Determination of optical and structural properties of lithium silicate ceramics with different ratios of Sm doped

In this study, the synthesis and luminescence characterization of Samarium (Sm³⁺) doped lithium metasilicate (Li₂SiO₃) phosphor ceramic were investigated. It was presented and discussed the results obtained on the luminescence and other optical studies such as X-ray diffraction (XRD), optical absorption and luminescence properties of Li₂SiO₃:Sm³⁺ phosphor ceramic. The Li₂SiO₃ compound was shown a characteristic phase in XRD. The doping in the lithium compound was not having a significant effect on the basic crystal structure of the material. The maximum photoluminescence (PL) emission for Sm³⁺ doped Li₂SiO₃ was observed at 554, 583, 641, 725 nm and bore resemblance to the visible region of the spectrum. The glow curves of all synthesized materials have a complex peak structure after being irradiated with a ⁹⁰Sr–⁹⁰Y beta source. In addition, the peak between 400 and 600 nm was seen in the radioluminescence (RL) spectrum because of a wide peak thought to be caused by silicate.     

Study on preparation and luminescent properties of Eu3+-doped LaAlO3 and GdAlO3

Eu³⁺-doped trigonal LaAlO₃ and orthorhombic GdAlO₃ phosphors have been successfully synthesized by sol–gel method. The crystallization processes of the phosphors have been characterized by X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC). The optical properties of these phosphors were investigated using the photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The influences of the different structures and bonding of the hosts on the luminescence performance of Eu³⁺ ion-doped LaAlO₃ and GdAlO₃ were investigated in detail based on chemical bond theory. Under appropriate UV-radiation, the reddish orange light emitted from GdAlO₃:Eu³⁺ was brighter than that from LaAlO₃:Eu³⁺. Such a brightly luminescent phosphor could be considered as an ideal optical material for the development of new optical display systems.     

A novel bifunctional Dy3+ activated RbCaF3 single phase phosphor: Facile synthesis and dual-luminescence properties for WLEDs and dosimetry applications

A series of Dy³⁺ activated RbCaF₃ phosphors was synthesized by the conventional high temperature solid state reaction technique under ambient atmosphere. The structural properties and morphology of synthesized compounds were analyzed by PXRD and FE-SEM, respectively. The chemical composition of synthesized phosphors was obtained by EDAX. The phosphor was excited at 386 nm and monitored at 484 and 574 nm, and the strongest peak was located at 484 nm (blue region). In addition, the point of RbCaF₃:Dy³⁺ with calculated chromaticity coordinates in the CIE diagram was located in the yellow region. TL characteristics of the RbCaF₃:Dy³⁺ phosphor was analyzed and the glow curve peak was emitted at 355 K. The symmetry factor, Balarin parameter, activation energy and frequency factor were calculated by Chen method from the TL glow curve, and the TL signal degradation was also analyzed.     

Co-existence phenomenon of Ce3+/Ce4+ and Tb3+ in Ce/Tb co-doped Zn2(BO3)(OH)0.75F0.25 phosphor: Luminescence and energy transfer

A serials of Zn₂(BO₃)(OH)_0.75F_0.25 (ZBF), Tb³⁺, Ce^3+/4+ single-doped ZBF and Tb³⁺/Ce^3+/4+ co-doped ZBF novel phosphors with belt-like morphology were obtained through hydrothermal reaction without any surfactant. The obtained samples were characterized by XRD, SEM, EDS, TEM, TGA, XPS, DR, PL, and DT. The TGA curve shows that the phosphor is thermal stability. XPS results show that Tb³⁺ is present in the Tb-doped phosphor, and the Ce³⁺/Ce⁴⁺ mixed valence is present in the Ce-doped phosphor. The PL results indicate that ZBF host material and ZBH:Ce^3+/4+ can emit blue light, ZBF:Tb³⁺ can emit green light. Compared with the Tb³⁺ single doped phosphor, the Tb³⁺/Ce^3+/4+ co-doped phosphors shown stronger emission and shorter decay time, which is attributed to the effective energy transfer from the Ce^3+/4+ to Tb³⁺ ions.     

Spectral and trapping parameters of Eu3+ in Gd2O2S nanophosphor

This paper reports the structural, photometric, spectral and trapping parameters of Eu³⁺-doped gadolinium oxysulphide nanophosphor. The X-ray diffraction (XRD) data show the presence of the hexagonal phase of Gd₂O₂S and a crystallite size in nanometre range. Different structural parameters were calculated from XRD data. The Fourier transform infrared (FTIR) spectrum also confirms the formation of a compound. Scanning electron microscope studies reveal the morphology and crystallite size of the prepared phosphor. The band gap of the phosphor was calculated from diffuse reflectance spectra using the Kubelka–Munk function at 4.76 eV. The phosphor was illuminated with ultraviolet light and shows the characteristic red luminescence corresponding to ⁵D₀→⁷F_J transitions of Eu³⁺. The Judd–Ofelt intensity parameters and spectral parameters were estimated from the photoluminescence data. The nanophosphor was irradiated with γ-rays in the dose range 15–50 Gy for thermoluminescence (TL) studies and a shifting of the peak towards lower temperatures was observed with increasing γ-dose. Trapping parameters were calculated from TL data using various glow curve analysis methods.     

Thermoluminescence characterization of Tb3+ and Ce3+ doped nanocrystalline Y3Al5O12 exposed to X- and β-ray irradiation

The thermoluminescence (TL) characterization of undoped, as well as Ce³⁺ and Tb³⁺ doped Y₃Al₅O₁₂ (YAG) nanocrystals, exposed to X- and β-radiation was performed. The samples were prepared by precipitation process and the crystalline structure was obtained after annealing at 1150 °C. The TL signal of the undoped samples indicates a high sensitivity to X- and β-ray irradiation. The introduction of the dopants ions induced changes in the TL glow curve structure and the kinetic properties modifying the radiative recombination efficiency. The TL results suggest that both undoped and doped YAG nanocrystalline phosphor present a good potential for X- and β-ray irradiation dosimeter applications.     

Tunable color emission and afterglow in CaGa2S4: Eu, Ho phosphor

The tunable color emission and persistent luminescence lifetime in phosphor CaGa₂S₄: Eu²⁺, Ho³⁺ were achieved through the introduction of alkaline earth elements Mg, Sr and Ba, in which the Ca was partially replaced. The duration of the persistent luminescence of the material CaGa₂S₄: Eu²⁺, Ho³⁺ was remarkably shortened as Al was introduced, substituting for Ga. The luminescent properties were investigated via thermo-luminescence (TL) glow curves, phosphorescence spectra and decay time curves. These results show that vast changes in trap levels and charge density takes place with introduction of other alkaline earth elements or Al. Trap depths and the trap density were also evaluated by simple methodologies.     

Optical characteristics and charge transfer band excitation of Dy3+ doped Y2O3 phosphor

Dy³⁺ ion-doped Y₂O₃ phosphors have been synthesized and characterized for structure and optical properties. Structural characterization reveals that the samples are well crystalline. The crystallinity and particle size increases as the sample is post annealed, while optical quenching entities are reduced due to which a significant enhancement in fluorescence is observed. The phosphor is efficiently excited by ultraviolet light and emits intense blue (486 nm), yellow (573 nm), red (666 nm), and near infrared (764 nm, 823 nm) light. The emission is also observed even if charge transfer band (CTB) is excited, via energy transfer from CTB to 4f levels of Dy³⁺ ion. The intensity of yellow transition band varies with a variation in concentration of Dy³⁺ ion as well as with excitation wavelength, while the intensity of other transitions remains unaffected. Thus a variation in yellow to blue color (Y/B) gives an opportunity for the development of color tunable phosphor.     

Hydrothermal synthesis of blue-emitting YPO<Subscript>4</Subscript>:Yb<Superscript>3+</Superscript> nanophosphor

The blue-emitting YPO₄ phosphors doped with Yb³⁺ were prepared by a simple hydrothermal method. All the products were characterized by XRD and TEM, which revealed that they were zircon structure with leaf-like morphology. According to the analysis of photoluminescence spectra, upon ultraviolet (275 nm) excitation, the Yb³⁺ doped YPO₄ phosphor showed an intense blue emission composed of two main bands at 420 and 620 nm assigned to charge transfer state (CTS) → ²F_5/2 and CTS → ²F_7/2, respectively. Moreover, the optimum doping concentration of Yb³⁺ in YPO₄ phosphor was 1%, which exhibited the maximum emission intensity. The possible physical mechanism of concentration quenching was discussed, and the critical transfer distance determined to be 23.889 Å. In particular, the color purity of the as-synthesized Yb³⁺ doped YPO₄ phosphor was as high as 83%, which made it an excellent candidate for blue-emitting materials.     

Swift heavy ion induced structural,optical and luminescence modification in NaSrBO3:Dy3+ phosphor

The effect of 120 MeVAg⁹⁺ ion irradiation on the structural, optical and luminescence properties of NaSr_1-xBO₃:xDy³⁺ (x = 0.5–2.5 mol%) phosphor synthesized by the conventional solid state reaction route is reported. The samples were irradiated with Ag⁹⁺ swift heavy ions (SHIs) using fluences of 1 × 10¹², 5 × 10¹² and 1 × 10¹³ ions cm^?2. The unirradiated as well as irradiated samples were characterized by powder X-ray diffraction (PXRD), diffuse reflectance (DR) and photoluminescence techniques. PXRD confirms no change in the phase after irradiation except that loss of crystallinity had been observed which may be due to the fragmentation caused by the SHI. A blue shift in the absorption band of the DR was observed, resulting in an increase in the band gap from 5.61 eV to 5.77 eV, after ion irradiation. An increase in photoluminescence intensity (excited at 385 nm) was observed with increased ion fluences. The ratio of the blue to yellow emission peaks (I₄₈₃/I₅₇₇) was calculated and found to be varying with ion fluences suggesting that the white light can be achieved by tailoring this yellow to blue ratio. The Commission Internationale de l’Eclairage coordinates were calculated and found to move toward the white region after irradiation.     

Sol-gel synthesis of single-phase Ca5MgSi3O12: Eu, Mn phosphors for white-light emitting diodes

A novel Ca₅MgSi₃O₁₂: Eu²⁺, Mn²⁺ phosphor has been prepared by a sol-gel method. X-ray diffractometer, spectrofluorometer were used to characterize structural and optical properties of the samples. The results indicate that Ca₅MgSi₃O₁₂: Eu²⁺, Mn²⁺ phosphors show two emission bands excited by ultraviolet light. Blue (around 450 nm) and green (around 502 nm) emissions originate from Mn²⁺ and Eu²⁺, respectively. With appropriate tuning the concentration ratios of Eu²⁺ to Mn²⁺, Ca₅MgSi₃O₁₂: Eu²⁺, Mn²⁺ phosphors exhibit different hues and relative color temperatures, which have potential to act as a single-phase phosphor for white-light emitting diode.     

Synthesis and luminescence properties of Tb<Superscript>3+</Superscript>-doped LiMgPO<Subscript>4</Subscript> phosphor

Polycrystalline sample LiMg_(1?x)PO₄:xTb³⁺ (x = 0.001, 0.002, 0.005, 0.01, 0.02) phosphor was synthesized via modified solid state method (MSSM). The prepared sample was characterized through XRD pattern (X-ray diffraction) and SEM (scanning electron microscope). Additionally, photoluminescence (PL), optically stimulated luminescence (OSL), thermoluminescence (TL) and other dosimetric properties including dose linearity, reusability and fading were studied. In OSL mode, sensitivity of prepared phosphor was found to be 2.7 times that of LiMgPO₄:Tb³⁺, B (BARC) phosphor and 4.3 times that of α-Al₂O₃:C (BARC) phosphor. The TL glow consists of overlapping peaks in temperature range of 50–400^°C and first peak (P₁) was observed at 150^°C, second peak (P₂) at 238^°C, third peak (P₃) at 291^°C and fourth peak (P₄) at 356^°C. The TL sensitivity of second peak (P₂) of LiMgPO₄:Tb³⁺ phosphor was compared with α-Al₂O₃:C (BARC) phosphor and found to be 100 times that of the α-Al₂O₃:C (BARC) phosphor. The minimum detectable dose (MDD) was found to be 5.6 μGy. Moreover, photoionization cross-sections, linearity, reusability, fading and kinetic parameters were calculated. Also, photoluminescence spectra of LiMgPO₄: Tb³⁺ shows characteristic green–yellow emission exciting at 224 nm UV source.     

Tuning of crystal phase and luminescence properties of Gd2(MoO4)3:Dy3+ phosphors

The orthorhombic and monoclinic Gd₂(MoO₄)₃:Dy³⁺ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd₂(MoO₄)₃:Dy³⁺ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd₂(MoO₄)₃:Dy³⁺ were discussed. The electric dipole–dipole interaction between Dy³⁺ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd_1.84(MoO₄)₃:Dy_0.16³⁺ can be considered as a suitable candidate for white light emitting diodes (W-LEDs).     

Luminescent properties of Eu3+ doped α-Gd2(MoO4)3 phosphor for white light emitting diodes

A novel red emitting phosphor α-Gd₂(MoO₄)₃:Eu³⁺ was developed for white light emitting diodes (LEDs). The phosphor was prepared by solid-state reaction. The effects of the flux content and the activator concentration on the crystal structure, morphology and luminescent properties were investigated by using XRD, SEM, and fluorescent spectra. These results showed that this phosphor can be effectively excited by ultraviolet (UV) (395 nm) and blue (465 nm) light, matching the output wavelengths of ultraviolet or blue LED chips. The α-Gd₂ (MoO₄)₃ phosphor may be a better candidate for solid state lighting application.     

Multilayer design of hybrid phosphor film for application in LEDs

Crosslinked polydimethylsiloxane (PDMS) composite coatings containing luminescent micrometer-sized yellow Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) particles were prepared by spraying for potential applications in solid-state lighting. Blue light was down converted by phosphor particles to produce white light, yet poor color properties of YAG:Ce³⁺ stemmed from a deficiency of red. When nitride-based red phosphor was simply blended into the system, the electrostatic interaction of negatively charged YAG:Ce³⁺ and positively charged red phosphor particles caused remarkable clustering and heterogeneity in particle dispersion. Consequently, the light is dominantly blue and shifted to cold white. In other case, phosphor particles were sprayed onto the diffused polycarbonate substrate in stacked layers. Coatings with >80% inorganic content by mass with a thickness of 60 μm were subjected to thermal crosslinking, which the presence of the phosphor particles obstructed, presumably due to the hindrance of large phosphor particles in the diffusion of PDMS precursors. The coating of YAG:Ce³⁺ first followed by red phosphor in stacked layers produced better light output and color properties than the coating obtained by spraying the mixture at once. Monte Carlo simulation validated the hypothesis.     

Up-conversion luminescence and optical temperature sensing behaviour of Yb3+/Er3+ codoped CaWO4 material

Present article report on structural and optical properties of Er³⁺/Yb³⁺ codoped CaWO₄ phosphors. Structural properties are explored using XRD and Raman technologies. The upconversion emission has been investigated with 980 nm excitation. The upconversion emission intensity is dependent on the concentrations of Yb³⁺ ions and reaches a maximum at 7%. Logarithmic plots of power dependencies reveal that the green and red emissions originate from a two-photon upconversion process. Based on the photon energy and the emission spectra, the possible upconversion processes and emission mechanisms are discussed. Finally, the optical temperature sensing properties has been performed using the fluorescence intensity ratio technique based on green upconversion emissions. Its temperature sensitivity is found to be above 0.0025 K^-1 in the whole temperature range of 300–540 K, revealing this phosphor to be a promising optical temperature sensing material.     

A novel green luminescent material AlPO4:Tb

A novel green phosphor Tb³⁺ doped AlPO₄ was synthesized by conventional solid-state reaction method. The phosphor showed prominent luminescence in green due to the ⁵D₄-⁷F₅ transition of Tb³⁺. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. The XRD measurements indicated that there are no crystalline phases other than AlPO₄. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 542 nm under UV excitation. It is shown that the 3 mol% of doping concentration of Tb³⁺ ions in AlPO₄:Tb³⁺ phosphor is optimum. The measured chromaticity for the phosphors AlPO₄:Tb³⁺ under UV excitation is (0.32, 0.53).     

Luminescent properties of Eu doped α-Gd2(MoO4)3 phosphor for white light emitting diodes

A novel red emitting phosphor α-Gd₂(MoO₄)₃:Eu³⁺ was developed for white light emitting diodes (LEDs). The phosphor was prepared by solid-state reaction. The effects of the flux content and the activator concentration on the crystal structure, morphology and luminescent properties were investigated by using XRD, SEM, and fluorescent spectra. These results showed that this phosphor can be effectively excited by ultraviolet (UV) (395 nm) and blue (465 nm) light, matching the output wavelengths of ultraviolet or blue LED chips. The α-Gd₂ (MoO₄)₃ phosphor may be a better candidate for solid state lighting application.     

Luminescence properties and energy transfer investigations of Ce3+/Tb3+ co-doped BaY2Si3O10 phosphor

A novel phosphor BaY₂Si₃O₁₀ (BYSO): Ce³⁺, Tb³⁺ was synthesized by the conventional solid-state reaction, which displays tunable color emission from blue to blue-green under ultraviolet excitation by adjusting the radio of Ce³⁺ and Tb³⁺ appropriately. Photoluminescence characteristics were carefully investigated. We demonstrate the existence of efficient energy transfer from Ce³⁺ to Tb³⁺ in BaY₂Si₃O₁₀: Ce³⁺, Tb³⁺ phosphor. The energy transfer Ce³⁺ → Tb³⁺ was proved to be governed by dipole–quadrupole interaction.     

A novel green emitting phosphor Ca2GeO4:Tb3+

A novel green emitting phosphor, Tb³⁺-doped Ca₂GeO₄ was prepared for the first time by a solid-state reaction. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄ → ⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 and 550 nm under UV excitation. In addition, Al³⁺ or Li⁺ co-doping enhances the green emission from Ca₂GeO₄:Tb³⁺ by about 18 and 4 times, respectively, under UV excitation. The excellent luminescence properties make it a possible candidate for flat panel display application.