A highly efficient deep red-emitting Mn4+-powered oxyfluoride nanophosphor developed for plant growth and optical thermometric applications.

This research mainly highlighted an intense deep red-emitting and Mn4+-powered oxyfluoride nanophosphor, Mg14Ge4.99O16F8:0.01Mn4+ (MGOF:Mn), which was synthesized via adopting a scalable synthesis route for commercial temperature sensing and artificial plant growth applications. The electron microscopic analysis confirmed the formation of nanosized particles without any defined shape or size distribution. The obtained nanophosphor exhibited sharp emission peaks at 659 nm and 631 nm under UV (317 nm) and blue excitation (417 nm) owing to Mn4+:2Eg → 4A2g and Mn4+:2T1g → 4A2g transitions, respectively. The emission spectrum is situated in the deep red region of the CIE color diagram where the red color purity approached 100% under both the excitations. The absorption efficiency and the internal and external quantum efficiencies of this red-emitting system were calculated to be 53%, ∼77%, and ∼41%, respectively, under blue excitation of 417 nm, which indicated its potential for indoor plant cultivation. A prototype red LED was fabricated by pasting the red-emitting MGOF:Mn4+ nanophosphor powder on a 410 nm blue LED chip. The resulting electroluminescence spectrum overlapped with those of the important organic pigments of normal plants. Importantly, the thermometric properties of the nanophosphor were evaluated in detail for FIR and lifetime-based thermometry applications. The examined nanophosphor showed an extreme absolute sensitivity of 0.00326 K-1 at 373 K with excellent reproducibility and temperature resolution. Because of the small particle size and high luminescence efficiency, the nanophosphor could be implemented in various nano-devices where non-contact optical thermometry is necessary for high performance.

Governing the crystallographic sites for tuning Eu2+ emission in an apatite oxyfluoride host to be applied for superior white light emitting diodes.

Single white light-emitting phosphors for near-UV-converted white light-emitting diodes (WLEDs) are the best alternatives to tricolour phosphor blends and blue light converted yellow-emitting garnets. Nevertheless, achieving white light with elevated colour rendering (CRI) from a single-phase phosphor activated with a lone activator ion is a major challenge. This study aimed at the generation of white light from a single-phase composition activated only with europium. The study started with structural evaluations of Eu3+-activated Ca4La6Si6O24F2 phosphors using X-ray diffraction (XRD) and Eu3+ photoluminescence to elucidate the local environment of rare-earth ions and the symmetric nature of the lattice sites. Ca4La6Si6O24F2 crystallized in the hexagonal P63/m space group. The predominant 5D0-7F2 electric dipole transition at 614 nm, and the non-splitting as well as the zero-shifting behaviour of 5D0-7F0 at 578 nm, suggested that the rare-earth ionic substitutions preferably took place at the larger asymmetric sites. Introducing Sr2+ ions in Ca4La6Si6O24F2:Eu3+/Eu2+ that is synthesized under a reducing atmosphere suppressed Eu3+ emission. From the optimized Ca1.98Sr1.98La6Si6O24F2:0.04Eu2+, a sequence of M2+-codoped (M = Mg/Ba) Ca1.98Sr1.98La6Si6O24F2:0.04Eu2+ phosphors were further developed. The substitutions of Mg2+ and Ba2+ altered the crystal field by changing the lattice parameters. The Mg2+ -doped samples showed a blue-shift from 520 nm (Mg2+ = 0) to 471 nm (Mg2+ = 1.0), whereas the Ba2+-doped compositions showed a red-shift from 520 nm (Ba2+ = 0) to 536 nm (Ba2+ = 1.2). The change of symmetry owing to the Mg2+/Ba2+ substitution could have led to the centroid shift, which was responsible for the blue- or red-shift of the emission spectra. The XRD of Ca1.38Sr1.38La6Si6O24F2:0.04Eu2+,1.2Ba2+ indicated a Ba2+-induced lattice site expansion. Keeping this in view, the Eu2+ ions concentrations were further enhanced from 0.04 to 0.3, and the resultant photoluminescence was further enhanced and red-shifted. The optimized sample showed better intensity compared with the commercial Y3Al5O12:Ce3+ and exhibited decent photoluminescence above 70% at 150 °C as compared with that at room temperature. Finally, several prototype WLEDs were fabricated using the single phosphor Ca1.365Sr1.365La6Si6O24F2:0.07Eu2+,1.2Ba2+ with near-UV and violet-LED chips. The outcomes indicated the promising nature of this single-composition phosphor for indoor lighting.

Realizing cool and warm white-LEDs based on color controllable (Sr,Ba)2Al3O6F:Eu2+ phosphors obtained via a microwave-assisted diffusion method.

Globally, phosphor converted white-LEDs (W-LEDs) are among the most suitable sources to reduce energy consumption. Nevertheless, modernization of efficient broadband emitting phosphors is most crucial to improve the W-LED performance. Herein, we synthesized a series of novel broadband emitting Sr2-xAl3O6F:xEu2+ phosphors via a new microwave-assisted diffusion method. Rietveld refinement of the obtained X-ray diffraction results was performed to recognize the exact crystal phase and the various cationic sites. Oxygen vacancies (VO) formed under synthetic reducing conditions enabled Sr2Al3O6F to demonstrate bright self-activated bluish emission. Doping of Eu2+ ions unlocked the energy transfer process from the host to the activator ions, owing to which, the self-activated emission diminished and the Eu2+-doped sample showed amplified bluish-green emission. The gradual increase in Eu2+ concentrations regulated the controllable emissions from the bluish (0.34, 0.42) to the greenish (0.38, 0.43) zone under UV excitation. Because of the different absorption preferences of Eu2+ ions located at the different Sr2+ sites, Sr2-xAl3O6F:xEu2+ exhibited bluish-white emission under blue irradiation. A further enhancement in PL intensity had been observed by the cation substitution of Ba2+ for Sr2+ sites in the optimum Sr1.95Al3O6F:0.05Eu2+ phosphor. The as-fabricated W-LEDs utilizing the optimized Sr1.75Ba0.2Al3O6F:0.05Eu2+ phosphor exhibited a cool-white light emission along with a 372 nm NUV-LED and a 420 nm blue-LED with a moderate CRI of 70 and a CCT above 6000 K. Such cool white emission was controlled to natural white with the CCT close to 5000 K, and the CRI above 80 via utilizing a suitable red emitting phosphor. The W-LED performances of the optimized phosphor justified its applicability to produce white light for lighting applications.

Multisite-Occupancy-Driven Intense Narrow-Band Blue Emission from Sr5SiO4Cl6:Eu2+ Phosphor with Excellent Stability and Color Performance.

The development of an efficient blue phosphor with remarkable thermal stability required for high-quality white-light-emitting diodes (WLEDs) remains an exigent task and mainly concerned BaMgAl10O17:Eu2+ (BAM:Eu). Despite the outstanding performance of BAM:Eu, the reduction in luminescence efficiency under long-term operation results in numerous researches on new hosts having lattice rigidity with symmetrical coordination environment. Therefore, we have synthesized a competent blue-emitting Eu2+-activated Sr5SiO4Cl6 (SSC) phosphors. The admirable rigidity of these phosphors with three Sr polyhedra Sr(I)O9, Sr(II)O7, and Sr(III)O8 assessed from Rietveld refinement indicate the dense connectivity in the crystal structure, and the ab initio calculations further support the firm electronic band structure. The broad excitation from 250 to 450 nm suitably matches the absorption band of a near-UV (n-UV) LED chip. The phosphor exhibited bright blue emission with internal quantum yield and color purity > 90% which contribute to the slender fwhm of 33 nm. The first-principle calculation indicates the most stable site for Eu2+ substitution as Sr(III)O8, and the experimental results agreed with this fact as well. The synthesized phosphor displayed an excellent thermal stability which is superior to that of the commercial BAM:Eu phosphor. The excellent thermal stability may be owed to the highly symmetric coordination environment of Eu2+ in the SSC host that are revealed from the distortion and charge density distribution calculation by density functional theory. The blue phosphor was further utilized for WLEDs and displayed white light with a high color-rendering index and suitable correlated color temperature, which is ideal for practical applications in warm WLEDs.

Influence of gold nanoparticles on the nonlinear optical and photoluminescence properties of Eu2O3 doped alkali borate glasses.

Alkali borate glasses activated with trivalent europium ions and rooted with gold (Au) nanoparticles (NPs) were synthesised through a melt quenching process involving a selective thermochemical reduction and their applicability as photonic materials was assessed in detail. Non-linear optical (NLO) measurements were performed using a Z-scan approach in the wavelength range of 700-1000 nm. The open aperture Z-scan signatures for the Eu3+-containing glasses embedded with and without the Au NPs established a reverse saturable absorption (RSA) at all of the studied wavelengths ascribed to the two-photon absorption (2PA). Surprisingly, the nonlinear optical absorption switched to a saturable absorption (SA) with an increase in the concentration of AuCl3. With the incorporation of the Au NPs, the UV excited photoluminescence (PL) intensity of the Eu3+-doped glasses increased first as a consequence of the local field enhancement by the Au NPs, and subsequently decreased at a higher concentration of AuCl3 due to the reverse energy transfer from the Eu3+ ion to the Au0 NPs. The electronic polarization effect of the host glass enhanced the 5D0→7F4 transition intensity on the incorporation of the gold NPs owing to the gold NP-embedded glasses showing a deep-red emission. The NLO and PL studies suggested that the investigated glasses containing a 0.01 mol% of AuCl3 is practically appropriate for photonic applications.

Ultra-bright emission from Sr doped TiO2 nanoparticles through r-GO conjugation.

Graphene and semiconductor nanocomposite garnered much interest in nanoscience and nanotechnology. In this research, TiO2, TiO2: Sr and TiO2: Sr/r-GO (reduced graphene oxide) nanocomposites have been successfully synthesized via a wet chemical synthesis method. The microscopic studies confirmed the formation of graphene sheets which looked like a paper which could easily wrap over the bacterial surface killing them. The optical band gap of these nanocomposites is determined by UV-visible absorption spectra which inferred that optical band gap decreases with Sr2+ incorporation and r-GO attachment. Furthermore, photoluminescence (PL) study revealed that the intensity of emission is prominent for TiO2: Sr/r-GO. The enhancement in PL intensity with r-GO is due to creation of more oxygen vacancies and defects which generally capture the photoinduced carriers inhibiting recombination rate of free carriers promoting the photocatalytic reactions.

Rapid synthesis of hybrid methylammonium lead iodide perovskite quantum dots and rich MnI2 substitution favouring Pb-free warm white LED applications.

We present a facile room temperature synthesis of CH3NH3Pb1-x Mn x I3 perovskite quantum dots (PQDs) substituting manganese (Mn2+) at the lead (Pb2+) sites to minimize environmental pollution and make it commercially feasible. By varying the concentration of Mn2+ from 0 to 60%, the PQDs exhibit strong color tunability from red to orange color suggesting successful energy transfer due to Mn2+ inclusion. We observed a high external photoluminescence quantum yield (PLQY) of 98% for unsubstituted CH3NH3PbI3 and >50% for up to 15% Mn2+ substituted PQDs. The average lifetime of PQDs was found to shorten with increasing Mn2+ replacement. We demonstrate a white LED prototype by employing the CH3NH3Pb1-x Mn x I3 PQDs with green QDs on a blue LED chip. The CRI and CCT value varying from 92 to 80 and 5100 K to 2900 K, respectively, indicate the usability of the Mn2+ substituted PQDs as efficient warm white LEDs with a promising CRI and good stability.

Promising Er3+/Yb3+-Codoped GdBiW2O9 Phosphor for Temperature Sensing by Upconversion Luminescence.

Yb3+/Er3+-codoped GdBiW2O9 phosphors are prepared via the solid-state route for application in upconversion temperature sensors. The structural analyses indicate that all phosphors possess a single-phased orthorhombic structure. Upon the excitation of a laser wavelength of 980 nm, Yb3+/Er3+-codoped GdBiW2O9 phosphors emanate green emission peaks, endorsed to the emission to the 4I15/2 state from the 4S3/2 and 2H11/2 states, respectively, and the weak emission (red) from the 4F9/2 state to the 4I15/2 state of Er3+ ion. The upconversion mechanism has been elucidated via the scheme of energy levels conferred from the pump power-induced upconversion characteristics. The temperature-dependent upconversion of GdBiW2O9 phosphors was investigated in detail along with the estimation of the stability and repeatability of the measurement. The obtained sensitivity data for the present materials with the corresponding sensing parameters show their probable outlook in temperature sensing applications.

Corrigendum: Synthesis of Sr2Si5N8: Ce3+ phosphors for white LEDs via efficient chemical vapor deposition.

This corrects the article DOI: 10.1038/srep45832.

Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via an efficient chemical vapor deposition [corrected].

Novel chemical vapor deposition (CVD) process was successfully developed for the growth of Sr2Si5N8:Ce3+ phosphors with elevated luminescent properties. Metallic strontium was used as a vapor source for producing Sr3N2 vapor to react with Si3N4 powder via a homogeneous gas-solid reaction. The phosphors prepared via the CVD process showed high crystallinity, homogeneous particle size ranging from 8 to 10 µm, and high luminescence properties. In contrast, the phosphors prepared via the conventional solid-state reaction process exhibited relative low crystallinity, non-uniform particle size in the range of 0.5-5 µm and relatively lower luminescent properties than the phosphors synthesized via the CVD process. Upon the blue light excitation, Sr2-xCexSi5N8 phosphors exhibited a broad yellow band. A red shift of the emission band from 535 to 556 nm was observed with the increment in the doping amount of Ce3+ ions from x = 0.02 to x = 0.10. The maximum emission was observed at x = 0.06, and the external and internal quantum efficiencies were calculated to be 51% and 71%, respectively. Furthermore, the CVD derived optimum Sr1.94Ce0.06Si5N8 phosphor exhibited sufficient thermal stability for blue-LEDs and the activation energy was calculated to be 0.33 eV. The results demonstrate a potential synthesis process for nitride phosphors suitable for light emitting diodes.

Structural evaluations and temperature dependent photoluminescence characterizations of Eu(3+)-activated SrZrO3 hollow spheres for luminescence thermometry applications.

This research is focused on the temperature sensing ability of perovskite SrZrO3:Eu(3+) hollow spheres synthesized via the sol-gel method followed by heating. The Rietveld refinement indicated that the precursors annealed at 1100 °C were crystallized to form orthorhombic SrZrO3. SrZrO3 particles exhibited non-agglomerated hollow spherical morphology with an average particle size of 300 nm. The UV-excited photoluminescence spectrum of SrZrO3:Eu(3+) consisted of two regions. One region was associated with SrZrO3 trap emission, and the other one was related to the emission of Eu(3+) ions. The intensity ratio of the emission of Eu(3+) ions to the host emission (FIR) and the emission lifetime of Eu(3+) ions were measured in the temperature range of 300-550 K. The sensitivity obtained via the lifetime method was 7.3× lower than that measured via the FIR. Within the optimum temperature range of 300-460 K, the as-estimated sensor sensitivity was increased from 0.0013 to 0.028 K(-1). With a further increase in temperatures, the sensitivity started to decline. A maximum relative sensitivity was estimated to be 2.22%K(-1) at 460 K. The resolutions in both methods were below 1K in the above temperature range. The results indicated the suitability of SrZrO3:Eu(3+) for the distinct high temperature sensing applications.

Enhanced upconversion of NaYF4:Er³âº/Yb³âº phosphors prepared via the rapid microwave-assisted hydrothermal route at low temperature: phase and morphology control.

Monophasic NaYF4:Er(3+)/Yb(3+) crystals were synthesized via the microwave-assisted hydrothermal route at 180°C. Microwave heating during the hydrothermal process substantially reduces the duration of reaction for the formation of cubic-NaYF4:Er(3+)/Yb(3+) nanocrystals from 6 h to 30 min. As the duration of the reaction increases, cubic-NaYF4:Er(3+)/Yb(3+) nanocrystals are transformed to uniform hexagonal-NaYF4:Er(3+)/Yb(3+) microprisms because of the enhanced reaction kinetics. Bright upconverted emission from the NaYF4:Er(3+)/Yb(3+) crystal, obtained by the efficient two-photon excitation, is related to crystal structure and morphology. The hexagonal microprisms exhibit better upconversion and are employed in security applications.