Orthosilicate Phosphors Research Articles

The Light Features and Bredigite Layout for Orthosilicate Phosphor in WLED Devices

The Light Features and Bredigite Layout for Orthosilicate Phosphor in WLED Devices

Giant enhancement of a long afterglow and optically stimulated luminescence phosphor BaCaSiO4: Eu2+ via Pr3+ codoping for optical data storage

The need for data storage is growing in modern society, and optical data storage (ODS) is considered one of the most promising storage techniques. However, significant challenges must be overcome, including improving the performance of volatile memory and expanding its storage capacity. In this study, we report a novel ortho-silicate phosphor, BaCaSiO4, doped with Eu2+, which exhibits sustained luminescence and optically stimulated luminescence (OSL). Following the Pr3+ co-doping, the long afterglow and OSL performance of BaCaSiO4: Eu2+ significantly improved owing to the substantial increase in trap density. Owing to numerous trapped and released electrons, the optical storage capacity of the OSL material significantly increased. As a proof-of-concept, ODS flexible media were fabricated using the obtained OSL material, based on which reversible information write-in and read-out were implemented using ultraviolet irradiation and optical/thermal stimulation, respectively. Furthermore, the OSL-based ODS mechanism was revealed through a comprehensive study of electron trapping, storage, and release kinetics.

White-emitting orthosilicate phosphor α-Sr2SiO4:Ce3+/Eu2+/K+: a bimodal temperature sensor with excellent optical thermometric sensitivity.

Non-contact temperature sensors with low cost, high reliability and high sensitivity have attracted increasing research interest in recent years. In this study, we synthesized a bimodal optical temperature sensor Sr2SiO4:Ce3+/Eu2+/K+ with excellent thermometric sensitivity through a high-temperature solid-state reaction method. In the matrix of α-Sr2SiO4, Ce3+ luminescence exhibits excellent thermal stability (∼129.1%@250 °C), while Eu2+ shows strong thermal quenching (∼21.7%@250 °C), leading to a significant change in the fluorescence intensity ratio (FIR) of Ce3+ (437 nm) and Eu2+ (550 nm) as a function of temperature. This feature enables the phosphor exhibiting outstanding sensitivity in the temperature range of 298-523 K. To be exact, it demonstrates a maximal relative sensitivity of 0.93% K-1 at 348 K. Its absolute sensitivity linearly increases and reaches 3.46% K-1 at 523 K. Besides, it has a large chromaticity shift (ΔE = 228 × 10-3 in 298-523 K) against temperature, making the temperature change visible to the naked eye. We first demonstrate a CIE chromaticity coordinate technique for temperature sensing with high accuracy and good sensitivity by using the function of x or (x2 + y2)0.5 against T. These unique optical thermometric features allow Sr2SiO4:Ce3+/Eu2+/K+ to serve as an accurate and reliable thermometer probe candidate for temperature sensing applications.

Centrosymmetric and non-centrosymmetric structural and optical study of Eu3+ ions in (Ba,Ca,Na)9(Al,Y)2Si6O24 orthosilicate phosphors

Trigonal Ba6-2mEumNamCa3Al2Si6O24 (m = 0.1–1) and Ba6Ca3-2nEunNanAl2Si6O24 (n = 0.1–1) orthosilicate phosphors were prepared using a solid-state method at high temperatures. The single phase of the obtained phosphors was identified by analyzing the indexed peak positions in the X-ray diffraction (XRD) patterns. Three different sites of Ba2+ and Ca2+ cations are occupied in the (Ba,Ca)9Al2Si6O24 host structure. The locations of Eu3+ and Na + ions substituting Ba2+/Ca2+ sites in the (Ba,Ca)9Al2Si6O24 host lattice were revealed by structural and optical investigations. The magnetic dipole 5D0–7F1 and electric dipole 5D0–7F2 transitions from the Eu3+ emission spectra assigned centrosymmetric and non-centrosymmetric sites, respectively, in the orthosilicate Eu3+-doped phosphors. The centrosymmetric Eu3+ behaviors in Ba5Eu0.5Na0.5Ca3Al2Si6O24, Ba5Eu0.5Na0.5Ca3AlYSi6O24, and Ba8Eu0.5Na0.5Y2Si6O24 phosphors are discussed based on distortions around the Ba2+(I) cation site.

Regulating electron traps of Eu2+-doped Ba1.6Ca0.4SiO4 persistent and optically stimulated luminescence phosphor toward optical data storage

Nowadays, the optical data storage (ODS) has already become one of the most promising data storage technologies in this digital era. Optically stimulated luminescence (OSL) material has recognized as a considerable potential candidate for the new-generation ODS. The improvement of volatile memory performance and the increase of storage capacity are two critical challenges to be solved. In this work which is reporting on, a new novel Eu2+-doped orthosilicate phosphor has been studied showing both persistent luminescence and OSL. The trap density is significantly enhanced by 10-fold via Dy3+ codoping. Information can be reversibly written into the traps by UV light illumination and then read out by optical or thermal stimulus. The capture and release dynamics of electrons by traps are studied in detail to reveal the OSL-based ODS mechanism. Moreover, as a proof-of-concept, ODS flexible medium is fabricated using the as-obtained OSL material to certify the application feasibility for erasable optical data write-in and read-out.

Luminescent performances of Ba9-Ca Al2Si6O24:Eu2+, Mn2+ orthosilicate phosphors along with Ca2+ contents

Optical materials composed of (Ba8.8-p-qCap)Eu0.2MnqAl2Si6O24 (p = 2–4, q = 0–0.2) were prepared via a solid-state reaction at high temperature. The X-ray diffraction patterns of the obtained phosphors were analyzed to index the peak positions. The single-phase phosphors showed a trigonal orthosilicate structure with R3‾H symmetry. The photoluminescence emission spectra of the (Ba8.8-pCap)Eu0.2Al2Si6O24 phosphors depending on the Ca2+ ion content (p) were exploited under 365-nm excitation. When the Mn2+ emitter was co-doped in the (Ba8.8-pCap)Eu0.2Al2Si6O24 structure, the energy-transfer mechanism from Eu2+ to Mn2+ was investigated, and their electric multipole interactions were examined. The Commission Internationale de I'Eclairage (CIE) coordinates near the blue-green to orange regions of the obtained phosphors were observed. Thermal quenching with the activation energy of (Ba8.7-pCap)Eu0.2Mn0.1Al2Si6O24 (p = 2–4) phosphors in the temperature range of 298–448 K was achieved under a 365-nm light-emitting diode (LED). The tendency of the internal quantum efficiency of the (Ba5.8-qCa3)Eu0.2MnqAl2Si6O24 (q = 0.01, 0.1, 0.2) phosphors on a 365-nm LED chip was measured in addition to the color-rendering index, correlated color temperature, and CIE coordinates for the white LEDs.

Studies on structural properties, luminescence behavior and zeta potential of Dy3+ doped alkaline earth ortho-silicate phosphors

Alkaline earth orthosilicate (Sr2SiO4) phosphor doped with Dy3+ was synthesized by a traditional high-temperature solid-state reaction method. XRDanalysis confirmed the formation of the phosphor with the orthorhombic crystal structure and their phase purity was checked using theoretical fitting Rietveld refinement. Zeta potential measurements of parent phosphor in different medium were performed to check its stability. The surface morphology and the elemental composition of the phosphors were examined using SEM and EDX, respectively. The optical behavior is determined by PL analysis. CIE coordinates of the phosphors represents the white light emission characteristics of Sr2SiO4: Dy3+ phosphors. Due to white light emission characteristic, this work will open a new window for its use in W-LED applications. Thermoluminescence (TL) behavior of phosphor was studied and its TL kinetic parameters were estimated based on computerized glow curve deconvolution (CGCD) fitting.

Synthesis and luminescence behavior of Ba2SiO4:Dy3+ phosphors in presence of charge compensator ions

A series of dysprosium (Dy3+) doped barium ortho-silicate (Ba2SiO4) phosphors were synthesized by conventional Solid State reaction technique. In order to find out the phase purity and crystal structure, characterization of the prepared powder samples was done by X-ray diffraction (XRD) method. FTIR method confirms the presence of all elemental compositions. Photoluminescence (PL) properties were studied. The PL spectra was observed to study the effect of concentration of Dy3+ ion and it is found that the prepared phosphors show two strong emission peaks in the blue and yellow region at 478 nm and 573 nm, respectively, when excited by the near-ultraviolet (UV) of wavelength 348 nm. The critical distance between the Dy3+ ions was calculated using Blasse’s equation. Effect of monovalent ion K+ was examined as a charge compensator ion and observed that co-doping of charge compensator ion enhances the luminescence intensity. Chromaticity coordinates of the phosphor are found near to white light region, which confirms their applicability in solid state lighting applications; especially in white-LEDs.

Thermoluminescence studies of Dy3+-doped calcium barium orthosilicate codoped with Li+ ion

Calcium barium orthosilicate (CaBaSiO4) phosphors having different concentrations of Dy3+ were prepared by solid-state reaction method, and phase structure of the sample was identified by X-ray diffraction (XRD) characterization. It is observed that the XRD pattern matched well with JCPDS file No. 48-0210. Thermoluminescence (TL) of the UV-irradiated (254 nm) samples was recorded using routine TL set-up Nucleonix TLD reader with constant heating rate 5 °C s−1. It is found that the sample containing 1 mol% of Dy3+ and exposed for 27 min gives optimum TL intensity at 130.14 °C and shows single TL glow peak. It order to examine the effect of charge compensator ion, Li+ ions are introduced and it is found the incorporation of charge compensator enhances the TL output. Samples having 1 mol% of Dy3+ and 6 mol% of Li+ exposed for 30 min to UV exposure show maximum intensity at 118 °C. It is also observed that temperature corresponding to TL peak varies with varying Li concentration (ranging from 105.76 to 123.88 °C). Samples having 1 mol% of Dy3+ and 6 mol% of Li+ exposed for 30 min to UV exposure were selected for further studies, such as activation energy, order of kinetics and frequency factor, and all these parameters were evaluated using peak shape method.

Thermal-stable and high-efficient orange-red emitting orthosilicate phosphors LiGd9(SiO4)6O2:Mn2+ for n-UV-pumped w-LEDs

Abstract A novel orange-red emitting orthosilicate phosphor LiGd9(SiO4)6:Mn2+ (LGS:Mn2+) belongs to hexagonal lattice with P63/m space group was synthesized via solid-state method and the phase composition, crystal structure as well as luminescence properties were examined for potential application in near ultraviolet (n-UV) pumped white light emitting diodes (w-LEDs). The as-prepared LGS:Mn2+ phosphor exhibits three excitation bands peaked at 273, 312 and 410 nm, which corresponds to the transitions of Gd3+ from ground state 8S7/2 to 6I7/2, 6P7/2 and Mn2+ from ground state 6A1(6S) to the individual components of the multiplets [4A1(4G), 4E(4G)], respectively. Upon excitation at 312 nm, the phosphors display an intense broad orange-red emission peaked around 594 nm, which ascribed to the typical spin-forbidden transition (4T1(4G)-6A1(6S)) of the Mn2+ ions. The concentration quenching mechanism and average separation distance in conjunction with fluorescence decay times of Mn2+ ions in LGS:Mn2+ phosphor were discussed. The indispensable parameters for application in n-UV high-powered w-LEDs, such as the thermal quenching of photoluminescence and internal quantum efficiency of LGS:Mn2+ phosphor, have also been investigated in detail. The above results indicate that LGS:Mn2+ could play a key role as an orange-red emission for potential application in n-UV-based w-LEDs.

Spectroscopic investigations on high efficiency deep red-emitting Ca2SiO4:Eu3+ phosphors synthesized from agricultural waste

Europium doped calcium orthosilicate (Ca2SiO4) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO2). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu3+ ions luminescent properties in Ca2SiO4 phosphors have been studied from the excitation, emission and decay curves analysis. The 5D0 → 7FJ transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu3+ ion. A charge transfer band (CTB) at around 260 nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu3+ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu3+ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu3+ ions (0.01–0.4 mol%) and the lifetimes varied from 2.67 to 2.78 ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.

Energy transfer between terbium and europium ions in barium orthosilicate phosphors obtained from sol-gel route

The present paper reports on the energy transfer mechanism between Eu3+ and Tb3+ in barium orthosilicate obtained from the sol-gel route, when both activators concentration is varied. The synthetic methodology was adjusted to provide high crystalline and monophasic Ba2SiO4. In the emission spectra under 250 nm excitation, both Eu3+ (5D0→7FJ) and Tb3+ (5D3→7FJ and 5D4→7FJ) transitions can be observed at low Eu3+ doping concentrations with an unexpected and intense blue emission from Tb3+. However, when the Eu3+ content is higher than that of the Tb3+, just the Eu3+ emission is noticed. Also, it is possible to tune the phosphor emission from red to pink by varying the Eu3+ and Tb3+ content. From the excitation spectra, we inferred that energy transfer (ET) from Tb3+ to Eu3+ occurs at any doping situation, nonetheless, the opposite process happens just when both activators amount is similar. An approach using the Tb3+ and Eu3+ lifetimes and the Eu3+ quantum efficiency confirms this observation, indicating that not only the matrix act as sensitizer to the Eu3+ ions, but also Tb3+ ions contribute by increasing the Eu3+ quantum efficiency in up to 20%. Finally, by using the Van Uitert theory, it was found for this system that the ET between the two rare-earth ions is dominated by the dipole-dipole mechanism.

Synthesis and photoluminescent properties of the Dy3+ doped YSO as a high-temperature thermographic phosphor

Dy3+-doped yttrium orthosilicate (Y2SiO5, abbreviated YSO) phosphors were synthesized: (1) by conventional high temperature solid-state method using two types of fluxes: lithium fluoride (LiF) and boron oxide (B2O3); (2) by metal alkoxide sol-gel method using isopropoxide assisted co-precipitation with subsequent annealing to explore its possible application in high-temperature thermometry. It was experimentally observed that the use of LiF flux affects the luminescent properties due to improvement of the crystal quality of crystallites and co-doping Li+ and F- ions. Herein, a strategy involving the use of different fluxes and concentration of Dy3+ ions has been developed to achieve high photoluminescence (PL) intensity and high intensity ratio of different PL peaks. The case of incorporated LiF in the host crystal lattices revealed strong enhancement of luminescence intensity of YSO:Dy (more than three times higher at 293K) compared to the luminescence intensity of the phosphors synthesized with B2O3. Based on the results of high temperature measurements, it can be stated that YSO:Dy is a favorable phosphor for high temperature measurement, with a temperature sensitivity range comparable to YAG:Dy but with a lower PL decay time which is reduced by about 60%. For temperatures up to 1250K the intensity ratio approach offers better measurement capabilities while the temperature sensitivity above 1250K is superior for the decay time approach.

Phosphor-based light conversion for miniaturized optical tools.

This paper describes the application of phosphor-based light conversion for its use in optogenetic experiments to tailor the wavelength of light emitted from implantable miniaturized light sources. Gallium-nitride-based blue light-emitting diodes are used in combination with orthosilicate phosphor immersed in an epoxy matrix and emitting in the yellow wavelength range. The miniaturization of the phosphor-containing polymer droplets toward diameters as small as 300μm provides the compatibility with implantable optical probes. The parameter study applied here varied the concentration of the phosphor material in the polymer matrix as well as the droplet height in order to tailor the characteristics of blue-to-yellow light conversion.

Exquisite morphology, highly emissive yellow Sr1.44Ba0.46SiO4:0.1Eu2+ phosphor synthesized by a liquid phase precursor process

Yellow phosphors are the major components of contemporary solid-state lights. YAG:Ce3+ is a widely adopted yellow phosphor component; however, it too has limitations. Here, we report the synthesis and application of a very highly efficient yellow-emitting orthosilicate phosphor. Yellow-emitting Sr1.44Ba0.46SiO4:0.1Eu2+ was synthesized by an unconventional cellulose template liquid phase precursor process (CTLPP). The naturally abundant and nonhazardous cellulose template facilitates efficient synthesis at lower temperatures. The synthesized phosphor was indexed to α-Sr2SiO4 phase and exhibited broad excitation and broad emission with a peak at 545 nm, very high intensity, almost 130% of commercial YAG upon excitation at 450 nm. The morphology of the phosphors was also nearly spherical, which also enables their use in WLEDs. Use of non-stoichiometric Si precursors (i.e. Sr1.44Ba0.46SixO4:0.1Eu2+, x = 0.95, 1.0 and 1.05) in the process resulted in remarkable effects on the morphology (size and surface) and luminescent characteristics and exceptional quantum efficiencies of the phosphors.

An excellent cyan-emitting orthosilicate phosphor for NUV-pumped white LED application

The Ba9Lu2Si6O24:Ce3+cyan phosphor has excellent luminescence properties and displays promising application in NUV-based white LEDs with high performance.

Dual color emitting Eu doped strontium orthosilicate phosphors synthesized by bio-template assisted ultrasound for solid state lightning and display applications

A novel Sr2SiO4:Eu (1–5mol %) superstructures (SS) were synthesized using bio-sacrificial A.V. gel assisted ultrasound method. Powder X-ray diffraction patterns confirmed the presence of both α and β phase formation. It was evident that the morphological growth was highly reliant on A.V. gel concentration, sonication time, pH and sonication power. The formation mechanisms for different hierarchical SS were proposed. From diffuse reflectance spectra, the energy band gap was estimated and found to be ∼4.70–5.11eV. The photoluminescence emission spectra for the excitation at 392nm, shows characteristic emission peaks at 593, 613, 654 and 702nm which were attributed to 5D0→7F0, 7F1,7F2 and 7F3 transitions of Eu3+ ions respectively. Conversely, when the samples were subjected to the heat treatment at 850°C for 3h under argon atmosphere, display an intense broad emission peak with two de-convoluted peaks at 490 and 550nm due to 4f65d1→4f1 (8S7/2) transitions of Eu2+ ions. The concentration quenching phenomenon was discussed which attributes to energy transfer, electron–phonon coupling and ion–ion interaction. The Judd–Ofelt intensity parameters and other radiative properties were estimated by using emission spectra. The CIE chromaticity coordinate values of Sr2SiO4:Eu2+ and Eu3+ nanophosphors were located in green and red regions respectively. The calculated CCT and CRI values specify that the present phosphor can be fairly useful for both green and red components of white LED’s. Luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting diodes. Overall, the results elucidated a rapid, environmentally benign, cost-effective and convenient method for Sr2SiO4:Eu3+ synthesis and for the possible applications such as solid state lighting and display devices.

Thermoluminescence, OSL and defect centers in Tb doped magnesium orthosilicate phosphor

Mg2SiO4:Tb phosphor exhibits four thermoluminescence (TL) peaks at 124, 244, 300 and 370°C for a heating rate of 2°C/s, 244°C peak being the main dosimetry peak. The irradiated phosphor exhibits CW-OSL response on stimulation with blue (470nm) light. Thermal decay of OSL shows that all the TL traps contribute to CW-OSL signal. Its TL and OSL sensitivities are 0.21 and 0.038, respectively, than that of Al2O3:C (Landauer Inc.). Its CW-OSL response increases linearly up to 30Gy, thereafter increase was supralinear up to the studied dose of 1000Gy. Electron Spin Resonance (ESR) studies were carried out to study the defect centers induced in the phosphor by gamma irradiation and also to identify the centers responsible for the TL process. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least three distinct centers. One of the centers (center I) with an isotropic g-factor 2.0122 is attributable to an intrinsic O- radical and this correlates with the main TL peak at 244°C. Center II with an isotropic g-factor 2.0012 is assigned to an F+-center (singly ionized oxygen vacancy) and is the likely recombination center for all the TL peaks. Both the centers grow with radiation dose at least up to 1 kGy. Center III with an axial symmetric g-tensor with principal g-values g||=2.0049 and g⊥=2.0029 is identified as an F+-center and is not related to the observed TL peaks in the phosphor.

Preparation and Luminescent Properties of Sm3+-Doped High Thermal Stable Sodium Yttrium Orthosilicate Phosphor.

Orange-red-emitting sodium yttrium orthosilicate NaYSiO4:xSm3+ (x = 0.005, 0.01, 0.02, 0.05, 0.10, 0.15, and 0.20) were synthesized. The phase structure and photoluminescence properties of these phosphors were investigated. The emission spectrum obtained by excitation into 406 nm contains exclusively the characteristic emissions of Sm3+ at 571 nm, 602 nm, 648 nm, and 710 nm, which correspond to the transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2, and 6H11/2 of Sm3+, respectively. The strongest one is located at 602 nm due to the 4G5/2 --> 6H7/2 transition of Sm3+, generating bright orange-red light. The optimum dopant concentration of Sm3+ ions in NaYSiO4:xSm3+ is around 2 mol%, and the critical transfer distance of Sm3+ is calculated as 23 Å. The thermal quenching temperature is above 500 K. The fluorescence lifetime of Sm3+ in NaYSiO4:0.02Sm3+ is 1.83 ms. The NaYSiO4:Sm3+ phosphors may be potentially used as red phosphors for white light emitting diodes.

Impulsive excitation of mechanoluminescence in europium activated strontium ortho-silicate phosphor

Europium doped strontium ortho-silicate (Sr2SiO4:Eu2+) phosphor was prepared by the traditional high temperature solid state reaction method. The crystal structure of sintered phosphor was consistent with the orthorhombic crystallography with space group Pmna. The surface of the prepared phosphor was not found to be uniform and particle distribution in different size. An energy dispersive X-ray spectroscopy (EDS) spectrum confirms the presence of elements in sintered phosphor. The mechanoluminescence (ML) intensity of Sr2SiO4:Eu2+ phosphor increases linearly with increasing impact velocity of the moving piston which suggests that these phosphors can be used as sensors to detect the stress of an object. Thus, the present investigation indicates the piezo-electricity is responsible to produce ML in prepared Sr2SiO4:Eu2+ phosphor. The time of the peak ML intensity and the decay rate did not change significantly with respect to increasing impact velocity of the moving piston and peak ML intensity increases linearly.