Co-doped La2O3 Research Articles

Photoluminescence of Sm3+ and Eu3+ co-doped La2O3–Ga2O3 glasses fabricated by an aerodynamic levitation furnace

A series of transparent (1-y)La2O3–Ga2O3-ySm2O3-xEu2O3 (where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, and y = 0, 0.04) were successfully synthesized using a containerless solidification process. Co-doping with Sm3+ and Eu3+ enhanced the energy absorption of Eu3+, notably improving the characteristic emission peak 5D0-7F2 of Eu3+. The peak emission intensity for y = 0.04 was observed at x = 0.08, attributable to the concentration quenching of Eu3+ ions. As the concentration of Eu3+ increased, the energy transfer effect on emission intensity diminished. Attributed to the energy transfer between Sm3+ and Eu3+, Sm3+ may primarily serve as the sensitizer, and Eu3+ as the activator. According to the Dexter theory, which suggests that the interaction between activator ions and their adjacent ions is the primary mechanism of energy transfer and quenching among Eu3+ ions and adjacent ions, an increase in Eu3+ concentration leads to a decrease in the distance between Eu3+ and adjacent ions, strengthening their interaction, and potentially inducing concentration quenching. Furthermore, with an increase in Eu3+ concentration, the CIE chromaticity coordinates for the samples co-doped with Sm3+ and Eu3+ shifted significantly, enhancing the color purity of the emitted light and bringing it closer to the NTSC color standard coordinates (0.67, 0.33).

Exploring luminescent color tunability and efficient energy transfer mechanism of a single-phased hexagonal nanophosphor for white light emitting diodes (WLEDs) application

Nowadays, NUV-triggered phosphor-converted white light-emitting diodes (pc-WLEDs) have gained prominence as substantial alternatives to conventional incandescent and fluorescent lamps as a source of illumination. In this study, we have successfully developed a Tm3+ codoped La2O3:Sm3+ nanophosphor and investigated its potential suitability for application in white light-emitting diodes (WLEDs). X-ray diffraction (XRD) analysis was conducted to examine the phase impurity and structural characteristics of the synthesized nanophosphor. The analysis confirmed the formation of a single-phase La2O3 nanophosphor with a hexagonal crystal structure. The FT-IR spectrum of the synthesized nanophosphor exhibited distinct peaks associated with the vibrational frequencies of La-O bonds. The peaks observed in the fingerprint region of the spectrum, indicate the presence of La-O atoms in the nanophosphor. However, the HR-TEM analysis confirmed that the prepared nanophosphor had a polycrystalline nature and the observed particle sizes lay within the nanoscale range. The incorporation of Tm3+ ions into the host matrix led to a reduction in the optical band gap, leading to enhanced emission intensity. The photoluminescence (PL) study reveals that the Tm3+ ion exhibited blue emission upon excitation at 360 nm, whereas the Sm3+ ion emits reddish-orange light when excited at 379 nm and 408 nm, respectively. However, under 325 nm excitation, the nanophosphor exhibited a white emission color that resulted from the blending of colors emitted by both Tm3+ and Sm3+ ions. This unique finding suggests that this nanophosphor has the potential to generate white light specifically under this particular excitation wavelength. The efficient energy transfer between Tm3+ and Sm3+ ions was attributed to the electric multipolar interaction between the nearest neighbor ions, leading to a quenching phenomenon. Furthermore, the photometric analysis revealed that the correlated color temperatures (CCTs) associated with the emitted white light were found to be higher than 4000 K. Thus, based on these characteristics, it can be inferred that the prepared nanophosphor has the potential to be utilized as a cool white-emitting nanophosphor for single-phased WLEDs application.

Effect of Mg2+ and Zn2+ addition on photoluminescent and photoacoustic spectroscopy of La2O3:Er3+/Yb3+ phosphors

Photoluminescence (PL) and photoacoustic spectroscopy (PAS) are important techniques for materials characterization. The La2O3: Er3+/Yb3+ phosphors samples were synthesized by combustion method and annealed at 800–1200 °C for 2 h for improved photoluminescence properties. XRD data confirmed that all samples have pure hexagonal phase and FE-SEM shows irregular granular-like morphological structures and particle size that improved with annealed temperature. Then the photoacoustic (PA) amplitude and upconversion (UC) emission intensity were successively measured by a homemade PA cell under 980 nm laser excitation. A comparative relationship was made between PA and UC varying excitation power. Then, the authors showed the effect of codoped Mg2+ and Zn2+ ions on the radiative and non-radiative properties. It is observed that UC emission intensity for Zn2+ codoped La2O3: Er3+/Yb3+ phosphor has maximum, and also observed prominent absorption peaks at 521, 658, and 955 nm. These results indicate its high potential for application in photo-thermal therapy and upconversion imaging.

Study on Er3+-Yb3+ co-doped La2O3–Al2O3 glasses for C-band optical waveguide amplifier with high luminous efficiency and low pump threshold

Efficient planar optical waveguide amplifiers at C-band are critical to the development of silicon photonics. In order to overcome the problem of low utilization efficiency of 980 nm pump for erbium-based planar optical waveguide amplifiers, an Er3+-Yb3+ co-doped La2O3–Al2O3 glass material for optical waveguide amplifiers was developed in this paper. While maintaining a high Er3+ doping concentration (∼1021 cm−3), the utilization efficiency of the material for 980 nm pumping is improved, so that the pump threshold of the waveguide amplifier fabricated with this material is lowered. Moreover, up-conversion and down-conversion luminescence are also suppressed in the material, resulting in a significant increase in the luminescence intensity of the C-band. A simple ridge waveguide simulation suggests that waveguide amplifiers fabricated by this material are expected to surpass the highest net gain reported so far for erbium-based planar waveguide amplifiers.

Optical properties and luminescence of Er3+/Yb3+ co-doped La2O3–Nb2O5–Ga2O3 glasses prepared by aerodynamic levitation method

40La2O3–20Nb2O5–40Ga2O3 and xYb2O3–5Er2O3–(35-x) La2O3–20Nb2O5–40Ga2O3 (x = 0, 1, 5, 10) spherical transparent glasses were prepared by aerodynamic levitation method. Upconversion and near-infrared luminescence characteristics have been studied. Moreover, the thermal, mechanical, refractive index, transmittance properties of the glasses have also been discussed. Hardness and density of the glasses increase with the increase of Yb3+ concentration. The hardness of all samples are above 8.4 GPa, and density increase from 5.2504 g/cm3 to 5.817 g/cm3. The blank LNG glass has a refractive index of 2.0217 and Abbe number of 88.84, which is an excellent glass with high refractive index and low dispersion. Through DTA analysis, it is found that this series of glasses has excellent thermal stability. The glasses transition temperature (Tg) is about 800 °C. With the increase of Yb3+ concentration, Tg does not change obviously, but the crystallization initial temperature To and △T (△T = To−Tg) increase at first and then decrease. Upconversion fluorescence spectra show that green and red emission bands of 551 nm, 558 nm and 674 nm are obtained under the pump of 980 nm laser, which are two-photon emission processes. And in the near infrared region, the near-infrared emission with the emission center at 1559 nm is obtained, which corresponds to the transition from 4I13/2–4I15/2 of Er3+. The full width at half maximum (FWHM) of the prepared samples is about 120 nm, which is larger than that of ordinary glass. At the same time, with the increase of Yb3+ concentration, the change trend of fluorescence lifetime is consistent with that of near-infrared emission intensity.

Improved NIR emission from Tb3+, Yb3+ and Nd3+ co-doped La2O3 nano-phosphor

NIR and visible emission have been reported from Tb3+, Nd3+ and Yb3+ doped La2O3. XRD, TEM and HRTEM corroborate good crystallinity of the nano-phosphor. The average particle size is around 15 nm examined via TEM and HRTEM. The photoluminescence up-conversion spectra of Tb3+ and Yb3+ co-doped La2O3 exhibited characteristic emission peaks of Tb3+ ion at 480, 544 and 610 nm. It is possible due to the absorption of two 980 nm pump photons by Tb3+ ion via Yb3+ sensitizer. The energy migration from Tb3+ to Nd3+ takes place so that the intensity of 820 nm (4F5/2, 2H9/2 → 4I9/2) is increased significantly. The energy transfer between these two ions reduces the intensity of 544 nm Tb3+ ion whereas the intensity of 820 nm improved. Energy transfer mechanism between Tb3+, Nd3+ and Yb3+ ions has been discussed in detail. It would be a promising candidate for solar cells and biomedical applications.

Thermal properties and upconversion luminescence of Er3+/Yb3+ co-doped La2O3–TiO2–WO3 glasses prepared by containerless processing

Er3+/Yb3+ co-doped La2O3–TiO2–WO3 (LTW) glass spheres with different WO3 concentrations were prepared by aerodynamic levitation method. The effects of WO3 concentration on thermal properties, Raman spectra, upconversion luminescence spectra and fluorescence lifetime were studied. Er3+/Yb3+ co-doped LTW glasses have high thermal stability. With WO3 concentration increasing, the thermal stability decreases, and the glass forming ability increases and then decreases. The glasses perform low phonon energy with the maximum phonon energy of 737 cm−1. WO3 show little effect on the phonon energy of the glasses. Green and red upconversion luminescence centered at 554 nm and 673 nm were obtained under 980 nm excitation. As WO3 concentration increases, the intensity of upconversion luminescence first increases and then decreases. The introduction of WO3 can reduce the red/green ratio sharply. Compared to green upconversion luminescence, WO3 plays a role in constraining the red emission. The measurements of fluorescence lifetime confirm the intensity change for green and red emissions. The fluorescence lifetimes at 673 nm are longer than those at 554 nm, leading to stronger red upconversion luminescence. Novel Er3+/Yb3+ co-doped LTW bulk glasses obtained by containerless processing exhibit promising application prospect in small optics devices.

Polyol derived Bi3+ and Er3+ co-doped lanthanum oxide nanophosphors for display & LED applications

Abstract Color tunable luminescence was observed from Bi3+ and Er3+ co-doped La2O3 nanophosphor. The nanophosphors were prepared using cost effective and low temperature polyol route. The crystal structure, morphology, photoluminescence (PL) and were investigated in detail. Hue of Color changed which is observed by PL emissions on heating, La2O3:Bi3+, Er3+ phosphor powders from 700 to 900 °C. The observed emission peaks in PL from phosphor powder materials were assigned to either the broad emission originating from the transition in Bi3+ or the visible emission peaks originating transition from the Er3+ ions. All emission peaks of PL are plotted using CIE coordinates.

Effect of Al2O3 and La2O3 on structure and spectroscopic properties of Nd-doped sol–gel silica glasses

Nd3+-doped sol-gel silica glasses with enhanced spectroscopic properties via co-doped Al2O3 and La2O3 are reported. Co-doped Al2O3 and La2O3 not only significantly increases the fluorescence intensity and prolongs the fluorescence lifetimes of Nd3+, but also has a large σems × τf of the Nd-doped sol-gel silica glasses. The Judd–Ofelt parameters were evaluated from the absorption spectrum of Nd3+-doped glass, and these were used to predict the effects of various Al2O3 and La2O3 contents. The structures resulting from co-doping Al3+, La3+, and Nd3+ ions in silica glass were analyzed by using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). It showed that La2O3 could change the chemical environment of Nd3+ ion and depolymerize the silica glass network. These results suggest that La/Al/Nd co-doped silica glass is a potentially useful material for developing optical devices and an ideal choice for lasers.

Improved photon upconversion photoluminescence and intrinsic optical bistability from a rare earth co-doped lanthanum oxide phosphor via Bi3+ doping

An Er3+, Yb3+, Bi3+ co-doped La2O3 phosphor shows upconverted emission and intrinsic optical bistability properties.

Nanostructured La2O3: Yb3+/Er3+: Temperature sensing, optical heating and bio-imaging application

Nanostructured Yb3+/Er3+ co-doped La2O3 with intense green-light emission has been successfully synthesized by solvothermal method with further calcination. The prepared La2O3: Yb3+, Er3+ are composed of approximate spherical nanoparticles with the size of about 50nm. Optical temperature sensing performances depended on the thermally coupled levels of Er3+ are evaluated by analyzing temperature-dependent up-conversion luminescence (UCL) spectra, and the maximum sensitivity is 0.0040K−1 at 315K in the physiological working temperature range (295K–315K). Furthermore, the heating effect is also investigated, which causes the temperature of the samples to increase from 300 to 341K with the variation of power density from 7.08 to 26.19W/cm2. In addition, cell toxicity experiment shows that the La2O3 has low cell cytotoxicity, and the confocal images of samples in HeLa cells are also obtained. All the results indicate that the nanostructured La2O3: Yb3+/Er3+ also may be used as fluorescent bio-imaging.

La2O3: Tm, Yb, Er upconverting nano-oxides for sub-tissue lifetime thermal sensing

The importance of non-invasive thermometry based on lifetime fluorescence in biomedical applications imposes the research and development of new phosphors. In this work, sub-tissue lifetime thermal sensing of La2O3: Ln3+ nanomaterials (Ln=Tm, Er and Yb) has been studied. Two oxides are investigated: Er3+, Tm3+, Yb3+ tri-doped La2O3 and Tm3+, Yb3+ co-doped La2O3. We have focused on the lifetime of the 1G4→3H6 transition that corresponds to the blue emission of Tm3+ ion, recorded at 480nm. We prove that tri-doped oxide has remarkable higher thermal sensitivity than the co-doped one, with a temperature coefficient estimated to 6.7×10−3°C−1, which is comparable to that of nanomaterials oxides previously studied for luminescence thermometry and reported in literature. We have described the setup used to carry out the sub-tissue lifetime thermal sensing realized on biological tissue in the temperature range between 25°C and 60°C.

Study on upconversion luminescence and thermal properties of Ho3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glasses

Bulk Ho3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glass spheres were fabricated by aerodynamic levitation method. High concentration of Yb3+ ions was successfully doped in glasses. The effects of Yb3+ concentration on mechanical properties, Raman, absorption spectra, thermal stability, and glass forming ability were studied systematically. Green, red, and infrared emissions centered at 550, 662, and 758 nm were obtained at 980 nm excitation. Yellow light from glass spheres can be easily observed by naked eyes. As Yb3+ concentration increases, the upconversion luminescence can be improved obviously. The upconversion luminescence mechanism is a two-photon process of energy transfer, excited state absorption, and energy back transfer. The emission intensity can be enhanced in the samples with high Yb3+ concentration, since the absorption for the incident laser and the energy transfer efficiency are increased, and the nonradiative relaxation probability is reduced. The light color referring to the ratio for red to green emissions can be tuned by Yb3+ concentration. Ho3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glasses show promising comprehensive properties and are helpful to speed the application of upconversion luminescence materials.

Latent fingermarks detection for La2O3:Er3+/Yb3+ phosphor material in upconversion emission mode: A comparative study

The authors in this manuscript present the results on synthesis of Er3+/Yb3+ codoped La2O3 upconverting phosphor and its demonstration on the development of latent fingermarks on the surfaces of semi-porous and non-porous objects. The samples were synthesized via combustion using urea as a reducing agent and chemical precipitation methods. The annealed samples showed enough intense green emission in the 520–550 nm range on 980 nm excitation. Excellent emission property of the samples in the green region showed an advantage to use it in latent fingermarks detection. A dry powder dusting technique is used to develop latent fingermarks and the results are compared. The studies reflected the superiority of upconversion phosphor materials for the detection of latent fingermarks over the traditional downconversion luminescence methods.

Infrared to infrared upconversion emission in Pr3+/Yb3+ co-doped La2O3 and La(OH)3 nano-phosphors: A comparative study

The Pr3+/Yb3+ 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 1I6→1G4 transition along with sharp green emission centerd at 513nm due to 3P0→3H4 transition are observed on excitation with 976nm laser. The emission intensity of Pr3+ 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.

The Er3+–Yb3+ codoped La2O3 phosphor in finger print detection and optical heating

The presence of impurities and morphological information about the Er3+–Yb3+ codoped La2O3 phosphors prepared by two different synthesis techniques have been obtained with the help of Fourier transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) respectively. The effect of synthesis process on the frequency upconversion (UC) emission with an excitation at 980nm from laser diode radiation has been performed. The use of codoped phosphor in latent finger print detection and laser induced heat generation has also been explored.

Simultaneous influence of Zn2+/Mg2+ on the luminescent behaviour of La2O3:Tm3+–Yb3+ phosphors

Appreciable enhancement of the UC emission bands due to incorporation of Zn2+ and Mg2+ ions in Tm3+–Yb3+ codoped La2O3 phosphor can be visualized from the figure.

Increase of the blue upconversion emission in Tm3 +/Yb3 + co-doped titanate glass–ceramics

Tm3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glass–ceramics with intense blue emission have been fabricated by containerless processing in an aerodynamic levitation furnace, following by heat treatment at different temperatures in the air. The intensity of blue upconversion luminescence increases two times compared with the precursor glass after a heat treatment process at 890°C. Blue and red emissions centered at 476nm and 650nm owing to the Tm3+ transitions 1G4→3H6 and 1G4→3F4 are achieved under the excitation of 980nm at room temperature. The upconversion luminescence is based on a two-photon process by the cooperative sensitization which transfers energy from Yb3+ to Tm3+. Furthermore, Tm3+ and Yb3+ ions are enriched in nanoparticles which disperse in glass matrixes. Dense lattice fields and strong partitions of nanocrystals reduce energy losses caused by mutual interactions among rare earth ions to obtain strong upconversion luminescence. The presented intense blue emission of Tm3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glass–ceramics shows potential promising perspective in the optical materials.

Facile fabrication and spectroscopic study of the energy transfer effect of Pr3 + and Tm3 + codoped La2O3 nanorod arrays

Pr3+ and Tm3+ codoped La2O3 nanorod arrays were synthesized firstly by electrochemical deposition and followed by calcination of the precursor at 700°C. The nanorods typically have an average diameter of 30–50nm and hexagonal structure. Bright photoluminescence at around 455nm, 495nm and 658nm is obtained in Tm3+ and Pr3+ codoped hexagonal La2O3 nanorods that is prepared by electrochemical methods method. Using 355nm laser to pump the codoped nanocrystal samples, we successfully observed the fluorescence emission originating from the energy transfer of Tm3+ to Pr3+. The luminescence properties and the mechanism of the energy transfer are investigated with laser spectroscopy.

Efficient UV–visible up-conversion emission in Er3+/Yb3+ co-doped La2O3 nano-crystalline phosphor

A nano-crystalline La2O3: Er3+/Yb3+ phosphor sample has been synthesized through the solution combustion route using urea as a reducing agent. Thermal, structural and optical characterizations have been carried out to explore several of its properties. By thermal analysis one concludes to the presence of moisture and hydroxide phases [La(OH)3 and LaOOH] of lanthanum in the as-synthesized sample, which further changes to La2O3 phase above 600°C temperature. Up-conversion (UC) study shows the intense emission bands in the UV, blue, green and red regions. This paper also reports the first observation of UC emission bands extending up to the UV (240 nm) region on excitation with 976 nm wavelength. Heat treatment of the samples shows a change in the crystallite phase along with crystallite growth and relative UC luminescence intensities. The input pump power dependence shows the involvement of up to four photons.