Luminescence Thermometry Based on the Upconversion Luminescence from the Stark Sublevels of BaY2F8:Yb3+, Tm3+ Phosphor.

Visible and near-infrared (NIR) upconversion luminescence (UCL) emissions originating from the BaY2F8: Yb3+, Tm3+ systems were investigated under a laser excitation at 980 nm. The BaY2F8:20 mol% Yb3+, x mol% Tm3+ and BaY2F8: y mol% Yb3+, 0.5 mol% Tm3+ phosphors showed prominent UCL at 800 and 810 nm. The optimized doping concentrations of Yb3+ and Tm3+ in the BaY2F8 host matrix were evaluated, their spectroscopic properties were determined, and studies on their temperature-dependent behaviour were carried out. The temperature-sensing properties were studied by generating the fluorescence intensity ratio (FIR) of the UCL peaks originating from the thermally-coupled energy levels of the Tm3+ ions. The Stark sublevels of 1G4 level of Tm3+ ions were utilized to estimate the temperature-sensing abilities of the phosphor.

Upconversion process in BaY2 F8 :Yb3+ ,Ho3+ phosphor for optical thermometry.

A BaY2 F8 :Yb3+ ,Ho3+ phosphor was synthesized using a simple precipitation method. The temperature-sensing properties of BaY2 F8 :Yb3+ ,Ho3+ phosphor were investigated using the fluorescence intensity ratio (FIR) of the thermally coupled energy levels (5 F4 and 5 S2 ) of Ho3+ . Energy transitions 5 F4 →5 I8 and 5 S2 →5 I8 gave rise to emission peaks at 538 nm and 549 nm, respectively. The areas under these two emission peaks were used to calculate the FIR. Temperature-dependent upconversion luminescence was recorded in the temperature range 303-623 K using a 980 nm laser excitation source. The results suggested that the BaY2 F8 :Yb3+ , Ho3+ phosphor has the potential to be used as a non-contact optical temperature sensor.

Green-light emission through energy transfer from Ce3+ to Tb3+ ions in the Li2 SO4 -Al2 (SO4 )3 system.

An energy transfer process from Ce3+ to Tb3+ ions was successfully achieved in a Li2 SO4 -Al2 (SO4 )3 mixed-sulphate system. A wet-chemical synthesis was employed to prepare the Li2 SO4 -Al2 (SO4 )3 system by doping Ce3+ and Tb3+ ions individually as well as collectively. The phases were identified using X-ray diffraction studies. The as-prepared samples were characterized by FT-IR and photoluminescence measurements. Green-light emission was exhibited by Ce3+ , Tb3+ co-doped Li2 SO4 -Al2 (SO4 )3 system, thus, indicating its potential as a material for display devices or in the lamp industry.

Study of luminescence properties of dysprosium-doped CaAl12 O19 phosphor for white light-emitting diodes.

Dy3+ -doped CaAl12 O19 phosphors were synthesized utilizing a combustion method. Crystal structure and morphological examinations were performed respectively using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques to identify the phase and morphology of the synthesized samples. Fourier transform infrared spectroscopy (FTIR) estimations were carried out using the KBr method. Photoluminescence properties (excitation and emission) were recorded at room temperature. CaAl12 O19 :Dy3+ phosphor showed two emission peaks respectively under a 350-nm excitation wavelength, centered at 477 nm and 573 nm. Dipole-dipole interaction via nonradiative energy shifting has been considered as the major cause of concentration quenching when Dy3+ concentration was more than 3 mol%. The CIE chromaticity coordinates positioned at (0.3185, 0.3580) for the CaAl12 O19 :0.03Dy3+ phosphor had a correlated color temperature (CCT) of 6057 K, which is situated in the cool white area. Existing results point out that the CaAl12 O19 :0.03Dy3+ phosphor could be a favorable candidate for use in white light-emitting diodes (WLEDs).

White Light Emitting MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) Phosphors for WLEDs.

A series of MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) phosphors were prepared by the solid state diffusion method. Confirmation of the phase formation and morphological studies were performed by X-ray powder diffraction (XRD) measurements and scanning electron microscopy, respectively. Photoluminescence (PL) properties of these phosphors were thoroughly analyzed and the characteristic emissions of Dy3+ ions were found to arise from them at an excitation wavelength of 351 nm. The PL emission spectra of the three phosphors were analyzed and compared. The CIE chromaticity coordinates assured that the phosphors produced cool white-light emission and hence, they are potential candidates for UV excited white-LEDs (WLEDs). Graphical Abstract ᅟ.

Orange light-emitting Ca3 Mg3 (PO4 )4 :Sm3+ phosphors.

This work reports the photoluminescence properties of Ca3 Mg3 (PO4 )4 :Sm3+ phosphors that were synthesized by the combustion method. The phase formation and morphology of the prepared phosphors were analysed by X-ray diffraction studies and scanning electron microscopy. Ca3 Mg3 (PO4 )4 :Sm3+ phosphors give orange light emission when excited by near-ultraviolet (NUV) and blue light. The photoluminescence characteristics of the as-prepared phosphors were investigated and their emission spectra showed three peaks due to 4 G5/2  â†’ 6 H5/2 , 4 G5/2  â†’ 6 H7/2 and 4 G5/2  â†’ 6 H9/2 transitions. The mechanism responsible for the concentration quenching of luminescence was found to be an electric dipole-dipole interaction. The CIE chromaticity coordinates suggested that the prepared phosphors are potential candidates for orange light-emitting diodes (LEDs).

Exploration of electron-vibrational interaction in the 5d states of Eu2+ ions in ABaPO4 (A = Li, Na, K and Rb) phosphors.

This work reports the theoretical analysis of the electron-vibrational interaction (EVI) in 4f-5d optical transitions of Eu2+ ions in ABaPO4 (A = Li, Na, K and Rb) systems. The EVI parameters were estimated from the recently reported room temperature photoluminescence results, by employing the spectrum-fitting method. Parameters such as the Huang-Rhys factor, effective phonon energy, Stokes shift and zero-phonon line position were estimated and are reported here. The estimated EVI parameters were validated by modeling the emission band and establishing the agreement between the experimental and modeled emission bands. Copyright © 2016 John Wiley & Sons, Ltd.

Photoluminescence properties of Eu(3+)/ Sm(3+) activated CaZr4(PO4)6 phosphors.

Solid state reaction method was employed for the synthesis of a series of CaZr4(PO4)6: Eu(3+)/Sm(3+) phosphors. The red-emitting CaZr4(PO4)6:Eu(3+) phosphors can be efficiently excited at 396 nm and thereby, exhibit a strong red luminescence predominantly corresponding to the electric dipole transition at 615 nm. Under 405 nm excitation, CaZr4(PO4)6:Sm(3+) phosphors display orange emission with color temperatures approximately around 2200 K. The acquired results reveal that CaZr4(PO4)6: RE(3+) (RE = Eu, Sm) phosphors could be potential candidates for red and orange emitting phosphor, respectively, for UV/blue-pump LEDs.

Synthesis and characterization of novel Na15 (SO4 )5 F4 Cl:Ce3+ halosulfate phosphors.

A series of Na15 (SO4 )5 F4 Cl phosphors doped with Ce3+ ions was prepared using the wet chemical method. X-Ray diffraction studies were used to determine their phase formation and purity. Fourier transform infrared spectroscopy effectively identified the chemical bonds present in the molecule. The photoluminescence properties of the as-prepared phosphors were investigated and the Ce3+ ions in these hosts were found to give broadband emission in the UV range. For the thermoluminescence study, phosphors were irradiated with a 5 Gy dose of γ-rays from a 60 Co source. Chen's half-width method was employed to calculate the trapping parameters from the thermoluminescence glow curve. Copyright © 2016 John Wiley & Sons, Ltd.

A perspective perception on the applications of light-emitting diodes.

Light-emitting diodes (LEDs) continue to penetrate the global market; their pervasiveness clearly being felt in such diverse fields as technological, socio-economic and commercial interests. The multi-billion dollar LED market is shared by various segments, including office and household lighting, street lighting, the automobile industry, traffic signals, backlighting for hand-held devices, indoor and outdoor signs and indicators, medicine, communication systems, crop cultivation using artificial light and many more. The technological development of LEDs has undergone many phases in different parts of the world. From the early discovery of luminescence to the invention of highly efficient organic LEDs, researchers have worked with the prime purpose of improving the performance of luminaires. The need to infuse the market with more efficient and cheaper products has been prevalent from the start. LEDs are a result of this uncontrolled desire of researchers to develop superior products that would displace existing products in the market. To understand what led to the current prominence of LEDs, we give a brief historical overview of the field followed by a thorough discussion of the positive features of LEDs. This work includes the basic requirements, advantages and disadvantages of LEDs in a variety of applications. A brief description of the diverse applications of LED in fields such as lighting, indicators and displays, farming, medicine and communication is given. Considerable importance is placed on discussing the possible difficulties that must be overcome before using LEDs in commercial applications.

High-contrast multi-surface imaging of latent fingerprints using color-tunable YOF:Tb3+,Eu3+ ultrafine nanophosphors with high quantum yield.

Visualization of latent fingerprints (LFPs) using conventional powders has faced challenges on multicolor surfaces. However, these challenges are addressed by the advent of fluorescent powders in LFP detection, and they have redefined the effectiveness of the powder dusting method. In this study, color-tunable YOF:Tb3+,Eu3+ nanophosphors were examined for LFP recognition and were evaluated for their practicality on different types of surfaces. Under 254 nm UV irradiation, the LFPs developed using these nanophosphors showed clear and distinct ridge patterns with level 1, 2, and 3 details. The ultrafine particles of these nanophosphors adhered to the ridge patterns and replicated the minutiae of the LFPs. Meanwhile, the variation of the Tb3+/Eu3+ ratio demonstrated multicolor fluorescence emission from the nanophosphors, which provided better contrast between the ridge patterns on complex surfaces. Furthermore, the high luminescence quantum yield of the nanophosphors ensured high-resolution fluorescence images of the LFPs with a well-defined pattern that was recognizable even without any microscope or sophisticated instrumentation.

Synthesis of cesium lead bromide nanoparticles by the ultrasonic bath method: A polar-solvent-free approach at room temperature.

Colloidal synthesis of CsPbBr3 nanoparticles (NPs) is often carried out by involving polar solvents that threaten the chemical stability of the NPs. Here, we report a polar-solvent-free synthesis of all-inorganic CsPbBr3 NPs by employing an ultrasonic bath approach. The phase evolution of the CsPbBr3 NPs strongly depended on the duration of ultrasonication. A secondary phase of Cs4PbBr6 was also found to evolve, which emitted narrow blue-emission bands. For the longest period of ultrasonication (12 h), the CsPbBr3 and Cs4PbBr6 phases co-existed to produce blue and green emission bands with a photoluminescence quantum yield (PLQY) of 53%. The purest form of CsPbBr3 phases was observed for the NPs produced by sonicating the precursors for 8 h. They exhibited narrow green emission bands with a PLQY of 50%. The power-conversion efficiency of a silicon solar cell was remarkably increased when coated with the CsPbBr3 NPs, thus, proving its potential to be used as a spectral downshifter for Si solar cells.

Assessment of electron-vibrational interaction (EVI) parameters of YAG:Ce3+, TAG:Ce3+ and LuAG:Ce3+ garnet phosphors by spectrum fitting method.

The electron-vibrational interaction (EVI) in 4f↔5d optical transitions of Ce3+ ions in YAG, TAG and LuAG garnet phosphors have been analysed in this work. The main EVI parameters that have been estimated and reported here are Huang-Rhys factor, effective phonon energy, Stokes shift, red shift and Zero-phonon line position. The EVI parameters were estimated from the room temperature photoluminescence results that were recently reported. The spectrum fitting method was employed to determine the EVI parameters. An emission band was modelled with the aid of the calculated EVI parameters. The agreement between the modelled emission bands with the experimentally obtained ones validated the estimated values of EVI parameters.