Combustion synthesis of borate phosphors for use in plasma display panels and mercury-free fluorescent lamps

Discussed are the photoluminescence properties of combustion synthesized red and green emitting borate phosphors—YBO₃ : Eu³⁺, BaZr(BO₃)₂ : Eu³⁺, YCaBO₄ : Eu³⁺, YAl₃(BO₃)₄ : Eu³⁺, YAl₃(BO₃)₄ : Tb³⁺, LaBaB₉O₁₆ : Tb³⁺, LaBaB₉O₁₆ : (Ce³⁺,Tb³⁺), and Na₃La₂(BO₃)₃ : Tb³⁺-promising for use in plasma display panels and mercury-free fluorescent lamps.     

Visible quantum cutting in Tb<Superscript>3+</Superscript> doped BaGdF<Subscript>5</Subscript> phosphor for plasma display panel

Visible quantum cutting (QC) via down-conversion and enhancement in photoluminescence properties has been observed in terbium (Tb³⁺) doped BaGdF₅ phosphor. This phosphor was synthesized by varying molar concentration of Tb³⁺ ions via co-precipitation method. The prepared phosphor was characterized through X-ray diffraction technique. The photoluminescence spectra of BaGdF₅:Tb³⁺ phosphor measured under vacuum ultraviolet or UV excitation. The QC process was observed in prepared phosphor due to cross relaxation and direct energy transfer between Tb³⁺ and Tb³⁺ or Tb³⁺ and Gd³⁺ ions depending on the excitation wavelength. The maximum quantum efficiencies were found to be 162, 174 and 177 %, under the excitation of 172, 187 and 240 nm respectively. The green emission of 544 nm was observed at excitation of 172 and 187 nm. Hence this phosphor may be prime candidate for application in plasma display panels and mercury free fluorescent lamps.     

Microwave-assisted synthesis and photoluminescence properties of $$\hbox {ZnS:Pb}^{2+}$$ nanophosphor for solid-state lighting

Nanocrystalline \(\hbox {ZnS:Pb}^{2+}\) phosphor was synthesized by microwave-assisted co-precipitation method. The phase purity and surface morphology of prepared material were investigated using an X-ray diffractometer (XRD) and a scanning electron microscope. The photoluminescence property was studied by near-UV (nUV) excitation. The XRD pattern of prepared phosphor matches well with that of an ICDD (International Center for Diffraction Data) file. Surface morphology of prepared phosphor was found to be in submicron range. As-prepared \(\hbox {ZnS:Pb}^{2+}\) phosphor shows a green emission under nUV excitation. As \(\hbox {Pb}^{2+}\) ions are located on a regular \(\hbox {Zn}^{2+}\) site they produce a green emission band in the range of 400–650 nm, centred at 500 nm, under excitation wavelength of 357 nm, exhibiting luminescence properties typically observed for \(\hbox {Pb}^{2+}\). Effect of concentration of \(\hbox {Pb}^{2+}\) ions on emission intensity was studied. The colour co-ordinates of prepared phosphor were calculated and found to lie in the green region of Commission Internationale de l’Eclairage diagram.     

A Novel Gd<Superscript>3+</Superscript>–Pb<Superscript>2+</Superscript> Doped LiSrPO<Subscript>4</Subscript> Phosphor for Phototherapy Lamp Applications

The phosphors LiSrPO₄:Gd³⁺ and LiSrPO₄:Gd³⁺, Pb²⁺ with different concentration of Gd³⁺ and Pb²⁺ were synthesized by combination of re-crystallization and modified solid state diffusion method. The synthesized phosphors were characterized using XRD, SEM and PL spectroscopies. The PL excitation spectra of LiSrPO₄:Gd³⁺ phosphor exhibit peak at 275 nm due to the ⁸S_7/2 →⁴I_J transition of Gd³⁺ ions and gave narrow UVB emission at 312 nm. The effect of Pb²⁺ ions on the PL properties of LiSrPO₄:Gd³⁺have also been investigated. Upon the addition of Pb²⁺ ions, the excitation of phosphors shows broad peak with maximum at 247 nm, overlapping the Hg 253.7 nm line. This addition of Pb²⁺ ions improved the emission intensity of narrow band UVB i.e. 312 nm under the excitation of 247 nm. The phosphor could be good candidate as phototherapy lamp phosphor material.     

Combustion synthesis and luminescence characteristic of rare earth activated LiCaBO3

Lithium calcium borate (LiCaBO3) polycrystalline thermoluminescence (TL) phosphor doped with rare earth (Tb3+ and Dy3+) elements was synthesized by novel solution combustion synthesis. The reaction produced very stable crystalline LiCaBO3:D(D=Tb3+ and Dy3+) phosphors. These rare earth doped phosphors material showed maximum TL sensitivity with favorable glow curve shape. TL glow curve of X-ray irradiated that LiCaBO3:Tb3+ and LiCaBO3:Dy3+ samples showed two major well-separated glow peaks. The TL sensitivity of these phosphors to X-ray radiation was comparable with that of TLD-100(Harshaw). Photoluminescence spectra of LiCaBO3:Tb3+ and LiCaBO3:Dy3+ showed the characteristic Tb3+ and Dy3+ peaks respectively. TL response to X-ray radiation dose was linear up to 25 Gy.     

Fabrication of polycaprolactone/zirconia nanofiber scaffolds using electrospinning technique

In the present study we have investigated the effect of Zirconia (ZrO₂) nanoparticles on the fiber morphology, swelling, degradation activity and enhanced cell adhesion of the electrospun polycaprolactone (PCL) non-woven nanofiber scaffolds. The composite nanofibers scaffolds were obtained with ZrO₂ weight contents varying in the range 6% to 30%. The effect of the ZrO₂ nanoparticles concentration on the fiber morphology was investigated using a Field effect scanning electron microscopy (FE-SEM). We also investigated the degradation and swelling activities of the fabricated material. The results demonstrated better swelling with controlled degradation in comparison to the PCL scaffolds. Cell viability studies proved the non toxic nature of the nanocomposite scaffolds. Interestingly, the scaffolds with ZrO₂ nanoparticles showed enhanced fibroblast proliferation and improved bioactivity of the scaffolds. Further, this is the first report regarding the ability of a biomaterial containing ZrO₂ nanoparticles to enhance cell adhesion and proliferation.     

Combustion synthesis and photoluminescence study of UV emitting LaBaB<Subscript>9</Subscript>O<Subscript>16</Subscript> phosphors

The borate phosphor LaBaB₉O₁₆ doped with Ce³⁺ ion intentionally and successfully synthesized using solution combustion rout using metal nitrates as precursors and urea as fuel. The phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy and photoluminescence spectroscopies. The XRD patterns of the phosphor confirmed the successful crystallization of LaBaB₉O₁₆. The average crystallite size calculated using the Debye Scherer equation. The PL excitation spectra of LaBaB₉O₁₆ exhibited broad spectra peaking at 275 nm. Upon excitation with ultraviolet (UV) radiation at 274 nm the phosphor exhibited a broad band UV emission peaking at a wavelength of 335 nm corresponding to the 4f⁰5d¹??4f¹ transition of the Ce³⁺ ion. Moreover the influence of concentration of Ce³⁺ ion on luminescence properties has also been studied. Optimum concentration of Ce³⁺ ions in the prepared phosphor was found to be 0.05 mol. For this concentration the critical distance R₀ was calculated to be 22.04 Å. Finally, the Stokes shift for the synthesized phosphor was calculated to be 6512 cm^??1 using corresponding excitation and emission.     

Near-infrared downconversion in Ce<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> co-doped YAG

The phosphors YAG co-doped with Ce³⁺–Yb³⁺ ion pair were successfully synthesized by solid state reaction method varying the concentration of Yb³⁺ ions from 1 to 15 % mol. The phosphors were characterized by powder X-ray powder diffraction and surface morphology was studied by scanning electronic microscope. The photoluminescence (PL) properties were studied by spectrophotometers in near infra red (NIR) and ultra violet visible region. The synthesized phosphors can convert a photon of blue region (469 nm) into photons of NIR region (979 and 992 nm). The co-operative energy transfer was studied by time decay curve and PL spectra. The theoretical value of quantum efficiency was calculated from steady time decay measurement and the maximum efficiency approached up to 145.19 %. Hence this phosphor could be used as a downconversion luminescent convertor in front of crystalline silicon solar cell (c-Si) panels to reduce thermalization loss due to spectral mismatch of the solar cells.     

TL/OSL Properties of Green Emitting LiMgPO<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript>, B (LMPTB) Phosphor for Radiation Dosimetry

The series of LiMgPO₄:Tb³⁺/Tb, B phosphors were synthesized via modified solid state method. The structural and morphological characterization was done through X-ray diffraction and Scanning Electronic Microscope. Additionally, photoluminescence (PL), thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of prepared phosphors were studied. Also Linear Modulated-OSL, Non Linear OSL, dose response, fading and reusability were studied. The LiMg_(0.85)PO₄:_0.005Tb³⁺, _0.01B (LMPTB) phosphor shows good OSL sensitivity, which was found to be 1.70 and 1.04 times more than α-Al₂O₃:C (BARC) and LiMgPO₄:Tb³⁺, B (BARC) phosphors respectively and minimum detectable dose was found to be 16.4 μGy with 3σ of background. The effective atomic number of LMPTB phosphor (Z_eff = 11.44) is nearly similar to Z_eff of α-Al₂O₃:C phosphor (Z_eff = 11.28). The prepared phosphor show linear dose response in the range 0.04–24 Gy and fading of the OSL signal was found to be about 34 % in 35 days. The TL glow curve of LiMgPO₄:Tb phosphor was stable after addition of boron. The PL spectra show characteristic emission of Tb³⁺ ion. This prepared phosphor is applicable personal monitoring and environmental monitoring.