Chromaticity Color Coordinates Research Articles

Influence of Modifier Cations on the Spectroscopic Properties of Dy3+ Doped Telluroborate Glasses for White Light Applications.

The effect of electronegativity and ion size of the modifier cations have been analyzed through a new series of Dy3+ doped telluroborate glasses prepared by melt quenching technique with the composition of 30TeO2+29.5B2O3+20MO+20MF2+0.5Dy2O3 (where M=Ba2+, Sr2+, Zn2+, Cd2+ and Pb2+). The various stretching and bending vibrational modes of borate and tellurite network have been identified through FTIR spectral measurements. The conversion of BO3 units into BO4 units increases NBOs in the glass network and the same is confirmed through FTIR spectra. The nephelauxetic ratio ([Formula: see text]) and bonding parameter (δ) value reveals that the Dy-O bond in prepared glasses possesses ionic nature. JO intensity parameters (Ω2, Ω4 and Ω6) of the present glasses follow the trend Ω2>Ω4>Ω6 uniformly in all the prepared glasses. Radiative parameters like transition probability (A), stimulated emission cross section[Formula: see text], branching ratio (βR) values have been predicted from the absorption spectra of Dy3+ ions using JO theory. Among the prepared glasses TBZnD glass posses a better CIE 1931 colour chromaticity coordinates (0.33, 0.39) and CCT value (5019K). Decay profile of 4F9/2 state of the Dy3+ ion exhibits non-exponential nature due to the interaction between Dy3+-Dy3+ ions. The nature of interaction between Dy3+-Dy3+ ions has been analyzed through Inokuti-Hirayama model and the best fit of S=6 indicates that the dipole-dipole interaction is responsible for the energy transfer between Dy3+-Dy3+ ions. The glass containing Zn2+ ions posses encouraging results such as higher Y/B intensity ratio, stimulated emission cross section and higher branching ratio (4F9/2→6H13/2). Thus the present study identified the Zn2+ ions as a better modifier ion to develop the Dy3+ doped glasses for various photonic applications.

Luminescence performance of Eu3+-doped lead-free zinc phosphate glasses for red emission

In this study, the luminescence performance of zinc phosphate glasses containing Eu3+ ion with the chemical compositions (60–x)NH4H2PO4-20ZnO-10BaF2-10NaF–x Eu2O3 (where x = 0.2, 0.5, 1.0 and 1.5 mol%) has been studied. These glasses were characterized by several spectroscopic techniques at room temperature. All the glasses showed relatively broad fluorescence excitation and luminescence spectra. Luminescence spectra of these glasses exhibit characteristic emission of Eu3+ ion with an intense and most prominent red emission (614 nm), which is attributed to 5D0 → 7F2 transition. Judd-Ofelt (Ω2, Ω4) parameters have been evaluated from the luminescence intensity ratios of 5D0 → 7FJ (where J = 2 and 4) to 5D0 → 7F1 transition. Using J-O parameters and excitation spectra, the radiative parameters are calculated for different Eu3+-doped glasses. Effect of γ-irradiation at fixed dose has been studied for all the Eu3+-doped glass matrices. The lifetimes of the excited level, 5D0, have been measured experimentally through decay profiles. The colour chromaticity coordinates are calculated and represented in the chromaticity diagram for Eu3+-doped zinc phosphate glasses for all concentrations.

Visible photon excited photoluminescence; photometric characteristics of a green light emitting Zn2TiO4:Tb3+ nanophosphor for wLEDs

A novel green light emitting Zn2TiO4:Tb3+ nanophosphor was synthesized via solution combustion synthesis and the final product was well characterized. From diffused reflectance spectra the energy band gap of the sample was estimated to be in the range 3.16–3.19 eV and the effect of Tb3+ on the electronic structure was calculated based on absolute electronegativity. The characteristic photoluminescence emission peak observed at 493 nm in the blue region was due to 5D3 → 7F3 and peaks at 515, 541, 579 and 620 nm corresponding to 5D4 → 7Fj (j = 6, 5, 4, 3), respectively, were due to f–f transitions of Tb3+ cations in the given host lattice upon 415 nm high energy visible photon excitation. Photometric characteristics suggest that the phosphors have a long lifetime, excellent color purity, color chromaticity coordinates and correlated color temperature values, so it is clearly evident that the optimized phosphor is quite useful for the green region of wLEDs, a ceramic pigment and for solid state display applications.

Synthesis and Optical Properties of Novel Red-Emitting PbNb2O6: Eu(3+) Phosphors.

Undoped and PbNb2O6:Eu(3+) (1.0≤x≤6.0mol%) phosphors were synthesized at 1100°C for 3.5h by the conventional solid state reaction method. Synthesized PbNb2O6:Eu(3+) phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed series of excitation peaks between 350 and 430nm due to the 4f-4f transitions of Eu(3+). For 395.0nm excitation, emission spectra of Eu(3+) doped samples were observed at 591nm (orange) and 614nm (red) due to the (5)D0→(7)F1 transitions and (5)D0→(7)F2 transitions, respectively. PL analysis results also showed that the emission intensity increased by increasing Eu(3+) ion content. No concentration quenching effect was observed. The CIE chromaticity color coordinates (x,y) of the PbNb2O6:Eu(3+) phosphors were found to be in the red region of the chromaticity diagram.

Synthesis and luminescent properties of KLa1−x−y(MoO4)2−z(WO4)z:xEu3+, yDy3+ phosphors for WLEDs

A series of Dy3+ or/and Eu3+ co-doped KLa(MoO4)2−z(WO4)z phosphors were prepared by a solid state reaction. The as-prepared samples were characterized by X-ray diffraction, field emission scanning electronic microscope, Raman spectra and photoluminescence spectra. The results indicated that the as-prepared samples had a monoclinic structure of KLa(MoO4)2 and both had tungstate and molybdate, and show irregular polyhedron. The optimal reaction temperature and time for synthesizing KLa(MoO4)1.5(WO4)0.5:Eu3+ samples were 900 °C and 4 h, respectively. The optimal doping concentrations of WO42−, Eu3+, and Dy3+ were about 50, 17 and 5 mol%, respectively. The KLa(MoO4)1.5(WO4)0.5:Eu3+ samples could be excited by near-UV chips (394 nm) and blue chips (465 nm), and could emit red light at about 618 nm. The Dy3+ doped KLa(MoO4)1.5(WO4)0.5 samples also could be excited by near-UV chips (389 nm) and emit yellow light due to the 4F9/2→6H13/2 transition of Dy3+. It was found that the emission intensity of Dy3+ decreased and that of Eu3+ declined with increasing Eu3+ concentration due to the energy transfer from Dy3+ to Eu3+. Moreover, the chromaticity color coordinates of Eu3+, and Dy3+ single-doped KLa(MoO4)1.5(WO4)0.5 and Eu3+ and Dy3+ co-doped KLa(MoO4)1.5(WO4)0.5 samples were close to red, green and white light region, respectively. All results indicated that this kind of phosphors exhibited a great potential application in the field of white light diodes.

Dy3+ ions as optical probes for studying structure of boro-tellurite glasses

Dy3+-doped glasses with various compositions (35+x)B2O3+ (45−x)TeO2+9.5ZnO+10Na2O+0.5Dy2O3 (x=0; 10 and 20) were prepared by a melt–quenching technique. The Dy3+ ions are used as an optical probe, of which the Judd–Ofelt parameters, the phonon-side band, and the Raman spectra were quantitatively estimated to search the change of glass structure (the change of the ratio of [BO4] to [BO3] units, formation of the non-bridging oxygens (NBO−), the change of [TeO3] to [TeO4] units) as a function of the B2O3 content. The Ω2 and Ω6 values of Dy3+-doped boro-tellurite samples are larger than that of Dy3+-doped borate or tellurite sample. The CIE chromaticity color coordinates were calculated for the luminescence spectra of Dy3+ ions of the glasses with the different compositions and they were all located in the vicinity of white light center of the color coordination diagram.

Effect of Tb3+ concentration on Sm3+ doped leadfluoro-borophosphate glasses for WLED applications

A new series of Sm3+/Tb3 co-doped leadfluoro-borophosphate glasses with the composition 50B2O3+(19.5−x)P2O5+10Li2O+10ZnF2+10PbO+0.5Sm2O3+xTb2O3 (where x=0, 0.05, 0.1, 0.25, 0.5, 1 and 2 in wt%) have been prepared following the melt quenching technique. The presence of fundamental vibrational groups such as BO3, BO4 and PO4 were explored through the FTIR and Raman spectral measurements. The nephelauxetic effect on the absorption transitions have been used to elucidate the bonding nature of the Sm3+ ions with the surrounding ligands thus reveal the predominant ionic nature. Effect of Tb3+ ions on the symmetry of the ligand field around the Sm3+ ions have been predicted using asymmetric intensity ratio values. It is observed that asymmetry around the Sm3+ ion increases with Tb3+ ion concentration upto 1wt% due to the chaos of both the rare earth ions and after that Tb3+ ion concentration dominates thus in-turn creates lower asymmetrical environment. Luminescence quenching effect due to the presence of RE3+ ions concentration has never seen upto almost 2.5wt% (for both RE ions) hence the present host possess the capability to incorporate more number of RE ions. The decay profile of the Tb3+ ion (5D4) is found tobe single exponential and Sm3+ ion (4G5/2) is found to be non-exponential nature. The decreasing trend in the experimental lifetime value of the Tb3+ ions confirms the energy transfer process takes place from Tb3+ ions to Sm3+ ions and the interaction takes place between Tb3+ and Sm3+ ions is of dipole-dipole nature and the same is analyzed using IH model. The energy transfer efficiency is found to increase from 47% to 54% with Tb3+ ion concentration. The CIE color chromaticity coordinates have been calculated to identify the characteristic emission of the prepared glasses and the correlated color temperature, color purity were also determined. All these results suggest that, BPLS0.5T glass is a potential candidate for warm white light applications with minimal blue hazards.

Synthesis and luminescence properties of double-perovskite white emitting phosphor Ca3WO6:Dy3+

A series of single-phase Ca3WO6:Dy3+ phosphors were successfully synthesized via a conventional solid state reaction process. X-ray diffraction and photoluminescence spectra were utilized to characterize the structure and luminescence properties of the as-synthesized phosphors. Under 351 nm excitation, the blue emission at 483 nm (4F9/2 → 6H15/2) and yellow emission at 577 nm (4F9/2 → 6H13/2) were observed in the phosphors. The band gap of Ca3WO6 was estimated to be about 3.82 eV from the diffuse reflection spectrum. The decay time values of Ca3WO6:0.04Dy3+ was calculated to be 0.908 ms. The thermal stability of luminescence of Ca3WO6:0.04Dy3+ phosphor was also investigated and the activated energy was deduced to be 0.105 eV, which shows good thermal stability. The Commission Internationale de L’Eclairage chromaticity color coordinates of the phosphors were found to be in the white light region of the chromaticity diagram. The results show that Ca3WO6:Dy3+ can be a promising white emitting phosphor for white LEDs.

Structural and optical investigations on Dy3+doped lithium tellurofluoroborate glasses for white light applications

Dy3+doped lithium tellurofluoroborate glasses were prepared with the chemical composition (40–x)B2O3+15TeO2+15Li2O+15LiF+15NaF+xDy2O3 (BTLNxD; where x=0.05, 0.1, 0.25, 0.5, 1.0 and 2.0 in wt%) following conventional melt quenching technique and characterized through FTIR, optical absorption, luminescence and lifetime measurements. The vibrations of the borate and tellurite network have been identified through FTIR spectral measurements. The optical properties have been explored from the absorption and luminescence spectra. The optical band gap of direct and indirect allowed transitions was determined from Tauc׳s plot and the variations in the band gap energy with structural arrangements in the prepared glasses is also discussed. Judd–Ofelt theory has been used to evaluate the intensity parameters Ω2, Ω4 and Ω6 using the experimental oscillator strengths and absorption energy levels. The radiative parameters such as transition probability (A), stimulated emission cross-section (σPE), branching ratios (βR) and radiative lifetime (τR) corresponding to the 4F9/2→6H11/2, 6H13/2 and 6H15/2 emission transitions were calculated from the luminescence spectra. The yellow-to−blue (Y/B) luminescence intensity ratios and colour chromaticity coordinates of the title glasses have also been estimated to evaluate the white light emission as a function of Dy3+ion concentration. These results have been used to identify the suitability of the prepared glasses for W-LED applications. The decay rates for the 4F9/2 level have been measured and found to deviate from exponential to non-exponential nature with the increase of Dy3+ion concentration. The non-exponential decay rates have been fitted with the Inokuti–Hirayama model for S=6 which indicate that dipole–dipole mechanism is responsible for the energy transfer processes through Dy3+–Dy3+interaction.

Luminescence optimization with color purity (orange to red) by increasing Gd3+ ions in Eu3+ doped phosphate synthesized by slow evaporation method

The increasing molar concentration of Gd3+ ions in Eu3+ doped phosphate were successfully synthesized by slow evaporation method. All as-prepared phosphors (YPO4:Eu3+, (Y0.3Gd0.7)PO4:Eu3+, Gd1.4PO4.2:Eu3+, Gd2.1PO5.55:Eu3+ and Gd3PO7:Eu3+) were characterized by powder X-ray diffraction pattern (XRD) for crystalline structure and photoluminescence (PL) were studied. The PL emission spectra of as-prepared phosphors indicated that the color purity changes by varying excitation wavelength. Interestingly as the molar concentration of Gd3+ ions increases in phosphate, then results showed outstanding improvement in color purity with enhancement of fluorescence emission intensity monitored at 254 and 275nm. The color chromaticity coordinates (CIE) were calculated.

Combustion synthesis and photoluminescence in novel red emitting yttrium gadolinium pyrosilicate nanocrystalline phosphor

Yttrium Gadolinium Pyrosilicate Y2-xGdxSi2O7:Eu3+ (x = 0.05, 0.10, 0.15) phosphor powder was prepared by facile and time efficient modified combustion method for the first time. The phosphor was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence excitation (PLE) and emission (PL) spectroscopy and color chromaticity coordinates. XRD revealed the monoclinic crystal structure with space group P1¯. The crystallite size was calculated by Williamson-Hall (W–H) analysis. Nanoplates-like morphology was observed in FESEM analysis with size in the range 50–80 nm. TEM images confirmed the particle size and shape. Upon excitation by 254 nm UV light, the phosphor showed the characteristic red emission peaks at 589 nm and 613 nm corresponding to 5D0 → 7F1 and 5D0 → 7F2 transitions respectively. It was observed that the nanocrystalline phosphor Y2-xGdxSi2O7:Eu3+can be tuned to emit orange to red color by adjusting the ratio Y/Gd. This phosphor thus can be a potential candidate as orange to red color emitting tunable nanocrystalline phosphor for optical devices.

Hydrothermal synthesis and multicolor luminescence properties of Dy3+/Eu3+ co-doped KLa(MoO4)2 phosphors

A series of Dy3+/Eu3+ co-doped KLa(MoO4)2 phosphors were synthesized by a hydrothermal method. The as-prepared samples were characterized by an X-ray diffraction (XRD), a field emission scanning electron microscope (FE-SEM), a photoluminescence (PL) excitation, emission spectra and decay curves. The samples have a single-phase monoclinic structure of KLa(MoO4)2 and consist of microspheres with the mean size of 1.5μm. Upon excitation at 389nm, KLa(MoO4)2:Dy3+ exhibits characteristic peaks at 485nm and 576nm. The optimal doping concentration of Dy3+ is about 7mol%. KLa0.93−y(MoO4)2:0.07Dy3+, yEu3+ samples show emission peaks of both Dy3+ and Eu3+ centered at 485, 576, 595 and 618nm under 389nm excitation. It can be found that the integrated emission intensity of Dy3+ is decreased and the lifetime of Dy3+ is declined with increasing Eu3+ concentration, which is due to the energy transfer from Dy3+ to Eu3+. Furthermore, according to Dexter's theory and Reisfeld's approximation, the quadrupole–quadrupole (q–q) interaction is the mechanism for energy transfer between Dy3+ and Eu3+. Moreover, the chromaticity color coordinates of KLa0.93−y(MoO4)2:0.07Dy3+, yEu3+ samples are tuned from the yellowish-white region to white light and eventually to the reddish-white region with increasing Eu3+ content. This kind of multicolor tunable phosphors exhibits the great potential applications in the fields of white light diodes, full-color displays and optoelectronic devices.

Spectroscopic Investigation and Optical Properties of Eu<sup>3+</sup>-Doped Fluorophosphate Glasses

Eu3+-doped fluorophosphate (PKACaLF: P2O5 – K2O – Al2O3 – CaF2 – LiF) glasses have been prepared by melt quenching technique. The structural and optical properties have been characterized through Raman, absorption, photoluminescence and decay time measurements. The Judd-Ofelt parameters have been obtained from the absorption spectrum and are found to be Ω2 = 5.21 x10-20 cm2, Ω4 = 8.11 x10-20 cm2 and Ω6 = 1.03 x10-20 cm2. These parameters have been used to calculate the radiative properties of PKACaLFEu10 glass. The relative luminescence intensity ratio of 5D0 → 7F2 to 5D0 → 7F1 transition (R(2/1)) has been evaluated and is found to be 3.25 which indicates moderate asymmetric nature around Eu3+ ions. The luminescence decay of 5D0 level exhibit single exponential nature and the lifetimes (~ 2.50 ms) are found to be almost constant with increasing Eu3+ ion concentration. The chromaticity color coordinates (x = 0.63, y = 0.31) are in the reddish orange region. From these results, it is confirmed that the present PKACaLF glasses are useful for the development of optical display devices.

Photoluminescence properties and energy transfer of a color tunable phosphor: Dy3+ and Tm3+ co-activated SrCaAl2SiO7

A series of single-phased emission-tunable SrCaAl2SiO7:Dy3+, Tm3+ phosphors were successfully synthesized by solid-state reaction process. By controling the energy transfer, the emission colors could be tuned from blue to yellow, including the white light region. It was discovered that the energy is transferred from Tm3+ to Dy3+ by luminescence spectra and decay curves. The resonance-type energy transfer from Tm3+ to Dy3+ was demonstrated to be via the dipole–dipole mechanism. By changing the doping concentration of Dy3+ and Tm3+ in SrCaAl2SiO7, the sample with corresponding color coordinates close to the white color chromaticity coordinates (x=0.33, y=0.33) could be realized.

Synthesis and photoluminescence properties of (La, Pr) co-doped InVO4 phosphor

(La3+, Pr3+) co-doped InVO4 phosphors were prepared using a sol–gel method. For the (In1−xPrx)VO4 (x=0–0.1) system, X-ray powder diffraction (XRD) patterns show that all of the peaks are attributed to the orthorhombic phase, and the scanning electron microscopy (SEM) images show that there is no obvious difference for the particle morphology between various Pr3+ ions doping. No emission peak characteristics of Pr3+ ions were observed under an excitation of 326nm. In the (In0.97−yLayPr0.03)VO4 (y=0–0.97) system, XRD patterns indicated that the crystal structure changed from the orthorhombic InVO4 structure to the monoclinic LaVO4 structure when the In3+ ions were gradually substituted by the La3+ ions. The location of excitation peaks shifted to short wavelength area (blue shift), and the characteristic f–f transition of Pr3+ ion was observed. With increasing La3+ ion concentration, a series of emission peaks assigned to the 3P0→3H4,5,6, 1D2→3H4, and 3P0→3F2 characteristic transitions of Pr3+ ion were observed in the emission spectra under an excitation of 315nm, and this indicated that the La3+ ion can act as a sensitizer for the (In0.97−yLayPr0.03)VO4 phosphor. The Commission Internationale de I'Eclairage (CIE) color chromaticity coordinates of (In0.97−yLayPr0.03)VO4 phosphors vary with the La3+ ion concentration from the yellowish light region, though the green-yellow and finally to the near-white light area as the La3+ ion concentration increased.

Concentration dependent spectroscopic behavior of Sm3+ doped leadfluoro-borophosphate glasses for laser and LED applications

A new series of Sm3+ doped leadfluoro-borophosphate glasses with the composition 50B2O3+(20−x)P2O5+10Li2O+10ZnF2+10PbO + xSm2O3 (where x = 0, 0.05, 0.1, 0.25, 0.5, 1 and 2 in wt%) were prepared by following the melt quenching technique and their structural and spectroscopic behavior were studied through XRD, FTIR, optical absorption, luminescence and decay measurements. The presence of fundamental vibrational groups such as BO3, BO4 and PO4 were explored through the FTIR spectral measurements and further increasing BO4 units with NBO were also found out. The nephelauxetic effect and Judd-Ofelt (JO) theory have been applied to investigate the nature of the Sm–O bond and the local environment around the Sm3+ ion site. The luminescence intensity decreases with the increase in Sm3+ ion concentration beyond 0.5 wt% and the same was discussed through various energy transfer mechanism which takes place between Sm3+ ions. The lasing parameters like stimulated emission cross-section (σpE), branching ratios (βR) and radiative lifetime (τcal) for the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 emission transitions have been calculated, discussed and reported. The R/O intensity ratios have been studied by varying the RE ion concentration and further CIE color chromaticity coordinates have also been calculated to characterize the emission of the prepared glasses. The color purity and the correlated color temperature were also calculated and the results were discussed in the present work. The decay of the 4G5/2 excited level is found to be single exponential upto 0.1 wt% and after that it changes into non-exponential for higher concentration and the non-exponential behavior arises due to the energy transfer between the Sm3+ ions through various cross-relaxation channels and the decay of the 4G5/2 excited level have been analyzed with IH model. Among the prepared glasses, BPLP0.5S glass exhibits higher σpE, βR, σpE × τR and σpE × Δλeff values corresponding to the 4G5/2 → 6H7/2 emission band and these are in turn specifies its suitability for LEDs and visible laser applications.

Synthesis, luminescence and photometric characteristics of Ca0.5La(MoO4)2:Ln3+ (Ln = Eu, Tb, Dy) phosphors

Ca0.5La(MoO4)2:Ln3+ phosphors, where Ln = 4, 8, 12, 16, and 20 mol% of Eu, Tb, or Dy, were successfully synthesized by a conventional solid-state reaction method at 900 °C for 3 h. The Ca0.5La(MoO4)2:Ln3+ phosphors exhibit a scheelite tetragonal crystal structure belonging to the I41/a space group. The strong absorption bands seen in Fourier transform infrared (FTIR) spectra confirm that F2(ν3) modes of vibration are IR active. The photoluminescence(PL) spectra reveal that, under optical excitation, the as-synthesized phosphors show high intensity narrow emission bands in the red (615 nm), and green (545 nm), and yellow (570 nm) regions for samples doped with Eu3+, Tb3+, and Dy3+ ions, respectively. The critical concentrations of Eu3+, Tb3+, and Dy3+ as dopants in Ca0.5La(MoO4)2 were found to be 16, 12 and 12 mol%, respectively. Thereafter, concentration quenching effect occurred in the solid solutions. The fluorescence decay times for the major transitions of 5D0 → 7F2, 5D4 → 7F5, and 4F9/2 → 6H13/2 were estimated for different doping concentrations of Eu3+, Tb3+, and Dy3+ in Ca0.5La(MoO4)2, respectively. To determine the color purity and emission quality of the phosphor, photometric parameters such as color chromaticity coordinates, color correlated temperature (CCT), color rendering index (CRI), and luminous efficacy of radiation (LER) were estimated using the spectral energy distribution functions of the Ca0.5La(MoO4)2:Ln3+ phosphors.

Synchronous Tricolor Emission-Based White Light from Quantum Dot Complex.

Herein we report the generation of synchronous tricolor emission for a single wavelength excitation from a quantum dot complex (QDC). The single-component QDC was formed out of a complexation reaction, at room temperature, between ligand-free Mn(2+)-doped ZnS quantum dots (Qdots) and a mixture of two organic ligands (acetylsalicylic acid and 8-hydroxyquinoline). Furthermore, the tunability in chromaticity color coordinates, which is important for solid-state lighting, was achieved following the synthesis of QDC. Moreover, the photostable QDC emitted white light (λex 320 nm) with (0.30, 0.33) and (0.32, 0.32) chromaticity color coordinates in the liquid and the solid phases, respectively. Hence, the white light-emitting QDC may be a superior material for light-emitting applications.

Photoluminescence properties of novel Sm3+ and Dy3+ co-activated CsGd(WO4)2 phosphors

CsGd(WO4)2 (CGW) phosphors with different concentration of singly-doped Sm3+ or Dy3+ ions and co-doped Sm3+/Dy3+ ions were prepared through polymeric sol–gel method. The phosphors were characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman and luminescence analysis. The excitation spectra of the phosphors reveal a broad charge transfer band in the short wavelength region and several sharp lines in the longer wavelength region which indicates that these phosphors can be effectively excited by UV and blue LED’s. The CGW: Dy3+, Sm3+ phosphors exhibit the emission peaks in the blue (4F9/2→6H15/2), yellow (4F9/2→6H13/2) and orange–red (4G5/2→6HJ=5/2, 7/2, 9/2) regions under the excitation wavelength of 365nm. The emission spectrum of the co-doped phosphors explains the spread of sensitizing effects from the Dy3+ ions to the Sm3+ ions. All the decay curves are well fitted by the bi-exponential functions. White color chromaticity coordinates (x=0.33, y=0.33) were achieved by optimizing the doping concentration of Sm3+ in Dy3+ doped CGW phosphors.

Synthesis and photoluminescence properties of Dy3+ doped white light emitting CdTa2O6 phosphors

The undoped and CdTa2O6:Dy3+ (0.2≤x≤2.0mol%) phosphors were synthesized at 1100°C for 12h by the conventional solid state reaction method. The synthesized CdTa2O6:Dy3+ phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and Photoluminescence (PL) analyses. The PL spectra showed the presence of excitation peaks between 310 and 440nm due to the 4f–4f transitions of Dy3+. The emission of Dy3+ ions at 353.0nm excitation was observed at 487.1nm (blue) and 577.8nm (yellow) due to the 4F9/2→6H15/2 transitions and 4F9/2→6H13/2 transitions, respectively. The PL analysis results also showed that the emissions increase with the increasing Dy3+ ion content. The emissions increased with the doping concentration of up to 1mol%, and above this level decreased due to concentration quenching effect. The CIE chromaticity color coordinates (x,y) of the CdTa2O6:Dy3+ phosphors were found to be in the white light region of the chromaticity diagram.