PL ) And Excitation Research Articles

Ultra-wideband phosphor Mg2Gd8(SiO4)6O2:Ce3+,Mn2+: Energy transfer and pressure-driven color tuning for potential applications in LEDs and pressure sensors

Energy transfer and pressure-driven color tuning phosphor Mg2Gd8(SiO4)6O2:Ce3+ (MGS:Ce3+), with ultra-wideband spectra was synthesized by high-temperature solid-state method. When the phosphor was excited by ultraviolet light, it emitted a sort of cold near-white light. The photoluminescence emission (PL) and excitation (PLE) spectra, luminescence sites of MGS:Ce3+ had been researched. In order to adjust the light color to achieve the purpose of spectral tuning, two methods had been implemented. The first method was doping Mn2+ into MGS:Ce3+. There was energy transfer from Ce3+ to Mn2+ in such phosphor, and the energy transfer had been researched in detail. After doping with Mn2+, the color coordinates positions and correlated color temperature (CCT) of phosphors were improved obviously. When fixed the concentration of Ce3+ and the doping concentration of Mn2+ is y = 1.0, 2.0 and 3.0, the phosphor can realize the warm white light emission. The second one was applying pressure to MGS:Ce3+, expecting to achieve the above purpose through the red shift of the spectrum. The results showed that the sample could withstand the high pressure of 26.03 GPa. A relatively rare phenomenon of pressure enhancement emission appeared when the pressure was between atmospheric pressure and 3.17 GPa. When the pressure exceeded 3.17 GPa, the luminescence intensity decreased regularly with the increase of pressure and the phosphor showed high pressure sensitivity (dλ / dP ≈ 1.8453 nm GPa−1). What’s more, the sample at compression environment made a significant red-shift about 60 nm of the emission bands. In the process of compression, the color coordinate shows that the light color of phosphor can be adjusted from blue-green light to yellow light region under the excitation of 355 nm. All above results revealed that the convenient synthetic method, effective light color coordinating made the MGS:Ce3+ and MGS:Ce3+,Mn2+ become a potential phosphor for (warm) white light. What’s more, the emission spectra red shift resulting from pressure change made it possible to be a potential optical pressure sensor.

Magnetic and Highly Luminescent Heterostructures of Gd3+/ZnO Conjugated to GCIS/ZnS Quantum Dots for Multimodal Imaging.

In recent years, the use of quantum dots (Qdots) to obtain biological images has attracted attention due to their excellent luminescent properties and the possibility of their association with contrast agents for magnetic resonance imaging (MRI). In this study, Gd3+/ZnO (ZnOGd) were conjugated with Qdots composed of a gadolinium-copper-indium-sulphur core covered with a ZnS shell (GCIS/ZnS Qdots). This conjugation is an innovation that has not yet been described in the literature, and which aims to improve Qdot photoluminescent properties. Structural and morphological Qdots features were obtained by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The photoluminescent properties were examined by emission (PL) and excitation (PLE) spectra. A new ZnOGd and GCIS/ZnS (ZnOGd-GCIS/ZnS) nanomaterial was synthesized with tunable optical properties depending on the ratio between the two native Qdots. A hydrophilic or lipophilic coating, using 3-glycidyloxypropyltrimethoxysilane (GPTMS) or hexadecyltrimethoxysilane (HTMS) on the surface of ZnOGd-GCIS/ZnS Qdots, was carried out before assessing their efficiency as magnetic resonance contrast agents. ZnOGd-GCIS/ZnS had excellent luminescence and MRI properties. The new Qdots developed ZnOGd-GCIS/ZnS, mostly constituted of ZnOGd (75%), which had less cytotoxicity when compared to ZnOGd, as well as greater cellular uptake.

Synthesis red-emitting Ca2LaNbO6:xSm3+ phosphors for good color-rendering-index white-LED devices

In this present work, single Sm3+ ion-activated Ca2LaNbO6 phosphors were successfully synthesized by simplify solid-state reaction method. The X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), elemental mappings, and some other characterizations were presented. The photoluminescence emission (PL) and excitation (PLE) spectra were recorded, and the optimum doping concentration was 5 mol% while the mechanism of concentration quenching was predominant by the diploe-diploe interaction. The optimal Ca2LaNbO6:0.05Sm3+ phosphor exhibited near red region with good thermal stability and lifetime. Eventually, the packaged white-LED device was achieved with a forward current of 300 mA, it could emit a dazzling white light with high CRI value of 86.87, revealing that Ca2LaNbO6: Sm3+ phosphors could be promised for high CRI white communication.

The photoluminescence, thermal properties and tunable color of bright green-emitting Ba3Sc(BO3)3:Ce3+/Tb3+ phosphors via efficient energy transfer

The single-phase Ba3Sc(BO3)3:Ce3+/Tb3+ samples were synthetized via high-temperature solid-state reaction. X-ray diffraction (XRD), Rietveld refinement and transmission electron microscopy (TEM) were used for characterizing the morphology and phase purity of Ba3Sc(BO3)3. The photoluminescence emission (PL) and excitation (PLE) spectra, lifetime decay behavior and thermal stability of the Ba3Sc(BO3)3:Ce3+/Tb3+ phosphors were discussed in detail. Site occupation of Ce3+ ions in Ba2+ and Sc3+ sites were explained through Gaussian fitting and Van Uitert empirical equation. All these properties are closely related to the intrinsic crystallization structure of the Ba3Sc(BO3)3 matrix, which is discussed in detail in this paper. Compared with Ba3Sc(BO3)3:1%Tb3+ sample, the luminous intensity of Tb3+ increased about 3.2 and 4.1 times for Ba3Sc(BO3)3:2%Ce3+,1%Tb3+ monitored at 342 and 313 nm, respectively. Energy transfer (ET) mechanism of Ce3+→Tb3+ were dipole-dipole interactions and quadrupole-quadrupole interactions at Ce3+(1) and Ce3+(2) sites, respectively. The temperature-dependent PL spectra of Ba3Sc(BO3)3: Ce3+,Tb3+ illustrated that this phosphor possesses excellent thermal stability and chromaticity stability. Finally, a white LED device was prepared via the combination of the n-UV chip (365 nm), commercial blue BAM:Eu2+ phosphor, green Ba3Sc(BO3)3:2%Ce3+,6%Tb3+ phosphor and commercial red Sr2Si5N8:Eu2+ phosphor, which showed bright warm-white light. These conclusions proved that the green Ba3Sc(BO3)3:2%Ce3+,6%Tb3+ phosphor is desirable for white LED applications.

Intense red emission via energy transfer from (Ce3+/Eu3+):P2O5+NaF+CaF2+AlF3 glasses for warm light sources

Europium (Eu3+)-doped fluorophosphate (PNCA:P2O5+NaF + CaF2+AlF3) glasses with the addition of cerium (Ce3+) ions were fabricated by the melt-quenching technique to know their ability for the bright red (615 nm) luminescence. The emission (PL) and excitation (PLE) spectra, decay curve measurements as well as energy transfer (ET) process of Ce3+→ Eu3+ were studied in detail. An excitation spectrum related to the 7F0→ 5D2 level of Eu3+ is used to estimate the phonon energy (1121 cm−1) of the title glass host. Under ultraviolet (UV) irradiation of 299 nm, the PL spectra of (Ce3+/Eu3+):PNCA glasses show intense red emission at 615 nm whereas the lifetime decrease with respect to increase of Eu3+ that could support the observed efficient ET from Ce3+ to Eu3+. The ET:Ce3+ →Eu3+ via quadrupole-quadrupole process was confirmed by Reisfeld's approximation and Dexter's ET formula. The ET efficiency (ηET) and critical distance (Rc) were also calculated. Interestingly, the (Ce3+/Eu3+):PNCA glasses showed intense red light emission with low correlated color temperatures and the corresponding color purity reached as great as 99%, indicating its potentiality as a red component for warm light sources.

Synthesis and optical properties of Mn-doped CaWO4 nanoparticles

Pure and Mn-doped calcium tungstate (Mn:CaWO4) nanoparticles (NPs) were synthesized by hydrothermal method which lead to the formation of high quality and narrow sized particles. The concentration of Mn in CaWO4 NPs was varied from 1% to 4% by weight. A distinct peak of Mn (d–d) transition was observed which is actually spin-forbidden but may be allowed due to crystal field effects. Electron spin resonance measurements revealed inclusion of Mn2+ at the substitutional site.. Room temperature photoluminescence emission (PL) and excitation (PLE) spectroscopies were carried out to understand the interactions of sp-d levels. PL spectra revealed the presence of both band-edge (∼450 nm) and Mn2+ related orange luminescence (∼530 nm). Time dependent photoluminescence (TDPL) studies were also carried out where the life time value of 4.3 ms obtained was in accordance with measurement for Mn in other systems. Thus TDPL further strengths the presence of Mn in 2+ state in CaWO4 NPs.

Effect of sintering temperature on luminescence properties of borosilicate matrix blue–green emitting color conversion glass ceramics**Project supported by the Science and Technology Planning Project of Zhejiang Province, China (Grant No. 2018C01046) and Enterprise-funded Latitudinal Research Projects, China (Grant Nos. J2016-141, J2017-171, J2017-293, and J2017-243).

The color conversion glass ceramics which were made of borosilicate matrix co-doped (SrBaSm)Si2O2N2: (Eu3+Ce3+) blue–green phosphors were prepared by two-step method in co-sintering. The change in luminescence properties and the drift of chromaticity coordinates (CIE) of the (SrBaSm)Si2O2N2: (Eu3+Ce3+) blue–green phosphors and the color conversion glass ceramics were studied in the sintering temperature range from 600 °C to 800 °C. The luminous intensity and internal quantum yield (QY) of the blue–green phosphors and glass ceramics decreased with the sintering temperature increasing. When the sintering temperature increased beyond 750 °C, the phosphors and the color conversion glass ceramics almost had no peak in photoluminescence (PL) and excitation (PLE) spectra. The results showed that the blue–green phosphors had poor thermal stability at higher temperature. The lattice structure of the phosphors was destroyed by the glass matrix and the Ce3+ in the phosphors was oxidized to Ce4+, which further caused a decrease in luminescent properties of the color conversion glass ceramics.

Synthesis and luminescence properties of novel NaSCN: xCe3+ phosphor

ABSTRACTThe blue-emitting novel phosphor NaSCN: xCe3+(x = 0.005,0.01,0.02) is reported here for the first time. The synthesis method is simple, time saving, and cost effective. X-ray power diffraction (XRD) analysis confirmed the formation of said phosphor, and SEM images were recorded for the surface morphology. Photoluminescence emission (PL) and excitation (PLE) measurements were also recorded. Variations in emission intensity with the Ce3+concentration were observed and recorded leading to determination of the critical concentration. The concentration quenching observed in this phosphor is due to mainly electric multipole interaction. The CIE1931 color co-ordinates and the critical distance were determined.

Double-site emission of Eu2+ ions in Sr4Al14O25: Eu2+ phosphors for self-calibrated optical thermometry

Eu2+ activated aluminate Sr4Al14O25 with dual-emitting centers were prepared via a solid-state method in a reductive atmosphere. Photoluminescence emission (PL) and excitation (PLE) spectra of phosphor along with the lifetimes were characterized, which confirm the 5d→4f energy transition behavior of Eu2+ between 400 nm and 490 nm emission. The fluorescence intensity ratio of I490 and I400 in the phosphors exhibits remarkable temperature dependence, owing to the diverse thermal quenching behaviors of Eu2+ emission centers. Using the phosphors to perform thermometry, excellent temperature sensitivity is achieved in the temperature range of 293–423 K. The maximum absolute and relative sensitivity are 0.004 K-1 and 0.624% at 373 K, respectively. In particular, the dual-site luminescence of Eu2+ ions can be used as the reference signal and the temperature signal of the fluorescence temperature sensor respectively. It will be helpful to develop a new self-reference optical temperature measurement technology with excellent performance.

Effects of Impurity Doping on the Luminescence Performance of Mn4+-Doped Aluminates with the Magnetoplumbite-Type Structure for Plant Cultivation.

Mn4+ activated LaMgAl11O19 (LMA/Mn4+) with red emitting phosphor was obtained by sintering under air conditioning. The X-ray diffraction pattern Rietveld refinement results reveal that three six-fold coordinated Al sites are substituted by Mn4+ ions. Furthermore, the chemical valence state of manganese in the LMA host was further confirmed through X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Photoluminescence emission (PL) and excitation (PLE) spectra of LMA/Mn4+ as well as the lifetime were measured, and the 663 nm emission is ascribed to the 2Eg→4A2g from the 3d3 electrons in the [MnO6]8− octahedral complex. The emission spectrum matches well with the absorption of phytochrome. Temperature-dependent PL spectra show that the color changes of the phosphor at 420 K are 0.0110 for Δx and −0.0109 for Δy. Moreover, doping Zn2+ and Mg2+ ions in the host enhances the emission intensity of Mn4+ ions. These results highlight the potential of LMA/Mn4+ phosphor for a light-emitting diode (LED) plant lamp.

A new yellow long persistent luminescence phosphor Ca2Al2SiO7:Eu2+,Tm3+ found by co-doping Ln3+ (Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) with Eu2+ in Ca2Al2SiO7 host

A series of Eu2+ doped Ca2Al2SiO7 (CASO) phosphors with or without Ln3+ (Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) co-dopant in the host were synthesized by solid-state reaction method in order to obtain long persistent luminescence (LPL). Their structural and photoluminescent properties were investigated by X-ray powder diffraction (XRD) and photoluminescence emission (PL) and excitation (PLE) spectra in detail. Meanwhile, the decay curve measurements were performed on those phosphors to study their afterglow properties. Among them, the Ca2Al2SiO7:Eu2+,Tm3+ (CASO:Eu,Tm) phosphor yielded a bright LPL in the yellow region with afterglow duration much longer than those of other samples. Its luminescence can be observed by human eye for more than 2 h after shutting down the 365 nm excitation source. Further thermoluminescence (TL) study on CASO:Eu,Tm phosphor indicated that the introduced Tm3+ ions indeed increased substantially the amount of charge carrier traps. A possible explanation were given to illustrate the LPL mechanism of CASO:Eu,Tm based on the experimental results. This work suggests that CASO:Eu,Tm phosphor is a promising yellow-emitting LPL phosphor.

Eu3+-doped highly thermal-stable barium yttrium aluminate as a red-emitting phosphor for UV based white LED

A series of novel Eu3+ activated aluminate Ba2Y1−xEuxAlO5 (x = 0.02–0.40) red-emitting phosphors were synthesized through a high-temperature solid-state route at 1380 °C. The phosphors were well crystallized in the space group P21/c (No. 14). Their photoluminescence emission (PL) and excitation (PLE) spectra were investigated. The results indicate that the Ba2YAlO5:Eu3+ phosphor can be excited effectively under 394 nm irradiation, which is suitable for UV LED chip. The obtained Ba2YAlO5:Eu3+ phosphor shows four peaks, corresponding to the 5D0–7FJ (J = 0, 1, 2, 3 and 4) transitions of Eu3+ upon 394 nm excitation. The optimal doping concentration of Eu3+ in Ba2YAlO5:xEu3+ was determined at 30 mol%. By temperature dependent emission spectra, the quenching temperature for Ba2YAlO5:0.30Eu3+ was found to be over 500 K. And the CIE chromaticity coordinates of Ba2YAlO5:0.30Eu3+ are very close to the National Television System Committee (NTSC) standard red.

Effect of sintering temperature on the photoluminescence properties of red-emitting color conversion glass

The red-emitting color conversion glasses were prepared by cosintering borosilicate glass frits and CaAlSiN3:Eu2+ phosphors at various temperatures in the 600–800 °C range. The effect of sintering temperature on the photoluminescence (PL) and excitation (PLE) of the color conversion glasses was investigated. Characteristics of color conversion glasses, with respect to excitation and emission intensity, quantum yield (QY) and CIE (Commission International de I’Eclairage) chromaticity were analyzed based on excitation and emission spectra. The glass, sintered at 600 °C, showed the best luminescence properties. Then, the intensity of excitation and emission peak decreased with the sintering temperature increasing. All excitation and emission peaks disappeared when the sintering temperature increased beyond 800 °C. The luminescence properties with the higher sintering temperature may be destroyed because of the lattice disturbance of CaAlSiN3 and oxidation of Eu2+, which is caused by reactions between glass matrices and CaAlSiN3:Eu2+ phosphors. The present study may promote the application of the red-emitting color conversion glasses in light emitting diodes encapsulation.

(Invited) Laser Sintering of Polycrystalline Ceramic Scintillators: The Case Study of YAG:Ce

Scintillators are sensors used for the detection and measurement of ionizing radiation that find application in numerous strategic fields. Among the many possible scintillator forms, polycrystalline ceramics have received increasing attention due to advantages over single crystals, including faster and lower cost fabrication methods, higher homogeneity of the dopant, greater shape control, and easier fabrication of materials with high melting temperatures. Polycrystalline ceramic scintillators are commonly fabricated by high temperature vacuum sintering [1] and more recently by spark plasma sintering [2,3]. However, additional high-cost processing by means of hot isostatic pressing is many times necessary especially because it has been shown that the use of sintering aids is detrimental to scintillation performance [4]. On the other hand, despite the advantages of extremely short sintering times and high heating rates, laser sintering remains mostly unexplored as a viable method to fabricate these materials. To date, the only polycrystalline ceramic scintillator fabricated by this method was Bi4Ge3O12 (BGO) [5-7]. In this work, the fabrication of Y3Al5O12:Ce (YAG:Ce) polycrystalline ceramic scintillators by laser sintering is evaluated against a Czochralski-grown single crystal in terms of the microstructure characteristics as well as luminescent and scintillating properties. YAG:Ce powders were prepared by a polymeric precursor method using Y(NO3)3×6H2O, AlCl3×6H2O, and CeH8O18N8 as metal precursors such that the concentration of Ce substituting for Y was 0.1 and 0.3 %. Metal precursors were dissolved in citric acid:distilled water solutions at 70 oC under continuous stirring followed by the addition of ethylene glycol. The final solution was heated up to 100 oC to eliminate water and promote polymerization. The resultant material was pre-calcined at 600 oC for 5 h followed by calcination at 1000 oC for 6 h, and then pressed into 4 mm dia. x 1.2 mm thick pellets. Laser sintering was executed using a Coherent GEM-100L CO2 laser generating a power density of ~3.3 W/mm2for 90 s. The microstructure was characterized by means of density, X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR), and X-ray absorption near edge structure (XANES) measurements. Optical transparency and luminescence were evaluated in terms of UV-visible transmittance, photoluminescence emission (PL) and excitation (PLE), radioluminescence (RL), and thermoluminescence (TL) measurements, while differential pulse height distribution measurements were used to characterize the scintillation response as a function of the gamma-ray energy. Density measurements revealed the laser beam-induced densification yielded 97-99 % relative density. SEM results confirmed the presence of pores and an average grain size of 2 mm was extracted from image analysis. These results justified the optically opaque nature of the polycrystalline ceramics due to light scattering at the numerous internal interfaces. In addition to that, a higher degree of structural disorder in the polycrystalline ceramics that was revealed by inhomogeneous broadening of the optical absorption, PLE and absorption ATR FTIR bands when compared to the single crystal. XANES results of the YAG:Ce polycrystalline ceramics together with Ce(OH)CO3 and CeO2 commercial powders used as references for the 3+ and 4+ oxidation states of Ce, respectively, demonstrated the dominance of the +3 state. PL and RL confirmed luminescence to be dominated by the emission of Ce3+, and showed the presence of F+-related centers and antisite defects in both the polycrystalline ceramics and the single crystal. TL analysis revealed the presence of four first-order kinetics glow peaks, with the trap depths of the single crystal being similar or deeper than those of the polycrystalline ceramics. In terms of scintillation response, the relative light yield of the polycrystalline ceramics was significantly lower than that of the single crystal as expected from its optically opaque nature. Also, the polycrystalline ceramics presented a less linear energy response than the single crystal. Acknowledgements This material is based upon work supported by the National Science Foundation under Grant no. 1207080. This work has been supported by the Brazilian Synchrotron Light Laboratory (LNLS) beamline XAFS2 under proposals 15871 and 18854.

Photoluminescence excitation spectroscopy of SiV− and GeV− color center in diamond

Color centers in diamond are important quantum emitters for a broad range of applications ranging from quantum sensing to quantum optics. Understanding the internal energy level structure is of fundamental importance for future applications. We experimentally investigate the level structure of an ensemble of few negatively charged silicon-vacancy (SiV−) and germanium-vacancy (GeV−) centers in bulk diamond at room temperature by photoluminescence (PL) and excitation (PLE) spectroscopy over a broad wavelength range from 460 to and perform power-dependent saturation measurements. For SiV− our experimental results confirm the presence of a higher energy transition at . By comparison with detailed theoretical simulations of the imaginary dielectric function we interpret the transition as a dipole-allowed transition from -state to -state where the corresponding a2u-level lies deeply inside the diamond valence band. Therefore, the transition is broadened by the diamond band. At higher excitation power of we indicate signs of a parity-conserving transition at supported by saturation measurements. For GeV− we demonstrate that the PLE spectrum is in good agreement with the mirror image of the PL spectrum of the zero-phonon line. Experimentally we do not observe a higher lying energy level up to a transition wavelength of . The observed PL spectra are identical, independent of excitation wavelength, suggesting a rapid decay to excited state and followed by optical transition to ground state. Our investigations convey important insights for future quantum optics and quantum sensing experiments based on SiV−-center and GeV−-center in diamond.

Deep red-emitting Ca14Al10Zn6O35:Mn4+ phosphors for WLED applications

Novel deep red-emitting Ca14Al10Zn6O35:Mn4+ (CAZ:Mn4+) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction patterns of CAZ:Mn4+ phosphors confirmed their cubic structure after annealing at 1200 °C. The photoluminescence emission (PL) and excitation (PLE) spectra were measured to examine the emission richness of CAZ:Mn4+ phosphors. The PLE spectra of CAZ:Mn4+ phosphor exhibited a broad band, between UV and blue regions, due to the charge transfer (CT) transition of Mn4+-O2- and 4A2g→4T2g, 4A2g→4T2g, 4A2g→4T2g of Mn4+ ions. The results showed that the deep red emission peak of the CAZ:Mn4+ phosphor was located at 714 nm due to the 2Eg→4A2g transition of Mn4+ ion, which was effectively excited by 450 nm. The optimum concentration of Mn4+ ion in Ca14Al10Zn6O35 host lattice was found to be at 3 mol%. Using CAZ:3Mn4+ phosphors, white light-emitting diode (WLED) was fabricated. The CIE chromaticity coordinates of CAZ:3Mn4+ and fabricated WLED located at (0.709, 0.291) and (0.338, 0.396), respectively, resulting in the generation of warm white light for indoor illumination.

The structure-dependent luminescence of Eu3+-activated MBaY(BO3)2 (M=Na, K) nanoparticles

Eu3+-doped MBaY1-xEux(BO3)2 (M = Na, K) red emitting nanophosphor was prepared via a sol-gel method. The phase purity and crystal structure of the nanophosphors were confirmed by X-ray diffraction (XRD) together with the Rietveld refinements. The surface morphology was characterized by scanning electron microscope (SEM). The luminescent characteristics of the particles were investigated by photoluminescence emission (PL) and excitation (PLE) spectra, decay curves and quantum efficiencies (QE). The phosphors present a very high optimal doping concentration of about 70 mol%. The phosphor presents the dominated 5D0 → 7F1 transition inducing reddish-orange color in lower doping, while it has a red emission at 613 nm from the electronic 5D0 → 7F2 dipole transition in a Eu3+-heavily doped sample. The thermal stabilities of the two phosphors were tested by measuring their temperature-dependent emission intensities. The luminescence differences between the Na- and K-compounds were presented and discussed base on the structure characteristics.

Ab Initio Site Occupancy and Far-Red Emission of Mn4+ in Cubic-Phase La(MgTi)1/2O3 for Plant Cultivation.

Mn4+-activated oxide phosphors La(MgTi)1/2O3 (LMT) with far-red emitting were prepared via a sol-gel route. The structures of samples were determined by X-ray diffraction (XRD) and Reitveld refinement. The occupied sites of Mn4+ (d3 electronic configuration) in host La(MgTi)1/2O3 were confirmed by ab initio calculations in which the system has the lower formation energy, stable lattice structure, and strong bonding state as Mn4+ enters into Ti site. The luminescent properties of Mn4+-doped samples were investigated; the samples emit far-red light centered at 708 nm with ultraviolet light (345 nm) or blue light (487 nm) excitation. According to the photoluminescence (PL) and excitation (PLE) spectra, the crystal field strength of the Mn4+-occupied environment was estimated. The thermal stability of phosphor was also evaluated through temperature-dependent PL intensity in a heating and cooling cycle process. The emission band is well-matched with the absorption band of phytochrome PFR under the excitation of light in near-ultraviolet to blue, which suggests that the LMT: Mn4+ phosphor has great potential applications in light-emitting diodes (LEDs) for modulating plant growth.

Site-Dependent Luminescence and Thermal Stability of Eu(2+) Doped Fluorophosphate toward White LEDs for Plant Growth.

Eu(2+) activated fluorophosphate Ba3GdNa(PO4)3F (BGNPF) with blue and red double-color emitting samples were prepared via a solid-state method in a reductive atmosphere. Their crystal structure and cationic sites were identified in light of X-ray diffraction pattern Rietveld refinement. Three different Ba(2+) sites, coordinated by six O atoms referred to as Ba1, two F and five O atoms as Ba2, and two F and six O atoms as Ba3, were partially substituted by Eu(2+). Photoluminescence emission (PL) and excitation (PLE) spectra of phosphor BGNPF:Eu(2+) along with the lifetimes were characterized at the liquid helium temperature (LHT), which further confirm the existence of three Eu(2+) emitting centers resulting in 436, 480, and 640 nm emission from the 5d → 4f transitions of Eu(2+) in three different Ba(2+) crystallographic sites. These emissions overlap with the absorption spectra of carotenoids and chlorophylls from plants, which could directly promote the photosynthesis. Temperature-dependent PL spectra were used to investigate the thermal stability of phosphor, which indicates that the PL intensity of BGNPF:0.9% Eu(2+) with optimal composition at 150 °C still keeps 60% of its PL intensity at room temperature, in which blue emission has higher thermal-stability than the red emission. Furthermore, the approaching white LED devices have also been manufactured with a 365 nm n-UV LED chip and present phosphor, which make operators more comfortable than that of the plant growth purple emitting LEDs system composed of blue and red light. Results indicate that this phosphor is an attractive dual-responsive candidate phosphor in the application n-UV light-excited white LEDs for plant growth.

Synthesis, structure and NIR luminescence properties of Yb3+ and Bi3+-activated vanadate GdVO4

Near-infrared emission of Yb3+ and Bi3+-co-doped GdVO4 vanadate phosphors obtained via the modified Pechini's method was reported. The phase purity and structure of samples were characterized by X-ray powder diffraction (XRD), X-ray energy dispersion spectroscopy (EDS), scanning electron microscopy (SEM), Raman and infrared (IR) spectroscopy. Photoluminescence emission (PL) and excitation (PLE) spectra were recorded and investigated in details. Results indicated that upon near-UV excitation (340 nm) in the (Bi3+-V5+) charge transfer state this phosphor had a strong broad band yellow-green emission (3P1→1S0) of Bi3+ ions and also NIR emission (2F5/2→2F7/2) of Yb3+ ions in the range of 950–1050 nm, which matched well with the spectral response of the silicon-based solar cells. The decreasing Bi3+ emission with increasing Yb3+ concentration proved the occurrence of energy transfer from Bi3+ to Yb3+ ions. Results demonstrated that Yb3+ and Bi3+-co-doped GdVO4 vanadate phosphors might act as a NIR down-conversion (DC) solar spectral converter to enhance the efficiency of the silicon-based solar cells.