Papers by Keyword: Phosphor

Abstract: Barium halide activated with Eu is a typical phosphor material used in imaging plates for computed radiography applications. In this study, BaBrX: Eu (X = Cl, I) was synthesized via the hydrothermal technique. The aim of this study is to further explore the feasibility of the hydrothermal method for synthesizing phosphor materials. This was determined by studying the effect of Eu addition on the structural and optical properties of BaBrX (X = Cl, I). X-ray diffraction (XRD) was employed to determine the crystallinity of the prepared samples, while optical properties were observed using photoluminescence (PL) spectroscopy. The sharp, narrow, and high-intensity peaks of XRD diffractogram indicated that all samples exhibited good crystallinity. The addition of the Eu element as an activator resulted in a blue-shift with broad and higher intensity of the main emission peak for several samples. This study demonstrates that the addition of the Eu element to the host materials has altered the structural properties and improved the optical properties of the prepared samples, significantly demonstrating the feasibility of the hydrothermal method for synthesizing phosphor materials.

Abstract: This study synthesized CaAl₂O₄:Eu²⁺ blue phosphors using the sol-gel method. The effects of incorporating citric acid, poly (oxyethylene) (PEG), and HCl in the precursor on the luminescent properties of phosphors were investigated. No significant changes were observed in the photoluminescence (PL) spectra of the phosphors when different precursor solutions were used. However, the use of PEG and citric acid led to a noticeable decrease in the PL intensity. Notably, the use of HCl resulted in an increase in PL. In addition, upon heating the phosphors from room temperature to 110 °C, the PL spectrum remained unchanged, whereas the PL intensity decreased linearly with increasing temperature. This indicated the suitability of CaAl₂O₄:Eu²⁺ for optical temperature-sensing applications.

Abstract: In the present work, NaBi(MoO₄)₂ (NBM) phosphor has been successfully synthesized by doping 1.0 mol% of Eu³⁺ via the conventional solid state reaction technique. The undoped synthesized NBM sample and 1.0 mol% Eu³⁺ doped phosphor were characterized to explore crystal structure, morphology, photoluminescence (PL) and colorimetric properties using various characterization techniques. The structural properties were analysed via x-ray diffraction and diffraction peaks were compared with the standard JCPDS (card no. 79-2240) pattern. The morphological studies of the sample have been done through FE-SEM micrograph. From the photoluminescence emission spectra, it has been observed that an intense peak was obtained in the at 615 nm under blue excitation. Colorimetric property of 1.0 mol% of Eu³⁺ doped NBM phosphor has been investigated and traced in the red region with high color purity of 92.79%. The aforementioned characteristics demonstrate that the NaBi(MoO₄)₂: 1.0Eu³⁺ phosphor has great potential in the field of w-LED applications.

Abstract: This article reports the study of photoluminescence spectra of Di Strontium Magnesium Silicate (Sr₂MgSi₂O₇) doped with various concentration of Europium (Eu³⁺) prepared using solid-state reaction technique. The doping concentration (s) of Eu3+ were 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 mol% respectively. Excitation spectrum monitored at 620 nm wavelength that exhibited two prominent peaks centered at 256 nm and 277 nm. Peak observed at 277 nm was more intense therefore the emission spectra were monitored at 277. Emission Spectra of all the samples revealed intense peaks centred at 607, 618 and 637 are attributed to ⁵D₀ ⁷F₂ of Europium (III) ions accommodated at various lattice sites having different energies. Overall emission was found in the red colour region which was confirmed using a CIE chromaticity diagram with coordinate (0.4805, 0.3763). Critical distance for energy transfer in the concentration, beyond which concentration quenching occurred in PL spectra, was calculated. In this case, the critical distance was found to be 19.87 Å, therefore the mechanism involved in concentration quenching of Sr₂MgSi₂O₇ doped with 2.0 mol % of Europium (III) must be only multipole-multipole exchange whereas the exchange interaction is ineffective.

Abstract: This research studied the preparation of luminescent glasses using 18SiO₂-35B₂O₃-22ZnO-20K₂O glass frits. The glass frits were first mixed with 15 wt.% of commercial SrAl₂O₄:Eu²⁺,Dy³⁺ phosphors and different B₂O₃ concentrations of 0-15 wt.%. The raw materials were then melted at 750-800°C for 1 hr. The results showed that the addition of B₂O₃ as a flux induced the crystallization of α-Zn₂SiO₄ phase and suppressed the luminescent properties of phosphor-in-glasses. This could be due to the dissociation of SrAl₂O₄ by the reaction of SrAl₂O₄ and B₂O₃. The higher sintering temperature at 800°C also further degraded the luminescent properties as a result of further phosphor degradation and the oxidation of Eu²⁺.

Abstract: M₂SiO₄: Tb³⁺, Mn²⁺, Nd³⁺ (M = Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) phosphors suitable for near-ultraviolet-violet radiation excitation were successfully prepared at 1400 °C in N₂ atmosphere by a high-temperature solid-state reaction, and their phase compositions and luminescent performance were also studied by X-ray diffraction (XRD), photoluminescence spectra. Results show that their emission intensity increases in the order of Ca₂SiO₄ > Mg₂SiO₄ > Sr₂SiO₄ > Ba₂SiO₄ matrix phosphor. Ca_1.94SiO₄: 0.02Tb^{3 +}, 0.02Mn²⁺, 0.02Nd²⁺ phosphor exhibits the best luminescence performance.

Abstract: LED healthy light source by using a blue LED chip to excite phosphor was prepared successfully. Four kinds of LED commercial phosphors (cyan phosphor with a peak wavelength of 498 nm, green phosphor with 520 nm, yellow-green phosphor with 546 nm, and red phosphor with 628 nm) were selected that could be excited by blue light. A series of experimental studies were carried out on the different amounts of glue, different powder-glue ratio, different combinations of phosphors, and the influence of different driving currents. Trough the optimization of the experimental scheme, we obtained a LED healthy light source spectrum with luminous efficiency higher than 124 lm/w, color rendering index higher than 80, color temperature around 4000 k. These spectra are in good agreement with the full spectrum of sunlight, and the spectral continuity and uniformity are better, which accord with the requirements of bright (dark) vision, and the proportion of the blue spectrum is less than 2.4%, which meets the high quality and healthy lighting requirements of safety and comfort.

Abstract: Water dispersions of shungite carbon (ShC) nanoparticles were used for modifying the particle surface of ZnS:Cu, commercial electrophosphor. The EPR spectrum of ZnS:Cu powder has parameters consistent with the paramagnetic centers of Mn⁺². Modifying the phodphor surface with ShC nanoparticles results in a non-monotonic change in line width, amplitude and integral intensity caused by nanoparticle concentration, which correlates with variations in the brightness of electroluminescence. Variations in the parameters of spectral lines with nanoparticle concentration and UHF saturation power are interpreted in terms of modification and creation of additional dislocations in the subsurface layer of phosphor with new physico-chemical properties.

Abstract: In thus study, Turmeric phosphor dye was extracted from Curcuma Longa L. via a simple technique using silica gel. The phosphor was used for light down-conversion of UV light for the manufacture white light emitting diode (WLED). The UV-LED was analyzed over 395nm wavelengths. The characteristics of the white light chromaticity were controlled by tuning the current and phosphor concentration. An optimum color rendering index (CRI) value of 63.4 was obtained. The chromaticity coordinates (CIE) and correlated color temperature (CCT) were measured for various currents and phosphor concentrations. The white phosphor exhibited CIE value of 0.355,0.338 and CCT of 4567 K. The concentration of phosphor and amount of applied current were confirmed to be major factors that control the intensity of white light emitted from the sample, where CIE and CRI of the emitted light steadily increased with the concentration of phosphor and current. Thus, phosphor concentration has a critical effect on conversion efficiency. Key words: Turmeric, phosphor, WLED, curcumin

Abstract: A new tungstate family, Li₃Ba₂Gd₃(WO₄)₈ doped with Tb³⁺ is synthesized by using a conventional high-temperature solid-state method to explore new pure green phosphors for white light-emitting diodes (WLEDs). The results from the X-Ray patterns show that the crystal structures of the hosts are composed of tungstate zigzags and the Gd³⁺-Gd³⁺ units, which are isolated by the [WO₄]^2- groups. The critical concentration of Tb³⁺ is up to x=2.0 in the singly doped phosphors, which is ascribed to the interaction of the isolated Gd³⁺ ions being mitigated by [WO₄]^2- groups. The characteristic green emission peaks at around 547 nm are also observed, which result from the ⁵D₄→⁷F₅ transition of Tb³⁺ ions, and the optimal doping concentration is x=2.0.