Photoluminescence behavior of rare earth doped self-activated phosphors (i.e. niobate and vanadate) and their applications.

In the present study, the photoluminescence behaviors of rare earth doped self-activated phosphors are discussed briefly. Different techniques were used to develop these phosphor samples. We prepared pure and rare earth doped phosphor samples to look for their various applications. The structural confirmations and surface morphologies were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. The upconversion (UC) phenomenon was investigated in Tm3+/Yb3+ and Ho3+/Yb3+ co-doped niobate and vanadate based phosphors, which gave intense blue/NIR and green/red emissions with a 980 nm diode laser as an excitation source. Pure niobate and vanadate phosphor materials are self-activated hosts which give broad blue emission under UV excitation. Upon UV excitation, intense broad blue emission along with sharp emissions due to Tm3+ and Ho3+ ions are observed via energy transfer between niobate/vanadate and rare earth ions. These self-activated hosts show prominent downshifting (DS) behavior. Broad band quantum cutting (QC) was observed in these self-activated hosts, in which a blue emitting photon is converted into two NIR photons by co-doping Yb3+ ions in it. The multimodal (upconversion, downshifting and quantum cutting) behaviors of these phosphors make them very promising in various applications, such as spectral converters to enhance the efficiency of a c-Si solar cell, security ink and color tunable materials.

Photoluminescence behavior of Eu3+ doped XAl2O4(X = Mg, Ca, Sr and Ba) phosphors: a comparative study.

In this work, the Eu3+doped stuffed tridymite type structure of alkaline earths aluminate i.e. XAl2O4(X = Mg, Ca, Sr and Ba) phosphor materials have been synthesized by conventional high temperature solid state reaction method at 1623 K. The Samples were structurally and morphologically characterized by x-ray diffraction (XRD) and Scanning electron microscope (SEM) measurements. The vibrational behavior of the phosphor samples were investigated by Fourier transform infrared (FTIR) measurements. The phosphor samples emit intense red emission in 610-615 nm range due to5D0 â†’ 7F2transition of Eu3+ion on excitation with charge transfer band (CTB) wavelength arising due to Eu3+-O2-and also by the discrete bands of Eu3+ions .The decay time of5D0level of Eu3+ion were recorded on excitation with 393 nm and by the CTB wavelength for all the four samples. The optimized 1 mol% Eu3+doped CaAl2O4phosphor exhibits optimum emission intensity and color purity under the excitation with 393 nm than others. The decay time is also found to be larger in the case of Eu3+doped CaAl2O4phosphor sample. Therefore, Eu3+doped CaAl2O4phosphor may be promising material for red color light emitting applications and white light generation.

Enhanced Upconversion and Downshifting emissions from Tb3+, Yb3+ co-doped CaZrO3 phosphor in presence of Li+ ions.

This paper reports the enhanced green photoluminescence from Tb3+, Yb3+ co-doped CaZrO3 phosphor in the presence of Li+ ion synthesized through solid state reaction technique. The structural studies show an increase in the particle size and a shrink in crystal lattice due to Li+ co-doping in the phosphor. The phosphor sample emits intense green upconversion emission (UC) due to Tb3+ ions on excitation with 980 nm radiation which is further enhanced ~ 28 times on Li+ co-doping. The lifetime of 5D4 level of Tb3+ ion decreases in the presence of Li+ ions due to increase in asymmetry in crystal field. The downshifting (DS) emission intensity monitored on 378 and 487nm excitations is also enhanced in the presence of Li+ ions. Thus, the Tb3+, Yb3+, Li+ co-doped CaZrO3 phosphor can be a suitable candidate for UC solid state lighting.

Enhanced upconversion emission of Er3+/Yb3+ and Er3+/Yb3+/Zn2+ doped calcium aluminate for use in optical thermometry and laser induced optical heating.

There are two key factors to design an efficient green upconversion (UC) emission based optical sensor for temperature. The primary need is to develop a thermally stable and economical material, for a stable sensor, and the second essence is to get an efficient green UC emission, for high sensitivity of the sensor. The proof of this concept is demonstrated on a model system CaAl2O4: Er3+, co-doped with Yb3+ and Zn2+. UC emission of Er3+ ion is enhanced, primarily, through co-operative energy transfer from Yb3+ to Er3+ ions. Secondly, we prove that, incorporation of Zn2+ ions alters local crystal field environment around Er3+ ions which causes an enhancement in green UC emission. The variation in intensity ratio of 2H11/2 â†’ 4I15/2 (green) and 4S3/2 â†’ 4I15/2 (green) transitions with temperature is studied to report the sensing property. We show that, sensitivity becomes better with an increase in UC efficiency and the best sensitivity is attained for CaAl(0.793)2Er0.007Yb0.05Zn0.15O4 sample, ∼0.0154 K-1 at 308 K. The obtained result is compared with other works and implies its better suitability. Further, the laser induced optical heating is also observed. The laser induced optical heating has been observed experimentally at 400 K above 1 W laser power. This has been further verified by theoretical justification of heating at various pump powers.

Investigation of Upconversion, downshifting and quantum -cutting behavior of Eu3+, Yb3+, Bi3+ co-doped LaNbO4 phosphor as a spectral conversion material.

This work presents the spectral conversion characteristics [upconversion (UC), downshifting (DS) and quantum-cutting (QC) optical processes] of Eu3+, Yb3+ and Bi3+ co-doped LaNbO4 (LBO) phosphor samples synthesized by solid state reaction technique. The crystal structure and the pure phase formation have been confirmed by x-ray diffraction (XRD) measurements. The surface morphology and particle size are studied by scanning electron microscopy (SEM). The rarely observed intense red UC emission from Eu3+ ion has been successfully obtained in Eu3+/Yb3+ co-doped LaNbO4 phosphor (on excitation with 980 nm) by optimizing the concentrations of Eu3+ and Yb3+ ions. The downshifting (DS) behavior has been studied by photoluminescence (PL) measurements on excitation with 265 nm wavelength from a Xe lamp source. A broad blue emission in the region 300-550 nm with its maximum ∼415 nm due to charge transfer band (CTB) of the host and large number of sharp peaks due to f-f transitions of Eu3+ ion have been observed. The energy transfer has been observed from (NbO4)3- to Eu3+ ion and the fluorescence emission has been optimized by varying the concentration of Eu3+ ion. An intense red emission has also been observed corresponding to 5D0 â†’ 7F2 transition of Eu3+ ion at 611 nm in LBO: 0.09Eu3+ phosphor on excitation with 394 nm. The luminescence properties of Eu3+ ion are enhanced further through the sensitization effect of Bi3+ ion. The near infra-red (NIR) quantum cutting (QC) behavior due to Yb3+ ion has been monitored on excitation with 265 as well as 394 nm. The NIR QC is observed due to 2F5/2 â†’ 2F7/2 transition of Yb3+ ion via co-operative energy transfer (CET) process from (NbO4)3- as well as Eu3+ ions to Yb3+ ion. This multimodal behavior (UC, DS and QC) makes this a promising phosphor material for multi-purpose spectral converter.

Effect of Bi3+ ion on upconversion-based induced optical heating and temperature sensing characteristics in the Er3+/Yb3+ co-doped La2O3 nano-phosphor.

The upconversion-based optical heating and temperature sensing characteristics are investigated in the Er3+/Yb3+/Bi3+ tri-doped La2O3 nano-phosphor synthesized through a solution combustion method. The structural measurements reveal an increase in lattice parameters and particles size of the phosphor on increasing the concentrations of Bi3+ ions. The energy dispersive spectroscopic (EDS) measurements confirm the presence of La, Er, Yb, Bi and O elements in the tri-doped phosphor. The absorption spectra show the large number of bands due to Er3+, Yb3+ and Bi3+ ions. The Er3+/Yb3+ co-doped phosphor gives strong green emission bands at 523 and 548 nm upon 976 nm excitation due to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ion, respectively. The emission intensity of these bands is enhanced upto 15 times in the presence of Bi3+ ions. The emission intensities of the 523 and 548 nm bands vary non-linearly with the pump power. The fluorescence intensity ratio (FIR) of the thermally coupled 523 and 548 nm emission bands shows efficient optical heating in the tri-doped phosphor. The FIR of the 523 and 548 nm emission bands further varies with the increase in temperature of the phosphor. The relative temperature sensing sensitivity has been calculated to be 71 × 10-4 K-1 at 450 K for the tri-doped phosphor. Thus, the Er3+/Yb3+/Bi3+ tri-doped La2O3 nano-phosphor may provide a platform to use it in the photonic devices, as an optical heater and temperature sensor.

Multifunctional role of dysprosium in HfO2: stabilization of the high temperature cubic phase, and magnetic and photoluminescence properties.

Hafnium oxide (HfO2) can exist in different crystalline structures such as monoclinic at room temperature, tetragonal at 1700 °C and cubic at 2600 °C. In the present study, nanocrystalline powders of HfO2 synthesized by a Pechini type sol-gel technique show a monoclinic phase, P21/c, at room temperature. By incorporating Dy into the HfO2 lattice, the intensity of all diffraction peaks corresponding to P21/c decreases and at a concentration of 11 at% of Dy, the monoclinic phase transforms completely to the cubic phase, Fm3[combining macron]m, showing a mixed phase of monoclinic and cubic at intermediate concentrations (5-9 at%) of Dy. For the first time, we have stabilized the high temperature cubic phase of HfO2 at room temperature by incorporating Dy. Selected area electron diffraction patterns confirm the monoclinic and the cubic phase as observed from the X-ray diffraction patterns. A mechanism for stabilization of the high temperature cubic phase in Hf1-xDyxO2 has been analyzed based on the substitution of dysprosium for hafnium ions and the formation of oxygen vacancies. While ferromagnetic ordering at room temperature observed in HfO2 nanoparticles is quenched after incorporating 1 at% of Dy, photoluminescence (PL) studies demonstrate excellent emissions in the blue and yellow region after exciting with UV light of wavelength 352 nm. Combining excitation and emission profiles, we have proposed a tentative energy band diagram illustrating the energetic processes taking place in Hf1-xDyxO2.

Sensitized green emission of terbium with dibenzoylmethane and 1, 10 phenanthroline in polyvinyl alcohol and polyvinyl pyrrolidone blends.

Tb doped polyvinyl alcohol: polyvinyl pyrrolidone blends with dibenzoylmethane (DBM) and 1, 10 Phenanthroline (Phen) have been prepared by solution cast technique. Bond formation amongst the ligands and Tb3+ ions in the doped polymer has been confirmed employing Fourier Transform Infrared (FTIR) techniques. Optical properties of the Tb3+ ions have been investigated using UV-Vis absorption, excitation and fluorescence studies excited by different radiations. Addition of dimethylbenzoate and 1, 10 Phenanthroline to the polymer blend increases the luminescence from Tb3+ ions along with energy transfer from the polymer blend itself. Luminescence decay curve analysis affirms the non-radiative energy transfer from DBM and Phen to Tb3+ ions, which is identified as the reason behind this enhancement. The fluorescence decay time of PVA-PVP host decreases from 6.02ns to 2.31ns showing an evidence of energy transfer from the host blend to the complexed Tb ions. Similarly the lifetime of DBM and Phen and both in the blend reduces in the complexed system showing the feasibility of energy transfer from these excited DBM and Phen to Tb3+ and is proposed as the cause of the above observations. These entire phenomena have been explained by the energy level diagram.

Effect of the concentration of the dopants (Er3+, Yb3+ and Zn2+) and temperature on the upconversion emission behavior of Er3+/Yb3+ co-doped SrAl2O4 phosphor.

Er3+/Yb3+ co-doped SrAl2O4 (SRA: Er3+, Yb3+) phosphor has been synthesized by high temperature solid state reaction technique. The pure phase formation has been confirmed by X-ray diffraction (XRD) measurements. The surface morphology is studied by scanning electron microscopy (SEM) technique. The FTIR measurements give the information of vibrational bands arising due to sample. The intense UC emission from SRA: Er3+, Yb3+ phosphor has been monitored on excitation with 980nm diode laser. The SRA: Er3+, Yb3+ samples prepared at 1473K show a dominant green emission. On the other hand it shows dominant red emission when the sample is heated to 1623K. Variation of concentration of Er3+ and Yb3+ ions in SRA: Er3+, Yb3+ phosphor suggests two possible mechanisms involved in UC emission process viz. cross relaxation (CR) process and energy back transfer (EBT) process, respectively. The cross relaxation mechanism seems to play a major role. The UC emission efficiency is enhanced several times on co-doping of Zn2+ ion replacing Al3+ or Sr2+ in SRA: Er3+, Yb3+ phosphor sample. The color of the UC emission can be tuned from green to red region by varying the concentration of zinc.

Physiochemical properties of greatly enhanced photoluminescence of aqueous dispersible upconversion CaF2:Yb/Er nanoparticles.

Crystal phase morphological structure and optical properties of the as-prepared upconversion CaF2:Yb/Er(core) and sequential coating of an inert crystalline material and silica layers surrounding the seed core-nanoparticles (NPs) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), optical absorption, FTIR spectroscopy and upconversion photoluminescence spectroscopy. Owing to the unique properties of CaF2 host matrix, we realized their practical applications in biomedical science to improve the upconversion luminescence property and aqueous dispersibility. The surface coating on the seed core particles will significantly influence the structural, optical band gap energy and upconversion luminescence properties. These NPs were well-dispersed in aqueous and non-aqueous solvents to form clear colloidal solutions. The colloidal solutions of three samples show a characteristic optical absorption band in UV/Visible region. As a result, optical band gap gradually decreases after sequential growth of the inert shell and amorphous silica due to an increase in the crystalline size. Comparative upconversion luminescence analysis showed that after inert shell growth, the upconversion intensity was greatly improved, and such an improvement was found to arise from efficient suppression of surface-related deactivation from the core nanocrystals. Interestingly, growth of an inert (CaF2) shell over the seed core NPs shows intense upconversion emission lines under 980 nm NIR laser excitation, highlighting their promising applications, such as multi-analyte biolabels, staining, displays and other photonic based technological applications.

Highly aqueous soluble CaF2:Ce/Tb nanocrystals: effect of surface functionalization on structural, optical band gap, and photoluminescence properties.

The design of nanostructured materials with highly stable water-dispersion and luminescence efficiency is an important concern in nanotechnology and nanomedicine. In this paper, we described the synthesis and distinct surface modification on the morphological structure and optical (optical absorption, band gap energy, excitation, emission, decay time, etc.) properties of highly crystalline water-dispersible CaF2:Ce/Tb nanocrystals (core-nanocrystals). The epitaxial growth of inert CaF2 and silica shell, respectively, on their surface forming as CaF2:Ce/Tb@CaF2 (core/shell) and CaF2:Ce/Tb@CaF2@SiO2 (core/shell/SiO2) nanoarchitecture. X-ray diffraction and transmission electron microscope image shows that the nanocrystals were in irregular spherical phase, highly crystalline (~20 nm) with narrow size distribution. The core/shell nanocrystals confirm that the surface coating is responsible in the change of symmetrical nanostructure, which was determined from the band gap energy and luminescent properties. It was found that an inert inorganic shell formation effectively enhances the luminescence efficiency and silica shell makes the nanocrystals highly water-dispersible. In addition, Ce3+/Tb3+-co-doped CaF2 nanocrystals show efficient energy transfer from Ce3+ to Tb3+ ion and strong green luminescence of Tb3+ ion at 541 nm(5D4→7F5). Luminescence decay curves of core and core/shell nanocrystals were fitted using mono and biexponential equations, and R 2 regression coefficient criteria were used to discriminate the goodness of the fitted model. The lifetime values for the core/shell nanocrystals are higher than core-nanocrystals. Considering the high stable water-dispersion and intensive luminescence emission in the visible region, these luminescent core/shell nanocrystals could be potential candidates for luminescent bio-imaging, optical bio-probe, displays, staining, and multianalyte optical sensing. A newly designed CaF2:Ce/Tb nanoparticles via metal complex decomposition rout shows high dispersibility in aqueous solvents with enhanced photoluminescence. The epitaxial growth of inert CaF2 shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable for luminescent biolabeling, and optical bioprobe etc.

Influence of Shell Formation on Morphological Structure, Optical and Emission Intensity on Aqueous Dispersible NaYF4:Ce/Tb Nanoparticles.

A highly water-dispersible NaYF4:Ce/Tb (core), NaYF4:Ce/Tb@NaYF4(core/shell) and NaYF4:Ce/Tb@NaYF4@SiO2 (core/shell/SiO2) nanoparticles (NPs) were synthesized via a general synthesis approach. The growth of an inert NaYF4 and silica shell (~14 nm) around the core-NPs resulted in an increase of the average size of the nanopaticles as well as broadening of their size distribution. The optical band-gap energy slightly decreases after shell formation due to the increase the crystalline size. To optimize the influence of shell formation a comparative analysis of photoluminescence properties (excitation, emission, and luminescence decay time) of the core, core/shell, and core/shell/SiO2 NPs were measured. The emission intensity was significantly enhanced after inert shell formation around the surface of the core NPs. The Commission International de l'Eclairage chromaticity coordinates of the emission spectrum of core, core/shell, core/shell/SiO2 NPs lie closest to the standard green color emission at 545 nm. By quantitative spectroscopic measurements of surface-modified core-NPs, it was suggested that encapsulation with inert and silica layers was found to be effective in retaining both luminescence intensity and dispersibility in aqueous environment. Considering the high aqueous dispersion and enhanced luminescence efficiency of the core-NPs make them an ideal luminescent material for luminescence bioimaging and optical biosensors.

Probing a new approach for warm white light generation in lanthanide doped nanophosphors.

Lanthanides are among the most acceptable activator ions for cool white light emission; however, solid state lighting for some applications requires a warm white light. Herein, the present work probes a new approach for color temperature tuning in such systems to get a warm white light. The idea is that the additional use of red spectral components in cool white light, to a certain extent, may lead to a perfect warm white light, which can be achieved by making use of the surface oxygen defects mediated red emission from ZnO. To realize this noble concept, white light was initially produced in Y(1.993)Dy(0.001)Tm(0.006)O3 and then further ZnO was added. The study includes detailed structural and optical (steady state and time domain) characterization, chromaticity coordinates (CIE) calculation and correlated color temperature (CCT) analysis. The results show that, initially, at low ZnO concentration, Zn(2+) ions prefer to go into the interstitial sites, due to the mismatch of ionic radius between Y(3+) (0.90 Å) and Zn(2+) (0.75 Å). However, beyond a 10 mol% concentration of ZnO, the solubility limit of Zn(2+) ions in the Y2O3 matrix is reached, which results in the development of a Y2O3-ZnO composite. The presence of the ZnO phase gives rise to defect level induced red emission, which tunes the color temperature from 6072 K to 3898 K, which is reasonably good warm white light for solid state lighting applications. This idea can also be generalized in other similar hosts for developing potential warm white light sources.

Infrared to infrared upconversion emission in Pr(3+)/Yb(3+) co-doped La2O3 and La(OH)3 nano-phosphors: a comparative study.

The Pr(3+)/Yb(3+) co-doped La2O3 and La(OH)3 nano-phosphors have been synthesized through solution combustion method. The structure and morphology of the samples have been studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The physical and optical properties of the samples have been measured and compared. A broad intense infrared emission centered at 850nm due to (1)I6→(1)G4 transition along with sharp green emission centerd at 513nm due to (3)P0→(3)H4 transition are observed on excitation with 976nm laser. The emission intensity of Pr(3+) is optimized with concentration and it is maximum at 0.08mol%. The annealed samples are found to be more crystalline and emit larger photoluminescence due to removal of quenching centers. The power dependent study of green upconversion emission indicates the involvement of two photons. The phosphor in La(OH)3 phase is more stable though the photoluminescence emission is slightly weak. La(OH)3 is less toxic compared to La2O3 and is biocompatible. It generates more heat and can be used in biothermal treatment.

Structural characterizations and intense green upconversion emission in Yb3+, Pr3+ co-doped Y2O3 nano-phosphor.

We report the structural and optical properties of Yb(3+), Pr(3+) co-doped Y2O3 nano-phosphor synthesized through solution combustion method. The structural studies reveal the nano-crystalline structure of the sample. The energy dispersive spectroscopy (EDS) measurements confirm the presence of Y, O, Pr and Yb elements in the sample. Fourier transform infrared studies show the vibrational features of the samples. The fluorescence spectra of the samples have been monitored on excitation with 976 nm and the intense green upconversion emission observed at 552 nm is due to (3)P0→(3)H5 electronic transition. The concentration of Pr(3+) ion in the sample is optimized and the fluorescence intensity is maximum at 0.08 mol% of Pr(3+). The power dependence studies reveal the involvement of two photons in the emission process. The possible mechanism of upconversion has been discussed on the basis of schematic energy level diagram. The sample annealed at higher temperature enhances the fluorescence intensity up to 8 times and this enhancement is discussed in terms of the removal of optical quenching centers. The nano-phosphor can be applicable in the field of display devices and green laser.

Enhanced up-conversion and temperature-sensing behaviour of Er(3+) and Yb(3+) co-doped Y2Ti2O7 by incorporation of Li(+) ions.

Y2Ti2O7:Er(3+)/Yb(3+) (EYYTO) phosphors co-doped with Li(+) ions were synthesized by a conventional solid-state ceramic method. X-ray diffraction studies show that all the Li(+) co-doped EYYTO samples are highly crystalline in nature with pyrochlore face centred cubic structure. X-ray photon spectroscopy studies reveal that the incorporation of Li(+) ions creates the defects and/or vacancies associated with the sample surface. The effect of Li(+) ions on the photoluminescence up-conversion intensity of EYYTO was studied in detail. The up-conversion study under ∼976 nm excitation for different concentrations of Li(+) ions showed that the green and red band intensities were significantly enhanced. The 2 at% Li(+) ion co-doped EYYTO samples showed nearly 15- and 8-fold enhancements in green and red band up-converted intensities compared to Li(+) ion free EYYTO. The process involved in the up-conversion emission was evaluated in detail by pump power dependence, the energy level diagram, and decay analysis. The incorporation of Li(+) ions modified the crystal field around the Er(3+) ions, thus improving the up-conversion intensity. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was evaluated using the fluorescence intensity ratio technique. Appreciable temperature sensitivity was obtained using the synthesized phosphor material, indicating its applicability as a high-temperature-sensing probe. The maximum sensitivity was found to be 0.0067 K(-1) at 363 K.

Down-shifting and upconversion photoluminescence in Ho(3+)/Yb(3+) codoped GdNbO4: effect of the Bi(3+) ion and the magnetic field.

A green emitting Gd(0.95-x)HoxYb0.05NbO4 phosphor (x = 0.001, 0.005, 0.01, 0.02, 0.03 and 0.035) has been synthesized by the solid-state reaction method. The phosphor samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman and upconversion (UC)/down-shifting (DS) photoluminescence measurements. The XRD analysis confirms the formation of pure phase GdNbO4. The FTIR and Raman spectra reveal the modes of vibration in GdNbO4. It also confirms that this host has a lower phonon frequency (806 cm(-1)) in comparison to the other well-known compounds of this family. The photoluminescence excitation (PLE) spectrum of GdNbO4 shows two broad bands at 270 and 303 nm corresponding to the NbO4(3-) group and Gd(3+) ion, respectively. On 270 nm excitation it shows a weak emission band with maximum at 442 nm. The intensity of this emission band strengthens on excitation with 303 nm. The PL measurements have shown the energy transfer from host to Ho(3+) ions. In addition, of Bi(3+) ions, the intensity of the PL band corresponding to the NbO4(3-) group increases, which facilitates a better energy transfer from host to the Ho(3+) ions. On 980 nm diode laser excitation, the phosphor shows strong green and rather weak red UC emission peaks. The influence of an external magnetic field on the UC emission has also been studied. It is found that the UC emission of Ho(3+) ions decreases in the presence of a magnetic field. It also shows the existence of optical bistability because of the presence of hysteresis behavior. Although this host has a low phonon frequency and shows paramagnetic behavior, it is not well explored yet. Our studies reveal that this host could have significant scientific and technological importance.

Bismuth induced enhanced green emission from terbium ions and their complex in thin films.

Bismuth nanoparticles (NPs) have been prepared by the pulsed laser ablation technique using the third harmonics of a Nd-YAG laser. UV-absorption and TEM micrographs show Bi NPs of spherical shape with the average particle size ranging from 15 to 20 nm. These NPs were dispersed with Tb(3+) ions and their complex with salicylic acid (Sal) in polyvinyl alcohol to obtain thin films. The influence of Bi NPs on the emissive properties of Tb(3+) ions and the [Tb(Sal)3(phen)] complex has been studied by luminescence spectroscopy using 266 nm and 355 nm as excitation wavelengths. The luminescence intensity of Tb(3+) ions complexed with Sal in the thin polymer films increased significantly as compared to the Tb(3+) ions in the presence of Bi NPs on excitation at 355 nm. However, terbium ions in the case of the [Tb(Sal)3(phen)] complex together with NPs show an intense and extended emission spectrum in the 375-700 nm range for transitions arising from (5)D3 and (5)D4 levels to different (7)F(J) levels on 266 nm excitation. The luminescence enhancement has also been supported by lifetime measurements.

Structural and optical properties of Eu3+, Sm3+ co-doped La(OH)3 nano-crystalline red emitting phosphor.

We report Eu3+, Sm3+ co-doped La(OH)3 nano-crystalline red emitting phosphor prepared following combustion synthesis protocol. The structural and morphological information about the synthesized samples have been explored using X-ray diffraction (XRD) and transmission electron microscopic (TEM) techniques. The optical properties of the samples have been investigated under 355 nm laser excitations. The sample emits intense red emissions at 625 and 707 nm due to 5D0→7F2 and 5D0→7F4 transitions in Eu3+ ion, respectively. The concentrations of both, Eu3+ and Sm3+ in the samples were optimized at 1 mol% to get maximum fluorescence. The presence of Sm3+ in the Eu3+ doped sample enhances the emission intensity up to two times. The samples annealed at higher temperature show significant enhancement in the emission intensity. The life time studies show an efficient energy transfer from Sm3+ to Eu3+ ions and have been discussed with the help of schematic energy level diagram. This enhancement in the emission intensity is discussed in terms of the rare earth ion concentration, annealing temperature and energy transfer.

Structural morphology, upconversion luminescence and optical thermometric sensing behavior of Y2O3:Er(3+)/Yb(3+) nano-crystalline phosphor.

Infrared-to-visible upconverting rare earths Er(3+)/Yb(3+) co-doped Y2O3 nano-crystalline phosphor samples have been prepared by solution combustion method followed by post-heat treatment at higher temperatures. A slight increase in average crystallite size has been found on calcinations verified by X-ray analysis. Transmission electron microscopy (TEM) confirms the nano-crystalline nature of the as-prepared and calcinated samples. Fourier transform infrared (FTIR) analysis shows the structural changes in as-prepared and calcinated samples. Upconversion and downconversion emission recorded using 976 and 532 nm laser sources clearly demonstrates a better luminescence properties in the calcinated samples as compared to as-prepared sample. Upconversion emission has been quantified in terms of standard chromaticity diagram (CIE) showing a shift in overall upconversion emission of as-prepared and calcinated samples. Temperature sensing behaviour of this material has also been investigated by measurement of fluorescence intensity ratio (FIR) of various signals in green emission in the temperature range of 315 to 555 K under 976 nm laser excitation.