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Indium-doped magnesium aluminate (MgAl 2 O 4 :03% In 3+ ) spinel powders were prepared by citrate sol-gel method. The effect of annealing period (AP) at a fixed annealing temperature (800 °C) and dopant concentration (0.3% In 3+ ) on the structure, particle morphology and photoluminescent properties of the powders were investigated. The X-ray powder diffraction (XRD) results showed that the crystalline quality and crystallite sizes of the powders were influenced by the AP. Doping with 0.3% In 3+ did not influence the major crystal structure of the MgAl 2 O 4 (host) material. The scanning electron microscope (SEM) image suggested that the AP influences the particle morphology of the nanophosphor. Transmission electron microscopy (TEM) image suggested that the crystallites sizes were in the region of 10 nm. The Photoluminescence (PL) results showed that the violet emission at 388 nm and green emission at 560 nm both originated from the host material and there was no evidence of any emission from the dopant (In 3+ ). Increasing the AP up to 2 h lead to luminescence enhancement, while further increase in AP lead to luminescence quenching. The Commision Internationale de l’Eclairage (CIE) co-ordinates results showed that the emission colour of all samples was in the blue region and it was not tuned by varying the AP. [ABSTRACT FROM AUTHOR]

ZnSe: x %Er3+ (0 ≤ x ≤ 1.8) thin films were deposited on the glass substrates using a photo-assisted chemical bath deposition method. The X-ray diffraction investigation revealed that the samples exhibited a hexagonal crystalline structure. The undoped ZnSe had a crystallite size of 21 nm, which decreased to 4 nm as the concentration of Er3+ increased. The Scanning electron microscopy images showed that the shape of the particles changed from nanoflakes to glass-like particles after the introduction of Er3+. The expected elemental composition was determined using energy-dispersive spectroscopy. The ultraviolet–visible spectroscopy analysis revealed that increasing the concentration of Er3+ modified the band gap energy within the range of 2.75–4.09 eV. The photoluminescence investigation revealed two distinguishable emission peaks at the energy of 1.79 and 2.34 eV when stimulated with an energy of 5.68 eV. These emission peaks were attributed to the presence of impurities in the host material. The Commission Internationale de l'Eclairage revealed that increasing Er3+ concentration shift the yellow emission from the host towards the light blue region. Incorporating Er³⁺ dopant into the ZnSe lattice significantly alters the structure and optical properties. [Display omitted] • Limited studies have explored the effect of Er3+ ions doped ZnSe on structural and optical properties. • A photo-assisted chemical bath deposition method prepared ZnSe: x %Er3+ (0 ≤ x ≤ 1.8) thin films. • The UV–vis results showed an energy band gap (E g) modification from 2.75 to 4.18 eV by varying Er3+ concentration. • The results revealed exponential luminescence intensity enhancement with increasing Er3+ concentration. • The CIE coordinates show ZnSe: x %Er3+ (0 ≤ x ≤ 1.8) thin films are tunable from yellow to light blue region. [ABSTRACT FROM AUTHOR]

Abstract Nanophosphor powders of the mixed phases of ZnAl 2 O 4 /ZnO/SrAl 2 O 4 /Sr 3 Al 2 O 6 (ZZSS) doped with Tb3+ (ZZSS:0.025%Tb3+) were successfully prepared by sol-gel technique. The effect of the annealing period at a fixed annealing temperature (1000 °C) and dopant concentration (0.025% Tb3+) on the structure and photoluminescence properties was investigated. X-ray diffraction results revealed that the crystallite size was influenced by the annealing period. Scanning electron microscopy showed that varying the annealing period influenced the particle morphology of the prepared nanophosphor material. High resolution transmission electron microscopy confirmed that the prepared material is on the nanoscale. The photoluminescence results showed that the ZZSS emits at 585 nm when excited at 374 nm, which is attributed to the defects centres within the ZnO phase. The Tb3+ doped samples showed emissions peaks at 545, 590 and 623 nm which were attributed to the 4f transitions of Tb3+, specifically 5D 4 → 7F J (J = 5, 4, 3). Increasing the annealing period up to 5.4 h led to luminescence enhancements, while a further increase led to quenching. The Commision Internationale de l'Eclairage coordinates showed that the greenish emission colour could be tuned by varying the annealing period. Highlights • The prepared nanophosphor resembles the mix phases of ZnAl 2 O 4 /ZnO/SrAl 2 O 4 /Sr 3 Al 2 O 6. • Annealing period influences the crystallite sizes of the prepared nanophosphor. • The morphology was greatly influenced by annealing period. • Photoluminescence (PL) results showed 5.4 h as the optimum annealing period of the prepared nanophosphor. • The greenish colour from terbium can be enhanced by varying the annealing period. [ABSTRACT FROM AUTHOR]

Abstract Barium magnesium aluminate nanopowders doped with holmium (Ba 0.5 Mg 0.5 Al 2 O 4 :x% Ho3+) were successfully prepared by the sol-gel method. The Ho3+ concentration was varied up to 2 mol%. X-ray powder diffraction results showed that the Ba 0.5 Mg 0.5 Al 2 O 4 nanopowders crystallized in the hexagonal phase of BaAl 2 O 4. Scanning electron microscopy images suggested that the doping influences the particle morphology. Photoluminescence results showed visible emissions observed at around 422 and 733 nm which originated from intrinsic defects within the host material as well as emissions at around 491, 550, 662 and 758 nm which were attributed to the 5F 3 → 5I 8 , 5F 4 /5S 2 → 5I 8 , 5F 5 → 5I 8 and 5S 2 → 5I 7 transitions of Ho3+ respectively. Infrared emissions around 1157 and 1200 nm were attributed to the 5S 2 ,5F 4 → 5I 6 and 5I 6 → 5I 8 transitions of Ho3+. Increasing the Ho3+ concentration up to x = 0.8% led to luminescence enhancement, while further increase led to luminescence quenching. Lifetime measurements revealed that the x = 0.8% sample with maximum emission intensity at 550 nm has a strong lifetime component of 7.79 μs and a small component of long lifetime 79 μs, while the x = 2% (maximum doped) sample exhibited some concentration quenching and the contribution of the medium (7.79 μs) component was lower. The Commission Internationale de l'Eclairage (CIE) co-ordinates showed that the emission colour could be tuned towards bluish-purple by mixing of the MgAl 2 O 4 and BaAl 2 O 4 components. The Ho3+ concentration influenced the proportion of green emission colour. Highlights • Ba 0.5 Mg 0.5 Al 2 O 4 :x% Ho3+ (0 ≤ x ≤ 2) series was successfully prepared by the citrate sol-gel method. • X-ray powder diffraction results showed that the Ba 0.5 Mg 0.5 Al 2 O 4 nanopowders crystallized in the hexagonal phase of BaAl 2 O 4. • The surface morphology was influence by doping. • Emissions from both the host material and Ho3+ were observed. • The Commission Internationale de l'Eclairage (CIE) co-ordinates showed that the emission colour could be tuned by varying the Ho3+ concentration. [ABSTRACT FROM AUTHOR]

Pristine and octadecylammine (ODA)-capped ZnO nanostructures were synthesized via the homogeneous precipitation method at a bath temperature of 80 °C and annealed in air at 700 °C for 2 h. Various molar concentrations of ODA ranging from 0.3 to 15 mol% ODA were used to study the effect of ODA capping into ZnO nanostructures. The x-ray diffraction (XRD) analyses revealed the hexagonal wurtzite structure for all prepared samples. The estimated average crystallite sizes were found to be in the range of 46–72 nm. It was found that the crystallite sizes increased with an increase in the amount of ODA molar concentration. The surface morphology studied using scanning electron microscopy (SEM) showed flower-like shapes for pristine ZnO and cylindrical nanorods features for ODA-capped ZnO nanostructures. Elemental energy dispersive (EDS) and mapping analysis conducted on the samples shows homogeneous distribution of Zn, O, and C ions. The Ultraviolet-visible diffusion reflectance spectroscopy showed a decrease in the band gap with an increasing of ODA molar concentration. The photoluminescence (PL) results demonstrated that the luminescence intensity increased up to 10 mol% ODA. However, further increase in ODA molar concentration revealed the decrease on the luminescence intensity. The approach in the present study opened a new way to tune band gap and luminescence intensity using ODA. [ABSTRACT FROM AUTHOR]

Nanocrystalline ZnAl 2 O 4 :x% Cu 2+ ( 0 < x ≤ 1.25 ) phosphor powders were prepared via the citrate sol-gel technique. The pure-phase cubic structures in this systems were verified by the powder X-ray diffraction. Energy Dispersive x-ray Spectroscopy analysis confirmed the presence of the expected elements (Zn, Al, O and Cu). Scanning Electron Microscopy showed that the morphology of the phosphor was dependent on the concentration of Cu 2+ . High-Resolution Transmission Electron Microscopy confirmed that the Cu 2+ concentration does not significantly influence the crystallites sizes of the phosphors. Ultraviolet–visible spectroscopy results showed that the Cu 2+ concentration influenced the band gap of the host. Photoluminescence results showed that the emission intensity of the powder sample was dependent on the Cu 2+ concentration. The emission from the host lattice was observed at 394 nm, while Cu 2+ showed major emission at 405 and minor emission at 574 nm. The emission at 405 nm was due to the 3d 8 4s 1 → 3d 9 transitions of Cu 2+ . The Commission on Illumination color coordinate evidently showed shifts from the bluewish to the greenish region with an increase in Cu 2+ concentration. [ABSTRACT FROM AUTHOR]

Undoped and europium ion (Eu 3+ ) doped ZnO nanostructures were synthesized via the chemical bath deposition method and annealed afterwards in air at 700 °C. The X-ray diffraction measurements confirmed the hexagonal wurtzite structure for all samples. The scanning electron microscopy (SEM) revealed that the nanopowder samples were assembled in flower-like shapes for undoped and hexagonal-shaped for Eu 3+ -doped ZnO. Elemental energy dispersive (EDS) analysis mapping conducted on the samples revealed homogeneous distribution of Zn, O, and Eu ions. The Ultraviolet–visible (UV–vis) diffusion reflectance spectroscopy showed a decrease in the band gap with an increasing Eu 3+ concentration. The photoluminescence (PL) results showed that by exciting Eu 3+ (4 mol%) doped ZnO with different excitation wavelength the highest luminescence intensity was observed at an excitation wavelength of 395 nm but no emissions were observed from Eu 3+ . By exciting further with 465 nm the Eu 3+ emissions were observed and emission from undoped ZnO was found for the first time. [ABSTRACT FROM AUTHOR]

Lead-doped zinc aluminate (ZnAl 2 O 4 :1.5% Pb 2+ ) spinel nanocrystals powders were prepared by the citric assisted sol-gel process. The effects of annealing temperature (AT) at a fixed dopant concentration on the structure, morphology and optical properties of the powders were investigated. Thermogravimetric analysis (TGA) showed that the minimum annealing temperature required to obtain single phase ZnAl 2 O 4 must be above 400 °C. Fourier transform infrared spectroscopy (FTIR) results suggest that heat treating destroys some of the bonds. From the XRD results, it was observed that the required structure started to grow at the AT of 500 °C. With an increase in AT > 500 °C the structure transformed to single phase of cubic ZnAl 2 O 4 spinel. The crystallinity increases upon further rise of AT to 800 °C. On heating at 600–800 °C, the powders had the average crystallite sizes of around 18–22 nm. Energy dispersive x-ray spectroscopy (EDS) analysis confirmed the presence of the expected elements (Zn, Al, O and Pb). The morphology of the prepared phosphor were influenced by the AT. Transmission electron microscopy (TEM) results revealed that the prepared powders are in the nano-scale range. The band gap of the sample annealed at 800 °C were estimated to be 3.2 eV. The emission position and intensity of the phosphor was dependent on the AT. Emissions arising from both the host and Pb 2+ ion were observed. Emission wavelength of the prepared phosphors can be tuned by varying the AT. The results suggest that ZnAl 2 O 4 :1.5% Pb 2+ is a promising candidate for blue-light emitting phosphor. [ABSTRACT FROM AUTHOR]

ZnSe: x % Eu3+ (0 ≤ x ≤ 2.0) thin films were deposited using the photo-assisted chemical bath technique. All the films samples revealed wurtzite phase and the diffraction peak intensities decreased with increased Eu3+ concentration, due to loss of crystallinity. Raman spectroscopy revealed two optical phonon peaks due to first and second order longitudinal modes. The films morphological transformed from flakes to spherical grains with an increased Eu3+ concentration. The presence of the anticipated elements was confirmed by energy dispersive X-ray spectroscopy. Atomic force microscopy showed an increase in surface roughness with increased Eu3+ concentration, which however decreased at x = 2.0%. The ultraviolet–visible spectroscopy results showed increased band gap energy with an increase in Eu3+ concentration. There was a blue shift in the transmittance edge with respect to the undoped sample due to the decrease in crystallite size. The undoped sample showed four luminescence peaks, which are due to the band-to-band and defects within the host material. Although there was no evidence of emission from the Eu3+ ions, increasing the Eu3+ doping concentration resulted in enhancement of the emission peak intensities. Chromaticity analysis showed that the blue emission color is not significantly influenced by the Eu3+ concentration. • ZnSe: x % Eu3+ (0 ≤ x ≤ 2.0) thin films were deposited on glass slide at 80 °C for 2 h. • Photo-assisted chemical bath technique was used for the deposition. • The films were annealed in air at temperatures at 250 °C for 3 h. • The films were of single wurtizite structure with no impurity phases. • Blue colour emission was observed with potential application in luminescent devices. [ABSTRACT FROM AUTHOR]

This paper reports on the effects of varying the Cu2+ doping concentration on the structure, morphology and optical properties of the BaAl 2 O 4 phosphor. BaAl 2 O 4 :x% Cu2+ (0 ≤ x ≤ 1) series were successfully synthesized via citrate sol-gel method. The X-ray diffraction (XRD) results revealed that the prepared phosphor sample consist of a single phase hexagonal structure. The presence of Ba, Al, O and Cu were confirmed by the energy dispersive X-ray spectroscopy (EDS). Scanning electron microscope (SEM) revealed that the morphology of the prepared samples highly depends on the Cu2+ concentration. Transmission electron microscopy (TEM) results revealed the hollow tubular and nano-nature of the crystallite sizes. When the un-doped sample was excited at 283 nm, the photoluminescence (PL) results revealed six emission peaks located at 420, 435, 457, 521, 612 and 722 nm, which were attributed to the intrinsic intra band gap defects within the BaAl 2 O 4 (host). The emission at 425 nm observed for the BaAl 2 O 4 :Cu2+ samples was attributed to the 3d84s1 → 3d9 transition in Cu2+ ion. The optimum doping Cu2+ concentration was found to be 0.075% Cu2+. Critical energy transfer distance (R c) of Cu2+ ions was found to be 12.01 Å, which suggested that the multipole-multipole interaction was the main reason for the luminescence quenching. The International Commission on Illumination (CIE) colour showed that the bluish emission colour of the prepared samples depends on the excitation wavelength and Cu2+ concentration. Thermo stimulated luminescence (TSL) of the host material showed the presence of both the swallow and deep traps respectively located at 75 and 240 °C. • Hexagonal nanocrystalline BaAl 2 O 4 :x% Cu2+ (0 ≤ x ≤ 1) phosphor powders were succesfully prepared via the citrate sol-gel technique. • Photoluminescence emission intensity of the powder sample was dependent on the Cu2+ concentration. • Both emissions from the host and Cu2+ were observed. • The Commission on Illumination color coordinate evidently showed that the bluish emission depends on the Cu2+ concentration. • Themoluminescence results showed the precence of both the shallow and deep level tranps in BaAl 2 O 4 : Cu2+ phosphor material. [ABSTRACT FROM AUTHOR]

A series of silica (SiO 2) nanoparticles doped with different concentrations of Sr2+ ions were successfully synthesized using the sol-gel method. The structural, morphological and optical properties of the phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) diffuse reflection and photoluminescence (PL) measurements. The XRD results showed that the amorphous SiO 2 changed to crystalline orthorhombic Sr 2 SiO 4 with the increase in Sr2+ concentration. The SEM micrographs show irregular agglomerated particles whose size decreased with an increase in the Sr2+ concentration. The EDS measurements confirmed the presence and uniform distribution of Si, O and Sr. TEM results confirmed that the prepared powders consisted of agglomerated crystallites. The UV–vis spectra analysis showed a red shift with an increase in the concentration of Sr2+. The PL results showed a change in the emission spectrum with the addition of the Sr2+ ions. The emission was attributed to the defects within the SiO 2 backbone of O–Si–O network. The highest emission intensity was found for the sample doped with 0.4 mol% Sr2+, with apparent luminescence quenching at higher concentrations. The CIE coordinates indicated that the blue color from the host defects could be tuned by varying Sr2+ concentration. Image 10421 • SiO 2 :xmol% Sr2+ phosphors were successfully prepared using the sol-gel method. • UV–vis showed red shift of the absorption edge with an increase in the Sr2+ dopant. • The PL showed that the highest emission intensity was obtained at x = 0.4 mol% Sr2+. • In this work, it was also found that Sr2+ induces more defects in SiO 2 lattices. • At 0.4 mol% Sr2+ the colour that corresponds to white light on CIE was observed. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) undoped, doped and co-doped with Ce3+ and Eu3+ were synthesized by the chemical bath deposition method. The nanopowders were spread through a polyvinyl chloride (PVC) polymer matrix via the solution casting method to prepare nanocomposite films. The X-ray diffraction patterns showed crystalline peaks corresponding to a hexagonal wurtzite ZnO structure. Scanning electron microscope showed aggregated structures. Energy dispersive X-ray spectrometer and Fourier-transform infrared spectroscopy respectively revealed the existence of the expected elemental composition and functional groups. Differential scanning calorimetry showed nanoparticles as the starting point for particle growth. Thermogravimetric analysis showed lowering in thermal stability of the nanocomposites. In the UV–vis study, PVC had the highest energy band gap than all powder and composite systems. The PVC nanocomposites showed an emission peak at around 444 nm, which differed from that of the nanopowders. The chromaticity diagram showed emission colours changed to the blue vertex regions for nanocomposite. • ZnO nanopowders spread through PVC polymer matrix by solution casting method. • The XRD showed crystalline peaks corresponding to a hexagonal wurtzite ZnO structure. • The TGA analysis showed a decrease in thermal stability of the nanocomposites. • There is a slightly red shift on both powder and nanocomposite samples. • Nanopowders emits at λ em = 622 nm while nanocomposites at λ em = 444 nm. [ABSTRACT FROM AUTHOR]