Bi Phosphors Research Articles

Synthesis and Luminescent Properties of Na<sub>5</sub>La<sub>x</sub>M<sub><i>1-x</i></sub>(WO<sub>4</sub>)<sub>4</sub> (M = Eu, Sm, Bi) Red Phosphors for WLED

A series of Na5La(WO4)4:M3+ (M = Eu, Sm, Bi) phosphors have been synthesized successfully by the solid-state reactions. The corresponding crystal structure and lattice parameters were refined by the Rietveld method, and the impact of doped metal ions upon the structure were also studied. The photoluminescent properties were investigated at room temperature. All the samples were observed a strong red emission under 395nm or 465 nm excitation, and the CIE chromaticity coordinates (x = 0.67, y = 0.33) was found to be close to the National Television Standard Committee (NTSC) standard red, implying high color purity. This kind of tungstate phosphor is a promising candidate as the red phosphor for white light-emitting diodes (WLED).

Photoluminescence of Bi^2+-doped BaSO_4 as a red phosphor for white LEDs

Bi(2+)-doped BaSO(4) phosphor was synthesized in air via solid state reaction method. Three excitation bands and one emission band were observed at 260 nm ((2)P(1/2) → (2)S(1/2)), 452 nm ((2)P(1/2) → (2)P(3/2)(2)), 592 nm ((2)P(1/2) → (2)P(3/2)(1)), and 627 nm ((2)P(3/2)(1) → (2)P(1/2)), respectively. W-LEDs were demonstrated by using a blend composition of BaSO(4):Bi(2+) and YAG:Ce(3+) phosphors pumped with a 455 nm blue LEDs chip. The results indicate that BaSO(4):Bi(2+) phosphor is suitable as potential red phosphor for application in W-LEDs excited with blue LEDs chip.

Enhanced luminescence of Sr2SiO4:Dy3+ by sensitization (Ce3+/Bi3+) and its composition-induced phase transition

Ce3+/Bi3+ codoped Sr2SiO4:Dy3+ phosphors were prepared by the solid-state reaction method using NH4Cl as the flux. Their phase compositions, photoluminescence properties and the energy transfer processes were systematically investigated. The composition-induced phase transition of (Sr0.99−xRx)2SiO4:Dy3+ (R=Ce3+/Bi3+) powders was dependent on the radius of doped ions and their concentrations. The doping of smaller ions was beneficial to the formation of α′-Sr2SiO4. The luminescence intensity of Dy3+ was enhanced 2 or 3 times by the sensitization of Bi3+/Ce3+ through the electric multipoles interaction. The bright white light was observed from the Sr2SiO4:Dy,Bi phosphors with stable CIE chromaticity coordinates. This phosphor has great potential to act as a single-matrix phosphor for white light emitting diodes.

Effect of Bi ion on Eu2+ ↔ Eu3+ conversion in CaF2:Eu phosphors for RPL dosimetry

UV photo-excited Eu2+ and Eu3+ luminescence from CaF2:Eu and CaF2:Eu, Bi phosphors were investigated. The effect of gamma exposure followed by temperature effect shows conversion mechanism between Eu2+ ↔ Eu3+ ion in CaF2:Eu and CaF2:Eu, Bi phosphors which were studied for RPL dosimetry. The photoluminescence and X-ray diffraction characterization are reported in this article.

Preparation and photoluminescence properties of Y2O3:Eu, Bi phosphors by molten salt synthesis for white light-emitting diodes

Y2O3:Eu, Bi red phosphors were first prepared by molten salt synthesis (MSS) method at a low temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The results show that as-obtained Y2O3:Eu, Bi phosphors have good cubic crystallinity, presenting octahedral morphology with smooth surface and relatively uniform particle size. Bi3+ ion as a sensitizer plays a significant effect on the emission intensity of Y2O3:Eu, Bi by energy transfer from Bi3+ to Eu3+ and the optimal concentration of Bi3+ is 1.5 mol%. Y2O3:Eu, Bi emits excellent red light as the excitation wavelength is between 330 and 420 nm or excited by 254, 466 nm. Meanwhile, its emission intensity is as strong as that of sample prepared by solid-state reaction. So the as-fabricated red phosphors by MSS method would have a promising application in the area of white light-emitting diodes.

Color control of emissions from rare earth-co-doped La 2O 3:Bi phosphor thin films prepared by magnetron sputtering

Multicolor photoluminescence (PL) and electroluminescence (EL) were observed from developed Bi- and rare earth (RE)-co-doped La 2O 3 (La 2O 3:Bi,RE) phosphor thin films. The phosphor thin films were prepared with various contents of co-doped RE, such as Dy, Er, Eu, Tb and Tm, by a combinatorial radio frequency magnetron sputtering deposition method. The obtainable luminance in EL and PL intensities changed considerably as the kind and content of RE were varied. Color changes from blue and blue-green to various colors in PL and EL emissions, respectively, were obtained in postannealed La 2O 3:Bi,RE phosphor thin films: films prepared by co-doping Bi at a constant content with various REs at varying levels of content. However, all of the observed emission peaks in PL and EL from La 2O 3:Bi,RE phosphor thin films were assigned to either the broad emission originating from the transition in Bi 3+ or the visible emission peaks originating from the transition in the co-doped trivalent RE ion. The difference between PL and EL characteristics in La 2O 3:Bi,RE phosphor thin films is mainly attributed to the difference in the excitation mechanism.

Luminescent Characteristics of Bi Co-doped ZnS:Mn Yellow Phosphors for White Light Emitting Diodes

Bi co-doped ZnS:Mn,Bi yellow phosphors for white light emitting diodes were prepared by the conventional solidstate reaction method. The optical and structural properties of ZnS:Mn,Bi phosphors were investigated by x-ray diffraction, scanning electro microscopy and photoluminescence. ZnS:Mn,Bi phosphors showed XRD patterns of hexagonal structure. The photoluminescence of ZnS:Mn,Bi phosphors showed spectra extending from 480 to 700 nm, peaking at 580 nm. The photoluminescence of 580 nm in the ZnS:Mn,Bi phosphors was associated with the 4T1 <TEX>${\rightarrow}$</TEX> 6A1 transition of the Mn2+ ions. The highest photoluminescent intensity of the phosphors under 405 nm and 450 nm excitation was obtained at Bi concentration of 7mol%. The optimum mixing conditions with epoxy and yellow phosphor for white light emitting diodes were observed in a ratio of epoxy:yellow phosphor of 1:3.5. The CIE chromaticity of the white LED at the 1:3.5 ratio was X = 0.3454 and Y = 0.2449.

EPR-TL correlation studies on Bi co-doped CaSO4:Dy phosphor

CaSO(4):Dy, CaSO(4):(Dy, Bi) and CaSO(4):Bi phosphors were prepared through re-crystallization method. Thermoluminescence (TL) characteristics of these phosphor samples were investigated. The radiation induced radical ions formed in these phosphors were investigated using electron paramagnetic resonance (EPR) spectroscopy. The main signals observed in both CaSO(4):(Dy, Bi) and CaSO(4):Bi were identified as SO(4)(-) (II), SO(4)(-) (⊥) and SO(3)(-) (isotropic) with "g" values 2.023, 2.0089 and 2.004, respectively. In order to understand the TL mechanism, CaSO(4):(Dy, Bi) phosphor samples were annealed between 100 and 250 °C and their EPR spectra were studied. It was observed that EPR signal intensities reduce drastically in 250 °C annealed phosphor confirming the role of SO(4)(-) and SO(3)(-) types of defect centers in the dosimetric peak. The reduction in the TL sensitivity with increase in Bi(3+) co-dopant in the phosphor samples was correlated with quenching of TL by Bi(3+) ions rather than the reduction in the concentration of the above defect centers. An effort was also made to use the Bi(3+) co-doped CaSO(4):Dy phosphor for dosimetry of chilled or frozen food irradiation.

Luminescent characteristics in blue-emitting Bi-activated multicomponent oxide phosphor thin films

The luminescent characteristics in developed blue-emitting Bi-activated multicomponent oxide phosphor thin films that are composed of various combinations of La2O3, Y2O3, and Gd2O3 as the host material are investigated; ((La2O3)1−X–(Gd2O3)X):Bi, (Gd2O3)1−Y–(Y2O3)Y):Bi, and ((Y2O3)1−Z–(La2O3)Z):Bi phosphor thin films were prepared on thick BaTiO3 ceramic sheets by either a conventional or a combinatorial rf magnetron sputtering deposition method using a powder target. The resulting phosphor thin films, which were prepared with various chemical compositions and postannealed above about 800 °C in an Ar gas atmosphere, all exhibited photoluminescent (PL) and electroluminescent (EL) emissions. However, the PL emission spectra observed from these phosphor thin films were considerably affected by the ultraviolet (UV) light used in the excitation. Intensive blue PL emissions were obtained in all of the phosphor thin films that were postannealed at 1050 °C and excited by an appropriate UV light. In comparison with the PL emission spectra, the EL emission spectra observed from thin-film electroluminescent (TFEL) devices fabricated using the Bi-activated multicomponent oxide phosphor thin films as the emitting layer exhibited a redshift of the emission band or an emergence of a new emission band accompanied by spectral broadening at longer wavelengths. In addition, high-luminance blue-green EL emissions were obtained in TFEL devices fabricated using the above phosphor thin films and driven by a sinusoidal wave ac voltage at 1 kHz.

Blue PL and EL emissions from Bi-activated binary oxide thin-film phosphors

The photoluminescent (PL) and electroluminescent (EL) characteristics in the thin films of various Bi-activated binary oxide phosphors have been investigated. La 2O 3:Bi, Gd 2O 3:Bi and Y 2O 3:Bi phosphor thin films were prepared on thick BaTiO 3 ceramic sheet substrates by r.f. magnetron sputtering depositions followed by postannealing. Intense blue PL emissions were observed from all Bi-activated binary oxide phosphor thin films postannealed at a high temperature. Blue, whitish blue-green or blue-green emissions were observed from thin-film electroluminescent (TFEL) devices fabricated with a La 2O 3:Bi, a Gd 2O 3:Bi or a Y 2O 3:Bi thin-film emitting layer, respectively. In addition, high luminance with good color purity in blue EL was obtained in a TFEL device using a La 2O 3:Bi thin film prepared under optimized conditions.

Photoluminescent and electroluminescent characteristics of various Bi-activated niobate-based oxide phosphor thin films

The photoluminescent (PL) and electroluminescent (EL) characteristics in the thin films of various Bi-activated niobate-based oxide phosphors have been investigated. LaNbO 4:Bi, GdNbO 4:Bi and YNbO 4:Bi phosphor thin films were prepared on thick BaTiO 3 ceramic sheet substrates by either a conventional or a combinatorial radio frequency magnetron sputtering deposition followed by postannealing at a high temperature. Blue PL emissions were observed from Bi-activated niobate-based oxide phosphor thin films postannealed at a temperature above approximately 800 °C in air or a pure Ar gas atmosphere. The excitation spectra of the blue PL emissions as well as the blue emission spectra observed from LaNbO 4:Bi, GdNbO 4:Bi and YNbO 4:Bi phosphor thin films exhibited an increasing red-shift in that order. In addition, blue, whitish blue-green or blue-green emissions were observed from thin-film electroluminescent devices fabricated with a LaNbO 4:Bi, a GdNbO 4:Bi or a YNbO 4:Bi thin-film emitting layer, respectively. However, the EL emission spectra observed from these TFEL devices exhibited a red-shift relative to the PL emission spectra observed from the respective phosphor thin films. The resulting difference between the observed PL and EL emission spectra may be explained by the 6 s 2–6 s6p transitions in Bi 3+ ions. In particular, the long-wavelength bands observed in the EL emissions may be attributable to the selection rule resolved by a high electric field applied to the phosphor thin films.

PL and EL Characteristics in New Blue Emitting La2O3:Bi Phosphor Thin Films

The electroluminescent (EL) and photoluminescent (PL) characteristics in new blue emitting Bi-activated La2O3 oxide phosphor thin films prepared using a conventional or a combinatorial r.f. magnetron sputtering deposition method followed by postannealing are investigated. Intense blue PL emission was observed from the prepared La2O3:Bi phosphor thin films. In addition, a high-luminance in blue EL emission was obtained in thin-film electroluminescent (TFEL) devices fabricated using the La2O3:Bi phosphor thin films as the emitting layer. Differences between the observed PL and EL emission spectra are attributed to the selection rule in the 6s2-6s6p transitions of Bi3+ being resolved by a high electric field applied to the La2O3:Bi phosphor thin film.

Photoluminescence of SrGa2S4:Bi Phosphor

Bi-activated SrGa2S4 (SrGa2S4:Bi) phosphor exhibits green luminescence with a peak wavelength of 533 nm and a full width half maximum of 58 nm. This luminescence is attributed to the 6p-6s transition in the 6s2 configuration of Bi3+. As SrGa2S4 is co-activated by the Bi3+ and Mn2+ ions, the excitation band around 400 nm is enhanced relative to that around 300 nm. Since the PL properties of SrGa2S4:Bi were similar to those of SrGa2S4:Eu, the SrGa2S4:Bi phosphors are potential alternatives to SrGa2S4:Eu phosphors.

A reinvestigation of luminescence properties of Bi 3+-activated MSb 2O 6 (M = Ca, Sr) phosphors

The photoluminescence (PL) properties of Bi 3+ in the MSb 2O 6 (M = Ca, Sr) have been reinvestigated. Our results are essentially different from the reported data. The PL spectra of MSb 2O 6:Bi consisted of an ultraviolet (UV) band due to 3 P 1– 1 S 0 transition of isolated Bi 3+ ions and a visible band due to Bi 3+ pairs (clusters), which have not been reported with high intensities even at room temperature. In CaSb 2O 6:Bi the visible emission (443 nm) predominated over the UV emission (297 nm), while in SrSb 2O 6:Bi the visible emission (487 nm) had similar intensity to the UV emission (319 nm). The maximum visible emission intensity was at x = 0.0075 ( x: the doping Bi concentration per mol of host) in MSb 2O 6:Bi (M = Ca, Sr), and the value in CaSb 2O 6:Bi was about six times higher than in SrSb 2O 6:Bi. The intense blue emission in CaSb 2O 6:Bi proves that the modified solid state reaction is a better method to synthesize a higher-performance CaSb 2O 6:Bi phosphor as a potential candidate for white-light-emitting diode pumped by UV chip (w-UVLED) and other display devices.

Influence of Eu 3+, Bi 3+ co-doping content on photoluminescence of YVO 4 red phosphors induced by ultraviolet excitation

Rare earth ion doped insulators have attracted a great deal of interest due to their wide variety of applications, including phosphors. YVO 4:Eu, Bi phosphor has a broad excitation band consisting of two peaks—one centered at from 260 to 320 nm and the other at a weak band at wavelength of 386–406 nm. Also, the emission spectrum exhibited a weak band for 5D 0 → 7F 1 at 595 nm and strong sharp peaks at about 616 and 620 nm due to the 5D 0 → 7F 2 transition of Eu 3+. With increasing Bi 3+ concentration, the band edge shifts to longer wavelengths, the band edge in the excitation spectrum moves from ∼254 to ∼328 nm as the Bi 3+ concentration is increased from 0 to 2 mol%. Moreover, with increasing Eu 3+ concentration, the intensity of the excitation spectra and the red emission increased continuously up to the Eu 3+ concentration of 3 mol%.

Hydrothermal synthesis and luminescent properties of LnPO 4:Tb,Bi (Ln=La,Gd) phosphors under UV/VUV excitation

Monoclinic LnPO 4:Tb,Bi (Ln=La,Gd) phosphors were prepared by hydrothermal reaction and their luminescent properties under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation were investigated. LaPO 4:Tb,Bi phosphor and GdPO 4:Tb phosphor showed the strongest emission intensity under 254 and 147 nm excitation, respectively, because of the different energy transfer models. In UV region, Bi 3+ absorbed most energy then transferred to Tb 3+, but in VUV region it was the host which absorbed most energy and transferred to Tb 3+.

Photoluminescence properties of Y2O3co-doped with Eu and Bi compounds as red-emitting phosphor for white LED

Bismuth doped Y2O3: Eu was used as a red phosphor with a very high efficiency and an appropriate emission wavelength of around 310–400 nm. This red phosphor was synthesized by the solid state reaction which is normally used in the field of white LEDs. In this study, we synthesized Y2O3: Eu, Bi phosphors using a solid state reaction. We investigated the effect of the Eu3 + and Bi3 + concentrations and additive fluxes on the emission characteristics. The fabricated phosphors were investigated by analyzing their particle size and crystal structure with scanning electron microscopy and X-ray diffraction (XRD). Their photoluminescence (PL) spectra were also measured at room temperature.

Defect centres and thermoluminescence in SrS:Bi phosphor

Thermoluminescence (TL) and electron spin resonance studies have been carried out on SrS:Bi phosphor. The TL glow curve is broad and indicates a dominant peak at 120 °C with two additional peaks, not clearly resolved, appearing as shoulders at around 180 and 250 °C. Two defect centres are observed at room temperature. One of them is characterized by an isotropic g-value 2.0034 and is assigned to an F+ centre. Step annealing measurements indicate a possible association between the F+ centre and the three TL peaks.

Cathodoluminescence Change of YNbO4:Bi Phosphor after Acid Treatment

The reason for the cathodoluminescence (CL) change of YNbO4:Bi after acid treatment is determined. It is observed that after acid treatment, the CL intensity of YNbO4:Bi decreased to a value below that of the untreated one at excitation energies lower than 1 keV. However, YNbO4:Bi was brighter than the untreated one at an excitation energy of 1 keV or higher. Meanwhile, ZnGa2O4 was compared with YNbO4:Bi in terms of luminescence properties. After acid treatment, ZnGa2O4 showed the same trend as YNbO4:Bi at excitation energies lower than 1 keV. However, the luminescence intensity of ZnGa2O4 did not increase at an excitation energy of 1 keV or higher. It was found that surface modification using an acid increases the luminescence efficiency of YNbO4:Bi by realizing stoichiometric composition at the phosphor surface.

P‐36: Investigation of Luminescence in Bi‐Doped YNbO4 Phosphor

AbstractThe luminescence behaviors of YNbO4 and YnbO4:Bi were investigated under UV and low voltage electron excitations and interpreted with the first‐principle calculations. The optimization of the cathodoluminescent properties was studied with control of Bi amounts and Y/Nb ratios. It was revealed that the luminance of YNbO4:Bi phosphors depends on the calcining conditions, Bi content, and particularly on the Y/Nb ratio. From our calculations and UV spectra, we were able to separate host contribution and Bi contribution and found that the shift in emission peak to longer wavelength is mainly due to Bi contribution.