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The series of novel phosphors Ca 9 La(PO 4) 5 [(Si 1- x Ge x O 4)]F 2 :0.15Dy3+ with x = 0, 0.25, 0.50, 0.75 and 1 (CLPS 1- x G x F:0.15Dy3+) with apatite-type structure (space group P 6 3 / m) has been synthesized. The crystal structure and electronic structure have been studied by powder X-ray diffraction (PXRD) in combination with the atomic-scale density functional theory (DFT) calculations. A combination of Raman, nuclear magnetic resonance (29Si NMR) spectroscopy and the evolution of Dy3+ ions photoluminescent properties was used to characterize the local crystal structure features. Based on the variation of the [SiO 4 ] by [GeO 4 ] tetrahedral substitutions in the apatite-type structure, the difference in the thermal stability and decay curves of CLPS 1- x G x F:0.15Dy3+ phosphors were referred to crystal chemical stability of as-prepared compounds, which is also confirmed by the values of polyhedral distortion, bond valence sum (BVS) and DFT calculations. The present study provides new insights the synthetic methodology and fundamental characterizations into the design of new phosphors combined with theoretical methods. [ABSTRACT FROM AUTHOR]

Ca9La(PO4)5(SiO4)F2:Tb3+,Dy3+ (CLPSF:Tb3+,Dy3+) phosphors were successfully prepared using the traditional solid‐state technique. The crystal structure was refined and the luminescence properties have been examined in detail. The band gap and electronic structure of Ca9La(PO4)5(SiO4)F2 were performed by the periodic density functional theory (DFT) calculation. The spectral and fluorescence decay dynamics of CLPSF:Tb3+,Dy3+ show that the energy transfer behavior between Tb3+ and Dy3+ ions is observed. The CLPSF:Tb3+,Dy3+ phosphors can be efficiently excitable at the wavelengths range from 300 to 500 nm. The emission spectrum covers the whole visible part of the spectra with the sharp emission bands in red, green, and blue regions. The correlated color temperature (CCT) and color rendering index (CRI) of white light emission could be improved by the fine‐tuning of the Tb3+ and Dy3+ ions ration in accordance with the energy transfer behavior. Thus, the CLPSF:Tb3+,Dy3+ phosphor could be used as a material for the near‐ultraviolet (n‐UV) and white light‐emitting diodes (w‐LEDs). [ABSTRACT FROM AUTHOR]

Abstract A set of Eu3+, Dy3+ and Tb3+ doped novel scheelite-type LiCaGd(WO 4) 3 (LCGW)-based phosphors was prepared via a conventional solid-state reaction method. The X-ray diffraction (XRD), transmission electron microscopy (TEM) analysis, characteristics of luminescence, PL thermostability, decay lifetimes, as well as CIE coordination were investigated to characterize the as-prepared samples in detail. The XRD analysis indicated that the Eu3+, Dy3+ and Tb3+ ions were incorporated into the LCGW host lattice. Under the ultraviolet radiation, the characteristic emission lines of Eu3+ (5D 0 –7F 2), Dy3+ (4F 9/2 –6H 13/2) and Tb3+ (5D 4 –7F 5) ions were observed. The Eu3+ and Tb3+ single-doped LCGW fluorescent powders showed bright red and green emissions, respectively, without concentration quenching. As well as the Dy3+ doped LCGW phosphors radiate a strong yellow light at optimal Dy3+ concentration 0.08 mol. The efficient energy transfer phenomenon was observed for the Eu3+/Dy3+ and Tb3+/Dy3+ ions. The emission color of the LCGW: x Tb3+/0.08Dy3+ samples was tuned from yellow (0.4074, 0.4727) to green (0.3604, 0.5521) via adjusting the Tb3+ concentration. The emission color of LCGW: y Eu3+/0.08Dy3+ can be tuned from yellow (0.491, 0.3856) to red (0.5694, 0.3512) by variation of the Eu3+/Dy3+ ratio. Additionally, the thermal stability of the luminescence in the LCGW phosphors doped by Eu3+, Tb3+, Dy3+ ions was studied. The results verified that the LCGW:Ln3+ (Ln = Tb, Eu, Dy) phosphors are promising for applications in white LEDs. [ABSTRACT FROM AUTHOR]

Abstract The novel apatite-type phosphor Ca 9 Tb(PO 4) 5 (SiO 4)F 2 :Mn2+ (CTPSF:Mn2+) has been successfully synthesized and it demonstrated a potential for optical thermometry. The energy transfer process between Tb3+ and Mn2+ was of resonant type via a dipole-dipole mechanism based on the Inokuti–Hirayama theoretical model, and the energy transfer (ET) efficiency and ET rate were estimated. In view of the energy transfer behavior, a strategy, involving the use of Tb3+ and Mn2+ dual-emitting centers with different thermal quenching behavior, has been developed to achieve temperature sensitivity and good signal discrimination. The temperature dependence of the fluorescence intensity ratios (FIR) for the dual-emission bands peaking at 548 and 595 nm was studied in the range of 298–573 K under excitation of 377 nm ultraviolet light and the maximum relative sensitivity was approximately 1.92% K−1 at 423 K. It is expected that this preliminary study will provide an important advance in exploring novel ratiometric optical thermometry. Highlights • Novel apatite-type phosphor Ca 9 Tb(PO 4) 5 (SiO 4)F 2 was synthesized. • Energy transfer mechanism is estimated based on Inokuti–Hirayama model. • Non-contact thermometry was developed with a new inorganic material. • The maximum S r of the as-prepared phosphor was as high as 1.92% K−1. • This work provides an insight to design ratiometric optical thermometry. [ABSTRACT FROM AUTHOR]

A series of novel luminescent emission-tunable phosphors Mg 2 La 8 (SiO 4 ) 6 O 2 :Ce 3+ ,Tb 3+ (MLS:Ce 3+ ,Tb 3+ ) have been prepared by a solid-state reaction. The phase formation was firstly confirmed through X-ray diffraction technique and refined by the Rietveld method. The MLS:Ce 3+ ,Tb 3+ phosphors, which crystallized in apatite-type hexagonal phase, exhibited a broad excitation band ranging from 200 to 400 nm and several emission bands centered at 426 nm and 551 nm. Energy transfer from Ce 3+ to Tb 3+ ions via a dipole-dipole mechanism occurred in the as-synthesized phosphors upon ultraviolet (UV) excitation. The energy transfer efficiency increases with increasing doping content of Tb 3+ ions, which was confirmed by the luminescence spectra and fluorescence decay curves of corresponding ions simultaneously. The energy transfer critical distance was calculated and evaluated by both the concentration quenching and spectral overlap methods. The chromaticity of emission-tunable phosphors was also characterized by the Commission International de l'éclairage (CIE) chromaticity indexes, and the color tone can be tuned from blue (0.179, 0.122) to green (0.267, 0.408) by controlling the ratio of Ce 3+ /Tb 3+ . [ABSTRACT FROM AUTHOR]

A series of solid solution phosphors Ca 9 La(PO 4 ) 5 [(Si 1- x Ge x )O 4 ]F 2 :Ce 3+ with apatite structure in the P 6 3 / m space group have been prepared. The novel solid solution phosphors show continuously controlled violet-blue emission. It is found that both substantial spectra broadening (45 → 100 nm) and red-shift (404 → 422 nm) can be realized with the continuous introduction of [GeO 4 ] 4- into the crystal lattice which has been simulated by a crystal-field model. The above results indicate that the tetrahedral substitution is interesting to induce spectral tuning properties based on the chemical composition control of the iso-structural solid solutions. [ABSTRACT FROM AUTHOR]

Single-phase KLaSr3( PO4)3F: Sm3+ phosphors with fluorapatite structure were prepared via high-temperature solid-state method in air atmosphere for the first time. The X-ray diffraction, scanning electron microscope, diffuse reflectance spectra, photoluminescence spectra, and temperature-dependent emission spectra, as well as lifetimes were measured to characterize the as-prepared phosphors. Phase results indicated that KLaSr3( PO4)3F: Sm3+ belongs to hexagonal system with a space group of P-6. Photoluminescence measurements showed the emission spectrum was composed of four sharp peaks at about 564, 602 (the strongest one), 646, and 702 nm, corresponding to the 4G5/2-6 H J ( J=5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ions. The optimum doping concentration of Sm3+ ions was turned out to be 0.03 (mol), and the mechanism of energy transfer among Sm3+ ions was considered to be dipole-dipole interaction by using Dexter's theory. In addition, the critical distance Rc for energy transfer among Sm3+ ions were calculated to be 9.97 Å according to Blasse concentration quenching method. The selected KLa0.97Sr( PO4)3F: 0.03Sm3+ exhibited high thermal stability with an activation energy of 0.163 eV. Besides, the Commission International de l'Eclairage chromaticity coordinate of the phosphor were located in the orange-reddish light region. [ABSTRACT FROM AUTHOR]

The Ca 9 La(PO 4 ) 5 (SiO 4 )Cl 2 :Dy 3+ (CLPSCl:Dy 3+ ) powder phosphor with apatite structure has been successfully synthesized via high-temperature solid state method. Single phase in such phosphor was verified through X-ray diffraction (XRD) technique. The Dy ions concentration dependent luminescence properties including emission, excitation and lifetimes of Dy ions were characterized using photoluminescence (PL) spectroscopy. The results showed that CLPSCl:Dy 3+ phosphor could efficiently assimilate the n -UV light and emit blue (~486 nm) and yellow light (~578 nm), originating from the f-f transitions of Dy 3+ . The critical Dy 3+ quenching concentration (QC) was determined to be about 12 mol%. The concentration quenching mechanism was also determined to be dipole–dipole interaction. [ABSTRACT FROM AUTHOR]

A series of novel KLaSr3−x(PO4)3F:xEu2+ phosphors were synthesized for the first time. The crystal structure, photoluminescence properties, concentration quenching, decay analysis, and the temperature dependent luminescence properties were investigated in detail. The unit cell parameters for KLaSr3(PO4)3F were estimated to be a = 9.8997 Å, c = 7.4075 Å, and V = 628.7 Å3. The photoluminescence excitation spectrum of KLaSr3(PO4)3F:Eu2+ shows a broad band from 225 nm to 450 nm with a maximum at about 320 nm. KLaSr3−x(PO4)3F:xEu2+ phosphors exhibit a wide emission band ranging from 425 to 550 nm. KLaSr3(PO4)3F:Eu2+ phosphors exhibit good thermal stability up to 423 K. KLaSr3(PO4)3F:Eu2+ was fabricated with commercial green (Ba,Sr)SiO4:Eu2+ and red CaAlSiN3:Eu2+ phosphors to obtain a white-light-emitting diode. All the results demonstrate that KLaSr3(PO4)3F:Eu2+ are promising blue phosphors for white-light ultraviolet light-emitting diode applications. [ABSTRACT FROM PUBLISHER]

Tb 3+ -Sm 3+ co-doped Sr 9 Gd(PO 4 ) 5 (SiO 4 )F 2 (SGPSF) phosphors were prepared through a solid-state reaction, and their luminescence properties as well as energy transfer mechanism have been investigated in detail. The SGPSF:Tb 3+ , Sm 3+ phosphors system could be efficiently excited at wavelengths ranging from 200 to 500 nm, which is well matched with the spectra of near ultraviolet chips. The emission of SGPSF:Tb 3+ , Sm 3+ phosphor covers the entire visible region with sharp peaks in the blue, green, and red regions. The emission color of SGPSF:Tb 3+ , Sm 3+ could be adjusted from green (0.275, 0.378) to red (0.519, 0.295) by controlling the doping content of Sm 3+ /Tb 3+ . [ABSTRACT FROM AUTHOR]

Tb 3+ –Sm 3+ co-doped Ba 3 NaLa(PO 4 ) 3 F phosphors with apatite structure have been prepared by a high temperature solid-state reaction, and their luminescence properties have been investigated in detail. The energy transfer (ET) mechanism was verified as the dipole–quadrupole mechanism, and the ET efficiency as well as the critical distance is also estimated. As a result of fine-tuning of the emission composition of the Tb 3+ and Sm 3+ ions, tunable luminescence properties can be realized by combining the emission of Tb 3+ and Sm 3+ in a single host lattice under UV light excitation. The emission color of the obtained phosphors can be modulated from green to yellow by controlling the doping content of the Sm 3+ ions with the fixed Tb 3+ content. Additional, as the temperature increases from RT to 150 °C, the PL intensities of Ba 3 NaLa 0.7 (PO 4 ) 3 F:0.10Tb 3+ ,0.20Sm 3+ decreased to 80.4% and 78.6% of the initial PL intensity, corresponding to the intensity of transition of Sm 3+ and transition of Tb 3+ in the Ba 3 NaLa 0.7 (PO 4 ) 3 F:0.10Tb 3+ ,0.20Sm 3+ phosphor, respectively. These results indicate the series of Ba 3 NaLa 1− x − y (PO 4 ) 3 F: x Tb 3+ , y Sm 3+ phosphors can be acted as a good candidate for the application in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

A series of Eu 2+ and Eu 2+ /Tb 3+ co-doped Ba 3 GdNa(PO 4 ) 3 F phosphors have been synthesized via a high temperature solid-state reaction. The relative intensity of PL spectra of Ba 3 GdNa(PO 4 ) 3 F: x Eu 2+ increases with increasing x value, and reaches a maximum at x =0.04. Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ phosphors exhibit a broad excitation band ranging from 220 to 450 nm, which matches perfectly with the characteristic emission of n -UV light-emitting diode (LED) chips. Upon 365 nm excitation, the Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ phosphors show two dominating bands peaked at 466 and 543 nm, which are assigned to the 4f 7 →4f 6 5d 1 transition of the Eu 2+ ions and the 5 D 4 → 7 F 5 transition of the Tb 3+ ions, respectively. In view of the energy transfer mechanism between Eu 2+ and Tb 3+ , the Ba 3 GdNa(PO 4 ) 3 F:Eu 2+ , Tb 3+ emission color can adjust from blue to green, and their chromatic coordinates ( x , y ) vary from (0.16, 0.135) to (0.254, 0.398). The critical distance was also calculated to be 16.90 Å. The above results indicate that the Ba 3 GdNa(PO 4 ) 3 F: Eu 2+ , Tb 3+ phosphors are a candidate for blue–green components in the application of n -UV w -LEDs. [ABSTRACT FROM AUTHOR]

BaLa2ZnO5:Er3+/Yb3+ has been synthesized via a high temperature solid-state method, and the tunable upconversion luminescence and energy transfer process between Yb3+ and Er3+ in this system have been demonstrated. Upon 980 nm laser excitation, the intense green and red emission around 527, 553, and 664 nm were observed for BaLa2ZnO5:Er3+/Yb3+, which can be assigned to the characteristic energy level transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 of Er3+, respectively. The critical Er3+ quenching concentration (QC) was determined to be about 5 mol%, and the power studies indicated that mixture of 2- and 3-photon process was responsible for the green and red upconversion luminescence. [ABSTRACT FROM AUTHOR]

Eu 2+ –Tb 3+ co-doped Sr 3.5 Y 6.5 O 2 (PO 4 ) 1.5 (SiO 4 ) 4.5 (SYPSO) phosphors with apatite structure have been synthesized via a high temperature solid-state reaction and their luminescence properties have been investigated in detail. The two kinds of cations׳ sites and complex phosphate-silicate anions׳ structural character of SYPSO host have been studied. The SYPSO:Eu 2+ ,Tb 3+ phosphors show a broad absorption band ranging from 250 to 420 nm, which is well matched with the emission of near ultraviolet (UV) chips, and it exhibited two dominating bands peaked at 502 and 543 nm upon 365 nm excitation. The emission color of SYPSO:0.05Eu 2+ , y Tb 3+ shows a controlled luminescence evolution of the color hue in the green area owing to the Eu 2+ –Tb 3+ energy transfer (ET) process, and their chromaticity coordinates ( x , y ) can be varied from (0.2723, 0.3766) to (0.2812, 0.4537). The ET efficiency as well as the critical distance is also estimated. The quantum efficiency and thermal quenching properties have also been studied in this paper in order to demonstrate its potential application for white light-emitting diodes ( w -LEDs) phosphors. [ABSTRACT FROM AUTHOR]

Abstract: We report a series of color-tunable Sr3.45Y6.5O2(PO4)1.5(SiO4)4.5:Eu2+,Mn2+ (SYPSO:Eu2+,Mn2+) phosphors in this work. The photoluminescence excitation and emission spectra, lifetime, and concentration-dependent effect were investigated, respectively. The energy transfer (ET) mechanism was verified as the dipole–dipole interaction, and the ET efficiency as well as the critical distance is also estimated. The emission colors of the obtained phosphors can be tuned from green to yellow by controlling the doping content of the Mn2+ ions with the fixed Eu2+ content. These results indicate that SYPSO:Eu2+,Mn2+ can be acted as a good candidate for the application in white light-emitting diodes. [Copyright &y& Elsevier]

Abstract: SiO2-coated Ca2BO3Cl:Eu2+ phosphors were prepared by the sol–gel method in order to enhance the chemical and thermal stabilities of Ca2BO3Cl:Eu2+ phosphor. The phase structures, microstructures and luminescence properties were studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrometer, respectively. The emission intensity of SiO2-coated Ca2BO3Cl:Eu2+ phosphor decreased a little compared to that of the uncoated phosphor. The moisture resistances of the phosphors were comparatively examined by the aging treatment experiment in the water, and the thermal stability was studied by the temperature dependent photoluminescence spectra. The results indicated that SiO2 coating on the surface of the phosphor particles improved the moisture-resistance and thermal stability to a large extent. [Copyright &y& Elsevier]

A greenish yellow-emitting phosphor Ba2Gd(BO3)2Cl:Eu2+ was synthesized by a conventional high temperature solid-state method. The phase structure was studied by the X-ray diffraction, and it testified that Ba2Gd(BO3)2Cl belonged to the successful isomorphic substitution for Gd3+ sites in the Ba2Yb(BO3)2Cl host, which crystallized in a monoclinic unit cell with space group P21/m. The photoluminescence properties investigations showed that Ba2Gd(BO3)2Cl:Eu2+ showed greenish yellow emission with peak near 546 nm upon near UV excitation. The critical quenching concentration of Eu2+ in Ba2Gd(BO3)2Cl:Eu2+ phosphor was about 0.05 mol%, and the corresponding concentration quenching mechanism was verified to be the electric dipole-quadrupole interaction. We have demonstrated that Ba2Gd(BO3)2Cl:Eu2+ phosphors exhibit potential to act as a kind of phosphor for near ultraviolet white light-emitting diodes (w-LEDs). [ABSTRACT FROM AUTHOR]

The Sr 2 La 8 (SiO 4 ) 6 O 2 :Ce 3+ powder phosphor with apatite structure has been successfully synthesized via a facile route of sol-combustion technique. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) spectroscopy were used to characterize the as-prepared samples. Sr 2 La 8 (SiO 4 ) 6 O 2 :Ce 3+ phosphor was composed of particles with average sizes range about 300 nm. The phosphor exhibited an absorption ranging from 220 to 390 nm in ultraviolet range and a broad blue-violet emission band peaked at 403 nm with a CIE coordinates of (0.167, 0.028). The concentration quenching mechanism was also determined to be dipole–dipole interaction. [ABSTRACT FROM AUTHOR]

A novel orange-red emitting orthosilicate phosphor LiGd 9 (SiO 4) 6 :Mn2+ (LGS:Mn2+) belongs to hexagonal lattice with P 6 3 / m space group was synthesized via solid-state method and the phase composition, crystal structure as well as luminescence properties were examined for potential application in near ultraviolet (n -UV) pumped white light emitting diodes (w -LEDs). The as-prepared LGS:Mn2+ phosphor exhibits three excitation bands peaked at 273, 312 and 410 nm, which corresponds to the transitions of Gd3+ from ground state 8S 7/2 to 6I 7/2 , 6P 7/2 and Mn2+ from ground state 6A 1 (6S) to the individual components of the multiplets [4A 1 (4G), 4E(4G)], respectively. Upon excitation at 312 nm, the phosphors display an intense broad orange-red emission peaked around 594 nm, which ascribed to the typical spin-forbidden transition (4T 1 (4G)-6A 1 (6S)) of the Mn2+ ions. The concentration quenching mechanism and average separation distance in conjunction with fluorescence decay times of Mn2+ ions in LGS:Mn2+ phosphor were discussed. The indispensable parameters for application in n -UV high-powered w -LEDs, such as the thermal quenching of photoluminescence and internal quantum efficiency of LGS:Mn2+ phosphor, have also been investigated in detail. The above results indicate that LGS:Mn2+ could play a key role as an orange-red emission for potential application in n -UV-based w -LEDs. • LiGd 9 (SiO 4) 6 O 2 :Mn2+ luminescent materials were synthesized successfully. • This phosphor have excellent thermal stability and emission efficiency. • High energy transfer efficiency could be obtained between Gd3+ and Mn2+ ions. [ABSTRACT FROM AUTHOR]

Abstract A series of novel luminescence phosphors Ca 9 La(PO 4) 5 (SiO 4)Cl 2 : x Eu2+ (CLPSCl:Eu2+) with apatite structure have been synthesized by a high temperature solid-state reaction. The phased purity of as-prepared phosphors was verified through XRD technique. For further discussion, a series of analysis were performed such as the photoluminescence emission and excitation spectrum and decay lifetime to identify the luminescent properties of CLPSCl:Eu2+ phosphors. The CLPSCl:Eu2+ displays broad excitation spectra ranging from 250 to 450 nm, and intends emission intensity at 461 nm under 345 nm. The optimum Eu2+ concentration of CLPSCl is 8 mol%. The luminescence decay lifetime of the optimum phosphors was measured to be 275 ns. All of the results obtained highly indicate that CLPSCl:Eu2+ is potentially blue-emitting phosphor for application in white LEDs. [ABSTRACT FROM AUTHOR]

Abstract A single-component white-emitting phosphor Sr 9 La(PO 4) 5 (SiO 4)F 2 :Dy3+ pumped for n -UV-light emitting diodes was firstly presented by solid state method and the crystal structures, luminescence properties, especially the concentration quenching behaviors were discussed in detail. Accordingly, the quantum efficiencies as well as lifetime studies of Dy3+ in CLPGF phosphor were also carried out. The results revealed that the Sr 9 La(PO 4) 5 (SiO 4)F 2 :Dy3+ phosphor could be efficiently excited in a broad wavelength ranging near ultraviolet (n -UV) regions, which matched perfectly with n -UV white light emitting diodes (w -LEDs) chips. Under the excitation at 349 nm, the phosphor exhibited three prominent emission peaks in the visible wavelength region located at 483, 578 and 670 nm, which is ascribed to the 4F 9/2 -6H 15/2 , 4F 9/2 -6H 13/2 and 4F 9/2 -6H 11/2 transitions of Dy3+, respectively. It was also proved that the dipole-dipole interactions results in the concentration quenching in Sr 9 La(PO 4) 5 (SiO 4)F 2 :Dy3+ phosphors. Fascinatingly, when the temperature turned up to 150 °C, the emission intensity at 483 and 578 nm was 83.4 and 89.1% of the initial value at room temperature. Additional, the corresponding activation energy Δ E was determined to be 0.16999 and 0.17451 eV, which indicated the excellent thermal stability of the samples. All these findings demonstrated that as-prepared phosphors could act as a high-performance candidate for the application. Highlights • A single-component white-emitting phosphor has been successfully prepared. • As-prepared phosphor has good thermal stability and luminescence efficiency. • The structural data of Sr 9 La(PO 4) 5 (SiO 4)F 2 :Dy3+ is firstly reported. [ABSTRACT FROM AUTHOR]

Ca9La(PO4)5 (SiO4)F2:Dy3+ is prepared by solid state reaction of stoichiometric quantities of CaCO3, (NH4)2HPO4, SiO2, Dy2O3, and excess NH4HF2 as a flux ( 5% H2/N2 reducing atmosphere, alumina crucible, 1450 °C, 5 h). [ABSTRACT FROM AUTHOR]

A novel apatite structure phosphor Ca 9 La(PO 4 ) 5 (GeO 4 )F 2 :Dy 3+ (CLPGF:Dy 3+ ) with a hexagonal lattice in the P 6 3 / m space group was synthesized via a facile solid state technique. The crystal and fine local structure as well as their photoluminescence properties were investigated in detail. The CLPGF:Dy 3+ phosphor can absorb in the UV-vis spectral region of 290–475 nm and exhibit two intense emission bands centered at 485 and 580 nm, which ascribes to 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions of Dy 3+ , respectively. The concentration quenching of Dy 3+ emission occurs via the energy transfer among the nearest-neighbor ions and the corresponding quenching mechanism was verified to be the dipole-dipole interaction. The quantum efficiencies of the phosphors were examined to be 72.9% and its luminescence intensity at 150 °C decreases to 93.8% and 98.6% of the initial value at room temperature, which corresponds to 4 F 9/2 to 6 H 15/2 transition and 4 F 9/2 to 6 H 13/2 transition of Dy 3+ ions, respectively. Their interesting photoluminescence properties indicate that the CLPGF:Dy 3+ phosphor is a promising white-emitting candidate for w -LEDs applications. [ABSTRACT FROM AUTHOR]

The simple high-temperature solid-state route was adopted to synthesize a series of related Ba 3 LaK(PO 4 ) 3 F: x Eu 2+ (BLKPF: x Eu 2+ ) blue phosphors. The photoluminescence (PL) and diffuse reflection spectra have been investigated in detail. These phosphors which can be well excited by the 388 nm near ultraviolet light, produce the emitted blue light peaks located at about 460 nm. The critical Eu 2+ concentration quenching mechanism was ascribed to the dipole–dipole interaction, and the optimum concentration was eventually proved to be 0.1 mol. All above results indicate that Ba 3 LaK(PO 4 ) 3 F: x Eu 2+ phosphor can act as an appropriate candidate of the blue phosphor in the future. [ABSTRACT FROM AUTHOR]

In this paper, La 1.45 Ce 0.05 Ba 3.5 (SiO 4 ) 1.5 (PO4) 1.5 F compound with apatite structure was synthesized via solid state reaction method. The phosphor exhibits two strong excitation bands at 279 nm and 345 nm in near ultraviolet light region. When excited at 345 nm, the emission peaks of the phosphor give a red-shift from 406 nm to 418 nm compared with that of 279 nm excitation. Besides, the site occupation of Ce 3+ was proposed based on structure refinement, luminescence, fluorescence decay curves, as well as CIE diagram. All the results indicated that Ce 3+ can occupy sites of La 3+ with nine and seven coordination and a possible mechanism was proposed to explain the luminescence properties observed. [ABSTRACT FROM AUTHOR]

A series of Dy3+-doped MGd 9 (SiO 4) 6 O 2 :Dy3+ (M = Li, Na, K) phosphors that generated white emission were prepared using the high temperature solid-state technique. Simultaneously, the phase composition, crystal structure, electronic structure, as well as the luminescence properties of the as-prepared phosphors were investigated in detail. The structural refinement showed that the MGd 9 (SiO 4) 6 O 2 crystallized with the hexagonal apatite-type structure. The unit cell parameters increased gradually and the main peaks of the samples in XRD patterns shifted towards high angles with the substitution of alkali-metal ions (from Li+ to K+). Under the excitation of 350 nm, the as-obtained MGd 9 (SiO 4) 6 O 2 :Dy3+ phosphors gave bright white emission with the major emission peaks centering at 454, 477 and 573 nm. And the R y/b , CIE chromaticity coordinate and the corrected color temperature (CCT) of the phosphors were adjusted from 0.96, (0.3256, 0.3625) and 4602 K to 1.13, (0.3369, 0.3582) and 4201 K attributing to the substitution in the crystal structure. The thermoluminescence study of MGd 8.90 (SiO 4) 6 O 2 :0.10Dy3+ (M = Li, Na, K) showed good stability and the decay lifetimes of the samples were estimated to be about 470 μs. All the results suggested that the luminescence properties could be modified by the substitution of alkali metal ions, and the MGd 9 (SiO 4) 6 O 2 :Dy3+ (M = Li, Na, K) phosphors have potential application as white emission candidate for w -LEDs. • Novel Dy3+ doped apatite structure phosphors were successfully synthesized. • The symmetrical environment could be modified to a certain extent owing to substitution of alkali metal ions. • The DFT calculation was used to check the electronic structure. [ABSTRACT FROM AUTHOR]

An appropriate solid-state route was adopted to synthesize a series of related Ba 3 Sc(PO 4 ) 3 : x Sm 3+ red-orange phosphors. The Rietveld method was used to explore the structure of the phosphor. At present the PL, PLE, diffuse reflection and decay curves have been investigated in detail. These phosphors can be accurately excited by the 406 nm n-UV light and produce the emitted red-orange light whose peaks locate at about 566 nm, 603 nm and 650 nm. The quantum efficiency of Ba 3 Sc 0.95 (PO 4 ) 3 :0.05Sm 3+ was 53.5%. All above results indicate that Ba 3 Sc(PO 4 ) 3 :Sm 3+ phosphor can act as a suitable candidate of the warm components of n -UV w-LEDs. [ABSTRACT FROM AUTHOR]

Ba 3 Sc(PO 4 ) 3 :Eu 2+ ,Tb 3+ (BSP:Eu 2+ ,Tb 3+ ) phosphors were successfully prepared via conventional high-temperature solid-state reaction, their luminescence properties as well as energy transfer mechanism have been investigated in detail. The energy transfer mechanism was proposed to be the dipole–quadrupole mechanism, and the energy transfer efficiency was also estimated. BSP:Eu 2+ ,Tb 3+ phosphors showed a broad emitting band centered at 518 nm and several sharp emission peaks, which were assigned to the 5 d →4 f allowed transitions of Eu 2+ ions and characteristic optical 5 D 4 – 7 F J ( J =6, 5, 4, and 3) transitions of Tb 3+ ions, respectively. The emission color of BSP:Eu 2+ , y Tb 3+ exhibited a controlled luminescence evolution in the green area owing to the Eu 2+ –Tb 3+ energy transfer process. [ABSTRACT FROM AUTHOR]

Er 3+ and/or Yb 3+ doped Sr 2 ScF 7 up-conversion (UC) phosphors were synthesized, and the optimum doping concentrations of Yb 3+ and Er 3+ in the Sr 2 ScF 7 host were found to be 20% mol and 7% mol, respectively. Under excitation of 980 nm laser, the UC spectra of the samples is composed of three green emission bands from 510 to 570 nm centered at 525, 543 and 551 nm and two red emission band from 640 to 690 nm with two peaks at 657 and 671 nm, which is attributed to the 2 H 11/2 , 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions of Er 3+ , respectively. The UC emission color of Er 3+ can be tuned by adjusting the intensity ratio of red to green emission through manipulating the population of red and green emitting states. [ABSTRACT FROM AUTHOR]

SrAl 2 Si 2 O 8 : x Eu ( x = 0.5–8%) phosphors were prepared by the high-temperature solid-state reaction in air atmosphere. The phenomenon of Eu 2+ /Eu 3+ coexistence was observed and the color of the SrAl 2 Si 2 O 8 : x Eu phosphor could shift from light pink to blue by controllable and reproducible means. Photoluminescence (PL), excitation (PLE) spectra, X-ray photoelectron spectroscopy (XPS), and the fluorescence decay curves were employed to detect the presence of Eu 2+ and Eu 3+ ions in the compound. Under ultraviolet excitation, the broad band emission peaked at 410 nm originated from the transition of 4 f 6 5 d –4 f 7 from Eu 2+ and narrow band emissions peaked at 591 nm, 614 nm, 655 nm, and 703 nm are derived from the 4 f –4 f transition of Eu 3+ ions, although the Eu 3+ precursors were employed. The reduction mechanism from Eu 3+ to Eu 2+ in this compound was discussed in detail and verified by photoluminescence properties through changing the addition amount of Eu, temperature rise and holding time. [ABSTRACT FROM AUTHOR]

Emission-tunable phosphors Ca 9 La(PO 4 ) 5 (SiO 4 )F 2 :Ce 3+ ,Tb 3+ with apatite structure were synthesized by a solid-state reaction. The phase structure, photoluminescence (PL) properties, lifetimes and the PL thermal stability were investigated, respectively. The phosphor exhibited an asymmetric broad-band blue emission (Ce 3+ ) with peak at 403 nm and the line-type green emission with peak at 543 nm (Tb 3+ ). The varied color of the phosphors from blue to green can be achieved by properly tuning the relative ratio of Ce 3+ /Tb 3+ through the energy transfer from Ce 3+ to Tb 3+ ions. The critical distance was calculated to be 8.78 Å by using the concentration quenching method. When the temperature turned up to 150 °C, the emission intensity of Ca 9 La(PO 4 ) 5 (SiO 4 )F 2 :Ce 3+ ,Tb 3+ phosphor was 77% of its initial value at room temperature, which indicated the good thermal stability of the sample. All the properties indicate that the Ca 9 La(PO 4 ) 5 (SiO 4 )F 2 :Ce 3+ ,Tb 3+ phosphor has potential application of color-tunable w -LEDs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel Na0.60Ca0.40Sc0.60Mg0.40Si2O6:Eu2+,Mn2+ phosphors have been prepared. [•] Full-color white emission can be realized in the single host with different emission centers. [•] A white LED lamp was fabricated to demonstrate good luminescence properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Blue-emitting phosphor K2Ca2Si2O7:Ce3+ was synthesized. [•] The critical quenching concentration and concentration quenching mechanism was discussed. [•] Ce3+ emission centre in K2Ca2Si2O7 were studied by the photoluminescence spectra and decay curves. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ca10(PO4)6F2:Bi3+, Eu3+ phosphors have been synthesized. [•] Energy transfer happens from Bi3+ to Eu3+ with an optimum efficiency of 50.3%. [•] The energy transfer mechanism has been discussed. [ABSTRACT FROM AUTHOR]

Abstract: Green-emitting phosphors Ca3SiO4Cl2:Eu2+ were prepared by the high temperature solid-state method. Sol–gel process was adopted to encapsulate the as-prepared phosphors with tetraethylorthosilicate (TEOS) as silicon coating reagent. Fluorescence spectrometer, scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) patterns were employed to characterize the emission spectra, the surface morphologies and the phase structures, respectively. The chemical stability testing was operated by the method of soaking the phosphors in deionized water and roasting them at different temperatures. The results indicated that the surfaces of the green phosphors were evenly coated by SiO2 and the phase structure of the coated phosphors remained the same as the uncoated samples. The luminance centre of Eu2+ did not shift after surface treatment and the luminance intensity of coated phosphors was lower than that of the uncoated samples. The results demonstrated that the water-resistance stability of the coated phosphor was improved to some degree because the pH value and the luminance intensity variation were both smaller than the uncoated phosphor after steeping within the same time. Moreover, the thermal stability of coated phosphors was enhanced obviously compared to the original samples based on the temperature dependent emission spectra measurement. [ABSTRACT FROM AUTHOR]

Ce3+ doped K 3 LuF 6 powders have been successfully elaborated via high-temperature solid state method. The structural and luminescent properties of these cryolite-type K 3 LuF 6 : x Ce3+ (x = 0.03, 0.05, 0.07, 0.10 and 0.13) phosphors have been investigated into detail. The results indicate that all phases belong to the monoclinic system with P2 1 /n space group and lattice parameters a = 6.295 (4) Å, b = 6.497 (5) Å, c = 8.992 (6) Å, β = 90.91 (3) ° for x = 0.05. Ce3+ is considered to substitute for Lu3+ in the octahedral [LuF 6 ] sites. Under UV light excitation at 307 nm, the photoluminescence spectra of the samples present one broad band centered around 432 nm which belongs to the purplish-blue region. The color coordinates of this phase are calculated to (0.1565, 0.0956). The influence of Ce3+ content on the luminescence properties is also established and the concentration quenching mechanism is due to dipole-quadrupole Ce3+-Ce3+ interactions in K 3 LuF 6 :Ce3+. Rietveld refinement of XRD pattern and crystal structure of K 3 LuF 6 :0.05Ce3+ (left); The PL spectra of K 3 LuF 6 :xCe3+ (x = 0.03, 0.05, 0.07, 0.10, and 0.13) monitored by excitation at 307 nm and the inset is dependence of PL intensity on the Ce3+ doping content (right). Image 1 [ABSTRACT FROM AUTHOR]

Highlights • The ET mechanism has been confirmed by the luminescence spectra and fluorescence decay curves. • The ET interaction mechanism was determined to be dipole–quadrupole interaction. • The emission color of as-prepared phosphor could be adjusted from green to yellow. Abstract The Ca 9 La(PO 4) 5 (SiO 4)F 2 :Tb3+,Sm3+ phosphor with apatite structure has been successfully synthesized by high temperature solid-state reaction, and its luminescence properties as well as energy transfer mechanism has been investigated in detail. The energy transfer (ET) efficiency increases with increasing Sm3+ doping content, that was confirmed by the luminescence spectra and fluorescence decay curves of corresponding ions. The ET interaction mechanism was determined to be dipole–quadrupole interaction. The emission color of Ca 9 La(PO 4) 5 (SiO 4)F 2 :Tb3+,Sm3+ phosphor could be adjusted from green (0.272, 0.489) to yellow (0.363, 0.395) area through controlling the dopant ratio of Tb3+/Sm3+. The above results indicate that the Ca 9 La(PO 4) 5 (SiO 4)F 2 :Tb3+,Sm3+ phosphor has a great potential in white light-emitting diodes application. [ABSTRACT FROM AUTHOR]

A series of novel Na 3 Ga (1- x ) F 6 : x Eu 3+ ( x  = 1%, 3%, 5%, 7% and 10%) phosphors were synthesized by hydrothermal synthesis method. The crystal structure and luminescence properties of Na 3 GaF 6 :Eu 3+ were characterized by X-ray powder diffraction (XRD), Scanning electron microscope (SEM), photoluminescence (PL) and photoluminescent excitation spectra (PLE) as well as decay curves. The results indicated that Eu 3+ can replace Ga 3+ in the lattice of Na 3 GaF 6 without any impurity. The micro-particle of the phosphor was uniform and regular with a smooth surface. Upon 395 nm excitation, the phosphors show intense reddish-orange color including a series of narrow peaks attributed to the typical f–f transition of Eu 3+ . Not like most of other rare-earth doped sample, the Na 3 GaF 6 :Eu 3+ phosphors show obvious anti-thermal quenching behavior. All the results demonstrated that Na 3 GaF 6 :Eu 3+ phosphors exhibit good luminescent properties and might have a potential to applications in lighting technology. [ABSTRACT FROM AUTHOR]

Samarium (III) doped fluorapatite phosphors La 6- x Ba 4 (SiO 4 ) 6 F 2 : x Sm 3+ (LBSF: Sm 3+ ) were synthesized for the first time, via the conventional high-temperature solid-state method in the air atmosphere. The samples were measured by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy, i.e. emission and excitation spectra, as well as luminescence decay curves. The as-prepared samples can be excited in the range from 300–500 nm, centered at 404 nm. Photoluminescence measurements showed the emission spectra are composed of four sharp peaks characteristic of Sm 3+ ions, at about 565, 603, 650 and 711 nm. The critical concentration for quenching of Sm 3+ ions in the LBSF matrix is about 0.12 mol. According to the Dexter's theory, the mechanism of energy transfer between Sm 3+ ions was considered to be dipole-quadrupole (d-q) interactions, with the critical distance calculated by the concentration quenching method to 9.89 Å. Moreover, the temperature-dependent emission spectra showed that the as-prepared phosphors have good thermal stability, with an activation energy of about 0.161 eV. Finally, according to the CIE coordination, the phosphor exhibited reddish-orange emission. Thanks to the mentioned favorable structural and optical properties, the Sm 3+ -doped La 6 Ba 4 (SiO 4 ) 6 F 2 phosphors have a potential application character, for the near ultraviolet white light emitting diodes. [ABSTRACT FROM AUTHOR]

Upconversion phosphors Sr 2 LaF 7 co-doped with Yb 3+ and Er 3+ are synthesized via hydrothermal method. The phase compositions of Sr 2 LaF 7 phosphors with different amounts of Yb 3+ and Er 3+ dopants, pH values, and complexing agents are characterized by X-ray diffraction (XRD). The crystal structure and morphology of Sr 2 LaF 7 phosphor doped with 15% Yb 3+ / 1% Er 3+ is refined by the Rietveld method and transmission electron microscopy (TEM). Under 980 nm laser excitation, Yb 3+ and Er 3+ co-doped Sr 2 LaF 7 phosphors exhibit red emission around 670 nm generated by the 4 F 9/2 → 4 I 15/2 transition and green emissions centering around 550 nm and 523 nm generated by the 4 S 3/2 → 4 I 15/2 and 2 H 11/2 → 4 I 15/2 transitions of Er 3+ , respectively. The optimum synthetic conditions for upconversion luminescence for Sr 2 LaF 7 co-doped with Yb 3+ and Er 3+ are discussed and determined to be 15% Yb 3+ / 1% Er 3+ with EDTA-2Na as the complexing agent under pH value = 8, and the corresponding Commission International de L′Eclairage (CIE) coordinates are calculated to be x  = 0.4293 and y  = 0.5589 with reddish yellow color visible to naked eyes under the 980 nm laser excitation. The related upconversion mechanisms of Yb 3+ and Er 3+ co-doped Sr 2 LaF 7 depending on the pump power are also studied in detail. [ABSTRACT FROM AUTHOR]

In this paper, Ce 3+ -activated iso-structural solid solutions La 5.99 Ce 0.01 M 4 (SiO 4 ) 6 F 2 (M = Ca, Sr and Ba) compounds were prepared for the first time. The structure and luminescence properties of the samples were investigated to explore the difference of cation substitution. The phase analysis indicated that all XRD peaks of the samples were indexed by a hexagonal cell with the space group of P 6 3 /m, and the phosphors showed strong blue light emission with broad bands. With the isomorphous substitution of Ba → Sr → Ca, the average bond length between Ce 3+ and anions is decreased and the crystal field around Ce 3+ is strengthened, resulting in the red-shift (from 410 nm to 423 nm) of the emission wavelength for La 5.99 Ce 0.01 M 4 (SiO 4 ) 6 F 2 (M = Ca, Sr, Ba). [ABSTRACT FROM AUTHOR]

Developing color-tunable phosphors via the introduction of co-doping activators and sensitizers to the host with energy transfer processes has been a state-of-the-art topic for a long time. In this work, novel emission-tunable oxyapatites-type Ba 10 (PO 4 ) 6 O:Eu 2+ ,Tb 3+ /Li + phosphors were prepared via a high temperature solid state reaction for the applications in white light emitting diodes ( w -LEDs) with higher color rendering index. Tunable colors from blue to green can be realized in the Ba 10 (PO 4 ) 6 O:Eu 2+ ,Tb 3+ /Li + by varying the relative ratios of Eu 2+ to Tb 3+ , showing good absorption in the range of 230–400 nm. The energy transfer mechanism from Eu 2+ to Tb 3+ ions was demonstrated to be a quadrupole-quadrupole interaction by combining the Inokuti-Hirayama (I H) model and Reisfeld's approximation. Importantly, a prototype white lamp was packaged by mixing Ba 9.83 (PO 4 ) 6 O: 0.03Eu 2+ , 0.07Tb 3+ , 0.07Li + and commercial red phosphor CaAlSiN 3 : Eu 2+ , and the lamp exhibits a higher color rendering index (Ra = 92 and R9 = 56) and warm correlated color temperature of 4361 K for the actual application. Better luminescent properties compared to commercial Y 3 A l5 O 12 :Ce 3+ -based w -LEDs, indicating that Ba 10 (PO 4 ) 6 O: Eu 2+ , Tb 3+ /Li + phosphors are emerging as potential phosphor-converted w -LEDs. [ABSTRACT FROM AUTHOR]

In this paper, a series of novel luminescent Sr 10− x (SiO 4 ) 3 (SO 4 ) 3 O: x Eu 2+ phosphors with apatite structure were synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, as well as the PL thermal stability were investigated. Sr 9.92 (SiO 4 ) 3 (SO 4 ) 3 O:0.08Eu 2+ phosphor exhibits better thermal quenching resistance, retaining the luminance of 66.55% at 150 °C compared with that at 25 °C. The quenching concentration of Eu 2+ in Sr 10 (SiO 4 ) 3 (SO 4 ) 3 O was about 0.08 (mol) with the dipole–quadrupole interaction. The Sr 10− x (SiO 4 ) 3 (SO 4 ) 3 O: x Eu 2+ phosphors exhibited a broad-band green emission at 538 nm upon excitation at 396 nm. The results indicate that Sr 10− x (SiO 4 ) 3 (SO 4 ) 3 O: x Eu 2+ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. [ABSTRACT FROM AUTHOR]

A series of blue-emitting La 5.90− x Ba 4+ x (SiO 4 ) 6− x (PO 4 ) x F 2 :0.10Ce 3+ ( x = 0, 1, 2, and 3) phosphors with apatite structure were synthesized by a solid-state reaction. The crystal structure and the photoluminescence properties were investigated in detail. The crystallographic occupancy of Ce 3+ in La 2.90 Ce 0.10 Ba 7 (SiO 4 ) 3 (PO 4 ) 3 F 2 and La 5.90 Ce 0.10 Ba 4 (SiO 4 ) 6 F 2 were studied based on Rietveld refinements results and the crystal chemistry rules. La 5.90− x Ba 4+ x (SiO 4 ) 6− x (PO 4 ) x F 2 :0.10Ce 3+ exhibited strong blue light emission in the range of 407–414 nm with high thermal stability upon excitation at 276 nm. Besides, the activation energy E of La 5.90 Ce 0.10 Ba 4 (SiO 4 ) 6 F 2 and La 2.90 Ce 0.10 Ba 7 (SiO 4 ) 3 (PO 4 ) 3 F 2 phosphors were calculated to be 0.152 and 0.177 eV. These results suggest that La 5.90− x Ba 4+ x (SiO 4 ) 6− x (PO 4 ) x F 2 :0.10Ce 3+ is a potential blue phosphor candidate for near-UV-pumped w -LEDs. [ABSTRACT FROM AUTHOR]

Single-phase La 6 Sr 4 (SiO 4 ) 6 F 2 : Ce 3+ , Tb 3+ samples with apatite-like structure have been synthesized via solid-state reaction method. The phase structure, luminescence properties, lifetime, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples. Effective energy transfer occurs from Ce 3+ to Tb 3+ in La 6 Sr 4 (SiO 4 ) 6 F 2 , which shows more intense Blue-Green light under UV light excitation. In addition, a possible mechanism of the energy-transfer from Ce 3+ to Tb 3+ ion is also proposed. The critical distance R C of Ce 3+ to Tb 3+ ions in La 6 Sr 4 (SiO 4 ) 6 F 2 host was calculated to be 11.878 Å. All the results indicate that La 6 Sr 4 (SiO 4 ) 6 F 2 :Ce 3+ , Tb 3+ phosphors have potential applications to be used as near UV-convertible phosphors for white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Single-phase Ba 10− x − y (PO 4 ) 6 O: x Eu 2+ , y Mn 2+ samples with apatite structure have been synthesized via a solid-state reaction method. The phase structure, luminescence properties, lifetime, PL thermal stability, as well as fluorescence decay curves of the samples were investigated. Effective energy transfer occurs from Eu 2+ to Mn 2+ in Ba 10 (PO 4 ) 6 O and a possible mechanism of the energy-transfer from Eu 2+ to Mn 2+ is proposed. The critical distances R c was calculated by concentration quenching and turned out to be about 0.817 nm ( x c =0.21). The CIE and thermally stable luminescence behaviors of Ba 9.94 (PO 4 ) 6 O:0.06Eu 2+ phosphor were also studied in detail. All the results indicate that Ba 10− x − y (PO 4 ) 6 O: x Eu 2+ , y Mn 2+ phosphors have potential applications as near UV-convertible phosphors for white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Up-conversion phosphors BaLa 2 ZnO 5 co-doped with Ho 3+ /Yb 3+ were synthesized by high temperature solid-state reaction method. The phase composition of the phosphors was characterized by X-ray diffraction (XRD). The structure of BaLa 2 ZnO 5 : 0.75% Ho/15% Yb phosphor was refined by the Rietveld method and results showed the decreased unit cell parameters and cell volume after doping Ho 3+ and Yb 3+ , indicating Ho 3+ and Yb 3+ have successfully replaced La 3+ . Under the excitation of 980 nm diode laser, the strong green and weak red up-conversion emissions centered at 548 nm, 664 nm and 758 nm were observed, which originating from 5 S 2 , 5 F 2 → 5 I 8 , 5 F 4 → 5 I 8 and 5 S 2 , 5 F 2 → 5 I 7 transitions of Ho 3+ ions, respectively. The optimum doping concentrations of Ho 3+ and Yb 3+ were determined to be 0.75% and 15%, and the corresponding Commission International de L'Eclairage (CIE) coordinates are calculated to be x =0.298 and y =0.692. The related UC mechanism of Ho 3+ /Yb 3+ co-doped BaLa 2 ZnO 5 depending on pump power was studied in detail. The results indicate that BaLa 2 ZnO 5 : Ho 3+ /Yb 3+ can be an effective candidate for up-conversion yellowish-green light emitter. [ABSTRACT FROM AUTHOR]

A series of novel luminescent phosphors Sr 10 (PO 4 ) 6 O:Eu 2+ with apatite structure were synthesized via a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples, and the selected Sr 9.97 (PO 4 ) 6 O:0.03Eu 2+ phosphor exhibits strong thermal quenching resistance, retaining the luminance of 88.73% at 150 °C. The quenching concentration of Eu 2+ in Sr 10 (PO 4 ) 6 O was about 0.03 attributing to the dipole–quadrupole interaction. The Sr 10 (PO 4 ) 6 O:Eu 2+ phosphor exhibited a broad-band blue emission at 439 nm upon excitation at 346 nm. The results indicate that Sr 10 (PO 4 ) 6 O:Eu 2+ phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. [ABSTRACT FROM AUTHOR]