Phosphor Films Research Articles

Influence of UV irradiation on the luminescence properties of CsPbBr3 perovskite quantum dots and CsPbBr3 perovskite quantum dots/PVDF composite film—for white LED application

Perovskite quantum dots (QDs) have been widely investigated for their excellent properties such as high color purity in displays, tunable emission wavelength, and high photoluminescence quantum yield. For device applications, improving the stability is an area of interest. In this study, the effects of UV irradiation on the structural and luminescence properties of CsPbBr3 perovskite quantum dots (CPB QDs) excited at 365 nm were investigated. To overcome the effects of UV irradiation, a CPB QDs/PVDF composite flexible film was prepared. It exhibits high structural and optical stability under UV irradiation and emits a highly intense green color. The emission wavelength and intensity were observed for three years, and the stability of the temperature-dependent emission intensity up to 400 K has been reported. In addition, it is stable in water. A white LED, fabricated by integrating a blue LED with CPB QDs/PVDF composite film and red phosphor, produces bright natural white light [(CIE x, CIE y) = (0.3704, 0.3611), and CCT = 4177 K] with a color gamut area coverage of 86.4% of the standard NTSC (1953) color space.&#xD.

Novel Orange-Emitting YPO4:Sm3+/Polymer Nanocomposite Phosphor Films for LED Applications.

A polymer based nanocomposite (NC) material embedded with highly luminescent nanopowders could be promising for replacing traditional luminescent materials from a technological pointof view.In this study, we have successfully obtained YPO4: Sm3+ /Polymer nanocomposite phosphor films by embedding YPO4: Sm3+ luminescent nanoparticles (NPs) for orange-light emitting diode (LED) applications. These luminescent NPs were synthesized using the sol gel method in different polymer matrices i.e. polystyrene (PS) and poly (methyl methacrylate) (PMMA) by using direct solution mixing. The structural, morphological, and photoluminescence characteristics of the nano-phosphors and resulting NC films were examined and discussed. The emission spectra of YPO4: Sm3+ (x at.%) nano-phosphors under near-UV excitation at 404nm were dominated by orange emission attributed to 6H5/2 4F7/2 (601nm) luminescence of Sm3+ ions. The optimum doping concentration of activator Sm3+ in YPO4 matrix was found to be 5 at.%. When the doping concentration of Sm3+ was higher than 5 at.%, concentration quenching occurred. The incorporation of YPO4: Sm3+ NPs into polymer matrices indicated that the NCs retained the original luminescence properties of the luminescent NPs, although a decrease in their emission intensity was observed for the NC films, attributable to a polymer matrix effect, which dominated in PS matrix. The fluorescence decay times of NPs in the NC films were measured and compared to those of proper YPO4: Sm3+ nano-phosphors. A decrease in decay time in NC film was observed due the effective refractive index effect. Temperature-dependent photoluminescence (TDPL) of PMMA NC film was studied in 100-400K range, investigating the thermal stability of the film. Additionally, CIE coordinates confirmed the red-orange light emission of the prepared phosphors and NC films. The obtained results indicate that the synthesized polymer-nanophosphor NC films are promising candidates for orange-LED applications.

Garnet-structure phosphors with ultra-high color purity red emission for potential warm WLED and flexible-transparent displays

Red-emitting phosphors play a pivotal role in the field of lighting technologies. This study introduces an innovative class of Li6SrEu2Sb2O12 garnet-structured phosphors, distinguished by the resistance to concentration quenching. A comprehensive examination of the crystal structure, electronic configuration, and photoluminescence characteristics has been conducted. Notably, the doping Eu3+ ions and their doping concentrations barely affected the crystal structure and morphology, and the band gap slightly decreased as the doping concentration increased. Interestingly, the obtained samples exhibit an ultra-high color purity, good thermal stability (78.60 % at 423 K), and suitable internal photoluminescence quantum yield (44.18 %). Consequently, a phosphor-converted white LED has been successfully fabricated, which boasts an outstanding correlated color temperature of 3271 K. Beyond conventional application, this research also introduces the concept of innovative flexible-transparent displays harnessing the phosphor film. Overall, this work has synthesized a groundbreaking red-emitting phosphor, poised to enhance traditional lighting sources and potentially pave the way for new applications in the field of advanced optical displays.

Scalable Fabrication of Black Phosphorous Films for Infrared Photodetector Arrays.

Bulk black phosphorous (bP) exhibits excellent infrared (IR) optoelectronic properties, but most reported bP IR photodetectors are fabricated from single exfoliated flakes with lateral sizes of <100µm. Here, scalable thin films of bP suitable for IR photodetector arrays are realized through a tailored solution-deposition method. The properties of the bP film and their protective capping layers are optimized to fabricate bP IR photoconductors exhibiting specific detectivities up to 4.0×108cm Hz1/2 W-1 with fast 30/60 µs rise/fall times under λ = 2.2µm illumination. The scalability of the bP thin film fabrication is demonstrated by fabricating a linear array of 25 bP photodetectors and obtaining 25×25pixel IR images at ≈203ppi with good spatial fidelity. This research demonstrates a commercially viable method of fabricating scalable bP thin films for optoelectronic devices including room temperature-operable IR photodetector arrays.

Performance improvement of reflective phosphor film via adjusting the thickness realizing bright and efficient laser lighting.

Phosphor-in-glass-film (PiG-F) has been extensively investigated, showing great potential for use in laser lighting technique. Thickness is apparently a key parameter for PiG-F, affecting the heat dissipation, absorption, and reabsorption, thus determining the luminous efficacy and luminescence saturation threshold (LST). Conventional studies suggest that thinner films often have lower thermal load than that of the thicker ones. Unexpectedly, we found that the Lu3Al5O12:Ce (LuAG:Ce)-based PiG-F with a moderate thickness (78 μm) yielded the optimal LST of 31.9 W (14.2 W·mm-2, rather than 28.0 W (12.3 W·mm-2) for the thinnest one (56 μm). This unexpected result was further verified by thermal simulations. With the high saturation threshold together with a high luminous efficacy (∼296 lm·W-1), an ultrahigh luminous flux of 7178 lm with a luminous exitance of 2930 lm·mm-2 was thus attained. We believe the new, to the best of our knowledge, findings in this study will substantially impact the design principles of phosphors for laser lighting.

Synthesis and characterization of rare earth ion doped YVO4 thin film phosphors grown by PLD

Synthesis and characterization of rare earth ion doped YVO4 thin film phosphors grown by PLD

Development of high conducting phosphorous doped nanocrystalline thin silicon films for silicon heterojunction solar cells application

We have investigated the plasma-enhanced chemical vapor deposition growth of the phosphorus-doped hydrogenated nanocrystalline silicon (n-nc-Si:H) film as an electron-selective layer in silicon heterojunction (SHJ) solar cells. The effect of power densities on the precursor gas dissociation are investigated using optical emission spectra and the crystalline fraction in n-nc-Si:H films are correlated with the dark conductivity. With the P d of 122 mW cm−2 and ∼2% phosphorus doping, we observed Raman crystallinity of 53%, high dark conductivity of 43 S cm−1, and activation energy of ∼23 meV from the ∼30 nm n-nc-Si:H film. The n-nc-Si:H layer improves the textured c-Si surface passivation by two-fold to ∼2 ms compared to the phosphorus-doped hydrogenated amorphous silicon (n-a-Si:H) layers. An enhancement in the open-circuit voltage and external quantum efficiency (from >650 nm) due to the better passivation at the rear side of the cell after integrating the n-nc-Si:H layer compared to its n-a-Si:H counterpart. An improvement in the charge carrier transport is also observed with an increase in fill factor from ∼71% to ∼75%, mainly due to a reduction in electron-selective contact resistivity from ∼271 to ∼61 mΩ-cm2. Finally, with the relatively better c-Si surface passivation and carrier selectivity, a power conversion efficiency of ∼19.90% and pseudo-efficiency of ∼21.90% have been realized from the SHJ cells.

The use of He buffer gas for moderating the plume kinetic energy during Nd:YAG-PLD growth of EuxY2−xO3 phosphor films

We have investigated the He buffer gas process of moderating the kinetic energy of the pulsed laser deposition (PLD) plume during EuxY2−xO3 phosphor film growth. When using a neodymium yttrium aluminum garnet laser for PLD thin film growth, the kinetic energy of the ablation plumes can be high enough to cause the formation of point defects in the film. The buffer gas pressure is an important process parameter in PLD film growth. We find that the presence of the He buffer gas reduces the kinetic energy of the laser deposition plume through many low-angle collisions in the gas phase by a factor of 7 without reducing the deposition rate. This is because He is much lighter than any of the elements in the plume and it does not affect the composition of the oxide films. Consequently, the resputtering of the Y2O3 film surface by the plume was significantly suppressed in the presence of the He gas moderator, leading to a decrease of the defect density in the Y2O3 films. The improvement of the film quality was verified by a systematic analysis of time-resolved photoluminescence (PL) data for EuxY2−xO3 composition–gradient films. The PL lifetime and intensity of Eu0.2Y1.8O3, which shows the highest PL intensity, increased by 13.3% and 36.4%, respectively, when the He gas moderation process was used. The He buffer gas process is applicable to the PLD growth of the other oxide materials as well, where the reduction of the kinetic energy of the plume would bring the PLD process closer to the molecular beam epitaxy growth condition.

HfTiO4 transparent thick film phosphors activated with Eu3+, Dy3+, and Tb3+ ions

Hafnium (Hf)-based double oxides show promise as high-efficiency scintillators due to large effective atomic numbers and high relative density. However, the preparation of these scintillation crystals is challenging due to their high melting points and incongruent melting behavior. In the present study, we demonstrated that the chemical vapor deposition (CVD) of single-phase HfTiO4 films on quartz glass substrate was successfully deposited at temperatures ranging from 973 to 988 K, with a TiO2 molar ratio in the precursor vapor of 25–45 mol% TiO2. The deposition rate of HfTiO4 reached 36 µm h−1. The films exhibited an in-line transmittance of 78 % relative to the raw glass substrate at a wavelength of 600 nm. When activated with Eu3+, Dy3+, and Tb3+ ions, the HfTiO4 films displayed red, yellow, and green photoluminescence emissions originated from the 4f–4f transitions of each trivalent rare-earth ion under ultraviolet light irradiation. HfTiO4 exhibited no intrinsic background emission, suggesting that the addition of a selected activator could yield a phosphor with the desired emission color range.

New optically stimulated luminescence dosimetry film optimized for energy dependence guided by Monte Carlo simulations

Optically stimulated luminescence (OSL) film dosimeters, based on BaFBr:Eu2+ phosphor material, have major dosimetric advantages such as dose linearity, high spatial resolution, film re-usability, and immediate film readout. However, they exhibit an energy-dependent over-response at low photon energies because they are not made of tissue-equivalent materials. In this work, the OSL energy-dependent response was optimized by lowering the phosphor grain size and seeking an optimal choice of phosphor concentration and film thickness to achieve sufficient signal sensitivity. This optimization process combines measurement-based assessments of energy response in narrow x-ray beams with various energy response calculation methods applied to different film metrics. Theoretical approaches and MC dose simulations were used for homogeneous phosphor distributions and for isolated phosphor grains of different dimensions, where the dose in the phosphor grain was calculated. In total 8 OSL films were manufactured with different BaFBr:Eu2+ median particle diameters (D50): 3.2 μm, 1.5 μm and 230 nm and different phosphor concentrations (1.6%, 5.3% and 21.3 %) and thicknesses (from 5.2 to 49 μm). Films were irradiated in narrow x-ray spectra (N60, N80, N-150 and N-300) and the signal intensity relative to the nominal dose-to-water value was normalized to Co-60. Finally, we experimentally tested the response of several films in Varian 6MV TrueBeam STx linear accelerator using the following settings: 10 × 10 cm2 field, 0deggantry angle, 90 cm SSD, 10 cm depth. The x-ray irradiation experiment reported a reduced energy response for the smallest grain size with an inverse correlation between response and grain size. The N-60 irradiation showed a 43% reduction in the energy over-response when going from 3 μm to 230 nm grain size for the 5% phosphor concentration. Energy response calculation using a homogeneous dispersion of the phosphor underestimated the experimental response and was not able to obtain the experimental correlation between grain size and energy response. Isolated grain size modeling combined with MC dose simulations allowed to establish a good agreement with experimental data, and enabled steering the production of optimized OSL-films. The clinical 6 MV beam test confirmed a reduction in energy dependence, which is visible in small-grain films where a decrease in out-of-field over-response was observed.

Assessment of Perception of Pain with E-Speed Film, CCD Sensor and Photostimulable Phosphor Plates for Intraoral Radiographs in Children using Three Pain Rating Scales

Abstract Background: Dental radiography is an integral part of intraoral evaluation. Children are often uncomfortable during the placement of film or sensor due to the impingement of the soft tissues. Thus, the perception of pain with three intraoral radiographic methods in children was evaluated using three subjective pain rating scales. Aim: To evaluate the discomfort with three different techniques, that is, intraoral periapical (IOPA) radiograph, charge-coupled device (CCD), and photostimulable phosphor (PSP) luminescence (PSPL), using the Wong–Baker Faces Pain Rating Scale (WBFPRS), numerical rating scale, and visual analog scale (VAS). Materials and Methods: A sample of 35 children aged 6–12 years were divided into two groups: group 1 (6–8 years) and group 2 (9–12 years). For each child, simulations of the three radiological methods (IOPA, CCD, and PSPL) were performed. The meaning of each facial expression on the WBFPRS, VAS, and the numbers on the numerical rating scale was explained to each child before the procedure. Statistical Analysis Used: A one-way analysis of variance (ANOVA) test and paired-samples t-test are used. Results: The results revealed that the CCD sensors elicited higher pain scores than those obtained with IOPA and PSPL, whereas the IOPA film showed the least pain score. Higher score values were obtained in group 1 than in group 2, indicating that children aged 6–8 years felt higher discomfort than the 9- to 12-year age group for the same procedure. This difference was statistically significant (P &lt; 0.001). Conclusion: It was concluded that conventional IOPA films were tolerated better by children when compared to PSP plates and CCD sensors.

Film characteristics of ZnS:Mn phosphor prepared by metal precursor sulfurization and its application to inorganic electroluminescent devices

A ZnS:Mn phosphor film for an inorganic electroluminescent (EL) device fabricated by metal precursor sulfurization was evaluated. Metallic ZnMn was thermally evaporated at room temperature and then sulfurized by sulfur gas flowing in a tube furnace at various temperatures from 400 to 800 °C. X-ray diffraction, energy dispersive x-ray spectroscopy, and photoluminescence observations indicated that a ZnS:Mn phosphor layer was formed after sulfurization. A thick-dielectric EL device was manufactured using the obtained ZnS:Mn phosphor. The EL luminance of 216 cd/m2 at 1.0 kHz was measured when the phosphor layer was sulfurized at 500 °C. A charge density versus voltage (Q-V) curve was also analyzed to evaluate the EL phosphor characteristics.

Highly Efficient Color Conversion of 3D Photonic Crystal Phosphor Films for Micro‐Light‐Emitting Diode Applications

The color conversion efficiency of phosphor films can be significantly improved by producing them in the shape of photonic crystals (PhCs). When light with photonic band‐edge wavelengths is incident on a PhCs phosphor film, the excitation photons are resonantly absorbed, enhancing the emission intensity. This study develops three‐dimensional PhC phosphor films based on self‐assembled inverse opal structures. PhC phosphors are constructed using a silk fibroin polymer and red organic fluorescent dyes (λpeak ≈ 610 nm) doped into it. The photonic structures are designed using electromagnetic wave simulations and photonic band structure analyses. The fabricated PhC phosphor films are integrated with blue micro‐light‐emitting diode (micro‐LED) chips (λpeak ≈ 452 nm), resulting in a color conversion efficiency increase of more than 1.5 times that of bulk phosphor films. Additionally, experiments are performed using various micro‐LED chips with a size of less than 100 μm. Overall, the results of this study demonstrate the potential of PhC phosphor films in future micro‐LED‐based devices and applications, including displays and communication systems.

The temporal response of inorganic temperature-sensitive phosphor films with different layer thickness and composition

The temporal response of inorganic temperature-sensitive phosphor films with different layer thickness and composition

Eu3+ activated non-crystalline BaTiO3 ultra-thin film phosphor with high purity, tailored red emission from n-UV excitation for WLEDs applications

As an alternative WLED red phosphor, BaTiO3 sol-gel based ultra-thin films were doped with various mol% of Eu3+ and annealed at 500 °C. The films were amorphous with short range ordered structure as seen via XRD and Raman analysis. Photoluminescence (PL) emission spectra enabled the determination of Eu3+ location asymmetry in the host via Judd-Ofelt (J-O) theory, from which Ω2=9.37×10−20cm2 and Ω4=1.55×10−20cm2 were derived, proving that the Eu3+ ions were non-centrosymmetrically located. This enhanced the Eu3+ 5D0 → 7F2 electric-dipole transition at 614.0 nm with the strongest emission from 30 mol% doping. 395 nm excited intense and narrow red spectral profiles which exhibited excellent colour coordinates (x = 0.657, y = 0.342), quantum efficiency (25.7% at a film thickness of ∼380 nm), and colour purity of (92.0%) whereby the red to orange ratio (R : O) enables colour tailoring with 5 mol% to 30 mol% Eu3+doping. This facilitates flexible control over the colour output, ensuring that it can be easily tailored to meet specific application requirements. The aforementioned results indicate that the red-emitting Eu3+ activated amorphous BaTiO3 ultra-thin film phosphors exhibit promising potential for application in n-UV excited WLEDs as a red phosphor with a branching ratio β0→2=81.43% making it a potential candidate for red laser materials too.

Introducing TiO2 to design high-reflectivity AlN composite substrates to synthesize green/white converters for high-brightness reflective laser illumination☆

Phosphor-in-glass (PiG) has been prepared into various types of phosphor films owing to its simplicity process, exceptional color purity, and convenient color adjustability. Nevertheless, existing reflective PiGs films have encountered limitations in terms of stability and feasibility as reliable color converters, mainly attributed to issues related to thermal deposition and insufficient optical efficiency. Herein, we propose to use AlN substrate with superior thermal conductivity to coat the TiO2 layer to obtain TiO2–AlN (TA), which enhances the reflectivity of blue light to facilitate the light conversion process. By incorporating highly thermally stable LuAG:Ce-PiGs on a TA substrate, the LuAG:Ce-PiTA converter exhibits a luminous flux of 1102 lm@6.4 W, and maintains a relative intensity of 94.6% at 473 K benefiting from the high thermal conductivity of 34.1 W/(m·K). The addition of CASN3:Eu to the color converter 50 L&10C-PiTA enables an impressive CRI of 90.7. Relative luminescence intensities of LuAG:Ce-PiTA and 50 L&10C-PiTA only decrease by 5.35% and 3.28%, respectively, in the 24 h illumination aging decay test of the reflective laser module. The results confirm the suitability of the optimally designed TA substrate for LuAG:Ce color converter applications in high-power reflective laser illumination.

Effect of Temperature Gradient on Particle Distribution of Phosphor Film During Curing

Effect of Temperature Gradient on Particle Distribution of Phosphor Film During Curing

Pixelated Phosphor Converter for Laser‐Driven Adaptive Lighting

AbstractWith the advent of artificial intelligence and unmanned driving, it is an inevitable trend to provide laser‐driven adaptive lighting with super‐brightness, high penetration, and high spatial resolution; one of the best solutions is to pump pixelated phosphor converters by laser diodes (LDs). However, achieving high‐performance pixelated phosphor converters remains a great challenge due to the large size of commercial phosphor particles. In this study, promising pixelated phosphor films are proposed to be fabricated by producing arrayed holes in the Ag substrate with the laser direct writing technology and then filling the holes with the mixture of phosphor particles and the heat‐resisting inorganic glue. A strong thermal transfer field grid is built in Y3Al5O12:Ce3+‐pixelated‐film@Ag, which can withstand a high luminance saturation threshold of over 18.08 W mm−2 pumped by blue LDs. The maximum luminous flux density is ≈1300 lm mm−2, and the luminance is 3.36 × 107 cd m−2 of the white pixel light with excellent uniformity. Further, based on this fabrication strategy, the full‐color‐pixelated‐film@Ag is successfully prepared for the first time. The realization of laser‐driven white pixel light and full‐color pixel light shows an interesting application in intelligent adaptive lighting, and this study paves an avenue for designing pixelated phosphor converters.

Tribocatalytically-active nickel/cobalt phosphorous films for universal protection in a hydrocarbon-rich environment

High-contact stresses generated at the sliding interfaces during their relative movement provide a unique combination of local heating and shear- and load-induced compression conditions. These conditions, when involving the sliding of surfaces with certain material characteristics, may facilitate tribochemical reactions with the environment, leading to the formation of a protective, damage-suppressing tribofilm directly at the contact. Here, we employ the electrodeposition process to design a coating composed of a hard cobalt-phosphorous matrix with the inclusion of tribocatalytically-active nickel clusters. The coating is optimized in terms of its relative composition and mechanical characteristics. We demonstrate the excellent tribological performance of the coating in the presence of a hydrocarbon environment, both in the form of a liquid lubricant and as a hydrocarbon-saturated vapor. Characterization of the wear track indicates that the origin of such performance lies in the formation of a protective carbon-based tribofilm on the surface of the coating during sliding. These results contribute to the advancement of knowledge on material transformations in the contact, thus providing a robust and versatile approach to addressing tribological challenges in mechanical systems.

Copper-based halide films with high photoluminescence quantum yield in the visible region deposited in situ by double source aerosol-assisted chemical vapor deposition

A huge family of luminescent low-dimensional metal halides for optoelectronic applications has emerged recently as a green alternative to the highly toxic lead halide phosphors. To date, studies on the controlled deposition of these materials as films to be integrated into optoelectronic architectures remain scarce. Here, the synthesis and characterization of highly luminescent films of copper halide phosphors with emissions in violet: K2CuCl3, blue: Cs5Cu3Cl6I2, and green: Cs3Cu2Cl5 are reported. The films were obtained by multisource aerosol-assisted chemical vapor deposition (AACVD) from methanolic solutions at low temperature and under ambient conditions. Photoluminescent quantum yield values obtained for the films deposited on quartz substrates have values of 52% for K2CuCl3, 85% for Cs5Cu3Cl6I2, and 99% for Cs3Cu2Cl5. These values were highly influenced by the substrate since for samples deposited on glass substrates the values are 26.17% for K2CuCl3, 60.47% for Cs5Cu3Cl6I2, and 59.7% for Cs3Cu2Cl5. Different textured morphologies, with valuable applications in light-harvesting, were found for each stoichiometry. Finally, x-ray photo-emitted spectroscopy was employed to demonstrate the existence of only Cu(I) highly emissive species, suggesting that AACVD could be an excellent alternative for metal halide film deposition.