction (XRD). Optimum doping concentration of NaBaBO3:Ce3+ is 0.5 %. Thermoluminescence (TL) kinetic analysis using Tm-Tstop, initial rise (IR), variable heating rate (VHR) and glow curve deconvolution (GCD) methods were performed on the glow curves of NaBaBO3:Ce3+ phosphor material. The Tm-Tstop analysis revealed that the whole glow curve measured without preheat of the prepared sample is composed of at least six overlapping glow peaks. The number of the glow peaks required to provide best fit to the glow curves of the sample are also estimated using GCD method and one found six glow peaks at all doses (FOM ≤ 1.84 %), which are similar to those from Tm-Tstop analysis. The dose response of NaBaBO3:Ce3+ phosphor sample exposed to beta irradiation is linear up to 10 Gy. The results from experiments indicates that main dosimetric peak of NaBaBO3:Ce3+ follows first order kinetic model, which was also supported by dose response plot. The Z effective value of this phosphor is calculated to be 46.66. Present findings confirm that NaBaBO3:Ce3+ phosphor sample is a promising candidate for applications in environmental dosimetry as one depicts good TL dose response with adequate sensitivity and linearity.

Synthesis and Luminescence Investigation of Eu3+ Doped Ca2KZn2V3O12 Phosphors: A Potential Material for WLEDs Applications

A series of white light emitting Ca2KZn2–xV3O12:xEu3+ (x = 0.1, 0.2, 0.3, 0.4 and 0.5) phosphor samples were successfully synthesized by the traditional solid-state reaction method. The powder X-ray diffraction (XRD) patterns of the as-prepared sample reveal the high degree of crystallinity of the cubical structure with $$Ia\overline{3}d$$ space group and without any other phase formation. Fourier transform infrared (FTIR) spectra confirmed the occurrence of characteristic vibrational bands of garnet vanadate. The optical diffuse reflectance spectra consisting of broad band absorption in the ultraviolet (UV) region and the sharp absorption in the visible region were ascribing to the charge transfer between ligand–metal in the VO4 tetrahedral group and Eu3+ ions. Under the UV and near-UV excitation wavelengths, the broad band emission and the sharp emission were ascribing to the host material charge transfer of the VO4 tetrahedral group and f-f transitions of the rare-earth Eu3+ ions respectively. Ultimately, through the doping concentration optimization, a high Color Rendering Index (CRI) and excellent Correlated Color Temperature (CCT) were achieved with cool white emission. Therefore, the contribution of Ca2KZn1.8Eu0.2V3O12 phosphor was significant to phosphor-converted white light emitting device (WLEDs) excited with near ultraviolet.