Phosphor Particles Research Articles

Thermally stable Mn2+‐activated zinc silicate nanophosphor for speedy recognition of high‐contrast latent fingermarks

AbstractCrystalline divalent manganese‐activated zinc orthosilicate (Zn2SiO4:Mn2+) nanophosphor has been synthesized via the solution‐based sol–gel process. Structural, morphological, and photoluminescence (PL) properties were explored. X‐ray diffraction pattern confirms the crystalline hexagonal structure of the single‐phase Zn2SiO4 powder. The size and shape of Zn2SiO4 powder were analyzed using micrographs, which implies that the prepared phosphor particles are in the nano range. PL spectra have been recorded as a function of Mn2+ dopant concentration. A dominant green (∼526 nm) emission broad peak was observed owing to the characteristic (4T1→6A1) transition of Mn2+ ion under UV/blue excitation. The green emission (∼526 nm) intensity depends upon the doping concentration of Mn2+ ion, and it is found to be optimum for 2.0 mol%, after that quenching phenomenon was registered. The CIE color coordinate of Zn2SiO4:Mn2+ lies in the bright green region under UV excitation with 94.3% color purity. Real‐time experiments have been carried out for speedy development of high‐contrast fingermarks using Zn2SiO4 nanophosphor on various porous and nonporous substrates.

Solvothermal synthesis and characterization of well-dispersed cerium-doped Y2SiO5 phosphor particles

Abstract Well-dispersed cerium-doped Y2SiO5 (Ce:YSO) phosphor particles with spherical morphology and good luminescence intensity have been achieved by a solvothermal method with ethanol and water as solvent media. X-ray diffraction, Fourier transform infrared spectroscopy, fluorescence spectrophotometry and transmission electron microscopy were employed to characterize the as-synthesized Ce:YSO precursor and powders. The results showed that pure-phase Ce:YSO powders with a mean particle size of about 162 nm were accurately available at 310°C and above. The fluorescence ability and persistent luminescence decay properties of the Ce:YSO powders were also studied, and the excellent fluorescence properties could be attributed to the homogeneous Ce:YSO particles obtained through the solvothermal method.

Synthesis and properties of YVO4:Ho and YVO4:Ho,Bi luminescent nanomaterials by combustion method

YVO4:Ho and YVO4:Ho,Bi nanophosphors were synthesized via combustion synthesis using urea as fuel and metal nitrates as precursor. Structures, morphologies and optical properties of YVO4:Ho and YVO4:Ho,Bi nanophosphors annealed at 900 °C were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescent (PL) and photoluminescent excitation (PLE) spectra. The clearly YVO4 tetragonal phase was obtained. The average diameters for the phosphor particles are 20-30 nm. The nanophosphors could be excited by 320 nm which correspond to the VO4 absorption and then PL spectra of YVO4:Ho and YVO4:Ho,Bi nanophosphors are described by the 5F8, 5S2 – 5I8, 5F5 – 5I8 và 5F4, 5S2 → 5I7 transitions of Ho3+ ions at 543, 655 and 755 nm. The effects of Ho3+ and Bi3+ concentrations on structure and optical properties have been investigated

In-cylinder thermographic PIV combined with phosphor thermometry using ZnO:Zn

Two-dimensional thermographic particle image velocimetry (T-PIV) is presented for the in situ measurement in optically accessible internal combustion (IC) engines. Temperature and velocity measurements are combined using thermographic phosphor particles as tracers for PIV. For three commercially available phosphors (BAM:Eu2+, ZnO, and ZnO:Zn), temperature sensitivity, luminescence intensity at high temperatures and laser-fluence dependence were evaluated for phosphor-coated surfaces in a high-temperature cell. ZnO:Zn was identified as the best-suited candidate for engine in-cylinder measurements and further analyzed in the aerosolized state at temperatures up to 775 K to generate calibration data required for signal quantification in engine experiments. T-PIV was successfully applied in the IC engine to simultaneously obtain instantaneous two-dimensional velocity and temperature fields using the intensity-ratio method. Despite a measurement uncertainty (±1σ basis) of only 3.7 K at 317 K (1.2%) to 24.4 K (4.2%) at 575 K, this technique suffers from low signal intensities due to thermal quenching at increasing temperatures, which leads to reduced accuracy as the piston approaches top dead center. Thermographic measurements were successful to visualize local temperature changes due to evaporative cooling after fuel injection. The measured mean gas temperatures agreed well with zero-dimensional simulations that use additional wall-temperature measurements from thermographic phosphor measurements based on the lifetime method as input for heat transfer calculations.

The effect of the grain size distribution (GSD) on the light emission performance of phosphor-based X-ray detectors

The light emission performance of indirect, phosphor-based, X-ray detectors has significantly affected image quality and diagnostic validity of the medical imaging examinations. This issue has been investigated by examining and further understanding the optical anisotropy in optical diffusion mechanisms. One crucial parameter of phosphor's structural properties that remarkably changes light distribution is the size of the phosphor particles. Up to now, the vast majority of studies have been carried out considering phosphor materials consisted of grains of equal size. In the present article an attempt is made to investigate the influence of grain size distribution (GSD) on light emitting characteristics and compare it with the condition of mean values assumptions. Our investigation was based on LIGHTAWE Monte Carlo simulation code with purpose to examine the Gd2O2S:Tb phosphor layer extracted from a mammographic Kodak Min-R 2 Cassette. The GSD was determined via scanning electron microscopy (SEM). Three cases of mean values were taken into account: (i) 1.48 μm obtained calculations of the aforementioned GSD, (ii) 2.50 μm and 7.00 μm taken from previous articles and manufacturer datasheets. Light emission was performed under different irradiation conditions (i. e., light quanta are produced by light source or an X-ray beam) and in terms of light amount and distribution. Our investigation showed that the optical distribution in real GSD was found: (a) sharper than the calculated mean value of the GSD and (b) broader than the mean value taken from the manufacturer datasheet. In particular, the deviation of GSD was found significantly high compared to 7.00 μm mean value. Examining the spatial resolution properties of both conditions, the deviation was around 16.5%, 18.2%, 14.8% assuming that the light source is situated within the phosphor mass, an X-ray beam of 20 keV and X-ray beam of 30 keV, respectively.

Photoluminescence Investigation of Tb Doped Yb2O3 Phosphors Produced by Precipitation Method

Un-doped and Tb doped ytterbium oxide (Yb2O3:Tb3+) particles with different dopant rates (2, 4, 6 and 8 at. %) were produced by precipitation method, subsequently by calcination at 1000 °C for 2 h. The crystal structure of all the particles had cubic Yb2O3 structure. The presence of Tb ion in Yb2O3 host structure has been proven from the XRD results. The crystal structure expanded compared to un-doped Yb2O3 particles with the dopant addition confirming lattice parameter (LP) values. LP and crystallite size (CS) values were in the range of 10.428 – 10.596 Å and 16 – 25 nm, respectively. Only one sharp peak was observed at 506 nm corresponding to 5D4 – 7F6 transition (green emission) from photoluminescence (PL) spectra of the phosphor particles. The PL emission intensities were strongly dependent on both CS and dopant rate. However, the dopant rate was more effective on the PL intensity than the CS.

A novel streak velocimetry technique based on 2D fits of decaying phosphor particle images

A new 2D velocimetry technique based on streaks formed by individual phosphor particles, which are moving during their luminescence decay following pulsed excitation is proposed in this study. Tin-doped phosphor particles (Sr,Mg)3(PO4)2:Sn2+ are dispersed into flows and excited by a pulsed UV light sheet. During the phosphor decay time (~27 µs), the emission streaks due to particle motion are recorded. A 2D fitting is then applied on each particle streak against the analytical expression of intensity distribution, to obtain the velocity information for each particle. Unlike Particle Tracking Velocimetry (PTV) this technique does not rely on any particle image searching procedure.

Low-temperature microwave synthesis and luminescence properties of far-red emission ZnGa2O4:Cr3+ phosphor for plant cultivation

In this work, microwave (MW) sintering method is employed to synthesize far-red (FR) emission ZnGa2O4:Cr3+ phosphor at a lower sintering temperature (900 °C), comparing with the conventional high temperature solid-state sintering (SS) method. Micrometer-size phosphor particles with smooth morphology are obtained due to the MW-induced small temperature gradient between the constituent particles upon the local dielectric volumetric heating. The MW sintering ZnGa2O4:Cr3+ phosphor exhibited excitable properties at the wavelengths of 260 nm, 410 nm and 550 nm, and the intensity of photoluminescence excitation (PLE) at 260 nm showed a dramatic enhancement, which is 2–3 times higher than that of SS sintering sample due to MW “non-thermal effect” in reducing the defect amount in the ZnGa2O4 host latices. These results together with decay time, thermal quenching and color coordinate evaluations showed that synthesis of FR emission ZnGa2O4:Cr3+ by MW-sintering method has advantages of high efficiency, energy saving and least environmental threats.

Simultaneous measurement of two-dimensional temperature and strain fields based on thermographic phosphor and digital image correlation

A two-dimensional (2D) phosphorescence-based method is presented for simultaneous measurement of strain and temperature. 6 μm Mg4FGeO6:Mn4+ phosphor particles were sprayed on the surface of the test target for use as a sensor. A measurement system was established, which included a high-speed camera, a 385 nm LED, and a signal generator. The signal generator controls the LED to output a 100 Hz light pulse to excite the phosphor. The phosphorescence is then detected by the high-speed camera with a frequency of 10 kHz. The temperature information is obtained from the phosphorescence decay rate using the lifetime method. A digital image correlation method was then used with the random markings formed by spraying. The 100 Hz temperature and strain measurement technique was implemented based on the current experimental conditions with an accuracy of 2% in temperature measurement and 16% and 9.3% in u- and v-direction respectively in strain measurement. The measurement procedure was used for measurements of temperature and deformation of an aluminum plate with a pulsed current in a temperature range of 0 °C–600 °C and a displacement range of 0–300 μm. The results from experiments show the possibility of 2D measurements of surface temperature and strain in a harsh environment with a non-invasive method.

Self-repairing inorganic phosphors/polymer composite film for restructuring luminescent patterns

Practical applications of phosphor particles in light sources and displays generally require the adhesion and support of polymer materials. However, these phosphor/polymer composites suffer from the difficulty in self-repairing after fracture. Inspired by the development of self-healing polymers, herein, we prepared phosphor/polymer composite films with self-repairing and restructuring properties. The N,N-dimethylformamide dispersant was used to uniformly disperse the phosphor particles in the self-healing polymer, which is considered to the key process for obtaining self-repairing properties. The developed self-repairing composite films are particularly suitable for restructuring luminescent patterns to provide multidimensional light-emitting modes including photoluminescence, persistent luminescence and mechanoluminescence. These results are expected to provide new insights for designing multifunctional self-repairing and reconstructing composites for anti-counterfeiting, integrated optics, optical communications, and artificial skins.

Study on Convective Flow Behaviors of Phosphor Particles During Curing Process of Silicone and the Influences on the Optical Performance of White LEDs

The correlated color temperature (CCT) variation of the phosphor-converted light-emitting diodes (LEDs) after curing is a common phenomenon. In the past, it was believed that the phenomenon was caused by the sedimentation of phosphor particles. However, not only sedimentation, but these particles can also flow with the natural convection of silicone because of nonuniform heating during curing. The convective flow of the phosphor particles during curing was studied in detail in this work. The CCT variation and phosphor particles flow in the LED device cup with different depths and wall inclination angles were studied. The results show that the CCT increases after curing when the depth of the device cup is shallow. The case is the opposite when the depth of the device cup is deep. The convective flow behaviors of the silicone were revealed in the simulation. The large-angle inclined wall can increase the silicone flow path length and inhibit the particles flow downward caused by the flow to a certain extent. It is envisioned that the findings will strengthen the understanding of the CCT variation phenomenon and guide the encapsulation structure design of LEDs for better color quality.

Effects of Bi3+ Ion-Doped on the Microstructure and Photoluminescence of La0.97Pr0.03VO4 Phosphor

The objective of this paper is to enhance the emission intensity of La0.97Pr0.03VO4 single-phased white light emitting phosphor. The Bi3+ ion-doped La0.97Pr0.03VO4 single-phased white light emitting phosphors are synthesized using a sol-gel method. The structure and photoluminescence properties of (La0.97-yBiy)Pr0.03VO4 (y = 0-0.05) phosphor are also examined. The XRD results show that the structure of La0.97Pr0.03VO4 phosphors with different concentrations of Bi3+ ion doping keeps the monoclinic structure. The SEM results show that the phosphor particles become smoother when the Bi3+ ion is doped. The excitation band for La0.97Pr0.03VO4 phosphor exhibits a blue shift from 320 nm to 308 nm as the Bi3+ ion contents are increased. The maximum emission intensity is achieved for a Bi3+ ion content of 0.5 mol%, which is about 30% greater than that with no Bi3+ ion doped. The CIE chromaticity coordinates are all located in the near white light region for different Bi3+ ion-doped La0.97Pr0.03VO4 phosphors.

Enhanced light harvesting in dye‐sensitized solar cells enabled by TiO 2 :Er 3+ , Yb 3+ upconversion phosphor particles as solar spectral converter and light scattering medium

To improve the light-harvesting properties of dye-sensitized solar cells (DSSCs), light from the ultraviolet (UV), visible, and infrared (IR) regions of the solar energy should be effectively harvested. Ru(II)-based dyes play a key role in harvesting energy from parts of the UV and visible regions but cannot absorb IR light. A strategy for improving the DSSC efficiency is to employ upconversion phosphors (UCPs) that can convert IR into visible light. In this study, using TiO2:Er3+, Yb3+ UCPs fabricated via a simple aerosol process and calcination, we examine the effects of upconversion and light scattering of UCPs added into the TiO2 thin-film-based photoelectrode on DSSC efficiency. Under IR irradiation, the fabricated TiO2:Er3+, Yb3+ UCPs emit visible light with emission peaks at 529, 550, and 650 nm. The power conversion efficiency (PCE) of the DSSCs is significantly improved by adding the optimized amount of UCPs with the average size of 500 nm in the TiO2 nanoparticles (NPs) matrix with the average size of 25 nm due to light upconversion and scattering effects. However, the addition of excess UCPs deteriorates the DSSCs efficiency owing to the rapid recombination between photogenerated electrons and holes and the increased interfaces between UCPs and TiO2. These results suggest that the light-harvesting efficiency of DSSCs in the IR region can be enhanced by employing the optimal amount of large-sized UCPs as light upconversion and scattering medium in the TiO2 thin-film-based photoelectrode.

Survivability of the thermographic phosphors YAG:Pr and SMP:Sn in a premixed flame

The survivability of two thermographic phosphors, YAG:Pr3+ and SMP:Sn2+ ((Sr,Mg)3(PO4)2:Sn2+), in a combustion environment is studied in the post-flame regime of a premixed propane/air flame. While the laser-induced luminescence of YAG:Pr3+ can be exploited for in situ temperature measurements in the exhaust gas above the flame, there is no in situ detectable luminescence for SMP:Sn2+ for any reaction conditions within the stability limits of the flame. The phosphor particles are recaptured above the flame and ex situ analyzed for chemical or structural changes using microscopic analysis (SEM/EDX) and x-ray diffraction. The microscopic analysis of post-flame YAG:Pr3+ does not show any alteration, whereas morphology and chemical composition of SMP:Sn2+ have been modified upon passing through the reaction zone, which is responsible for the loss of its luminescence properties.

Fabrication of mesostructured Y2O3:Eu3+ materials from metal–organic frameworks and their H2O2-sensitive turn-off luminescence

Mesostructured Y2O3:Eu3+ phosphor particles were fabricated by a pyrolytic conversion from a pertinent metal–organic framework (MOF), namely, MOF-76(Y):Eu with 1,3,5-benzenetricarboxylic acid ligands, aiming at luminescence sensing of H2O2. Large rod-like MOF-76(Y):Eu particles 301 ± 150 μm in average length were initially obtained by a reaction at 80 °C for 24 h. They were converted to rod-like Y2O3:Eu3+ particles 122 ± 34 μm in average length after heating at 500 °C. The Y2O3:Eu3+ particles actually consisted of primary nanoparticles 7.55 ± 1.43 nm in average size and had a mesoporous structure with a high specific surface area of 80.8 m2 g−1. The photoluminescence intensity of the Y2O3:Eu3+ particles decreased after treating with an aqueous H2O2 solution, which was recognized as H2O2-responsive turn-off luminescence. Three other kinds of Y2O3:Eu3+ particles, including those obtained from other MOF particles synthesized at room temperature, were also prepared and the effects of the microstructure on the degree of turn-off luminescence were examined. It was then observed that the H2O2-sensitivity was enhanced more effectively by using the MOF-derived Y2O3:Eu3+ particles having the higher specific surface area.

Comparative Investigation on Upconversion Luminescence Properties of Lu2O3:Er/Yb and Lu2O2S:Er/Yb Phosphors

A series of (Lu0.99−xEr0.01Ybx)2O3 and (Lu0.99−xEr0.01Ybx)2O2S (x = 0—0.1) phosphor particles are prepared to investigate their upconversion luminescence properties. Under 980 nm pumping laser, the two phosphors both exhibit strong green emission at ≈520—573 nm and weak red emission at ≈648—688 nm arising from 4S3/2/2H11/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3+, respectively. The optimum concentrations of Yb3+ sensitizers are found to be 1.0 at% in oxide and 0.5 at% in oxysulfide, and their corresponding CIE chromaticity coordinates are (0.29, 0.69) and (0.33, 0.65). The Lu2O2S:Er/Yb phosphor exhibits ≈42 times higher luminescence intensity than the Lu2O3:Er/Yb contrast. More Yb3+ addition further increases the proportion of red emission by the cross‐relaxation between adjacent Yb3+ and Er3+ and the multiphonon relaxation. The luminescence intensities of the two phosphors gradually increase as the laser output power increases and the upconversion mechanisms are both identified to be two‐phonon processes. The Lu2O2S:Er/Yb phosphor has a shorter lifetime than the Lu2O3:Er/Yb counterpart, whereas the lifetime for the red emission is longer than that for the green emission in each case.

Characterization of Plasmonic Scattering, Luminescent Down-Shifting, and Metal-Enhanced Fluorescence and Applications on Silicon Solar Cells.

This paper studied characterized the plasmonic effects of silver nanoparticles (Ag-NPs), the luminescent down-shifting of Eu-doped phosphor particles, and the metal-enhanced fluorescence (MEF) achieved by combining the two processes to enhance the conversion efficiency of silicon solar cells. We obtained measurements of photoluminescence (PL) and external quantum efficiency (EQE) at room temperature to determine whether the fluorescence emissions intensity of Eu-doped phosphor was enhanced or quenched by excitation induced via surface plasmon resonance (SPR). Overall, fluorescence intensity was enhanced when the fluorescence emission band was strongly coupled to the SPR band of Ag-NPs and the two particles were separated by a suitable distance. We observed a 1.125× increase in PL fluorescence intensity at a wavelength of 514 nm and a 7.05% improvement in EQE (from 57.96% to 62.05%) attributable to MEF effects. The combined effects led to a 26.02% increase in conversion efficiency (from 10.23% to 12.89%) in the cell with spacer/NPs/SOG-phosphors and a 22.09% increase (from 10.23% to 12.48%) in the cell with spacer/SOG-phosphors, compared to the bare solar cell. This corresponds to an impressive 0.85% increase in absolute efficiency (from 12.04% to 12.89%), compared to the cell with only spacer/SOG.

Fabrication of color conversion layers using adhesive transfer of phosphor particles for improving light extraction efficiency and uniformity of down-conversion white OLED

The down-conversion white OLED is one of the simple and effective ways for OLED display and lighting; it consists of a color conversion layer (CCL) and a blue-emitting source of the OLED. This paper introduces a process for adhesive transfer (AT) of phosphor particles to improve the light extraction efficiency and uniformity. The CCL formed by AT shows a surface fill factor of 91.6%, and is 5.5 times thinner than the one formed by wet-casting. In particular, the CCL fabricated by AT on a blue OLED achieved a 166% higher luminous efficiency than the wet-cast CCL. The effect of an extra non-emitting particle layer on top of the CCL fabricated by AT was also investigated and significant improvement was observed in both areal and angular uniformities (up to 99%). This transfer process for fabricating the CCLs is expected to play an important role in producing OLED displays and lighting with high efficiency at low cost.

Highly Efficient Liquid-Quantum Dot/Melamine- Modified Urea-Formaldehyde Microcapsules for White Light-Emitting Diodes

A liquid matrix is beneficial for improving the luminescence performance of quantum dots (QDs), although it is difficult to be packaged with light-emitting diode (LED) chips. In this study, liquid-QDs with chlorobenzene solution and melamine-modified urea-formaldehyde (MUF) were used as the core and shell structures, respectively, successfully yielding liquid-QD/MUF microcapsules for white LED packaging. The concentration of the liquid-QDs in the microcapsules was optimized, demonstrating an increase of 15.9% in the luminous efficiency, as compared to the traditional solid-QDs at a specific QD energy proportion. The efficiency roll-off can be attributed to the increased reabsorption and back-scattering loss at higher liquid-QDs and microcapsules concentrations. It was also confirmed that the liquid-QD/MUF microcapsules have an excellent thermal stability below 200 °C, owing to the protection of the MUF shells. Finally, white LEDs compounding the red liquid-QD/MUF microcapsules and YAG phosphor particles were fabricated, achieving a high luminous efficiency of 149.2 lm/W at 20 mA, correlated color temperature of 3301 K, and color rendering index of 88.8. This study will open new research avenues for liquid-QD packaging in white LEDs.

High-resolution velocimetry technique based on the decaying streaks of phosphor particles.

This Letter introduces a new, to the best of our knowledge, particle streak velocimetry technique based on decaying streaks formed by individual phosphor particles following pulsed excitation. Tin-doped phosphor particles are dispersed into flows and excited by a pulsed UV laser light sheet. Emission streaks are recorded as a result of particle motion during the persistence of luminescence (here ∼27µs). The two components of the flow velocity are derived from the streaks without directional ambiguity by applying to each streak a two-dimensional fit describing a linearly moving point source with a mono-exponential decaying emission. This technique can achieve high spatial resolution compared to particle image velocimetry (PIV), while also requiring much fewer computational resources than particle tracking velocimetry (PTV) at high seeding densities. The wavelength-shifted luminescence also allows rejection of reflected laser light. The approach was validated in a free jet against simultaneous PTV and PIV and then successfully applied to measure a canonical boundary layer flow.