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The luminescent materials incorporated with rare earth (RE)/transition metal (TM) ions that possess up/down conversion phenomena have found widespread applications in sensing, optical thermometry, photovoltaic/solar cells, biomedical fields and wLEDs. The augmented studies on such materials have been conducted to explore their luminescent properties for the aforementioned applications. However, how to precisely design appropriate luminescent material for certain application, how to evaluate adequacy of synthesized phosphor and finally to accomplish targeted irradiation for its desirable and practical utilization are urgently need to be clarified. In this article, a thorough overview is presented on recently explored phosphors doped with different RE/TM ions to acquire in depth knowledge about such materials and to answer the above-mentioned issues. Herein, desirable light quality for targeted application, frequently-used activators and quantitative verification methods such as cytotoxicity test and good contrast are respectively discussed for drug delivery and bio-imaging applications. The role of thermally and non-thermally coupled levels in phosphors to serve as an excellent material for thermal sensing application is reviewed. Various materials with up/down conversion are studied for improving solar cell efficiency. Different materials used for display devices and wLEDs are discussed to understand the need of developing novel materials for enhancing quantum efficiency of commercial white light emitting devices. Finally, remnant challenges in these emerging fields are addressed, our perspectives for further investigations are presented with hope that this review can pave the way for future researchers to design and study phosphors for these applications. • This review article focuses on different applications of phosphors. • The rare earth/transition metals doped phosphors have down as well as up conversion. • In drug delivery, drugs loaded phosphor materials tested for cytotoxicity. • Bioimaging applications require phosphor materials excited under NIR region. • Thermal sensing application uses FIR method to account potentiality of phosphors. • Up-conversion & downshifted phosphors are useful for solar cell applications. [ABSTRACT FROM AUTHOR]

Gadolinium (Gd3+) ion-activated SrY2O4 phosphors with varying concentrations of Gd3+ ions were prepared using sol–gel synthesis. The photoluminescence spectra were recorded to study the luminescence behavior of the as-synthesized phosphors. Upon excitation at 275 nm, the material displayed two bands, one at 309 nm (6P5/2 → 8S7/2) and the other at 315 nm (6P7/2 → 8S7/2), in the narrowband ultraviolet (UV) spectral regions. The strong emission at 315 nm indicated that the phosphors could be used as a narrowband UV light source. Electron paramagnetic resonance spectra showed a foremost Gd3+ center with weak signals. Several resonance signals revealed that Gd3+ ions underwent different Zeeman interactions and exhibited varying crystal field strength. The results suggest the potential utility of Gd3+ doped-SrY2O4 phosphors for phototherapy lamp applications which require UV emission. [ABSTRACT FROM AUTHOR]

A series of Mn2+ activated Sr2ZnSi2O7 phosphors with variable Mn2+ ions concentration were prepared via citrate sol–gel method. The systematic analysis of structure and luminescent properties were carried out by recording x-ray diffraction patterns, scanning electron micrographs, excitation and emission spectra along with electron paramagnetic resonance (EPR) spectra. The optimization of Mn2+ ion concentration in the synthesized phosphors was done by analyzing emission spectra. The Mn2+ activated Sr2ZnSi2O7 phosphors exhibit green emission under 263 nm excitation. The EPR spectra exhibit sextet hyperfine lines with resonance at g ≈ 2.0 indicating tetrahedral symmetry and covalent bonding between Mn2+ ions and O2− ligand ions bound to it. All the aforesaid results support the suitability of Mn2+ activated Sr2ZnSi2O7 phosphors as visible green emitters in optoelectronic display devices. [ABSTRACT FROM AUTHOR]

Left. Synthesis procedure of Bi3+ doped and Bi3+/Eu3+ co-doped CAZ phosphor. Right. Energy level diagram of Bi3+/Eu3+ co-doped CAZ phosphor. [Display omitted] • Bi3+, Bi3+/Eu3+ doped CAZ phosphor prepared by sol–gel method. • Under UV excitation, blue emission and under blue excitation red emission is achieved. • Energy transfer through dipole–dipole interaction leads to concentration quenching. • Color tunability under different excitation in the phosphors under investigation is observed. • Relatively good thermal stability of the CAZ phosphors is observed from TDPL measurements. • These studies suggest the utility of the said phosphors in photonic devices. Bi3+/Eu3+ co-driven calcium aluminozincate (CAZ) phosphor prepared by sol–gel route. Structural analysis was conducted based on X-ray diffractogram. Scanning Electron Microscope images were recorded using Carl Zeiss microscope. Luminescent traits of the said phosphors were identified using excitation and emission spectroscopy at room temperature and elevated temperature. The emission spectra recorded at room temperature under different excitations exhibit variation in spectral behavior. The Commision Internationale de-lElcairage coordinates shown in chromaticity diagram indicate the change in emission hue as pure blue, bluish red and finally pure red by varying the excitation wavelengths. The temperature dependent emission spectra show decrease in emission intensity with temperature and activation energy found to be 0.280 eV. The decay curves were also recorded to determine lifetime and study energy transfer between Bi3+ and Eu3+ ions. Auzel's fit conducted based on the decay lifetimes helps in evaluating quantum efficiency theoretically. All these investigations authorize the potential of Bi3+/Eu3+ doped CAZ phosphors for their utilization as color-tunable phosphor in photonic applications. [ABSTRACT FROM AUTHOR]

Calcium aluminozincate phosphor, Ca 3 Al 4 ZnO 10 (CAZ) doped with Eu3+ has been synthesized using solid-state reaction (SSR), combustion (CS) and sol-gel (SG) methods for relatively improved luminescence performance and to optimize synthesis method. The X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) and PL decay measurements have been recorded for the detailed investigation of the luminescence properties of the as-synthesized phosphor. The thermoluminescence (TL) spectral study has been done to estimate the trap depth of the defect centres. The XRD peaks confirm the complete matching of the diffraction peaks of the as-synthesized sample with the standard data for Ca 3 Al 4 ZnO 10. The morphology of the sample synthesized via SG method shows agglomerated particles with average particle size smaller than the samples synthesized via CS and SSR method. The detailed investigation shows significant red emission enhancement in Eu3+ doped CAZ phosphor synthesized via SG method. The obtained results suggest that the Eu3+ doped CAZ phosphor synthesized via SG method could be a great choice as red emitter for applications in solid state lighting. • Optimized synthesis technique for calcium aluminozincate (CAZ) phosphors. • Phase confirmation observed in solid-state, combustion and sol-gel method. • Enhancement in red emission under blue excitation for sol-gel synthesized phosphors. • CIE coordinates are close to commercial red phosphor. • Conducted thermoluminescence studies to identify trap centres in CAZ phosphors for the first time. [ABSTRACT FROM AUTHOR]

Partial energy level diagram representing energy level of Dy3+ and Eu3+ ions and transitions observed in calcium aluminozincate phosphor. • Dy3+/Eu3+ co-doped CAZ phosphors were synthesized by using Pechini sol-gel method. • The as synthesized phosphors show intense white emission under 363 nm excitation. • The energy transfer between Dy3+ and Eu3+ ions is via dipole-dipole interaction. • The thermoluminescence study reveals presence of shallow and deep trap centres. Dy3+ doped and Dy3+/Eu3+ co-doped calcium aluminozincate (CAZ) phosphor synthesized by Pechini sol-gel method. Structural and morphological analysis were carried out by using X-ray diffractometer (XRD) and field emission scanning electron microscope (FE-SEM). The photoluminescent (PL) spectra were recorded and energy transfer mechanism between Dy3+ and Eu3+ ions were studied using Dexter and Reisfeld's approximation. The colorimetric properties were studied by evaluating CIE coordinates and correlated color temperature (CCT). The energy transfer mechanism was analysed by applying Inokuti-Hirayama (I-H) model on decay curves as well. The thermoluminescence (TL) glow curve analysis reveals two trap centres in the present host. The obtained results indicate that the CCT can be tuned from warm to cool region and color tunability can also be achieved in Dy3+/Eu3+ co-activated CAZ phosphor by varying the excitation wavelength or activator concentration in the host lattice and hence can be effectively utilized in white light emitting diodes (wLEDs). [ABSTRACT FROM AUTHOR]

Trivalent europium ions (Eu 3+ ) doped calcium aluminozincate (CAZ) phosphors blended with various fluxes (NaF, NaCl and Na 2 B 4 O 7 ) have been synthesized by conventional solid-state reaction method. The structural, morphological and luminescent properties along with lifetimes have been investigated in detailed. The Judd-Ofelt (J-O) analysis has been carried out to get insight of optical properties. The X-ray diffraction (XRD) pattern confirms the single phase orthorhombic structure for Eu 3+ doped CAZ phosphor with NaCl and Na 2 B 4 O 7 fluxes; whereas the phase purity has not been achieved in NaF assisted Eu 3+ doped CAZ phosphor. The as-synthesized phosphor has uneven agglomerated micron sized particles. The photoluminescence (PL) studies exhibit significant enhancement in the red emission for Eu 3+ doped CAZ phosphor with the addition of Na 2 B 4 O 7 . The emission intensity has been found to increase approximately 1.5 times using NaCl and 2.5 times for Na 2 B 4 O 7 in Eu 3+ doped CAZ phosphor as compared to the phosphor without any flux. The emission spectrum of optimized Eu 3+ doped CAZ phosphor added with Na 2 B 4 O 7 flux has been compared with the commercial Y 2 O 3 : Eu 3+ phosphor. The CIE chromaticity coordinates and color purity calculated for Na 2 B 4 O 7 in Eu 3+ doped CAZ phosphor is close to commercial red phosphor. The decay curves show bi-exponential behaviour with experimental lifetimes in the range of microseconds for the as-prepared phosphors. All these results indicate that the Na 2 B 4 O 7 flux assisted Eu 3+ doped CAZ phosphor can serve as an efficient red phosphor under blue light for applications in white light emitting devices. [ABSTRACT FROM AUTHOR]

A series of Pb 2+ -doped SrZrO 3 phosphors with a varying Pb 2+ concentration has been successfully synthesized using the sol-gel method. The structural, morphological, and luminescence properties along with the electron paramagnetic resonance (EPR) properties have been investigated in details. The structural analysis was carried out by recording X-ray diffraction (XRD) patterns, which confirms the pure-phase formation of the synthesized phosphors. The morphological study was performed using a scanning electron microscope (SEM) that showed micron-sized particles with irregular morphologies. The photoluminescence excitation and emission spectra were also recorded. The emission intensity shows the maximum at 360 nm that was pumped at 278 nm for SrZrO 3 :Pb 2+ . The optimized Pb 2+ concentration is 0.015 mol. Investigations of un-doped and Pb 2+ doped SrZrO 3 phosphor have been carried out using electron paramagnetic resonance (EPR) technique. Pure SrZrO 3 exhibits an axially symmetric EPR line with g || = 1.93 and g ⊥ = 1.99. These lines are ascribed to Zr 3+ ion. Additional lines are not observed in the Pb 2+ doped phosphors. [ABSTRACT FROM AUTHOR]

Monophase Calcium Aluminozincate (Ca 3 Al 4 ZnO 10 ) phosphor doped with Sm 3+ ions by varying concentrations have been prepared at 1300 °C using conventional solid state reaction technique. The crystal structure and phase analysis of the as-prepared phosphor has been carried out by X-ray Diffraction (XRD) studies. Morphology and functional groups present in the phosphor have been investigated thoroughly by using Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FT-IR) spectral measurements, respectively. Under 401 nm excitation, the as-prepared phosphor exhibit intense visible orange emission at 601 nm. It has been observed that 1.0 mol% of Sm 3+ ions concentration is optimum to give intense visible orange emission. The PL analysis reveals that the dipole-dipole interaction is primarily responsible for the concentration quenching observed beyond 1.0 mol% of Sm 3+ ions. The TR-PL study reveals a bi-exponential behavior of decay curves with an average lifetime of the order of microseconds. The CIE coordinates ( x =0.574 and y =0.424) measured for the optimized phosphor are very close to the intense orange emission coordinates specified by Nichia Corporation developed Amber LED NSPAR 70BS (0.570, 0.420). The spectroscopic, PL and TR-PL studies suggest the potential use of Sm 3+ doped calcium aluminozincate phosphors for display and white light emitting devices. [ABSTRACT FROM AUTHOR]

A novel calcium aluminozincate phosphor doped with Eu 3+ ions has been synthesized by conventional solid state reaction method and characterized by using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Diffuse Reflectance Absorbance (DRA) and Spectrofluorophotometer to study the structural, morphological and photoluminescence (PL) properties. All the XRD peaks are matching well with the standard ICDD card confirm that the prepared phosphors consist of single phase orthorhombic structure (Ca 3 Al 4 ZnO 10 ) having Pbc2 space group. The PL spectra recorded under near-UV/blue excitations demonstrates a very distinct and intense red emission from all the phosphors. In the present investigation, we found that 2 mol% of Eu 3+ ions concentration is optimum in this host to give intense red emission. This result is also in consistent with the CIE chromaticity coordinates measured from the PL spectra of the samples under investigation. The results obtained for the optimized phosphor in the present investigation such as PL and CIE coordinates (x = 0.629 and y = 0.370) are close to the commercial red phosphor Y 2 O 2 S: Eu 3+ (x = 0.622 and y = 0.351) and also very near to the coordinates specified by National Television Standard Committee (NTSC). [ABSTRACT FROM AUTHOR]

A series of Mn(II)-doped hardystonite phosphors was obtained by using a sol-gel technique. Structural, morphological, and optical properties of the prepared samples were investigated by X-ray diffraction, Fourier transform infrared, scanning electron microscopy and diffuse reflectance spectrum. The photoluminescence excitation and emission spectra of the prepared phosphors exhibited a strong band at ~ 254 nm and an intensified emission band at ~ 525 nm, respectively. Of all the prepared phosphors, 0.03Mn(II) doped hardystonite phosphor possessed a highly intense emission band, which demonstrated that 0.03 mol was the optimized concentration of Mn(II) ions. All the prepared phosphors emitted a bright green color, as confirmed by the Commission International de I′Eclairage co-ordinates. Electron paramagnetic resonance study suggested the existence of Mn(II) ions at sites with octahedral symmetry (g value ~2) and the dominance of covalent bonding in the prepared phosphors. [ABSTRACT FROM AUTHOR]

A series of calcium aluminate phosphors doped with Tm3+ ions at various molar concentrations was prepared via sol-gel route. Various characterizations were conducted to identify the structural and luminescence properties. The XRD patterns of the prepared series suggested that the pure phase was attained. Fourier transform-IR spectrum was recorded to identify various bonds involved in the structure of calcium aluminate. Diffuse reflectance was studied and a Tauc plot was prepared to determine the band gap. Photoluminescence studies were conducted to check the viability of the prepared material in w-LEDs. The prepared calcium aluminate phosphors exhibited 459 nm emission under n-UV excitation. The evaluated CIE coordinates showed core blue emission with high color purity. All the investigations carried out for the prepared phosphors suggested their potential for application as blue emitters in w-LEDS. [ABSTRACT FROM AUTHOR]

A series of CaY 2 Al 4 SiO 12 garnet phosphor doped with different concentrations of Sm3+ varying from 0.01 mol to 0.11 mol was prepared by using the sol-gel method. Structural investigations were conducted by recording the X-ray diffraction (XRD) patterns. The UV-Vis diffuse reflectance spectrum was recorded to identify the optical band gap. The luminescence behavior was studied by recording the excitation and emission spectra. The emission spectra recorded under 403 nm excitation revealed emission peaks due to f-f transitions of Sm3+ ions. The optimum amount of Sm3+ was also identified by studying the concentration effect. The studied colorimetric properties revealed the orange color emission of the prepared garnet phosphors. These results support the potential utility of the prepared garnet phosphor in display and lighting devices. [ABSTRACT FROM AUTHOR]

Terbium (Tb3+) ions doped calcium aluminozincate (CAZ) phosphors with different concentration of Tb3+ ions (0.0–5.0 mol%) have been successfully prepared by sol-gel method. The crystal phase analysis and morphology of the as prepared phosphors have been studied from X-ray diffraction (XRD) patterns and field emission scanning electron microscope (FE-SEM) image. The luminescence behaviour of Tb3+ doped CAZ phosphors have been studied relative to variable dopant ion concentration. The intense emission has been observed at 543 nm under 238 nm excitation for all the phosphors. The decay curve analysis manifests the energy transfer as a consequence of dipole-dipole interaction between Tb3+ ions in the host. The colorimetric property has been understood on the basis of evaluated CIE color coordinates. The systematic study of Tb3+ doped CAZ phosphors determine the potential utility of these phosphors in lighting and display applications. Partial energy level diagram of Tb3+ ion in CAZ phosphor. Image 1 • Tb3+ ions doped calcium aluminozincate phosphors synthesized by sol-gel method. • Transition from 5D 3 and 5D 4 levels exhibit emission in blue and green regions. • Energy transfer from 5D 3 to 5D 4 energy level at 4.0 mol%. enhance green emission. • Color tunability is achieved in Tb3+ doped as synthesized phosphors. • These studies suggest the utility of above mentioned phosphors in lighting and display devices. [ABSTRACT FROM AUTHOR]

MgY 2-x Al 4 SiO 12 :xCr3+ garnet phosphors doped with different concentrations of Cr3+ (0.01–0.07 mol) were prepared using the sol-gel method, and their structural, luminescent, and electron paramagnetic resonance (EPR) properties were studied. Structural and morphological measurements were made by powder X-ray diffraction and scanning electron microscope, respectively. Cubic-structured garnet phosphors were observed. The diffuse reflectance spectrum of 0.02 mol Cr3+ doped MgY 2 Al 4 SiO 12 phosphor was studied to estimate the crystal field parameters (Dq and B). The emission spectrum depicts intense emission in the far-red region under 580 nm excitation. The optimized concentration of Cr3+ ions is identified as 0.02 mol, for which the emission intensity is maximum. The CIE coordinates measured from the emission spectra for the as-prepared phosphors fall in the red region of the visible spectrum. The EPR spectra recorded at room temperature reveal five g -values at ~3.90, ~3.57, ~2.67, ~2.46, and ~1.97, corresponding to isolated Cr3+ ions and exchange-coupled Cr3+-Cr3+ pairs. • By sol-gel synthesis, Cr3+ incorporated MgY 2 Al 4 SiO 12 matrix obtained. • Prepared phosphors characterized using XRD, SEM, EPR, UV–Vis and PL spectroscopy. • Upon 580 nm light excitation, far-red region 689 nm emission observed. • EPR reveal five g -values corresponding to isolated Cr3+ ions and exchange-coupled Cr3+–Cr3+ pairs. [ABSTRACT FROM AUTHOR]

We investigated the structural and luminescence characteristics of Ba 2 YZrO 6 :xGd (0.01 ≤ x ≤ 0.11) perovskite ceramic phosphors prepared by sol-gel with dominating cubic phase. The Fourier transform infrared (FT-IR) spectrum depicted various shoulders attributed to the functional groups present in the host matrix. The photoluminescence (PL) spectroscopy exhibited the emission at 315 nm under the excitation of 229 nm light, owing to the P 6 7 / 2 → S 8 7 / 2 transition. We also observed concentration quenching in the prepared phosphor. Further, the electron paramagnetic resonance (EPR) spectra recorded for the samples under room temperature discerning three main resonance signals with effective g-values 6.02, 2.45, and 1.32. [ABSTRACT FROM AUTHOR]

Sm3+-doped CaAl 4 O 7 phosphor has been synthesized using the sol-gel method with a varying doping concentration of Sm3+ ions. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images were used to study the structural and morphological properties of the material. The UV-VIS-NIR spectrum was also recorded to analyze the optical transitions of CaAl 4 O 7 phosphor doped with Sm3+ ions. The photoluminescence (PL) spectra of the phosphors were also recorded to examine the luminescence properties. The PL spectra exhibit intense orange emission at 602 nm that was obtained for the prepared samples using the 403 nm excitation. The optimized concentration of Sm3+ ions in CaAl 4 O 7 was found to be 0.03 mol, beyond which concentration quenching was observed. The CIE color chromaticity coordinates of all the synthesized phosphors lie in the orange region of the chromaticity diagram. All of these results indicate the candidature of CaAl 4 O 7 phosphor doped with Sm3+ ions for lighting and display applications. Image 1 • The orange-emitting Sm3+ doped CaAl 4 O 7 phosphor obtained via sol-gel method. • The Sm3+ emission is quenched at 0.03 mol. • Synthesized phosphor could be a potential material for lighting and display applications. [ABSTRACT FROM AUTHOR]

SrMgSi 2 O 6 :Gd3+ phosphor was prepared by sol-gel method and characterized using X-ray diffraction (XRD), photoluminescence (PL) and Fourier transform infrared (FT-IR) spectroscopy. XRD pattern revealed the tetragonal phase of the synthesized sample. The PL of SrMgSi 2 O 6 :Gd3+ phosphors exhibited a characteristic emission peak at 313 nm associated with 6P 7/2 →8S 7/2 transition of Gd3+ ions corresponding to the UVB region. The electron paramagnetic resonance (EPR) spectrum of SrMgSi 2 O 6 :Gd3+ phosphor provided the g-values along with understanding of the environment around Gd3+ ions in the host. [ABSTRACT FROM AUTHOR]

Tb3+ activated Na 3 YSi 2 O 7 phosphor for different amounts of Tb3+ ions were developed using sol-gel process. Structural analysis was conducted using Fourier Transform Infrared (FT-IR) spectroscopy and X-ray diffractograms. Further, luminescence behavior was analyzed by recording excitation and emission spectra of the mentioned phosphors. To obtain insight into the luminescence characteristics, these phosphors were excited under VUV wavelength (147 and 172 nm) along with UV excitation of 234 nm to elucidate the emission behavior. Colorimetric and photometric analyses were also conducted to establish the visible emission of the sol-gel derived phosphors. The photoluminescence study reflected the utility of Tb3+ doped Na 3 YSi 2 O 7 phosphor in plasma display panels. [ABSTRACT FROM AUTHOR]

Fig. Energy level diagram showing energy transfer involved in Sm3+/Eu3+ ions co-doped LiBiAlBSi glasses. These glasses help to improve the efficiency of red color in white LEDs and PV cells. [Display omitted] • Sm3+/Eu3+ ions co-doped LiBiAlBSi glasses prepared via melt quenching method. • PL shows transitions of both RE ions under n-UV and blue excitation. • The energy transfer mechanism from Sm3+ to Eu3+ was dipole–dipole in nature. • Energy transfer efficiency (η T) & probability rate (P T) upsurge with Eu3+ concentration. • Tunable color emission from reddish-orange to red region with Eu3+ ion codoping. • Good thermal stability of optimized LiBiAlBSiSE10 glass has high activation energy. The Sm3+, Eu3+ single doped, and Sm3+/Eu3+ co-doped lithium bismuth alumino borosilicate (LiBiAlBSi) glasses were prepared by using the melt quenching method and studied photoluminescence (PL) excitation, PL emission, and PL decay to have a better insight into their utility as red emission element for white LEDs. Sm3+ doped LiBiAlBSiSm05 glasses exhibit admirable emission features in the reddish-orange region under n-UV excitation (402 nm). Sm3+/Eu3+ co-doped LiBiAlBSi glasses can be adeptly excited by the blue and n-UV region which is confirmed from the excitation spectrum. In the Sm3+/Eu3+ co-doped LiBiAlBSi glasses, the PL decay lifetime for the Sm3+ emitting level (4G 5/2) declines and the energy transfer efficiency increases with an upsurge in Eu3+ ion content, which suggests the energy transfer (ET) process occurs from Sm3+ to Eu3+ ions. The ET process from Sm3+ to Eu3+ ions is also suggested by Dexter's ET method and Reisfeld's approximation by using emission spectra due to non-radiative dipole-dipole (d-d) interaction. The calculated values of CIE chromaticity coordinate for the as-prepared glasses under n-UV excitation shifted from reddish-orange to the red spectral part with the upsurge in Eu3+ concentration. The temperature-dependent PL studies of the optimized LiBiAlBSiSE10 glass revealed its superior thermal stability. All the results obtained finally suggest that, the Sm3+/Eu3+ co-doped LiBiAlBSi glass with 0.5 mol% of Sm3+ ions and 1.0 mol% of Eu3+ ions is a thermally stable candidate to produce intense red color needed to fabricate white LEDs under n-UV and blue excitation through the downshifting process. [ABSTRACT FROM AUTHOR]

La 1−x P 3 O 9 :xTb3+ (x = 0.005 ≤x ≤ 0.11) phosphors were prepared via the co-precipitation method. The crystal phase was analyzed by X-ray diffraction and the various functional groups in the host were investigated using Fourier transform infra-red (FT-IR) spectroscopy. The luminescence properties of the Tb3+ ions were studied using photoluminescence (PL) excitation and emission spectra. The PL analyses under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation both gave almost similar results. The green emission was observed at 546 nm, corresponding to the transition 5D 4 →7F 5 under 251, 147 and 172 nm excitation. The optimum concentration was 0.09 mol. The calculated CIE coordinates were shifted towards the intense green region from the pale white region with increasing Tb3+ ion concentration. The obtained results demonstrated the potential for LaP 3 O 9 as a candidate in lighting and plasma display panel (PDP) applications. [ABSTRACT FROM AUTHOR]

The citrate sol-gel method was used to synthesize a set of KNa 3 Al 4 Si 4 O 16 :xTb3+ phosphors (x = 0.005, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13 mol). Powder X-ray diffraction (XRD) was carried out for structural investigations and Fourier transform infrared (FT-IR) spectra for identification of functional groups. The crystallite size of the phosphors was estimated by employing the well-known Debye-Scherer equation. Scanning electron microscopy (SEM) was performed to gather the morphological information. For photoluminescence (PL) studies, excitation and emission spectra were recorded for different concentrations of trivalent terbium (Tb3+) ion. Commission International de I′Eclairage (CIE) coordinates were calculated. The results confirmed the green emission from the prepared samples and the potential of this candidate as a green emitter for lighting applications. [ABSTRACT FROM AUTHOR]

CaLa 4 Si 3 O 13 phosphors were successfully prepared by the sol-gel method by incorporating different amounts of Gd3+ ions as dopant. The crystalline phase and compositional arrangement of the host lattice were elucidated by XRD and FT-IR. The crystal sizes of the prepared samples were evaluated using the Scherrer formula. The luminescent properties of the CaLa 4 Si 3 O 13 :Gd3+ phosphors were studied by using PL spectroscopy. The electron paramagnetic resonance spectra of the sample revealed resonance signals arising on account of Gd3+ ion occupancy at sites with low symmetry. The studies conducted for the prepared samples confirmed that Gd3+ ions in the CaLa 4 Si 3 O 13 matrix are useful as UVB emitters. [ABSTRACT FROM AUTHOR]

In this study, the sol-gel method was used to synthesis highly crystalline, Er3+-doped Ca 2 La 8 (SiO 4) 6 O 2 phosphors. XRD, SEM and FT-IR analysis were conducted to determine the phase, surface morphology and bond formation inside the host lattice. The results of diffuse reflection studies of the samples were matched well with the PL excitation studies. Under 379 nm UV excitation, these phosphors exhibited intense green emission. PL studies conducted on the prepared phosphors revealed that at high concentration of the doped rare earth (RE) ion, the distance between Er3+-Er3+ decreased, leading to the formation of clusters. Such clusters induced non-radiative energy losses in the prepared phosphors. These investigations conducted on the prepared phosphor demonstrate its utility in the area of solid-state lighting (SSL). [ABSTRACT FROM AUTHOR]

A batch of Ho3+-doped Sr 2 La 8 (SiO 4) 6 O 2 phosphors with holmium ion dopant concentration ranging from 0.01 to 0.11 mol was synthesized successfully using the sol-gel method. The structural information was gathered by studying X-ray diffraction (XRD) patterns and Fourier transform infrared (FT-IR) spectroscopy. The optical properties were explored using diffuse reflectance (DRS) and photoluminescence (PL) spectral measurements. The colorimetric behavior was determined using emission spectra to obtain the CIE coordinates. The optimized Ho3+ dopant concentration was 0.05 mol in the Sr 2 La 8 (SiO 4) 6 O 2 host. The prepared phosphors emitted green color in visible domain and thus have potential applications in w-LEDs lighting and displays. [ABSTRACT FROM AUTHOR]

This study presents photoluminescence studies conducted on gadolinium (Gd) -doped Ca 2 La 8 (SiO 4) 6 O 2 phosphors prepared via sol gel method. The phosphors were further examined by XRD, SEM and FT-IR to assess the phase, morphology and functional groups present in the host matrix. To determine the optical properties, these phosphors were subjected to excitation and emission studies. Under 230 nm excitation, a sharp band was observed in the UVB region due to 6P 7/2 → 8S 7/2 transition. EPR was conducted to analyze the site symmetries in the prepared phosphor. Strong narrow emissions in the UVB regions make these phosphors ideal for many phototherapy and therapeutic applications, along with the standard solid-state lighting applications. [ABSTRACT FROM AUTHOR]

The structural and photoluminescence characteristics of sol-gel-derived Y 2 SiO 5 activated with triply ionized samarium ions were examined. Structural analysis was performed using XRD (X-ray diffraction) and FT-IR (Fourier Transform Infrared) spectral measurements. Lattice expansion was observed with an increased concentration of Sm3+ ions in the Y 2 SiO 5 phosphor due to increased crystallite size. The observed spectra of diffuse reflectance and emission spectra of Y 2 SiO 5 phosphors doped with Sm3+ ions were used for the analysis of optical and luminescence characteristics. J-O intensity parameters, Ω 2 = 0.16 × 10−20 cm2, Ω 4 = 0.16 × 10−20 cm2 and Ω 6 = 0.16 × 10−20 cm2 were obtained for the Y 2 SiO 5 :0.03Sm3+ phosphor. Radiative transition probabilities (A rad), radiative lifetimes (τ rad), and branching ratios (β) for a certain Sm3+ ion transition are presented. Photoluminescence spectra of Sm3+ activated Y 2 SiO 5 phosphors show an orange emission under the n-UV excitation of phosphor. Dexter's theory on emission spectra supports the existence of dipole-dipole interactions between dopant ions. Furthermore, photometric and colorimetric studies were also accomplished to determine the emission behavior of the synthesized phosphors for their application in w-LEDs. • Sm3+ activated Y 2 SiO 5 material has been synthesized. • The high-intensity emission transition is 4G 5/2 → 6H 7/2 , seen in the visible orange region. • The Judd-Ofelt intensity parameters were estimated using the absorption spectrum. • Photometric analysis determines the orange color emission from the phosphors. [ABSTRACT FROM AUTHOR]