Thermoluminescence characteristics and dosimetric aspects of fluoroperovskites （NaMgF3：Eu2＋,Ce3＋）

The perovskite-like NaMgF3 polycrystalline powder samples, pure and rare earth doped, were synthesized by conventional solid state reaction method. The perovskite material was doped with 0.2 mol.% of EuF3 and CeF3 impurity. Phase purity of synthe-sized compounds was analyzed by powder X-ray diffraction technique. The thermoluminescence response of polycrystalline samples showed a linear response up to 12 Gy and then became sub linear at higher doses. The order of kinetics （b）, activation energy （E） and other trapping parameters were calculated using peak shape method and variable heating rate method. From glow curve analysis the symmetric factor was calculated. The glow curve showed two peaks at 404 and 488 K, and both of them confirmed the thermolumi-nescence in the phosphor, which obeyed second-order kinetics. The experimental resulted showed that this phosphor could have po-tential applications in radiation dosimetry.     

Photoluminescence properties of Sm3＋-doped LiY（Mo04）2 red phosphors

A series of novel Sm3＋-doped LiY（MoO4）2 red phosphors under the UV excitation were synthesized by solid state reaction at 800 ℃ for 7 h. The data measured by X-ray diffraction （XRD） indicated that the samples were all pure phases of LiY（MoO4）2. Their excitation spectra had a broad band ranging from 250 to 350 nm and several sharp peaks. The centers of the peaks were located at about 365 nm （6H5/2→4D3/2）, 378 nm （6H5/2→rp7/2）, 406 nm （6H5/2→4FT/2）, 420 nm （6H5/2→6ps/2）, 442 nm （6H5/2→4Gg/2）, 471 nm （6H5/2→4I13/2） and 482 nm （6H5/2→419/2）, respectively. The strongest emission was excited by 406 nm, and the main emissions were located at 568 nm （4G5/2→6Hs/2）, 610 nm （4Gs/2→rH7/2）, 649 nm （4G5/2→6H9/2） and 710 nm （4Gs/2→6HII/2）. Photoluminescence prop- erties were determined for various concentrations of Sm3＋-doped LiY（MoO4）2 host, and the luminescence intensity had the best value when x=0.02 in LiYix（MoO4）2：xSm3＋.     

Luminescent properties of Ba3Gd（BO3）3：Eu^3＋ phosphor for white LED applications

Luminescent material Ba3Gd(BO3)3 doped with Eu3+ ion was prepared by high temperature solid-state method. The preparing conditions, luminescent properties, and particle morphology of Ba3Gd(BO3)3:Eu3 + phosphor were studied with X-ray diffraction (XRD), fluorescence spectroscopy, and scanning electron microscopy (SEM). The results obtained by XRD showed that pure phase of Ba3Gd(BO3)3 was obtained at 1000℃. Images from SEM displayed that the particles of Ba3Gd(BO3)3:Eu3+ phosphor had a spherical shape with an average diameter of about 200-400 nm. The luminescence spectra showed that Ba3Gd(BO3)3:Eu3+ phosphor was effectively excited by the near ultraviolet (UV) light (396 nm) and blue light (466 nm). The main emission peaks of Ba3Gd(BO3)3:Eu3+ phosphor were assigned to the supersensitive transition 5D0-7F2 (611 and 616 nm) of Eu3+ ion when samples were excited at 255 and 396 nm, respectively, and the luminescent intensity of Ba3Gd(BO3)3:Eu3+ at 611 and 616 nm reached to the maximum when the doped content of Eu3+ ion was 10mol.%. Therefore, this phosphor could be a promising red component for possible applications in the field of white LED.     

Luminescence investigation of Eu~（3＋）-Bi~（3＋） co-doped CaMoO_4 phosphor

A series of Eu³⁺-Bi³⁺ co-doped CaMoO₄ red phosphors were synthesized via the solid-sate reaction method. The crystal structures of the obtained samples were identified by X-ray powder diffraction (XRD). The photoluminescence property was investigated, and the results showed that the intensity of excitation spectra and emission spectra could be changed with different doping ratios of Bi³⁺/Eu³⁺. The proposed explanation of these changes was from the energy transfer between Bi³⁺ and Eu³⁺ and the unbalanced charge from the substitution of Eu³⁺ and Bi³⁺ for Ca²⁺ in CaMoO₄. The obtained samples are a promising red light emitting phosphor for the needs of different excitation sources with near-UV and blue GaN-based chips.     

Photoluminescent properties of SreSiO4：Eu^3＋ and Sr2SiO4：Eu^2＋ phosphors prepared by solid-state reaction method

Eu²⁺ and (or) Eu³⁺ doped Sr₂SiO₄ phosphors particles were synthesized by a conventional solid-state reaction technique, and their structural and optical properties were investigated. The X-ray diffraction (XRD) results showed that the obtained phosphors were composed of orthorhombic α'-Sr₂SiO₄ and monoclinic β-Sr₂SiO₄ phase. When excited under 256 nm, Sr₂SiO₄:Eu³⁺ phosphors showed intense emission in the red region. Sr₂SiO₄:Eu³⁺ phosphors exhibited white emissions (x=0.30, y=0.40, T_C=6500 K) ranging from 425 to 650 nm when it was excited by near-ultraviolet (near-UV) light, indicating that Sr₂SiO₄:Eu²⁺ was a good light-conversion phosphor candidate for near-UV chip.     

Luminescence Properties of （ Y, Gd） Al3 （BO3） 4 ： Eu^3＋ under VUV excitation

(Y, Gd)Al3 (BO3)4:Eu^3 samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered at about 170 and 250 nm respectively. In the emission spectra, the peak wavelength is about 616 nm under 147 nm VUV excitation. The luminescent chromaticity coordinate and the relative intensity change along with Gd^3 mole concentration in the range of 0.15 to 0.85 mol (and Eu^3 mole concentration, 0.02 to 0. 1 mol). The correlative data show that the concentration quenching occurs when the Eu^3 mole concentration ranges from 0.02 to 0.1 mol, and the Gd^3 →Gd^3 , Gd^3 →Eu^3 and host→Eu^3 , Gd^3 energy transfers exist, and Gd^3 mole concentration influences Eu^3 emission.     

Luminescent properties of blue long-lasting phosphorescence phosphors Sr6Al18Si2O37：Eu2＋,RE3＋

A series of novel blue long-lasting phosphorescence phosphors Sr6A118Si2037：Eu^2＋,RE^3＋ （RE3＋=Ho^3＋, Gd^3＋, Dy^3＋ and Pr^3＋） were prepared by the conventional high-temperature solid-state reaction in a reductive atmosphere. Their properties were systemati- cally investigated utilizing X-ray diffraction （XRD）, photoluminescence, phosphorescence and thermoluminescence （TL） spectra. The phosphors emitted blue light that was related to the emission of E~＋ due to 5d-4f transition. Bright blue long-lasting phosphorescence （LLP） could be observed after the excitation source was switched off. For the optimized sample, the blue long-lasting phosphores- cence could last for nearly 4 h in the light perception of the dark-adapted human eye （0.32 mcd/m2）. The effects of RE3＋ ions on phosphorescence properties of the phosphors were studied, and the results showed that the co-doping of RE^3＋ ions greatly enhanced the intensity of the peak around 315 K which was related to the long lasting phosphorescence of the phosphors at room temperature and consequently improved the performance of the blue phosphorescence such as intensity and persistent time.     

Blue-green BaAl_2O_4：Eu~（2＋）,Dy~（3＋） phosphors synthesized via combustion synthesis method assisted by microwave irradiation

Blue-green luminescent BaAl2O4:Eu2+,Dy3+ phosphor powders were synthesized via combustion synthesis method assisted by microwave irradiation in air. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer. The XRD results revealed that when the concentration of urea was over 3 times higher than theoretical quantities, a BaAl2O4 single hexagonal phase was obtained. The SEM results revealed that the surface of the BaAl2O4:Eu2+,Dy3+ pow...     

Enhanced photoluminescence of CaTiO3：Eu3＋ red phosphors prepared by H3BO3 assisted solid state synthesis

CaTiO₃:Eu³⁺ red phosphors were prepared using H₃BO₃ assisted solid state synthesis. The structure and morphology of the obtained sample were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). And the luminescence property was measured using photoluminescence excitation (PLE) and photoluminescence (PL) spectra, respectively. In the excitation spectra, main excitation peaks of the prepared samples were centered at 397 and 465 nm, revealing that these phosphors could be excited by commercial GaN- and InGaN-typed light emitting diodes (LEDs). Dominant emission peaks of the phosphors were located at 616 nm, owing to the transition of ⁵D₀→⁷F₂ of Eu³⁺. In the optimum condition, CaTiO₃:3%Eu³⁺ phosphor was obtained at a sintering temperature of 1200 °C in air with a content of 20 mol.% H₃BO₃ addition. When excited by 397 nm irradiation, the PL intensity of as-prepared red phosphor was 2.2 times higher than that of samples obtained by traditional solid state synthesis, while the PL intensity was 3 times higher than that excited by 465 nm irradiation. The added H₃BO₃ improved the crystallinity, and increased the color purity, implying the potential to be a promising red phosphor in white light emitting diodes (WLEDs).     

Luminescent characteristics of Ba3Y2（BO3）4：Eu^3＋ phosphor for white LED

The Ba3Y2（BO3）4：Eu^3＋ phosphor was synthesized using a high temperature solid-state reaction method and the luminescent characteristics were investigated. The emission spectrum exhibited one strong red emission at 613 nm, corresponding to the electric dipole 5D0-TF2 transition of Eu^3＋, under 365 nm excitation. The excitation spectrum of 613 nm indicated that the Ba3Y2（BO3）n：Eu^3＋ phosphor was effectively excited by ultraviolet （UV） （254, 365 and 400 nm） and blue （470 nm） light. The effect of Eu^3＋ concentration on the 613 nm emission of the Ba3Y2（BO3）n：Eu^3＋ phosphor was measured. The results showed that the emission intensity increased with increasing Eu^3＋ concentration, and then decreased. The CIE color coordinates of Ba3Y2（BO3）4：Eu^3＋ phosphor were x=0.641 and y=0.359 at 15 mol.% Eu^3＋.     

Synthesis and photoluminescence properties of a red emitting phosphor NaSr2（NbO3）5：RE3＋（RE=Sm,Pr） for white LEDs

Rare earth Sm3＋, Pr3＋doped NaSr2（NbO3）5 red phosphors were successfully synthesized. X-ray diffraction analysis indi-cated that all the samples were single phased. The luminescence property was investigated in detail by diffuse-reflectance spectra and photoluminescence spectra measurement. Both NaSr2（NbO3）5：Sm3＋and NaSr2（NbO3）5：Pr3＋phosphors showed strong absorption in near ultraviolet region, which was suitable for application in LEDs. When excited by UV light, they both emitted bright red emission with CIE chromaticity coordinates （0.603, 0.397） and （0.669, 0.330）, respectively. The optimal doping concentration of Sm3＋doped NaSr2（NbO3）5 was measured to be 0.04 and that for Pr3＋doped NaSr2（NbO3）5 was 0.01. The integral emission intensity was also measured and compared with the commercial red phosphor Y2O3：Eu3＋. The results indicated that NaSr2（NbO3）5：RE3＋（RE=Sm, Pr） have potential to serve as a red phosphor for UV pumped white LEDs.     

Role of monovalent co-dopants on the PL emission properties of YAI3（BO3）4：Ce3＋ phosphor

The cerium （Ce3＋） doped yttrium aluminium borate （YAB） phosphor was synthesized by modified solid state reaction. The phosphor＇s phase purity and its emission properties were studied using powder X-ray diffraction pattern and photoluminescence spectroscopy. The synthesized YAB had rhomobohedral crystal structure. The phosphor had two different excitation and emission spectra. By 325 nm excitation, the phosphor had emission at 373 nm and with 363 nm excitation; the phosphor gave violet-blue emission at 418 nm. The UV emission of the phosphor originated due to Ce3＋ ions at the yttrium site and violet-blue emission owing to Ce3＋ ions at non-regular sites viz., A13＋ and interstitial sites. The emission intensity of the phosphor was enhanced when monovalent ions （K＋, Na＋, and F） were added as co-dopants. The crucial role of ionic radii of monovalent co-dopants on the emission enhancement of the YAB：Ce3＋ phosphor was reported. Thermogravimetric study showed that the YAB possessed high thermal stability at up to 900 ℃.     

Synthesis and optical properties of Dy~（3＋）, Li~＋ doped CaMoO_4 phosphor

A series of CaMoO4 phosphors doped with trivalent dysprosium ions (Dy3+) and lithium (Li+) were prepared by solid state method at 750 °C for 3 h. X-ray diffraction (XRD) confirmed the crystal structure and quality of phosphors. Scanning electron microscopy (SEM) in- dicated that the phosphors presented good crystalline state, and the crystalline grain sizes were about 0.5-3.0 μm. The emission spectra showed that the phosphors had intense emission at 480 (4F9/2→6H15/2), 576 (4F9/2→6H13/2) and 660 nm (4F9/2→6...     

Photoluminescence properties of（Gd1-xEux）Ba3B9O18 red emitting phosphors

Eu3+-activated GdBa3B9O18 phosphors were prepared by solid-state reaction at high temperature, and their photoluminescence (PL) properties were investigated. (Gd1-xEux)Ba3B9O18 formed solid solutions in the range x=0-1.0. The optical band gaps calculated from absorption spectra were 5.54 eV for GdBa3B9O18 and 5.17 eV for EuBa3B9O18. Unactivated GdBa3B9O18 exhibited a typical characteristic excitation and emission of Gd3+ ion. The (Gd1-xEux)Ba3B9O18 phosphors showed well-known Eu3+ excitation and emission. The energy transfer from Gd3+ to Eu3+ was verified with PL spectra. The dependence of PL intensity on Eu3+ concentration was also studied in detail. The luminescence decay measurements indicated that the lifetimes of 5D0→7F1 transition of Eu3+ were in the order of millisecond.     

Single-phase full-color Ba_3Lu_2（SiO_4）_3：Eu~（2＋） phosphor for white-light emitting diodes

we developed a new silicate-based full-color phosphor Ba3Lu2(SiO4)3:Eu2+ through solid state reaction.The host crystal structure was isostructural with Ca3Y2(SiO4)3 instead of garnet-type.The phosphor absorbed near-ultraviolet light from 250 to 400 nm,which was very suitable for a color converter of white LED that used UV-LED as the primary light source.The photoluminescence peak wavelength of Ba3Lu2(SiO4)3:Eu2+ was about 461 nm and a shoulder peak was around 522 nm,which resulted from the 5d-4f transition ...     

Luminescent properties and energy transfer of color-tunable Sr3Y2（SiO3）6：Ce3＋,Tb3＋ phosphors

Phosphors with controlled emission spectra are of great interest due to their application for white light emitting diodes.Herein, a new class of Sr3Y2（SiO3）6：Ce3＋,Tb3＋ phosphors were synthesized by a facile sol-gel combustion method. The phase structure,morphology, and luminescence properties of the phosphors were characterized by using powder X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and photoluminescence excitation and emission spectra,respectively. The results on luminescence properties indicated that co-doped Ce3＋ ions served as UV-light sensitizers with excitation energy partially transferred to Tb3＋ ions, leading to green emission from Tb3＋. Particularly, the corresponding emitting colors of the phosphors could be well-tuned from deep blue（0.16, 0.05） to green region（0.25, 0.45） by adjusting the molar ratio of Ce3＋/Tb3＋.     

Enhanced photoluminescence properties of （Y,Bi） BO_3：RE~（3＋） （RE=Eu,Tb） phosphors synthesized at low temperature

Eu3+ or Tb3+ doped Y(1-x)BixBO3 (0.1≤x≤0.4) phosphors were synthesized using the simple solid state method at low temperature from 700 to 870 ℃. The analysis of the X-ray diffraction (XRD) indicated that the system of Y(1-x)BixBO3 (0.1≤x≤0.4) had the same structure as that of YBO3. The excitation spectra, emission spectra and decay lifetimes of all samples were measured in detail. All the samples exhibited characteristic luminescence of Eu3+ or Tb3+. Y0.65Bi0.2Eu0.15BO3 and Y0.8Bi0.1Tb0.1BO3 samples had the...     

Preparation and luminescence properties of the red-emitting phosphor（Sr1-xCax）2Si5N8：Eu^2＋ with different Sr/Ca ratios

A series of Eu2+-doped ternary nitride phosphors, with a formula of (Sr1-xCax)2Si5N8: Eu2+, were synthesized by high-temperature solid-state method. The structure and luminescence properties were characterized, indicating the potential application as a red phosphor in the phosphor-converted white light-emitting diodes. The X-ray diffraction patterns showed that the Sr2Si5N8 and Ca2Si5N8 phases were generated at each end of (Sr1-xCax)2Si5N8: Eu2+ and coexisted in the range of 0.5≤x≤0.75. The emission spectra showed broad emission bands originating from the 4f65d1→4f7 transition of Eu2+ ions. The emission peak changed with the variations in Ca2+ concentration.     

Effect of gadolinium incorporation on optical characteristics of YNbO_4：Eu~（3＋） phosphors for lamp applications

Eu3+-doped (Y,Gd)NbO4 phosphor was synthesized by solid-state reaction for possible application in cold cathode fluorescent lamps. A broad absorption band with peak maximum at 272 nm was observed which was due to the charge transfer between Eu3+ ions and neighboring oxygen anions. A deep red emission at the peak wavelength of 612 nm was observed which could be attributed to the 5D0→7F2 transition in Eu3+ ions. The highest luminance for Y1-x-yGdyNbO4:Eux3+ under 254 nm excitation was achieved at Eu3+ concentration of 18 mol.% (x=0.18) and Gd3+ concentration of 8.2 mol.% (y=0.082). The luminance of Y0.738Gd0.082NbO4:Eu3+0.18 was higher than that of a typical commercial phosphor Y2O3:Eu3+ and the CIE chromaticity coordinate was (0.6490, 0.3506), which was deeper than that of Y2O3:Eu3+. The particle size of the synthesized phosphors was controlled by the NaCl flux and particle size as high as 8 μm with uniform size distribution of particles was obtained.     

Combustion synthesis and luminescence properties of Ca4Y6（SiO4）60：Eu3＋ red phosphor for white LEDs

Eu3＋ activated Ca4Yt（SiO4）60 phosphors were prepared by combustion synthesis method, and their morphologies and lu- minescent properties were investigated. Field scanning electron microscopy （FSEM） confirmed that the crystallite sizes of nanoparti- cles with narrow diameter ranging from 30 to 60 rim. The excitation spectra of CaaY6（SiO4）60：Etl3＋ showed that there existed two strong excitation bands at around 399 nm （TFo----~SL6） and 469 nm （TF0---＊SD2）, which were consistent with the output wavelengths of near-UV and blue LEDs, respectively. The emission spectra of Ca4Y6（SiO4）60：Eu3＋ were dominant by a red peak located at 614 nm due to the 5Do→7TF2 transition of Eu3＋. With the increase of Eu3＋concentration, the luminescence intensity of the red phosphor reached maximum and then decreased. The optimum concentration for Eug＋in Ca4Y6（SiO4）60 was 21 mol.%.