Phosphor Thin Films Research Articles

Structure and Photoluminescence Properties of Rare-Earth (Dy3+, Tb3+, Sm3+)-Doped BaWO4 Phosphors Synthesized via Co-Precipitation for Anti-Counterfeiting.

Barium tungstate (BaWO4) powders with various sintering temperatures, and BaWO4:Dy3+ phosphor samples with concentrations of different rare-earth (RE) activator ions (Dy3+, Sm3+, Tb3+) were prepared through co-precipitation. The structural, morphological, and photoluminescent characteristics of barium tungstate phosphors depend on the concentration of RE ions. The crystallographic characteristics of the synthesized BaWO4 were analyzed using X-ray diffraction (XRD) patterns. The size and shape of the crystalline particles were estimated based on images measured with a field emission scanning electron microscope (FE-SEM). As the sintering temperature of the BaWO4 particles increased from 400 °C to 1000 °C, the size of the particles gradually increased and showed a tendency to clump together. In the sample doped with 7 mol % Dy3+ ions, the intensity of all emission bands reached their maximum. The emission spectra of the RE3+-doped BaWO4 powders by excitation at 325 nm were composed of yellow (Dy3+), red (Sm3+), and green (Tb3+) band at 572, 640, and 544 nm. This indicates that most of the RE3+ ions absorbed the position without reversal symmetry in the BaWO4 lattice. These results propose that strong emission intensity and tunable color for the phosphors can be accomplished by rare-earth doped host with an suitable quantity. In addition, the phosphor thin films, having high transparency from aqueous colloidal solutions, were deposited on banknotes, and it is considered whether it is suitable for anti-counterfeiting applications.

Retraction Note to: The effect of deposition pressure on the material properties of pulsed laser deposited BaAl2O4:Eu2+, Dy3+ thin films

BaAl2O4:Eu2+, Dy3+ thin films have been successfully deposited by pulsed laser deposition (PLD) method. Formation of crystalline phase was confirmed by X-ray diffraction (XRD) measurement. The average crystallite size calculates using the Scherer’s formula was found to be between 15.2 and 30.5 nm. Scanning electron microscopy (SEM) micrograph revealed that, the films have non uniform morphology with variable grain size for all the deposition conditions. The surface morphology displays some tendency for agglomeration as a function of increasing deposition pressure, which may be due to the sintering or coalesce of small particles into clusters. Atomic force microscopy (AFM) measurements also show an increase in surface roughness as the oxygen deposition pressure is increased. The BaAl2O4:Eu2+, Dy3+ thin-film phosphors exhibit photoluminescence (PL) emission at 495 nm upon 254 nm excitation. This can be attributed to the electronic transition of Eu2+ ions from 4f65d1 to 4f. The present study recommends that this phosphor could be used as luminescent materials for light emitting diode applications.

Role of Pr3+ ions as hole-trapping centers for the electroluminescence of (Ca0.6Sr0.4)0.998Pr0.002Ti0.9Al0.1O3−δ thin films

Thin-film electroluminescent devices composed of an (In0.975Sn0.025)2O3 anode, a phosphor, and a Sn0.95Sb0.05O2 cathode were prepared by a sol–gel and firing method. The phosphor thin films were composed of four layers, (Ca0.6Sr0.4)0.998Pr0.002Ti0.9Al0.1O3–δ or Ca0.6Sr0.4Ti0.9Al0.1O3–δ. The relation between the space distribution of Pr3+ ions and the electric/electroluminescence properties were investigated. The electroluminescence occurred predominantely at (Ca0.6Sr0.4)0.998Pr0.002Ti0.9Al0.1O3–δ layer closest to the anode. We suggested the electroluminescence mechanism that a hole injected from the anode is trapped at a Pr3+ ion, an electron injected from the cathode recombines with the trapped hole, and the Pr3+ ion is excited to emit a photon.

Cation-Deficiency-Induced Crystal-Site Engineering for ZnGa2O4:Mn2+ Thin Film.

Zn-deficient spinel-type ZnGa2O4:Mn2+ phosphor thin films were prepared using pulsed laser deposition. With an increase (decrease) in the Zn deficiency (concentration) of the films, changes in lattice constant, optical band gap, and photoluminescence spectra were observed. All films without γ-Ga2O3:Mn showed green luminescence attributable to the transition from the 4T1 state to the 6A1 state. In addition, the spectral shape changed depending on the temperature. The luminescence spectra have two peaks resulting from the Mn2+ ions located in the tetrahedral and octahedral sites. These peaks had different thermal quenching temperatures, which were around 320 and 260 K, respectively. Therefore, the spectral shape changed with increasing temperature. The spectral shape also depended on the Zn concentration. With an increase (decrease) in the Zn concentration (deficiency) of the films, the intensity of emission from Td increased in comparison with that from Oh. Therefore, the position of Mn2+ was controlled by Zn deficiency similarly to the effect of crystal-site engineering.

Preparation of boron carbon oxynitride phosphor film via laser chemical vapor deposition and annealing

The present study demonstrates the synthesis of a boron carbon oxynitride (BCNO) phosphor film by laser annealing treatment of a boron carbonitride (BCN) film via laser chemical vapor deposition (CVD) using a single precursor source. A dense and uniform BCN film (B0.38C0.37N0.25) was prepared on a fused quartz substrate at a high deposition rate of 18.4 μm h−1 via laser CVD at a deposition temperature of 1373 K using only tetrakis(dimethylamino) diboron with argon (Ar) as a carrier gas. The surface of the BCN film was subsequently annealed in air at 1223 K by laser irradiation for 300 s to obtain a BCNO thin film. A disordered boron nitride (BN) layered structure, turbostratic BN, with a one-dimensional orientation was formed in the BCNO thin film. Upon excitation at 375 nm, the BCNO thin film exhibited photoluminescence with a broad emission band at 580 nm. The combination of CVD using a less-hazardous precursor and short-time annealing using a high-power laser enabled the preparation of a thin BCNO phosphor film.

Structural and Optical Properties of Sm-doped BaMoO4 Phosphor Thin Films Deposited by Radio-Frequency Magnetron Sputtering

BaMoO4:Sm3+ phosphor thin films were prepared using radio-frequency magnetron sputtering at several growth temperatures, followed by rapid thermal annealing. All the phosphor thin films revealed tetragonal structures with preferential (112) orientation. The emission and the excitation intensities, transmittances, and band gap energies of the phosphor thin films were found to depend significantly on the growth temperature. The excitation spectrum consisted of a strong broad band centered at 261 nm in the range 210–310 nm arising from charge transfer transitions between O−2 and Sm3+ and three weak bands, one each at 370, 406, and 475 nm. The emission spectra of the phosphor thin films under excitation at 267 nm showed six emission bands located at 451, 558, 595, 640, 700, and 762 nm, respectively which were due to the typical 4f − 4f transitions of Sm3+ ions. The highest emission intensity of the BaMoO4:Sm3+ phosphor thin film was achieved at a growth temperature of 400 °C, where the optical band gap was 4.70 eV and the color chromaticity coordinate was (0.492, 0.353). These results suggest that the BaMoO4:Sm3+ phosphor thin film is a promising candidate for application in red-light-emitting devices.

Fabrication of electroluminescent carbon fiber composite for damage visualization

Conventional damage inspection methods and characterization of carbon fiber (CF) composites are typically destructive, expensive, and do not provide spatial resolution. Non-destructive monitoring of carbon fiber composites is presented with an electroluminescent (EL) thin-film dielectric phosphor sandwiched between compacted and semi-transparent dispersed CF composite lamina. Different fractural states in the CF composite cause EL luminance changes which allows for damage detection and localization in the CF through visual inspection. The proposed methodology offers simple and effective structural health monitoring to any product manufactured from CF ranging from aerospace to high-performance sporting goods.

Characterization, packaging, and optical model of single-primary color phosphor thin films and LEDs

Blue, green, and red phosphor thin films (PTFs) used for NUV LED were prepared by hot pressing method. The excitation spectrums of PTFs have broadband absorption characteristics owing to the 4f7 → 4f65d transition of Eu2+; the emission peaks are 445 nm, 520 nm, and 627 nm, respectively. The phosphor conversion efficiency (PCE) gradually increases and finally remains unchanged with phosphor mass fractions because of absorption saturation effect. Different color LEDs are packaged by NUV chips and PTFs; spectral decomposition and data fitting methods are used to achieve the fitting of the relationship between the phosphor mass fraction and the emission light intensity of the NUV chip and phosphor. The double Gaussian model is used to express the spectral power distribution (SPD) of a single-primary color LED and compare it with the measured results. White LEDs (WLEDs) were prepared by two methods, the first is the combination of multi-LEDs, the second is NUV chip pumps three-color-mixed phosphor directly. Experimental results showed that the WLEDs prepared by first method with the light color parameters of CCT = 5342 K, LER = 274 lm/W, show small parameter difference of ΔCCT = 24 K, ΔLER = 15 lm/W, NCC = 98.94% compared with the calculated results. The WLEDs prepared by second method with the light color parameters of CCT = 5292 K, LER = 263 lm/W shows a 4.0% decrease in LER.

Control of Eu Oxidation State in Y2O3-xSx:Eu Thin-Film Phosphors Prepared by Atomic Layer Deposition: A Structural and Photoluminescence Study.

Structural and photoluminescence studies were carried out on Eu-doped Y2O3−xSx thin films grown by atomic layer deposition at 300 °C. (CH3Cp)3Y, H2O, and H2S were used as yttrium, oxygen, and sulfur precursors, respectively, while Eu(thd)3 was used as the europium precursor. The Eu oxidation state was controlled during the growth process by following the Eu(thd)3 pulse with either a H2S or O3 pulse. The Eu(thd)3/O3 pulse sequence led to photoluminescence emission above 550 nm, whereas the Eu(thd)3/H2S pulse sequence resulted in emission below 500 nm.

Blue and green emission from Ho3+ doped zinc titanate phosphor thin films by sol-gel

Zinc titanate ZnTiO3 phosphor thin films doped with 1, 2, and 3 mol% of Ho3+ ions were fabricated using sol-gel method a combined with dip-coating technique on silica glass substrate and subsequent thermal annealing in the range of 600–900 °C. Effects of annealing temperature and Ho3+ ions concentration on the structure and optical properties of these phosphor thin films were investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible transmittance spectroscopy, excitation, and emission spectroscopy. Results revealed that ZnTiO3 nanocrystals were formed upon 600 °C annealing temperature. At 900 °C polycrystalline films including ZnO and TiO2 anatase phase were observed. The average diameter of nanocrystals showed temperature dependence and was varied in the range-over 15–48 nm which was revealed by SEM images with cracks free. The EDS showed homogenous distribution of Ho3+ ions in the thin film specimens. It was found that Ho3+ ions incorporated into the nanocrystals. As a result, the room temperature luminescence color emission of the synthesized phosphor thin film specimens can be tuned from blue to green by switching the excitation wavelength from 360 nm to 430 nm. The achieved result makes these phosphor thin films promising for several applications such as optoelectronics and light-emitting.

Effect of background atmosphere and substrate temperature on SrO:Bi3+(0.2 mol%) thin films produced using pulsed laser deposition with different lasers

SrO:Bi3+ (0.2 mol%) phosphor thin films were grown by pulsed laser deposition (PLD) on Si (100) substrates in vacuum and different O2 atmospheres at different substrate temperatures using a Nd:YAG laser (266 nm) with energy 33.3 mJ/pulse, a KrF laser (248 nm) with energy 300 mJ/pulse or a ArF laser (193 nm) with energy 150 mJ/pulse. The microstructure and photoluminescence (PL) of these films were found to be highly dependent on the background atmosphere and substrate temperature. X-ray diffraction (XRD) analysis showed that the SrO:Bi3+ (0.2 mol%) films varied from amorphous to highly crystalline depending on the deposition conditions. Atomic Force Microscope results showed that the surface roughness decreased as the substrate temperature increased. The main PL emission peak position of the thin films showed a shift to shorter wavelengths at 427 nm, when compared to the powder (445 nm). The difference in wavelength was attributed to the Bi3+ ions, which are very sensitive towards the environment. Time of flight secondary ion mass spectroscopy depth profiles for the samples deposited in vacuum and O2 at different substrate temperatures look similar, except for a slight thickness variation.

Spectral Re-Absorption Effect of Multi-Primary Phosphor Thin Films and Various Package Structures on the Performance of Near-Ultraviolet White LED

We prepared blue, green and red phosphor thin films (PTFs) with different phosphor concentrations used for near-ultraviolet (NUV) LEDs respectively, and then investigated their spectral re-absorption/excitation/emission process. The functional relationship between optical powers and concentrations were established by using the exponential equation. The relationship between the spectral deformations and concentrations were evaluated by the correlation coefficient. Based on NUV LED chip, eight package structures of white LEDs were prepared. The luminous efficiency (LE) of white LED based on Blue/Green/Red@NUV laminate structure reached 85.48 lm/W, which was 27.7% higher than that of hybrid structure, correlated color temperature (CCT) was 3518K, Rf was 83, Rg was 106, and when hybrid structure thickness was reduced to one-third points, the LE increased by 21.5% to 81.36 lm/W, CCT was 4200K, Rf was 93, Rg was 101, CCT uniformity test showed that the uniformities of laminated and hybrid structures were 80.06% and 96.91% respectively. The results showed that the laminated structure was beneficial to improve the LE, while the hybrid structure had the advantage of uniformity improvement and spectrum continuity due to multi-particle scattering and spectral deformation of the phosphor.

Substrate-dependent luminescent properties of thin-film phosphors: Comparative study of Eu3+-doped ZnO films deposited on SiO2, Si, and sapphire substrates

Photoluminescence from Eu3+-doped ZnO (ZnO:Eu) thin films deposited on SiO2 substrates was compared with that of films on Si(100) and sapphire C-plane substrates in terms of correlation with crystallinity. Common to the three kinds of substrate, deposition with H2O vapor followed by post annealing resulted in reasonably intense Eu3+ emissions upon bandgap excitation. For the films on SiO2, the emission intensity increased for Eu contents up to 3 at.%, whereas concentration quenching prevailed at Eu contents above 1 at.% on Si and sapphire substrates. Such differences demonstrate the advantages of SiO2 substrate over Si and sapphire. Its tolerance against high-density doping was due to moderately c-axis-oriented ZnO crystals on SiO2. The amorphous network of SiO2 may absorb strain in the ZnO crystal when Zn2+ sites are substituted with Eu3+ ions, and thus, degradation in the crystallinity of the ZnO host is suppressed. Another difference between the films on Si and SiO2 substrates was in the defect emission spectra superimposed on the Eu3+ emission. Only a single broad deep-level emission peak centered at 600 nm was observed for films on Si substrates, whereas multiple peaks at 520, 590, and 690 nm appeared for films on SiO2. Thus, the defect species created by annealing of ZnO host films on Si were different from those on SiO2 substrates, and this led to the distinct deep-level emission characteristics.

RETRACTED ARTICLE: The effect of deposition pressure on the material properties of pulsed laser deposited BaAl2O4:Eu2+, Dy3+ thin films

BaAl2O4:Eu2+, Dy3+ thin films have been successfully deposited by pulsed laser deposition (PLD) method. Formation of crystalline phase was confirmed by X-ray diffraction (XRD) measurement. The average crystallite size calculates using the Scherer’s formula was found to be between 15.2 and 30.5 nm. Scanning electron microscopy (SEM) micrograph revealed that, the films have non uniform morphology with variable grain size for all the deposition conditions. The surface morphology displays some tendency for agglomeration as a function of increasing deposition pressure, which may be due to the sintering or coalesce of small particles into clusters. Atomic force microscopy (AFM) measurements also show an increase in surface roughness as the oxygen deposition pressure is increased. The BaAl2O4:Eu2+, Dy3+ thin-film phosphors exhibit photoluminescence (PL) emission at 495 nm upon 254 nm excitation. This can be attributed to the electronic transition of Eu2+ ions from 4f65d1 to 4f. The present study recommends that this phosphor could be used as luminescent materials for light emitting diode applications.

Depth profiling and photometric characteristics of Pr3+ doped BaMoO4 thin phosphor films grown using (266 nm Nd-YAG laser) pulsed laser deposition

Abstract Pr3+ doped BaMoO4 nano thin films have been deposited by pulsed laser deposition on a glass substrate using a Nd-YAG laser (λ = 266 nm). The thin phosphor films were deposited in an ultra-high vacuum at a substrate temperature of 400 °C at different oxygen partial pressures. The crystal structure, surface morphology, film thickness and composition were examined by X-ray diffraction patterns, scanning electron microscope and energy-dispersive X-ray spectroscopy, respectively. The binding energy of the core levels, chemical state, atomic fractions, depth profiling of the thin film were investigated by X-ray photo-electron spectroscopy. The photoluminescence excitation, emission spectra and energy transfer process involved in Pr3+ doped BaMoO4 thin films were analyzed. The color chromaticity co-ordinates, fluorescence decay time and the photometric properties of the as-deposited thin phosphor films were examined.

Effect of Substrate Temperature on the Properties of Eu-Doped SrSnO₃ Phosphor Thin Films Grown by Sputtering.

Eu3+-doped SrSnO₃ (SrSnO₃:Eu3+) phosphor thin films are deposited on sapphire substrates by radio-frequency magnetron sputtering. The substrate temperature is varied from 25 to 400 °C. All SrSnO₃:Eu3+ films show amorphous behavior, while the band gap energies decrease with an increase in the substrate temperature and are determined to be 4.16-4.26 eV. The optical transmittance spectra exhibit an average transmittance of approximately 91% in the wavelength range 500-1100 nm; a gradual increase in emission intensity arising from the 5D0→7F₂ transition (618 nm) of Eu3+ is observed with increasing substrate temperature. These results suggest that the optimum substrate temperature for depositing SrSnO₃:Eu3+ red-emitting phosphor thin films is 400 °C.

Tunable color emission of transparent boron nitride nanophosphors towards anti-counterfeiting application

Water-dispersible transparent nanophosphors based on boron nitride nanoparticles were prepared by pyrolysis of boric acid-melamine molecular adduct. Intense blue-green emission was activated by concomitant incorporation of Ce3+ and Tb3+ when excited by near-UV light. Color emission from the nanophosphor was modified from blue to green by tuning atomic ratio of Ce3+ and Tb3+ without disturbance of crystal structure of hexagonal boron nitride. The intense green emission with high quantum efficiency (∼0.74) was realized in BN: Ce3+,Tb3+ phosphors at [Tb3+]/[Ce3+] = 0.62. However, further addition of Tb3+ ions induced formation of non-luminescent TbBO3 phase and mitigation of luminescence intensity. From the steady state and time-resolved photoluminescence spectra, the luminescence of Ce3+ was quenched with Tb3+ by energy transfer process of efficiency approaches to unity. Transparent thin films were deposited from aqueous colloidal solution of nanophosphors on various substrates to demonstrate high transparency of phosphor thin films feasible to anti-counterfeiting application which requires concealment and identification by naked eyes. Extreme sustainability of nanophosphors in high temperature environment was also confirmed from thermal treatment at 1200 °C for 5 h in air.

Effect of Deposition Temperature on the Optical Properties of La 2 MoO 6 :Dy 3+ ,Eu 3+ Phosphor Thin Films

Effect of Deposition Temperature on the Optical Properties of La 2 MoO 6 :Dy 3+ ,Eu 3+ Phosphor Thin Films

Effect of particle sizes and mass ratios of a phosphor on light color performance of a green phosphor thin film and a laminated white light-emitting diode.

Green phosphor thin films with different silica resin/phosphor mass ratios and phosphor particle sizes were prepared by the hot pressing method. A 405 nm near-ultraviolet light-emitting diode (LED) chip was used to package the laminated white LED (WLED), and the correlated color temperature, luminous efficiency of radiation, light color uniformity, and color coordinate of the laminated WLED were obtained. An increase in the mass ratio and decrease in particle size can effectively affect the scattering coefficient of phosphor photons and the efficiency of the absorption–excitation–emission process, increasing the efficiency and light color uniformity of phosphor thin films and laminated WLEDs. By comprehensive evaluation of various light color parameters, a laminate was prepared with a mass ratio of silica resin/phosphor = 6 : 0.75, and the optimum value of the WLED was obtained. According to the IES TM30 standard, its Rf reached 92, Rg reached 101, and Rg and color distortion icons showed increased saturation for green color. Its luminous efficiency of radiation value of 270.21 lm W−1, correlated color temperature of 4423 K, and neutral white characteristics indicate that it is a device suitable for lighting applications.

Enhancement of efficiency and CCT uniformity for red phosphor thin films, red LEDs and laminated white LEDs based on near-ultraviolet LEDs using MgO nanoparticles.

Red phosphor thin films (PTFs) with different MgO nanoparticle concentrations for near-ultraviolet (NUV) LEDs were prepared based on their strong scattering effect; red LEDs and laminated white LEDs were packaged further. SEM and XRD showed that CaAlSiN3:Eu2+ (CASN) and MgO nanoparticles were uniformly distributed in silicone resin and their crystal structure remained unchanged. The phosphor conversion efficiency (PCE) had a maximum value of 83.15% when the MgO nanoparticle concentration was 15 wt%. An increase of concentration can improve the spatial distribution uniformity of photonics for 410 nm, 627 nm and 660 nm. Fluorescence lifetime showed that the value is positively correlated with concentration change. The packaged red LED luminous flux reaches a maximum of 20.337 lm at a concentration of 15 wt%. The laminated white LED showed that the MgO nanoparticle concentration can be used to adjust the correlated color temperature (CCT) from 4322 K to 1987 K. Under similar CCT, the red phosphor concentration is only 1.83 wt%, the dosage is reduced by 56.12%, and the corresponding luminous efficiency of radiation (LER) and luminous efficiency (LE) are 296.03 lm W−1 and 73.72 lm W−1 respectively. The increase was 11.42%, the decrease was 10.14%, the color rendering index (CRI) increased from 90.6 to 91.8, and CCT uniformity increased from 82.04% to 89.27% with an increase of 8.81%. Research shows that MgO nanoparticles have potential application value in the preparation of high-quality white LEDs.