Sudipta Som

Defect correlated fluorescent quenching and electron phonon coupling in the spectral transition of Eu3+ in CaTiO3 for red emission in display application

This paper reports on the defect correlated self-quenching and spectroscopic investigation of calcium titanate (CaTiO3) phosphors. A series of CaTiO3 phosphors doped with trivalent europium (Eu3+) and codoped with potassium (K+) ions were prepared by the solid state reaction method. The X-ray diffraction results revealed that the obtained powder phosphors consisted out of a single-phase orthorhombic structure and it also indicated that the incorporation of the dopants/co-dopants did not affect the crystal structure. The scanning electron microscopy images revealed the irregular morphology of the prepared phosphors consisting out of μm sized diameter particles. The Eu3+ doped phosphors illuminated with ultraviolet light showed the characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+. As a charge compensator, K+ ions were incorporated into the CaTiO3:Eu3+ phosphors, which enhanced the photoluminescence (PL) intensities depending on the doping concentration of K+. The concentratio...

Synthesis of strong red emitting Y2O3:Eu3+ phosphor by potential chemical routes: comparative investigations on the structural evolutions, photometric properties and Judd–Ofelt analysis

In the present paper, a comparative investigation on the structural and photoluminescence properties of Y2O3:Eu3+ phosphor prepared by different wet chemical synthesis routes such as sol-lyophilisation (SL), combustion (CR), hydrothermal (HT) and microwave assisted hydrothermal combustion (MHWC), has been reported for the first time. The MHWC derived phosphor exhibited better photoluminescence than that of the samples obtained with other adopted methods. Such outcomes were due to the increased crystallinity, well defined morphology and improved compositional homogeneity in the MWHC technique. The growth of the prepared phosphors was explained in the light of chemical kinetics. Jorgensen formula and nephelauxetic ratio was used to understand the ligand behavior of Eu–O bond and to estimate the electron phonon coupling in Y2O3:Eu3+ phosphor. The spectroscopic behavior of Y2O3:Eu3+ phosphor, prepared by different routes, was determined using Judd–Ofelt theory. Thermal stability, purity and efficiency of the emitted colour were checked on the basis of different synthetic approach. An efficient synthesis method for Y2O3:Eu3+ phosphor, compatible for industrial appliances, was proposed.

Structural evaluations and temperature dependent photoluminescence characterizations of Eu3+-activated SrZrO3 hollow spheres for luminescence thermometry applications

This research is focused on the temperature sensing ability of perovskite SrZrO3:Eu3+ 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:Eu3+ consisted of two regions. One region was associated with SrZrO3 trap emission, and the other one was related to the emission of Eu3+ ions. The intensity ratio of the emission of Eu3+ ions to the host emission (FIR) and the emission lifetime of Eu3+ 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:Eu3+ for the distinct high temperature sensing applications.

The role of growth atmosphere on the structural and optical quality of defect free ZnO films for strong ultraviolet emission

Highly c-axis oriented wurtzite structured ZnO thin films were deposited on silicon substrates using pulsed laser deposition (PLD) by ablating a ZnO target in different atmospheres, including vacuum, argon and oxygen in the deposition chamber. The stress in the films was shown to vary from −3.83 to −0.03 GPa as a function of the chamber atmosphere. The minimum compressive stress (−0.03 GPa) was observed for the oxygen atmosphere. X-ray photoelectron spectroscopy data indicated that the O1s peak consists of three components designated as O1 (due to ZnO), O2 (due to defects) and O3 (due to adsorbed species). A small defect level emission was obtained in the luminescence spectra of the ZnO film deposited in the oxygen atmosphere, while strong ultraviolet (UV) emission was observed for the ZnO films deposited in the vacuum and argon atmosphere. These PLD grown ZnO thin films have the potential to be used as sources of UV radiation in light emitting devices.

Enhanced upconversion of NaYF₄:Er³⁺/Yb³⁺ 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.

Synthesis of Sr 2 Si 5 N 8 :Ce 3+ phosphors for white LEDs via efficient chemical vapor deposition

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.

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 and characterization of high concentration Nd3+ doped YAG nanopowders for laser applications

Herein, neodymium-doped yttrium aluminum garnet (Nd:YAG) ceramic powders were fabricated via a wet chemical reaction method followed by heating in air. The structural studied confirmed the formation of single phase Nd:YAG nanocrystallites without any intermediate phase at 1000 °C, and the average particle size was calculated to be 260 nm. According to the reflectance results, the highest absoption of the synthesized powders was observed at 808 nm. Therefore, A laser diode (808 nm) with power output about 1000 mW was used as a pump source and the emission spectra was recorded. Upon IR excitation, the present sample showed intense emission at around 1064 nm and found to be potential for solid state lasewr devices.