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Persistent luminescence phosphors have attracted much attention in the realm of anti-counterfeiting and information storage because of their characteristic properties of optical information storage, long persistent luminescence, and simplicity of design. At present, traditional anti-counterfeiting persistent luminescence phosphors are based on single-colour luminescence and generally have poorly secure anti-counterfeiting capabilities. In this work, Ca1−1/2xCd1−1/2xGe7O16:xSm3+ (x = 0, 0.0025, 0.005, 0.01, 0.015, 0.02, and 0.025) phosphors were synthesized using a high-temperature solid-state reaction method, which demonstrated potential as multi-colour and two-mode anti-counterfeiting persistent luminescence materials. With an increase in doping concentration of Sm3+ ions in the host, the materials could emit blue-to-pink photoluminescence under 254 nm UV lamp illumination. After excitation under a 254 nm UV lamp, the materials showed persistent luminescence performance with a pink persistent luminescence colour, and the duration could exceed 4 h. The persistent luminescence mechanism and electron traps inside the samples were analyzed by plotting their thermoluminescence curves after excitation cessation. The results show that at least two types of traps existed in the Ca1−1/2xCd1−1/2xGe7O16:0.01Sm3+ phosphor. The phosphors were used to synthesize anti-counterfeiting ink, which was then used to make an optical anti-counterfeiting pattern through screen printing. The pattern could barely be observed on white paper in sunlight but was visible in different colours under an irradiation of 254 nm and in a low light environment. The results show that the produced phosphors have a high level of application potential for use in enhanced optical anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

Chromium is a common heavy metal element that is harmful to the ecosystem as well as human health, so sensitive detection of chromium ions in solution is important for life and health. In this paper, a series of Eu3+-doped KBi3F10 fluorescent powders were successfully synthesized by a one-step solvothermal method for the selective detection of Cr3+, CrO42− and Cr2O72− ions in an aqueous solution. When adjusting the pH value to 3 and adding PVP as an additive, the obtained KBi3F10:12%Eu3+ phosphor showed excellent red luminescence. Due to the competitive absorption and the inner filter effect of Cr3+, CrO42− and Cr2O72− ions, the red emission from Eu3+ ions produces fluorescence quenching, which can be used to detect them with good selectivity. And the detection limits are as low as 0.19 μM, 0.38 μM and 0.094 μM for Cr3+, CrO42− and Cr2O72− ions, respectively. Other metal ions and common anions showed little interference with chromium ion detection. The obtained fluorescent probe has good recyclability, accurate and reliable detection results, simple operation and low cost and is easy to promote, which make it an excellent three-in-one probe for chromium detection. [ABSTRACT FROM AUTHOR]

In this paper, a three-wavelength exciting and temperature-sensing Gd1.559Y0.03Lu0.02Er0.13Yb0.26Ho0.001O2S phosphor excited by 980 nm, 1064 nm and 1550 nm was prepared for the first time by a coprecipitationhigh temperature solid-state reaction (HSR). Three different up-conversion changes were observed with an increase in temperature under 980 nm, 1064 nm and 1550 nm laser excitation. The fluorescence intensity ratio (FIR) equations of the sample excited by 980 nm, 1064 nm and 1550 nm were obtained at 313-553 K. The three kinds of absolute sensitivity were 0.0016 (479 K), 0.0096 (553 K) and 0.1528 (553 K). The upconversion process excited by 980 nm, 1064 nm and 1550 nm laser radiation was analyzed and the causes of the three different changes are explained. The stability of the Gd1.559Y0.03Lu0.02Er0.13Yb0.26Ho0.001O2S phosphor as a temperature sensor was tested by a cyclic test. It is proved that the Gd1.559Y0.03Lu0.02Er0.13- Yb0.26Ho0.001O2S phosphor is a novel and valuable up-conversion optical temperature sensor. [ABSTRACT FROM AUTHOR]

Anti-counterfeiting using multiple optical output modes has drawn considerable attention for enhancing anti-fake measures. Herein, a multimodal dynamic optical information coding from the self-activated Na2-CaGe2O6 phosphor is developed. Na2CaGe2O6 phosphor exhibits two distinct emission bands associated with the intrinsic defects of oxygen vacancies (V••o) and inverse-site defects (Ge••A). The incorporation of Bi3+ ions results in an increased concentration of defects, which in turn facilitates the modulation of the corresponding photoluminescence color from purple to red with prolonged ultraviolet (UV) irradiation. Moreover, the recovery of the corresponding emission color is observed for thermal disturbance. Besides, an improved optical storage behavior as the long persistent and photo-stimulated luminescence is achieved for the incorporation of Bi3+ ions. Consequently, a multimode dynamic color-changing code is constructed using screen-printing technology, offering an alternative approach for advanced anticounterfeiting. [ABSTRACT FROM AUTHOR]

Yb3+/Er3+-doped Bi2(MoO4)3−z(WO4)z phosphors were synthesized via a hydrothermal method combined with subsequent calcination. Under the excitation of a light source of 980 nm, Bi2(MoO4)3:Yb3+/Er3+ phosphors exhibited strong upconversion green light and weak red light emissions. By doping WO42− in Bi2(MoO4)3:Yb3+/Er3+ phosphors, the upconversion luminescence intensity of the phosphors significantly enhanced, which is 42 times higher than that of the undoped WO42− phosphor. With an increase in WO42− doping content, the final color coordinates of Bi2(MoO4)3−z(WO4)z:Yb3+/Er3+ phosphors were (0.2352, 0.7274), which is closer to the standard green CIE coordinates. The maximum CP of WO42−-doped phosphors is as high as 116.68%, which is 74.44% higher than that of the undoped WO42− phosphor. Based on the thermally coupled energy levels (TCLs) of Er3+ (2H11/2/4S3/2 → 4I15/2) in Bi2(MoO4)2.7(WO4)0.3:14%Yb3+,3%Er3+ phosphor, the SR value reached a maximum of 0.0081 K−1 at 323 K and the SA value reached a maximum of 0.0099 K−1 at 398 K. The obtained Bi2(MoO4)3−z(WO4)z:Yb3+/Er3+ phosphors are suitable for upconversion luminescent materials for green displays and have potential advantages in optical temperature measurement. [ABSTRACT FROM AUTHOR]

Exploring efficient, energy-saving and environmentally friendly phosphors is important for developing solid-state white light-emitting diodes (w-LEDs). Herein, we report a novel highly efficient green-emitting Ce3+-activated Ca2LuScAl2Si2O12 (abbreviated as CLSAS:Ce3+) garnet phosphor with high quantum efficiency and good thermal stability. These garnet phosphor samples doped with different Ce3+ ion concentrations were synthesized using a high-temperature solid-state method. The crystal structure and Ce3+ concentration-dependent luminescence properties of the phosphors were systematically studied. The as-prepared CLSAS:Ce3+ garnet phosphors exhibit broadband absorption in the spectral range of 250–510 nm with a maximum excitation wavelength of around 452 nm, matching well with the emission wavelengths of commercial blue LED chips. Under an excitation of 452 nm, the optimal CLSAS:4%Ce3+ sample exhibited a broad green emission band (emission peak: 531 nm; bandwidth: 114 nm) with CIE color coordinates of (0.3293, 0.5453) and high luminescence efficiency (internal quantum efficiency: 87.3%; external quantum efficiency: 56.6%). The CLSAS:4%Ce3+ sample also showed good thermal stability in the temperature range of 303–443 K. Its emission intensity at 423 K reached 79% of the emission intensity at 303 K, and it exhibited outstanding color stability with a small color chromaticity shift (ΔE = 1.07 × 10−3) at 423 K. Importantly, the fabricated w-LED device exhibits excellent photoelectric properties (CCT = 4978 K; Ra = 92.4; LE = 69.59 lm W−1). The obtained efficient CLSAS:Ce3+ green phosphors have the potential for application in high-quality w-LEDs. [ABSTRACT FROM AUTHOR]

In this paper, a series of Eu3+/Tb3+ doped La3Ga5SiO14 (LGS:Eu3+, Tb3+) phosphors with excellent performance have been synthesized by high-temperature solid-phase method. The effects of Eu3+ and Tb3+ doping in LGS on the host lattice were analyzed by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) proved that the Eu3+ and Tb3+ ions were successfully doped into the LGS host. The doped Eu3+/Tb3+ ions only occupy the eight-coordinated La3+ sites. The concentration quenching points of LGS:Eu3+ and LGS:Tb3+ phosphors were determined to be 0.16 and 0.18, respectively. The luminescence performance and fluorescence lifetime of LGS:Eu3+, Tb3+ were studied. LGS:Eu3+, Tb3+ phosphors successfully realized Tb3+ → Eu3+ energy transfer to enhance Eu3+ luminescence. The energy transfer mechanism is speculated on using the experimental results. The energy transfer efficiency from Tb3+ to Eu3+ is about 66.83% in La2.46Tb0.18Eu0.36Ga5SiO14. The LGS:Eu3+, Tb3+ phosphors can achieve tunable luminescence by controlling the doping concentrations of Eu3+ and Tb3+. The ΔE is calculated to be 0.2567 eV for the La2.70Eu0.12Tb0.18Ga5SiO14 phosphor. [ABSTRACT FROM AUTHOR]

Mechanoluminescence (ML) materials can convert mechanical stimuli into visible signals for real-time visualization of stress sensing. Since stress sensing solely based on ML absolute strength is susceptible to the external environment, ratiometric ML detection approach is expected to provide stress description with improved accuracy and stability. In this study, a stress-dependent ratiometric ML is achieved using the Eu2+ and Mn2+ co-doped SrMg2(PO4)2 (SMP) phosphors, enabling color-resolved visualization of uploaded stress stimulus. Moreover, the linear relationship between the ML intensity ratio (MLIR) and the applied stress leads to an obvious variation in ML color upon different applied stress. Herein, the as-explored ML composites films as an artificial skin could provide a visualization and quantification tool for monitoring human knee motion with great accuracy and precision. [ABSTRACT FROM AUTHOR]

BaY2Al2Ga2GeO12 (BYAGGO):Eu3+ and BaY2Al2Ga2GeO12:0.03Bi3+, yEu3+ phosphors have been prepared via a high-temperature solid phase method. BYAGGO:Eu3+ has a stronger characteristic emission of Eu3+ at 592 nm attributed to magneto-dipole transitions under 245 nm excitation, indicating that Eu3+ is more inclined to occupy the central lattice of the octahedron with inverted symmetry. The lattice of Eu3+ ions expands to the asymmetric dodecahedron center in Eu3+ and Bi3+ ions co-doped in BYAGGO. The emission of BYAGGO:Bi3+ overlaps the excitation of BYAGGO:Eu3+, implying that energy transfer (ET) from Bi3+ to Eu3+ is possible. Furthermore, the fluorescence decay lifetime is the direct proof of energy transfer in BaY2Al2Ga2GeO12:0.03Bi3+, yEu3+. The energy transfer efficiency reaches 72% at y = 0.25. Finally, BYAGGO:0.03Bi3+, 0.09Eu3+ phosphor is employed for a WLED device with a color temperature of 3825 K and a color rendering index (Ra) of 88.75. [ABSTRACT FROM AUTHOR]

Monoclinic AgTbW2O8:Eu3+ crystals were prepared by a simple one-step hydrothermal method. The phase, morphology and luminescence properties of the obtained phosphors were systematically characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and photoluminescence (PL). The effects of solution pH, W/Tb molar ratios and reaction temperatures as well as reaction times on the size and morphology of the final products were discussed, and the possible formation mechanism of the almond-like structure was proposed. The down-conversion luminescence properties and energy transfer behavior of the AgTbW2O8:Eu3+ phosphors were studied under ultraviolet light excitation. The emission lights were obtained from green to yellow-green to yellow to red by setting different ratios of Tb3+/Eu3+. The temperature-dependent fluorescence test data showed that AgTbW2O8:Eu3+ phosphors have good temperature stability. In addition, by doping alkali metal ions Li+, Na+, and K+ in AgTbW2O8:Eu3+ phosphors, it is found that the luminescence intensity of phosphors doped with alkali metal ions is enhanced compared with that of phosphors without alkali metal ions, and the phosphor doped with K+ has the largest luminescence intensity, which is due to the introduction of K+ making the crystal field produce the greatest asymmetry. [ABSTRACT FROM AUTHOR]

Well-dispersed uniform spheres (∼0.7–1.5 μm in diameter) of YPO4 and (Y,Ln)PO4 (Ln = Eu, Tb, Dy, Ho, Tm, Ce, and Eu/Tb) tetragonal phosphate hydrates have been directly synthesized via microwave-assisted processing. The polycrystalline spheres, which are made of confined 10–17 nm nanocrystals, are direct solid solutions rather than a mechanical mixture of individual particles. Their growth follows an aggregation process, maintaining the composition of the material. The phosphate hydrates converted into anhydrous tetragonal materials via calcination, and the spherical shape and excellent dispersion of the original particles were well retained up to 1000 °C. Upon UV excitation, the YPO4:Ln3+ samples exhibit characteristic emissions of Ln3+ (Ln = Eu, Tb, Dy, Ho, Tm, and Ce) and yield red, green, near white, green, blue, and blue-green emissions, respectively. The color-tunable emissions (from green to red) can be varied by increasing the Eu content, and the Tb3+→ Eu3+ energy transfer process was observed for the tetragonal phosphate in the Y/Tb/Eu system. The efficiency of the Tb3+→ Eu3+ energy transfer was discovered to be ∼28% for (Y0.88Tb0.02Eu0.10)PO4. The thermal stability of (Y0.88Tb0.02Eu0.10)PO4 is lower than that of (Y0.98Tb0.02)PO4 and (Y0.95Eu0.95)PO4. Thus, the 5D4→7F5 transition of Tb3+ at 546 nm splits into UGRAPHIC DISPLAY="INLINE" ID="UGT1" SRC="UGT1"/→7F5 (at ∼538–546 nm) and UGRAPHIC DISPLAY="INLINE" ID="UGT2" SRC="UGT2"/→7F5 (at ∼557 nm) transitions during the heating process. This phenomenon has been ascribed to the variation of the Tb3+ crystal environment. The UGRAPHIC DISPLAY="INLINE" ID="UGT3" SRC="UGT3"/ energy level gradually shifts to a higher one at an elevated temperature, inducing more and more excited electrons transferring from the higher UGRAPHIC DISPLAY="INLINE" ID="UGT4" SRC="UGT4"/ energy level to the lower UGRAPHIC DISPLAY="INLINE" ID="UGT5" SRC="UGT5"/ one via nonradiative relaxation. Therefore, an enhanced emission intensity at ∼557 nm (UGRAPHIC DISPLAY="INLINE" ID="UGT6" SRC="UGT6"/→7F5 transition) and a weakened one at ∼538–546 nm (UGRAPHIC DISPLAY="INLINE" ID="UGT7" SRC="UGT7"/→7F5 transition) were observed. (Y0.95Eu0.05)PO4/PVA transparent films were successfully fabricated by solution casting, and they exhibit both outstanding flexibility and high transmittances of ≥83% in the 400–850 nm region. The hybrid films can be coated on paper money for anti-fake labeling applications. [ABSTRACT FROM AUTHOR]

As a representative of III–V semiconductor materials, InP/ZnS quantum dots are regarded as the star material in the field of light-emitting devices due to their low toxicity and suitable luminescence range. However, there are still some major problems in the preparation process of InP/ZnS QDs, such as phosphine precursors are expensive and difficult to preserve, the nucleation time of short wavelength InP/ZnS QDs is too short and the size distribution is too large. In this paper, we'll replace the traditional tris(trimethylsilyl)phosphine with tris(diethylamino)phosphine as a cheaper phosphine precursor and propose a novel and convenient method for adjusting the luminescence wavelength of InP/ZnS QDs. Different from the traditional method to adjust the emission wavelength by changing the nucleation time, the emission wavelength of InP/ZnS QDs was regulated by changing the number of initially formed cores. Zeolites provide a nucleation site for the InP cores. InP/ZnS QDs that emit between 522 nm and 589 nm were obtained. Moreover, the obtained InP/ZnS QDs have good monochromaticity, and the minimum half-width (half-full width) is up to 48 nm. This method provides a new way to adjust the size of quantum dots with good performance. [ABSTRACT FROM AUTHOR]

New series of Ho3+/Yb3+ and Tm3+/Yb3+ codoped Na5Rb7Sc2(WO4)9 phosphors have been prepared by a conventional solid state reaction method. A powder XRD study has revealed that all the synthesized tungstates are isostructural and crystallize in the trigonal crystal system (sp. gr. R32, Z = 3). Upconversion luminescence in the 460–850 nm spectral range, associated with transitions in Ho3+ or Tm3+ ions, has been detected under 980 nm laser diode excitation. The optimal Ho3+/Yb3+ and Tm3+/Yb3+ ratios have been determined. Possible mechanisms of energy transfer between lanthanide ions have been discussed. The luminescence characteristics of the representative samples, Na5Rb7Sc1.925Yb0.045Ho0.03(WO4)9 and Na5Rb7Sc1.9Yb0.09Tm0.01(WO4)9, have been studied at 298–498 K to evaluate their temperature measurement performance. The calculated values of the absolute and relative sensitivities indicate that the studied tungstates are promising phosphors for non-contact thermometry. [ABSTRACT FROM AUTHOR]

Y2O3:Eu3+,Tb3+,Ce3+ phosphors were prepared by the co-precipitation method and the optimal component formulations of the samples were determined by a combination of controlled variable method and orthogonal experiments. The experimental results show that doping with appropriate amounts of Tb3+ and Ce3+ significantly improved the luminescence performance of Y2O3:Eu3+ phosphors. In the Y2O3:Eu3+,Tb3+,Ce3+ phosphors system, Tb3+ could be used as a carrier to transfer energy for Ce3+–Eu3+, eliminating the presence of metal–metal charge transfer (MMCT) between the two ions. The direction of energy transfer which is from Ce3+ → Tb3+ → Eu3+ has been confirmed by emission spectrum and calculation results show that the mechanism of Tb3+ to Eu3+ energy transfer and Ce3+ to Tb3+ energy transfer in Y2O3 matrix are both quaternary–quaternary interactions. As the doping concentration of Tb3+ and Ce3+ increases, the emission peak position of phosphor was shifted toward the blue region. Their structure and micromorphology have been analyzed by X-ray diffraction and scanning electron microscopy, the test results show that ion doping does not cause changes in the crystal structure of Y2O3 and the samples are approximately spherical in shape. This work provides a new idea to study the UV detection and multi-ion inter-energy transfer model. [ABSTRACT FROM AUTHOR]

Eu3+ single doping and Eu3+, R+ (R = Li, Na, K) charge compensation co-doped orange-red MgZn2(PO4)2 phosphors were prepared by high-temperature solid-state method. The effect of charge compensation agent R+ on the luminescence properties of MgZn2(PO4)2:Eu3+ phosphors was investigated. The morphology and composition of the samples were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field (HAADF), and energy dispersive spectroscopy (EDS) techniques. The photoluminescence properties were studied using excitation and emission spectra. In this study, R+ is used as charge compensation to improve the emission intensity of Eu3+ and the physical explanation is given. The optimal doping concentration of Eu3+ in MgZn2(PO4)2 was obtained to be 5 mol%. Under ultraviolet (396 nm) excitation, a strong orange-red luminescence corresponding to the 5D0 → 7Fi- (i = 1, 2, 3, and 4) transition of Eu3+ is observed. The CIE coordinates and decay lifetimes of typical samples are discussed. The chromaticity coordinates of the two samples were (0.604, 0.392) and (0.616, 0.382), respectively, both located in the orange-red region. The fluorescence lifetime of MgZn2(PO4)2 phosphors co-doped 5% Eu3+ and 5% R+ (R = Na and K) is obviously improved. The results show that MgZn1.9 R0.05(PO4)2:0.05Eu3+ (R = Na and K) is a kind of orange-red phosphor with high efficiency under near ultraviolet excitation. [ABSTRACT FROM AUTHOR]

Yb2(MoO4)3:Ln3+ (Ln = Ho, Tm, Er) phosphors were synthesized by a hydrothermal method with further calcination. The crystal structure and morphology of the samples were characterized by X-ray diffraction and scanning electron microscopy. The effects of rare earth ion interaction in the Yb2(MoO4)3:Ln3+ phosphors on the upconversion (UC) luminescence properties and energy transfer process at different doping concentrations were discussed. It is concluded that by doping Ho3+, Tm3+, and Er3+ in the Yb2(MoO4)3 host, the phosphors emit orange-yellow, blue and green light, respectively, and the energy transfer from Yb3+ -- Ho3+/Er3+ and Yb3+ -- Tm3+ is a two and three photon process, respectively. Under the excitation of a 980 nm laser, by changing the Ho3+/Tm3+ ratio in doped Yb2(MoO4)3, we have realized the transition of phosphors from cold white light to warm white light. The temperature sensitivity of the ²H11/2 and 4S3/2 energy levels of Yb2(MoO4)3:Er3+ in the range of 323-573 K was studied by the FIR technology. The experimental results show that the maximum absolute sensitivity was 0.0081 K-1 at 573 K and the maximum relative sensitivity was 0.01 K-1 at 323 K. Compared with other materials, the Er3+ doped Yb2(MoO4)3 phosphor is an excellent optical temperature sensing material. [ABSTRACT FROM AUTHOR]

The effects of composition and preparation conditions of palmierite-type K5Yb1−xEux(MoO4)4 (KYEMO) compounds on their structural and luminescence properties were studied in this work. The solid solutions were obtained in three ways: 1) annealing at 893 ± 10 K (low-temperature (LT) phases); 2) slow cooling to room temperature from 1123 ± 10 K (intermediate (IM) phases); 3) quenching in liquid nitrogen from 1123 ± 10 K (high temperature (HT) phases). As a result, three modifications, α-phase (space group (SG) R3¯m), β-phase (superspace group (SSG) C2/m(0β0)00 or X2/m(0β0)00), and γ-phase (SG C2/c) were obtained and characterized. The regions of existence of various modifications of the solid solutions were established. α-KYEMO (0 ≤ x ≤ 1 solid solutions, HT-) and LT- and IM-phases with 0.8 ≤ x ≤ 1 have trigonal symmetry (SG R3¯m). The LT- and IM-phases with 0.3 ≤ x < 0.8 have monoclinic symmetry (SG C2/m). The incommensurately modulated structure of β-K5Yb0.3Eu0.7(MoO4)4 was refined from synchrotron XRD data by the Rietveld method in the superspace group C2/m(0β0). The luminescence characteristics of the series of KYEMO solid solutions were studied. The influence of the Eu3+ concentration on the PL spectra of α-KYEMO under excitation at the 7F0 → 5L6 Eu3+ transition (λex = 395 nm) and CTB (λex = 260 nm) and the influence of synthesis conditions on the luminescence intensities of Eu3+ and Yb3+ emission were investigated. Increasing the concentration of Eu3+ shifts the CIE coordinates from an orange to an orange-red region. The synthesis method, composition and structure affect the color change from light orange to orange in the order HT → LT → IM for x = 0.5 and LT → HT → IM for x = 0.8. Periodic (γ-phase) and aperiodic (β-phase) ordering of K1 and Yb in M1 positions in the structure is more preferable for the emission of 2F5/2 → 2F7/2 transition of Yb3+ ions than a random distribution of the cations in the α-phase structure. The 5D0 → 7F0 and 5D0 → 7F2 Eu3+ transition intensities and the Eu3+/Yb3+ emission ratio depend on the excitation. From the PLE spectra for β-KYMO, the optical band gap was determined to be 4.13 eV. The quantum yield measured for α-K5Yb0.3Eu0.7(MoO4)4 has a very high value of 62%. The intensities of Eu3+ and Yb3+ emission depend on the Eu3+/Yb3+ ratio as well as the excitation wavelength. The structural and optoelectronic characteristics make the K5Yb1−xEux(MoO4)4 phosphors strong contenders for near UV-WLEDs. [ABSTRACT FROM AUTHOR]

The influence of preparation techniques on the structure and luminescent properties of K5Eu(MoO4)4 (KEMO) was investigated. KEMO phosphors were synthesized by three different techniques: solid state and sol–gel (sg) methods as well as the Czochralski (CZ) crystal growth technique. Laboratory powder X-ray diffraction (PXRD) studies revealed that all KEMO samples had a structure analogous to that of other high temperature α-K5R(MoO4)4 palmierite-type phases (space group (SG) R3¯m). Contrary to laboratory PXRD data, electron diffraction revealed that the KEMO crystal grown by the CZ technique had a (3 + 1)D incommensurately modulated structure (super space group (SSG) C2/m(0β0)00) with the modulation vector q = 0.689b*. A detailed analysis of electron diffraction patterns has shown formation of three twin domains rotated along the c axis of the R-subcell at 60° with respect to each other. Synchrotron XRD patterns showed additional ultra-wide reflexes in addition to reflections of the R-subcell of the palmierite. However, the insufficient number of reflections, their low intensity and large width in the synchrotron X-ray diffraction patterns made it impossible to refine the structure as incommensurately modulated C2/m(0β0)00. An average structure was refined in the C2/m space group with random distribution of K1 and Eu1 in [M1A2O8]-layers of the palmierite-type structure. The dependence of luminescent properties on utilized synthesis techniques was studied. The emission spectra of all samples exhibit intense red emission originating from the 5D0 → 7F2 Eu3+ transition. The integrated intensity of the emission from the Eu3+ 5D0 term was found to be the highest in the crystal grown by the CZ technique. The quantum yield measured for KEMO crystals demonstrates a very high value of 66.5%. This fact confirms that KEMO crystals are exceptionally attractive for applications as a near-UV converting red phosphor for LEDs. [ABSTRACT FROM AUTHOR]

This paper reports on a facile hydrothermal route that has been developed to synthesize a precursor Gd(OH)2.14F0.86 and a novel phosphor host Gd6O5F8. The morphology of the micro-sized Gd(OH)2.14F0.86/Gd6O5F8 can be easily tuned in a controlled manner by altering the fluorine sources, alkali solutions, reaction time and the pH values of the initial solution. Under ultraviolet (UV) light, vacuum ultraviolet (VUV) light and low-voltage electron beam excitation, the Gd(OH)2.14F0.86/Gd6O5F8:Ln3+ (Eu, Tb and Tm) samples show the characteristic f–f transitions of the Ln3+ ions and give bright red, green and blue emissions, respectively. The results prove that the as-synthesized Gd6O5F8 are excellent host lattices for rare earth luminescence, which may find potential applications in solid-state light, field emission displays (FEDs). [ABSTRACT FROM AUTHOR]

The article presents cover arts for a journal based on the two different topics of chemical Science experiments where the images are presented by Professor Jerry L. Atwood and Dr. Didier Pribat. It also includes a table of contents of the journal with topics including the study of Metal–organic frameworks of luminescent substances to gain nitroaromatics sensing and a synthesis on solar cells without electrodes and contains respective names of the editorial staff and editorial board members.

This paper reports on a facile hydrothermal route that has been developed to synthesize a precursor Gd(OH)2.14F0.86 and a novel phosphor host Gd6O5F8. The morphology of the micro-sized Gd(OH)2.14F0.86/Gd6O5F8 can be easily tuned in a controlled manner by altering the fluorine sources, alkali solutions, reaction time and the pH values of the initial solution. Under ultraviolet (UV) light, vacuum ultraviolet (VUV) light and low-voltage electron beam excitation, the Gd(OH)2.14F0.86/Gd6O5F8:Ln3+ (Eu, Tb and Tm) samples show the characteristic f–f transitions of the Ln3+ ions and give bright red, green and blue emissions, respectively. The results prove that the as-synthesized Gd6O5F8 are excellent host lattices for rare earth luminescence, which may find potential applications in solid-state light, field emission displays (FEDs). [ABSTRACT FROM AUTHOR]

This work begins with a study of the synthesis of multi-color luminescence phosphors, which is followed by a discussion of the temperature sensitivity of AgBi(MoO4)2:Yb3+/Er3+. Uniform and approximately spherical particles of AgBi(MoO4)2-based phosphors were prepared by a simple one-step hydrothermal method without adding any surfactant. We obtained a series of rich green, yellow, blue, and white luminescence phosphors by doping Ln3+ (Ln3+ = Yb3+, Er3+, Ho3+, Tm3+) into the AgBi(MoO4)2 matrix, and an analysis of various correlative factors was made, especially for the amounts of doping ions. Furthermore, the investigation of the temperature sensitivity of AgBi(MoO4)2:Yb3+/Er3+ revealed that the fluorescence intensity becomes lower with increasing temperature from 323 to 573 K. The fluorescence intensity ratio (FIR) of the two thermal coupling energy levels (2H11/2, 4S3/2) of Er3+ was calculated, and the absolute sensitivity of the obtained phosphor reached a maximum value of 1.32% K−1 at 463 K, as obtained by fitting the FIR as a function of temperature, which is a relatively high level compared with other related materials. This material is expected to be used as a highly sensitive FIR thermometer. [ABSTRACT FROM AUTHOR]

Here we constructed a series of novel non-centrosymmetric structure phosphors [Rb2Zn3(P2O7)2:Mn2+] by a high-temperature solid-state reaction. The multiband emission can be designed by Mn2+ preferentially occupying three types of crystallographic sites in Rb2Zn3(P2O7)2:Mn2+. The emission color could be continuously tuned from yellow-green to orange-red via multiple synergies among crystallographic site engineering, energy transfer, and Mn–Mn dimmers alone through the dopant concentration. These color-tunable phosphors have good thermal stability (I150 °C/I25 °C = 91%). The as-prepared pc-WLED has a low corresponding color temperature (CCT = 4820 K) and a high color rendering index (Ra = 90.4) with CIE color coordinates of (0.351, 0.358). These results show that emission-tunable Rb2Zn3(P2O7)2:xMn2+ phosphors are potential candidates for application in n-UV-based pc-WLED devices. This study offers a new insight for wide-range tuning of PL properties by using crystallographic site engineering through changing the doping level in Mn-activated phosphors. [ABSTRACT FROM AUTHOR]

The (NH4)3Sc(SO4)3:0.005Eu3+ phosphor has been synthesized as rod-like microparticles by crystallization from an aqueous solution. Its crystal structure belongs to the monoclinic system, space group P211/C, = 4. An enantiotropic first-order phase transition from monoclinic to high-temperature rhombohedral structure (space group R3c) occurs at 350--355 K and compound decomposition begins only above 573 K. Under 248 nm excitation, the compound exhibits luminescence corresponding to the characteristic 5D0 → 7F2 transitions in Eu3+ ions. The absence of an inversion center in the sites occupied by Eu3+ causes a high intensity of spectral lines at 602--642 nm associated with hypersensitive induced electric dipole 5D0 → 7F2 transitions. Heating of the (NH4)3Sc(SO4)3:0.005Eu3+ sample to a temperature of 393 K is accompanied by considerable distortion of the Eu3+ coordination by the phase transition, manifesting a gradual increase in the asymmetry ratio ( ) between the integral intensities of the lines at 602--642 nm (5 D4 → 7F2 transition) and at 581--602 nm (5 D0 → 7F1). When the heating is suppressed, the level returns to the original value, confirming the reversibility of the structural transformation. A good reproducibility of the obtained values has been revealed during 4-fold thermal cycling. [ABSTRACT FROM AUTHOR]

In this work, a series of Dy3+-doped, Tm3+-doped, and Dy3+/Tm3+ co-doped NaGd(MoO4)2 (NGM) phosphors were successfully prepared via a high-temperature solid-state method. The crystal structure, band structure, elemental composition, and photoluminescence (PL) properties were investigated in detail. These crystals showed a tetragonal structure with the space group I41/a (88), which endowed NGM with excellent chemical and thermal stability. The positions of the diffraction peaks of the doped samples were slightly righted shift, indicating that the Dy3+ and Tm3+ ions occupied the position of the Gd3+ ions. The photoluminescence results showed that bright white light emission could be achieved by adjusting the excitation wavelength or controlling the ratio of the Dy3+ and Tm3+ ions concentration. The obtained optimal chromaticity coordinate (0.3334, 0.3310) for the NGM: 0.06Dy3+, 0.12Tm3+ phosphor was very close to the standard white light (0.333, 0.333) coordinate under near-ultraviolet (364 nm) excitation. Additionally, the temperature-dependent spectra were also investigated, which indicated that this phosphor has excellent thermal stability under 423 K. In conclusion, Dy3+/Tm3+ co-doped NGM has potential for application in white LEDs. [ABSTRACT FROM AUTHOR]

Broadband near-infrared (NIR) luminescent materials have recently attracted significant attention as advanced smart optical sources for NIR spectroscopy. In this work, a broadband NIR emission from 650 nm to 950 nm with a full width at half maximum up to 160 nm was acquired in a Cr3+-activated Li3Mg2NbO6 phosphor under blue excitation. Based on the structural simulation and spectral characteristic analysis, this broad spectrum is inferred to be composed of emissions from Cr3+ substituting three different crystallographic sites with different crystal field environments. The temperature-dependent luminescence properties of Li3Mg2NbO6:Cr3+ were revealed to be multiple thermal processes related to the multi-site occupation behaviors of Cr3+ ions in the host. A 10 mW NIR output was achieved from the phosphor-converted LEDs fabricated by the as-prepared Li3Mg2NbO6:Cr3+ phosphor and blue InGaN chip. The obtained results have offered significant insight into exploring novel transition metal ion-based broadband NIR materials for phosphor-converted LEDs. [ABSTRACT FROM AUTHOR]

In this work, multi-component fluoride phosphors BaxNay-nMnYzF2x+y+3Z+3m : Er3+ m (M = Li and K) sensitive to 1550 nm were synthesized by the low-temperature combustion synthesis (LCS) method. The optimum batch formula was determined by orthogonal experiments. The effects of introducing alkali ions (Li+, K+) on phase formation and luminescence intensity were systematically studied. The results indicate that the luminescence intensity of 0.2 mol% Li+ ions entering the lattice gap that changes the local symmetry of Er3+ ions. The phase composition and morphology of phosphors were analyzed by X-ray diffraction and scanning electron microscopy (SEM). The product exhibited Er+ ions entering the lattice gap that changes the local symmetry of Er3+ ions. The phase composition and morphology of phosphors were analyzed by X-ray diffraction and scanning electron microscopy (SEM). The product exhibited Er3+ ion characteristic emission under 1550 nm excitation, and its luminescence mechanism was studied. This work provides a new idea for improving the luminescence intensity of up-conversion luminescent materials (UCL) under 1.5 µm excitation. [ABSTRACT FROM AUTHOR]

Mg–CaCO3:Eu3+ phosphors with various initial magnesium ion concentrations were successfully synthesized by a simple carbonation method without using any surfactant, catalyst, or template. It was shown that the different contents of magnesium ions in calcite play a crucial role in the morphology, structure, and luminescence properties. The morphologies of Mg–CaCO3:Eu3+ phosphors could be varied from spindle, dendritic, coral-like, and micron-flower-like to finally club-like by adjusting the initial magnesium ion mole percentage. The modified titration experiment indicated that not all magnesium ions had lattice substitutions. In addition, the photoluminescent properties and lifetimes of Eu3+ ions changed with the morphological and structural changes of the Mg–CaCO3:Eu3+ crystal, which was analyzed by Judd–Ofelt theory. Furthermore, temperature was also found to be a significant factor in the variation of the properties of Mg–CaCO3:Eu3+ phosphors. Finally, a crystal structure ball-and-stick model of Mg–CaCO3:Eu3+ phosphors was built and the possible mechanism of action was analyzed. This study provides an idea for the preparation of new hetero-ion phosphors. [ABSTRACT FROM AUTHOR]

Two-dimensional all-inorganic halide perovskites (CsPbX3, X = Cl, Br or I) have emerged as prominent materials due to their unique properties, including ultrathin thickness in high surface area for catalysis, good mechanical flexibility for flexible electronics/optoelectronics, and high charge extraction and transport for photodetectors. However, the high luminescence of two-dimensional Mn-doped CsPbX3 that is crucial to light-emitting diodes and display applications remains unfulfilled. The existing synthesis approaches of two-dimensional Mn-doped CsPbX3 usually result in low luminescence because of either low solubility of precursors at low temperature or high concentrated nanocubes at high temperature (e.g. 180 °C). Herein, we report a moderate-temperature and atmospheric approach to synthesize highly luminescent Mn-doped CsPbCl3 nanoplatelets with only 4 monolayers. Different Mn–Pb feed ratios are explored to study the morphology evolution from nanocubes to nanoplatelets and the corresponding influence of two emission peaks at around 400 nm and 600 nm. The photoluminescence quantum yield (PLQY) of our Mn-doped CsPbCl3 nanoplatelets is up to 53.76%, which is the highest reported value in Mn-doped two-dimensional all-inorganic halide perovskites. The nanoplatelets exhibit excellent stability at room temperature in air (over 60 days). For the first time, both orange-red and warm white light-emitting diodes (LEDs) have been achieved through the nanoplatelets as the color conversion materials. Moreover, flexible composite fluorescent polymer films based on the nanoplatelets are demonstrated with high luminescence and stability (over 6 months), which indicate prominent potential in flexible displays. [ABSTRACT FROM AUTHOR]

The microscopic, short-range coordination environments and mesoscopic, long-range structures of Eu3+ in contact with tetra-n-octyl diglycolamide (TODGA) confined on ordered mesoporous carbon (OMC) nanoparticles and Amberchrom CG-71 resin were probed using Eu L3-edge extended X-ray absorption fine structure (EXAFS) as well as small-angle and wide-angle X-ray scattering, SAXS and WAXS, respectively. A homoleptic Eu(TODGA)33+ coordination complex typical of liquid–liquid extraction (LLE) chemistry is present under low Eu3+ loading conditions on both solid supports. Deviations from this traditional structure motif appear at hyperstoichiometric Eu3+ loadings, above the 1 : 3 Eu3+ to TODGA mole ratio. Microcrystalline-like domains with multinuclear Eu speciation are templated by use of these high Eu3+ loading conditions with the functionalized OMC materials, highlighting a major departure of liquid–solid extraction chromatography (EXC) from the coordination chemistry of LLE. No such long-range spatial coherence was observed for analogous polyacrylic resin materials. These results demonstrate both the similarities and differences between multiscale structures in LLE and EXC, underscoring the opportunities for improved separation techniques based on solid supports with long-range spatial coherence (e.g., OMC systems) and without it (e.g., resin materials). Since crystallization was the first approach to adjacent lanthanide separations, the prospect of templating microcrystalline TODGA–lanthanide complexes that are otherwise not prone to crystallization by use of OMC nanoparticles represents a new entry to addressing long-standing issues in purification by liquid–solid phase separation. [ABSTRACT FROM AUTHOR]

In this work, the Eu(III) and Sm(III) coordination polymers {[Eu(2-stp)2(H2O)6]·2(4,4′-bipy)·4(H2O)}, denoted as (1), and {[Sm(2-stp)2(H2O)2]·2(4,4′-bipy)·5(H2O)}n, denoted as (2), (2-stp = 2-sulfoterephthalate and 4,4′-bipy = 4,4′-bipyridine) were synthesized. Different concentrations of these complexes were combined with the polymer matrix of poly(methylmethacrylate) (PMMA) via the electrospinning technology to form a series of Eu@PMMA and Sm@PMMA nanofibers. The morphology, structure, luminescence and magnetic properties of the synthesized materials were investigated by a variety of techniques. The results indicated that the photostability and thermal stability of the composite nanofibers were greatly improved because the PMMA provided a solid environment for the complexes. Moreover, as the incorporation of complexes into PMMA increased, the luminescence intensities were significantly enriched and the emission color coordinates changed with the concentration of the complexes in the PMMA substrate. Color tunability was achieved with the luminescence changing from reddish orange in the bulk state to near-white light in nanofiber stage. [ABSTRACT FROM AUTHOR]

Eu3+-Doped Ba3In(PO4)3 was synthesized through a high-temperature solid-phase method. According to the structure refinement based on X-ray diffraction and density functional theory, the crystal and energy band structures of Ba3In(1−x)(PO4)3:xEu3+ were studied and analyzed in detail. The effect of Eu3+ doping concentrations on emission was studied at an excitation wavelength of 393 nm. For the material Ba3In(1−x)(PO4)3:xEu3+(x = 0.01–0.30), the optimal doping level is confirmed to be 0.18. Due to the thermal quenching differences of Eu3+ at the 5D0 and 5D1 energy levels, and based on the temperature-variable fluorescence intensity ratio between emission peaks, the optical temperature measurement performance of this material in the temperature range from 298.15 K to 623.15 K was characterized, and the maximum absolute and relative sensor sensitivities (Sa and Sr) were determined to be 0.1002 K−1 and 4.058%, respectively. With temperature as the only variable, the color of the phosphor changes from red to yellow light with rising temperature. Besides, Sa and Sr values of this phosphor are comparable to other sensing materials. The results indicate that Eu3+-doped Ba3In(PO4)3 phosphors have great potential to be applied in optical temperature sensing. [ABSTRACT FROM AUTHOR]

Eu3+/Tb3+ codoped phosphors usually present multi-color emitting performances ranging from green and yellow to red, which not only have theoretical but also practical significance. In this work, we prepared a new langbeinite-type compound, K2TbHf(PO4)3, determined its structure via single-crystal X-ray diffraction, and prepared solid solutions of K2Tb1−xEuxHf(PO4)3 (x = 0–1) with multi-color emitting properties. The structure of the solid solutions was refined by the Rietveld method, showing a constant lattice structure with a change in Eu3+ concentration from 0 to 100%. For the typical sample, K2Tb0.99Eu0.01Hf(PO4)3, both Tb3+ and Eu3+ emission peaks were observed upon excitation by near ultraviolet light of 378 nm, whereas only the characteristic peaks of Eu3+ were observed when the excitation source was 393 nm. This suggests that the energy transfer from Tb3+ to Eu3+ occurred, but not the reverse transfer. The emitting color of K2Tb1−xEuxHf(PO4)3 could change from green and yellow to red by simply modulating the concentration of Eu3+. Meanwhile, the temperature-dependent analysis proved the high thermal stability of the prepared phosphor. Finally, green, yellow, and red near-ultraviolet pumped LEDs were fabricated using three typical phosphors with x = 0, 0.005, and 0.10, respectively. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) have become one of the first choices in the field of lighting due to their unique advantages. In the traditional system of near-ultraviolet (NUV) chips combined with blue/green/red-emitting phosphors, the partial absence of a blue-green cavity makes it difficult to achieve full-spectrum emission. Accordingly, cyan-emitting phosphors can effectively compensate for this missing part. Therefore, it is necessary and urgent to explore the cyan-emitting phosphor with excellent luminous performance. Herein, we have designed and prepared a novel cyan-emitting borosilicate phosphor Ba3Ca4(BO3)3(SiO4)Cl:xEu2+ (BCBS:xEu2+). Its crystal structure was determined by powder X-ray diffraction and Rietveld methods. The BCBS:xEu2+ phosphors have a wide excitation band covering the UV-NUV region and can emit a broad cyan light. The emission peaks at 488 nm have a large full width at half maximum (FWHM) of 118 nm, excited by 350 nm. There are three different Eu2+ luminescence centers in BCBS:xEu2+, which are determined by analyzing the structure and decay curves. The optimal concentration was x = 0.04 and the quantum efficiency of the BCBS:0.04Eu2+ sample was 31.2%. In addition, by combining BCBS:Eu2+, Sr2SiO4:Eu2+ and (Ca,Sr)AlSiN3:Eu2+ phosphors with a 395 nm NUV chip, a WLED lamp was obtained. The emitted white light can display excellent performances of CIE = (0.3655, 0.3641), CCT = 4337 K and CRI = 90.1. All the results demonstrate that the BCBS:Eu2+ phosphors have potential applications in full-visible-spectrum lighting. [ABSTRACT FROM AUTHOR]

Lactic acid (LA) was originally employed as a cosolvent for solvothermal synthesis of LaPO4:Ce3+, Tb3+, Sm3+ nanocrystal phosphors, whose effect on crystal growth was revealed by the combined techniques XRD, FE-SEM and TEM. It was shown that LA not only remarkably restricted the intrinsic one-dimensional (1D) growth of hexagonal LaPO4 crystals along the [001] direction, resulting in a shape variation from microwires to nanoparticles, but also promoted crystallite growth. With more efficient Ce3+ → Tb3+ energy transfer resulting from larger crystallite size, the h-(La0.90Ce0.05Tb0.05)PO4 nanoparticles presented more intense and thermally stable green emission of Tb3+ as compared to the nanowires. Moreover, a series of (La0.93−xCe0.05TbxSm0.02)PO4 (x = 0–0.40) nanocrystals, with the emission color varying from blue to green and eventually to yellow, were successfully prepared through adjusting the concentration of Tb3+, in which the Tb3+ ion acted as an energy transfer bridge between Ce3+ and Sm3+. The mechanism of Ce3+ → Tb3+ → Sm3+ energy transfer was proposed, and the optimal Tb3+ content for Sm3+ emission was determined to be x = 0.20. The optimized (La0.73Ce0.05Tb0.20Sm0.02)PO4 phosphor exhibited good thermal stability for Sm3+ emission, whose activation energy for thermal quenching was found to be ∼0.33 eV. [ABSTRACT FROM AUTHOR]

Pure hexagonal phase KSc(MoO4)2 crystals with a hexagonal block shape were successfully synthesized via a one-step hydrothermal method. It was confirmed that neutral conditions were the most favorable for the crystal growth by manipulating the pH environment of the reaction mixture. The process of doping Ln3+ (Ln = Yb, Er, Tm, Ho) into the KSc(MoO4)2 matrix required the assistance of citric acid. The up-conversion photoluminescence properties and mechanism of KSc(MoO4)2: Ln3+ phosphors were investigated with an excitation of 980 nm single-wavelength diode laser, and the energy transfers Yb3+ → Er3+/Ho3+ and Yb3+ → Tm3+ were two and three photon processes, respectively. Since the red light emission of Er3+ in KSc(MoO4)2 was basically negligible, the tri-doping of Yb3+, Ho3+ and Tm3+ was selected to achieve white light adjustment. The blue emission at 478 nm due to the 1 G4 → ³ H6 transition of Tm3+ and the green/red emission at 540/660 nm from the 5 S2, 5 F4 → 5 I8/ 5 F5 → 5 F8 transitions of Ho3+ were observed in the KSc(MoO4)2:Yb3+, Ho3+, Tm3+ phosphors. Based on the RGB (primary colors of light), multicolor, especially white (CIE: x = 0.3424 and y = 0.3517), light can be obtained by adjusting the relative ratios of the doped ions. The assynthesized phosphors might have a potential application value in many fields such as multicolor imaging, data storage and fluorescence coding. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) to visible upconversion (UC) luminescence in activator Er3+ and sensitizer Yb3+ codoped systems has been extensively studied. In this work, we report the results of Er3+-sensitized Yb3+ NIR UC emission at ∼1000 nm originating from 2F5/2 → 2F7/2 transition under infrared (IR) excitation at ∼1500 nm responsible for Er3+ 4I15/2 → 4I13/2 transition absorption. The IR to NIR UC is a desirable strategy to increase solar light utilization by reducing the spectral mismatch between the solar spectrum and crystalline silicon (c-Si) solar cells. Er3+ singly doped phosphors are mostly used for realizing the IR to NIR UC emission derived from Er3+ 4I11/2 → 4I15/2 transition centered also at ∼1000 nm. The efficiency of this transition, however, is limited by multiphonon relaxation and radiative transition to the 4I13/2 state. Here, Yb3+ ions are codoped in Y2O3:Er3+, and NIR UC emission with the intensity enhanced 1.5 times is achieved due to efficient energy transfer from Er3+ to Yb3+ and highly efficient Yb3+ emission. The influence of the dopants' concentrations on UC dynamics is studied. The optimal concentration under IR excitation is 5% Er3+ and 1% Yb3+. Our results indicate that introducing Yb3+ ions in Er3+ singly doped phosphors may notably improve the IR to NIR UC performance. [ABSTRACT FROM AUTHOR]

Si3N4:Al microbelts with tunable bandgap energy and resultant yellow-orange phosphors are prepared through a facile direct nitridation method. The bandgap energy of Si3N4:Al microbelts has been gradually trimmed from 2.58 eV to 2.67, 2.74 and 2.85 eV by regulating the Si/Al molar ratio from 1000 : 1 to 50 : 1. Si3N4:Al:Eu phosphors display a wide emission ranging from 500 to 800 nm when excited by a 450 nm blue LED light source. The crystal structure of Si3N4:Al microbelts is of the α-Si3N4 phase as characterized by X-ray diffraction, high-resolution TEM and crystal models. Si3N4:Al microbelts grow along the (012) stacking direction in a low doping concentration case and grow along the (011) stacking direction in a high doping concentration case. Theoretical calculation results show that Al prefers to occupy the low energy interstitial sites in the (012) plane. There are more substitutional sites in the (011) plane occupied by Al in the high doping concentration case with increasing the bandgap energy of Si3N4:Al. Warm white light emission has been achieved by precoating Si3N4:Al:Eu phosphors onto a blue LED chip, whose correlated color temperature (CCT) can be tailored from 3000 K to 6500 K by altering the phosphor amount, indicating a promising potential application of Si3N4:Al:Eu phosphors in warm white LEDs. [ABSTRACT FROM AUTHOR]

This study describes the influence of annealing temperature on the structure and luminescence properties of KGd1−xEux(MoO4)2 (0 ≤ x ≤ 1). Compounds with the general formula (A′, A′′)n[(W, Mo)O4]m are investigated as luminescent materials for photonic applications such as phosphor-converted LEDs (light-emitting diodes). Herein, the KGd0.8Eu0.2(MoO4)2 light-rose crystal was grown by the Czochralski technique. Moreover, three polymorphs of KGd1−xEux(MoO4)2 were present in the 923–1223 K range of annealing temperatures under ambient pressure: a triclinic α-phase, a disproportionately modulated monoclinic β-phase and an orthorhombic γ-phase with a KY(MoO4)2-type structure. The different behaviors of KGd(MoO4)2 and KEu(MoO4)2 were revealed by DSC studies. The number and the character of phase transitions for KGd1−xEux(MoO4)2 depended on the elemental composition. The formation of a continuous range of solid solutions with the triclinic α-KEu(MoO4)2-type structure and ordering of K+ and Eu3+/Gd3+ cations were observed only for α-KGd1−xEux(MoO4)2 (0 ≤ x ≤ 1) prepared at 923 K. The structures of γ-KGd1−xEux(MoO4)2 (x = 0 and 0.2) were studied using electron diffraction and refined using the powder X-ray diffraction data. The luminescence properties of KGd1−xEux(MoO4)2 prepared at different annealing temperatures were studied and related to their different structures. The maxima of the 5D0 → 7F2 integral emission intensities were found under excitation at λex = 300 nm and λex = 395 nm for triclinic scheelite-type α-KGd0.6Eu0.4(MoO4)2 and monoclinic scheelite-type β-KGd0.4Eu0.6(MoO4)2 prepared at 1173 K, respectively. The latter shows the brightest red light emission among the KGd1−xEux(MoO4)2 phosphors. The maximum and integral emission intensity of β-KGd0.4Eu0.6(MoO4)2 in the 5D0 → 7F2 transition region is ∼20% higher than that of the commercially used red phosphor Gd2O2S:Eu3+. Thus, β-KGd0.4Eu0.6(MoO4)2 is very attractive for application as a near-UV convertible red-emitting phosphor for LEDs. [ABSTRACT FROM AUTHOR]

Novel La8Ba2(Si4P2O22N2)O2:Eu2+/Ce3+/Tb3+ apatite phosphors with tuneable light emission have been successfully synthesized by the conventional solid-state method. The structural and luminescence properties of the newly obtained samples have been studied systematically. The photoluminescence properties show that the Eu2+-, Ce3+- and Tb3+-doped La8Ba2(Si4P2O22N2)O2 samples have strong absorption in the near ultraviolet (n-UV) region. Under n-UV light irradiation, Eu2+-doped samples exhibit a narrow bluish green emission band peaking at 496 nm with a full width at half-maximum (FWHM) of 55 nm, which is comparable to the commercial blue emitting BaMgAl10O17:Eu2+ (FWHM = 55 nm) phosphor, while La8Ba2(Si4P2O22N2)O2:Ce3+,Tb3+ presents adjustable emission colour from violet to green by adjusting the concentration of Tb3+. The energy-transfer efficiencies and mechanisms have been discussed in detail. The temperature dependent luminescence measurements show that the obtained samples have low thermal quenching. Moreover, a series of white LED devices have been obtained by using the La8Ba1.99(Si4P2O22N2)O2:0.01Eu2+/(Sr,Ca)AlSiN3:Eu2+/(Ba,Sr)SiO4:Eu2+/(Sr,Ba,Ca)10(PO4)Cl2:Eu2+/Sr2SiO4:Eu2+ phosphor blend. By adding the as-prepared narrow bluish-green-emitting La8Ba1.99(Si4P2O22N2)O2:0.01Eu2+ phosphor, the Ra values can increase from 68 to 98, the R9 values increase from 42 to 95, and the corresponding CCT continuously decreases from 6210 to 3086 K, respectively. Our results reveal that the Eu2+, Ce3+ and Tb3+ activated phosphors are promising candidates for WLEDs. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) have been considered as the next generation lighting technology due to their advantages such as high efficiency and environmental friendliness. However, current mainstream WLEDs, which are based on blue chips and the Y3Al5O12:Ce3+ yellow phosphor, suffer from the problem of low color rendering index (CRI). To solve this problem, a yellowish-green phosphor Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ (CYAS:Ce3+) based on the garnet structure has been designed in this study. Its crystal structure, band structure, and luminescence properties have been investigated in detail. CYAS:Ce3+ exhibits efficient and thermal-stable yellowish-green emission. The 5d centroid shift and crystal splitting of the Ce3+ ion in CYAS have been analyzed together with the structure. Moreover, good warm white light with a low correlated color temperature (3210 K), high color rendering index (85.1) and luminous efficacy (88.5 lm W−1) has been obtained by combining CYAS:Ce3+ and the red phosphor CaAlSiN3:Eu2+ with a blue LED chip. [ABSTRACT FROM AUTHOR]

A narrow-band green-emitting phosphor ZnB2O4:Mn2+, Mg2+ was prepared by solid-state reactions. X-ray diffraction (XRD) and the Rietveld structural refinements were performed. The results show that the introduction of Mg2+ may suppress the formation of an impurity phase. The micro-structure, photoluminescence (PL) and reflectance spectra, PL decay curves as well as thermal quenching behavior were investigated. The phosphors exhibit a broad absorption band from 200 to 510 nm, while the emission spectra show a narrow band centered at 538 nm with a full-width at half-maximum (FWHM) of about 34 nm. Furthermore, after the introduction of Mg2+, the luminescence intensity of phosphor ZnB2O4:0.07Mn2+, 0.10Mg2+ is significantly enhanced by about 2 times, and it presents a relatively low thermal quenching behavior. The corresponding mechanisms for performance improvement were investigated in detail and the ion-size compensation effect of Mg2+ to Mn2+ is proposed. Additionally, the high activation energy (0.202 eV) and ultra-high color purity (97%) were calculated. These results imply that the ZnB2O4:Mn2+, Mg2+ phosphor has broad application prospects in the field of advanced backlight display. Moreover, the introduction of Mg2+ may be useful as an effective strategy to enhance the luminescence properties and thermal stability of Mn2+ or even other element-doped phosphors. [ABSTRACT FROM AUTHOR]

Ca9−xMgxEu(PO4)7 solid solution with a β-Ca3(PO4)2-type (β-TCP) structure was obtained using a solid-state technique and studied by X-ray diffraction, and luminescence and dielectric spectroscopy. The luminescent properties were measured, and the optical properties were related to the structural properties of the material. The number of bands for the 5D0 → 7F0 transition in the emission spectra depended on the cationic composition. Detailed investigation of the 5D0 → 7F0 transition of Eu3+ in the host lattice revealed changes in the number of Shtark components and, thus, europium-occupied sites in the structure. This data, in conjunction with the dielectric loss tangent (tan δ), indicate the appearance of the center of symmetry with increasing magnesium concentration up to 1. The analysis of different approaches allowed the establishment of three compositional areas in Ca9−xMgxEu(PO4)7 solid solution: 0 ≤ x ≤ 0.5 (R3c, ferroelectric phase), 0.5 < x < 0.8 (R3c + R3¯c), and 0.8 ≤ x ≤ 1.0 (R3¯c, antiferroelectric phase). The X-ray diffraction method does not allow these phases to be distinguished. It was found that magnesium cations have a significant effect on the luminescent properties of Ca9−xMgxEu(PO4)7 solid solution. The present research reveals that Eu3+ emission luminescence spectroscopy can be used as a method for the determination of the symmetry of crystalline phases that are very similar in structure. [ABSTRACT FROM AUTHOR]

The appearance of a cyan cavity is unavoidable in the 480–520 nm wavebands when combining n-UV LED chips (380–420 nm) with trichromatic phosphors to obtain white-light-emitting devices. Here, a concentration perturbation effect is proposed to improve the properties of phosphors via trace substitution of Mn2+, Mg2+ or Zn2+ cations for Ba2+ and Y3+ in Ba0.97Y2Si3O10:Eu. Based on local structure distortion or electron cloud interaction, the emission band corresponding to Eu2+ is broadened with a full width at half maximum (FWHM) more than 125 nm due to redistribution of Eu2+ and the emission color can be tuned to the cyan region. The coexistence of the above two effects on the photoluminescence can be further evidenced by the shifts of emission energy for the two sites in these systems. The quenching temperature for all the samples is observed over 473 K and even higher than that for the non-substituted Ba0.97Y2Si3O10:0.03Eu and it is discussed combined with Pauling's principles, average Uiso and the distortion degree of polyhedra, which could provide some references for improvement of thermal stability. Moreover, the valence mismatch between Mn2+/Mg2+/Zn2+ and Y3+ ions leads to the coexistence of Eu2+–Eu3+, which thus realizes color selective manipulation and even white light emission in Ba0.98−nMg0.02Y2Si3O10:nEu. Our results demonstrate that the concentration perturbation effect-assisted synthesis strategy has potential in improving the properties of phosphors for WLEDs, and it can also be extended to adjusting the coordination environment of activators whose properties are sensitive to local lattice variations and electronic surroundings. [ABSTRACT FROM AUTHOR]

A series of Ce-doped YAG-Al2O3 eutectics were grown by the micro-pulling-down (μ-PD) method, for the purpose of high power white light emitting diodes. The eutectic structure was investigated. A calibrated integrating sphere spectrometer setup was used to measure the white LED properties of eutectic samples. The CIE color coordinates can be regulated easily by altering the Ce3+ doping concentration and sample thickness of the Ce:YAG-Al2O3 eutectics. A 1 W white LED device based on Ce:YAG-Al2O3 eutectics at a rated current of 350 mA emitted a bright white light with a CIE coordinate of (0.319, 0.334), a luminous efficacy of 83.0 lm W−1 and a Duv value of 0.003. The results showed that Ce:YAG-Al2O3 eutectics have better luminescence properties than commercial powder phosphors at a high current density. [ABSTRACT FROM AUTHOR]

A novel silicate-based phosphor Ba5SiO4Cl6:Eu2+ (BSOC:Eu2+) was successfully designed and investigated through the solid-state method. The crystal structure, band structure, photoluminescence and cathodoluminescence characteristics were investigated in detail. Under excitation at 345 nm, a narrow blue emission band with a peak at 440 nm (FWHM ∼ 32 nm) could be observed. Moreover, BSOC:Eu2+ showed higher color purity when compared with a commercial BAM phosphor. Under sustained low-voltage electron-beam excitation, the BSOC:Eu2+ phosphor exhibited blue emission with distinguished degradation resistance and perfect colour stability. By combining the BSOC:Eu2+ blue phosphor with green and red phosphors and an n-UV chip, a pc-WLED with a high color rendering index and low correlated color temperature was obtained. The results show that the BSOC:Eu2+ phosphor has wide application prospects in n-UV LED applications and FED devices. [ABSTRACT FROM AUTHOR]

Non-rare earth doped oxides with red emission are one of the current research hotspots for achieving the warm white light range in the phosphor converted white light emitting diodes (pc-WLEDs) field. In the current work, a novel Mn4+-activated La2CaHfO6 red phosphor is reported for the first time and its crystal structure is analyzed by Rietveld refinement. The photoluminescent properties of La2CaHfO6:Mn4+ are investigated in detail with the help of diffuse refletance spectroscopy, photoluminescence spectroscopy, and temperature-dependent PL spectroscopy. Based on the diffuse refletance spectra, the calculated optical band gap for La2CaHfO6 is 4.9 eV, indicating that La2CaHfO6 could be a suitable host for activators' doping. Under 380 nm near-ultraviolet (n-UV) light excitation, the as-prepared La2CaHfO6:Mn4+ displays intense red emission centered at 693 nm. Through an accurate calculation of Dq/B (2.47) and nephelauxetic effect β1 (0.949), the origination of strong crystal field (CF) and deep-red emission is demonstrated. By combining the representative La2CaHfO6:0.002Mn4+, blue BAM:Eu2+, and green (Ba,Sr)2SiO4:Eu2+ phosphors with a 380 nm UV chip to fabricate the pc-WLEDs device, a white light is obtained with low correlated color temperature (CCT = 5165 K) and high color rendering index (Ra = 87.8), demonstrating that the as-prepared La2CaHfO6:Mn4+ phosphors can be used as red-emitting candidate in pc-WLEDs lighting. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) nanostructured metal borates have drawn considerable attention owing to their versatile applications in a multitude of fields, but it is still a great challenge to achieve a high aspect ratio in these materials via a facile and feasible route. Herein, ultralong Ca2B2O5·H2O nanowires with a length of 110–230 μm and ultrahigh aspect ratio of 240–750 are successfully synthesized for the first time via a facile water-bath pretreated eco-friendly hydrothermal technique in the absence of any additives, using low cost CaCl2, H3BO3 and NaOH as the raw materials. The formation mechanism of the ultralong nanowires is studied in detail by varying the process parameters (water-bath and hydrothermal temperature, duration time, etc.). The water-bath treatment plays a key role in the formation of thin hexagonal Ca(OH)2 nanoplates, favoring subsequent conversion to ultralong nanowires with a high aspect ratio. The as-obtained Ca2B2O5·H2O:5.0%RE3+ (rare earth, RE = Eu, Tb) nanophosphors exhibit strong photoluminescence emission and excitation performance, with corresponding Commission Internationale de l'Eclairage (CIE) values determined as (0.635, 0.364) and (0.320, 0.597) within the red and green regions, respectively. This not only suggests that the ultralong Ca2B2O5·H2O nanowires are promising structure- and function-integrated photoluminescent host candidates, but also provides a novel and facile route for the formation of high aspect ratio 1D nanostructures of other metal borates. [ABSTRACT FROM AUTHOR]

Columnar Gd2O3:Eu3+/Tb3+ phosphors were successfully prepared by a solvothermal method and subsequent calcination process. The structure, morphology and luminescence properties of the as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectra. The XRD results indicate that the precursor sample is hexagonal Gd(OH)3 while the calcinated sample is cubic Gd2O3. SEM and TEM images show that both the precursor and the calcined samples are columnar, with lengths of 220 nm and 214 nm and diameters of 130 nm and 126 nm, respectively. The fluorescence spectrum shows that Gd2O3:Eu3+ generates a characteristic red emission when stimulated by ultraviolet light with a wavelength of 250 nm, which corresponds to the 5D0→7F2 transition of Eu3+. Gd2O3:Tb3+ generates a characteristic green emission when stimulated by ultraviolet light with a wavelength of 240 nm, which corresponds to the 5D4→7F5 transition of Tb3+. [ABSTRACT FROM AUTHOR]