Absolute Quantum Efficiency Research Articles

Efficient conversion from UV light to near-IR emission in Yb3+-doped triple-layered perovskite CaLaNb3O10

Yb3+-doped triple-layered perovskite CaLaNb3O10 micro-particles were synthesized via the solid-state reaction method. The crystal structure and morphology of the polycrystalline samples were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. The reflectance spectra, photoluminescence (PL) excitation and emission spectra, the decay curves, and the absolute quantum efficiency (QE) of the near-infrared (NIR) emission (910–1100nm) were measured. Under excitation of UV light, Yb3+-doped perovskite shows an intense NIR emission attributed to the 2F5/2→2F7/2 transitions of Yb3+ ions, which could match maximum spectral response of a Si-based solar cell. This is beneficial for its possible application in an enhancement of the photovoltaic conversion efficiency of solar energy utilization. The efficient energy transfer in Yb3+-doped CaLaNb3O10 from NbO6 groups into Yb3+ ions was confirmed by the spectra and fluorescent decay measurements. Cooperative energy transfer (CET) was supposed to be the NIR emission mechanism.

Synthesis and photoluminescence properties of a cyan-emitting phosphor Ca3(PO4)2:Eu2+ for white light-emitting diodes

In this paper, a cyan-emitting phosphor Ca3(PO4)2:Eu2+ (TCP:Eu2+) was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 250–450nm region, but the emission spectrum is prominent at around 480nm. The emission intensity of the TCP:Eu2+ was found to be 60% and 82% of that of the commercial BaMgAl10O17:Eu2+ (BAM) under excitation at 340nm and 370nm, respectively. Upon excitation at 370nm, the absolute internal and external quantum efficiencies of the Ca3(PO4)2:1.5%Eu2+ are 60% and 42%, respectively. Moreover, a white LED lamp was fabricated by coating TCP:Eu2+ with a blue-emitting BAM and a red-emitting CaAlSiN3:Eu2+ on a near-ultraviolet (375nm) LED chip, driven by a 350mA forward bias current, and it produces an intense white light with a color rendering index of 75.

Photoemission and optical constant measurements of a Cesium Iodide thin film photocathode

The performance of cesium iodide as a reflective photocathode is presented. The absolute quantum efficiency of a 500nm thick film of cesium iodide has been measured in the wavelength range 150nm–200nm. The optical absorbance has been analyzed in the wavelength range 190nm–900nm and the optical band gap energy has been calculated. The dispersion properties were determined from the refractive index using an envelope plot of the transmittance data. The morphological and elemental film composition have been investigated by atomic force microscopy and X-ray photo-electron spectroscopy techniques.

A Novel Blue‐Emitting Phosphor of Eu2+‐Activated Magnesium Haloborate Mg3B7O13Cl

Eu2+‐doped magnesium haloborate Mg3B7O13Cl was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction (XRD) measurements and structure refinement. The photoluminescence excitation and emission spectra, and decay curves were measured. Under the excitation of near‐UV light, Eu2+‐doped Mg3B7O13Cl presents a narrow blue‐emitting band centered at 423 nm. The maximum absolute quantum efficiency (QE) of Mg3B7O13Cl:Eu2+ phosphor was measured to be 80% excited at 385 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects. Moreover, Mg3B7O13Cl:Eu2+ phosphor shows scintillation characteristics excited by X‐ray irradiation at room temperature and presents a blue luminescence band with a fast lifetime of 600 ns.

Combustion synthesis and photoluminescence properties of a novel blue-green-emitting Er3+ and Li+ co-doped LaNbTiO6

A single-phase blue-green light emitting phosphor, LaNbTiO6: Er3+, Li+, was synthesized by using a simple and facile sol–gel combustion approach. Its structure and photoluminescence (PL) properties were investigated as a function of Er3+ and Li+ ion concentration. The luminous mechanisms of the Er3+ doping and Er3+/Li+ co-doping in the LaNbTiO6 host were also discussed, including the intra-4f-transitions of Er3+ and the charge compensation of Li+. The incorporation of Li+ ions into LaNbTiO6 lattice further altered the local structure and symmetry of the crystals field around Er3+. Concentration quenching occurred when Er3+ and Li+ reached certain levels. Furthermore, the critical transfer distance of Er3+ → Er3+ in the phosphor was calculated. The absolute quantum efficiencies and the fluorescence decay time of the phosphors were studied. The phosphor produced blue-green light, presenting CIE chromaticity coordinates of (0.211, 0.277) and (0.214, 0.320).

Measurement of the absolute Quantum Efficiency of Hamamatsu model R11410-10 photomultiplier tubes at low temperatures down to liquid xenon boiling point

We report on the measurements of the absolute Quantum Efficiency(QE) for Hamamatsu model R11410-10 PMTs specially designed for the use in low background liquid xenon detectors. QE was measured for five PMTs in a spectral range between 154.5 nm to 400 nm at low temperatures down to -110°C. It was shown that during the PMT cooldown from room temperature to -110°C (a typical PMT operation temperature in liquid xenon detectors), the absolute QE increases by a factor of 1.1–1.15 at 175 nm. The QE growth rate with respect to temperature is wavelength dependent peaking at about 165 nm corresponding to the fastest growth of about -0.07%QE/°C and at about 200 nm corresponding to slowest growth of below -0.01%QE/°C. A dedicated setup and methods for PMT Quantum Efficiency measurement at low temperatures are described in details.

Determination of absolute quantum efficiency of X-ray nano phosphors by thin film photovoltaic cells.

The absolute optical power at 611 nm emitting from Eu doped Gd2O3 nano phosphors upon X-ray excitation from a microfocus X-ray source operated at 100 kV was measured with thin film photovoltaic cells (TFPCs), whose optical response was calibrated using an He-Ne laser at 632 nm. The same TFPCs were also used to determine the absorbed X-ray power by the nano phosphors. These measurements provided a convenient and inexpensive way to determine the absolute quantum efficiency of nano phosphors, normally a difficult task. The measured absolute X-ray-to-optical fluorescence efficiency of the nano phosphors annealed at 1100 °C was 3.2%. This is the first time such efficiency for Eu/Gd2O3 nano phosphors is determined, and the measured efficiency is a fraction of the theoretically predicted maximum efficiency of 10% reported in the literature.

Preparation and spectral characteristics of Ce3+-activated boroaluminate LaAl2B3O9

Ce3+-activated (1.0–10 mol%) aluminoborate LaAl2B3O9 was prepared via the chemical sol–gel method. The phosphors were characterized by X-ray diffraction and scanning electron microscopy measurements. The luminescence performances such as photoluminescence excitation and emission spectra, the thermal quenching, and the luminescence decay curves (lifetimes) were detected to the phosphors. The influences of Ce3+ activator concentration on the phase evolution and luminescence properties were investigated. Ce3+ ion has only one crystallographic site occupying on La3+ site in LaAl2B3O9 lattice, which results in the typical doublet blue emission band due to 4f 65d → 4f 7 transition. The 2FJ (J = 7/2, 5/2) energy gap of Ce3+ ions in this host is about 2,100 cm−1. In total, 7 mol% of Ce3+-doped LaAl2B3O9 exhibits the brightest blue luminescence color with CIE coordinates of (x = 0.149, y = 0.123) and an absolute quantum efficiency of 76.0 %. The thermal stability of the luminescence was evaluated by the temperature-dependent luminescence intensity. The luminescence of phosphor shows a good thermal quenching with a high activation energy of ΔE = 0.34 eV, indicating it could be used at operation temperature 100–150 °C.

Conversion and quantum efficiency from ultraviolet light to near infrared emission in Yb 3+ -doped pyrovanadates M ZnV 2 O 7 ( M = Ca, Sr, Ba)

Abstract Yb3+-doped CaZnV2O7, SrZnV2O7 and BaZnV2O7 were synthesized via the solid-state reaction. The polycrystalline samples were investigated by XRD and SEM measurements. The reflectance spectra, photoluminescence (PL) excitation and emission spectra, the absolute quantum efficiency (QE) of the IR emission (900–1100 nm) were measured. The efficient conversion from ultraviolet (UV) light to near-infrared (NIR) emission has been demonstrated in the Yb3+-doped pyrovanadates by the broadband down conversion from VO43− to Yb3+ ions. Under UV light excitation, an intense NIR emission around 1000 nm ascribed to the 2F5/2 → 2F7/2 transition of Yb3+ ions has been observed, which just corresponds to the spectral response of Si solar cells. The NIR emission efficiency is observed to depend on the lattice of pyrovanadate. The mechanism of the NIR emission ascribed to energy transfer is discussed by taking into account the experimental results and the crystal structures.

Coprecipitation synthesis, structure and photoluminescence properties of Eu3+-doped sodium barium borate

Micro-sized phosphors of Eu3+-doped NaBaBO3 (0.5–12mol%) were prepared by the modified co-precipitation synthesis. The samples were characterized by scanning electron micrograph (SEM) images and electron dispersive X-ray (EDX). The polycrystalline samples are well developed to the regular plate-like particles with the uniform morphology. The single crystal-phase NaBaBO3 of the Eu3+-doped sample was confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The optical properties are evaluated by photoluminescence (PL) excitation and emission spectra, and decay curves. The absolute luminescence quantum efficiency (QE) and the activation energy (ΔE) are reported. Eu3+-doped NaBaBO3 presents a bright red-emitting color under the excitation of near-UV light around 400nm. The maximum absolute QE of NaBaBO3:Eu3+ is estimated to be 53% at 300K. The phosphor shows an excellent thermal stability on temperature quenching effects. The results were discussed on the relationship between the structure and the luminescence properties.

Synthesis and Luminescence Properties of Blue‐Emitting Phosphor Eu2+‐Doped Zinc Fluoro‐Phosphate Zn2[PO4

Eu2+‐doped zinc fluoro‐phosphate Zn2[PO4]F was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction measurements and the structure refinement. The photoluminescence excitation and emission spectra, and the decay curves were measured. The natures of the Eu2+ emission in inorganic hosts, e.g., the emission and excitation properties, the chromaticity coordinates, the Stokes shifts, the absolute quantum efficiency, and the luminescence thermal stability were reported. Under the excitation of near‐UV light, Eu2+‐doped Zn2[PO4]F presents a narrow blue‐emitting band centered at 423 nm. The thermal stability of the blue luminescence was evaluated by the luminescence intensities as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects.

Eu2+‐Doped Yellow‐Emitting CsBaB3O6 Glass‐Ceramic Prepared by Melt Quenching and Re‐Crystallization Method

Eu3+‐doped cesium barium borate glass with the composition of Cs2O·2BaO·3B2O3 was prepared by the conventional melt quenching method. The glass‐ceramic sample was obtained from the re‐crystallization of the as‐made glass to change the amorphous glass into a crystalline host. This reduces the Eu3+ in glass to Eu2+ ions resulting in a yellow‐emitting phosphor of Eu2+‐activated CsBaB3O6. The samples were investigated by the XRD patterns and SEM micrograph, the optical absorption, the photoluminescence spectra, and decay curves. The as‐made glass has only Eu3+ centers. Under the excitation of blue or near‐UV light, Eu2+‐doped CsBaB3O6 presents yellow‐emitting color from the allowed inter‐configurational 4f–5d transition in the Eu2+ ions. The maximum absolute luminescence quantum efficiencies of Eu2+‐doped CsBaB3O6 phosphor was measured to be 47% excited at 430 nm light at 300 K. By taking into account the efficient excitation in blue wavelength region, this new phosphor could be a potential yellow‐emitting phosphor for an application in white light‐emitting diodes fabricated with blue chips.

Spectral Conversion From Ultraviolet to Near Infrared in Yb3+‐Doped Pyrovanadate Zn2V2O7 Particles

Yb3+‐doped Zn2V2O7 particles were synthesized via the Pechini method. The crystal structure and morphology of the polycrystalline samples were investigated by X‐ray powder diffraction and scanning electron microscopy measurements, respectively. The reflectance spectrum, photoluminescence excitation, emission spectra, and the absolute quantum efficiency of the IR emission (900–1100) were measured. The intense near‐IR emission around 1000 nm attributed to the 2F5/2 → 2F7/2 transition of Yb3+ was observed under the excitation of ultraviolet light in the Yb3+‐doped pyrovanadate. The efficient energy transfer from VO4 groups into Yb3+ ions was confirmed by the optical spectra and fluorescent lifetime measurements. These results demonstrate that the Yb3+‐doped pyrovanadate particles are promising materials for spectral conversion from visible sunlight to near‐infrared emission and it may have potential application for spectral convertor to enhance the photoelectric conversion efficiency of c‐Si solar cells.

Ortho-vanadates K3RE(VO4)2 (RE = La, Pr, Eu, Gd, Dy, Y) for near UV-converted phosphors

The orthovanadate poly-crystals K3RE(VO4)2 (RE = La, Pr, Eu, Gd, Dy, Y) were synthesized via the solid-state reaction route. The crystal phase formation was verified through X-ray diffraction (XRD) studies and was performed by structural refinements. The optical properties were also investigated in detail. K3RE(VO4)2 (RE = Eu, Dy, Gd, Pr, La, Y) phosphors present different luminescence behaviors: the profiles of excitation and emission spectra, the spectra shift, the luminescence decay lifetimes, the absolute quantum efficiency (QE), and the CIE color coordinates are very different. The luminescence of K3RE(VO4)2 (RE = La, Gd, Y, Pr) presents yellow or yellowish green color, while, K3Dy(VO4)2 and K3Eu(VO4)2 show white and red luminescence, respectively. This was discussed on the base of the different micro-structure, activator centers, and the charge transfer transitions from [VO4]3− groups in the lattices. K3Y(VO4)2 and K3Eu(VO4)2 show higher QE values of 47.0% and 45.0% at room temperature, respectively. All the phosphors have efficient absorption in the region of near-UV wavelengths or blue wavelength region. This can well match with the light from UV-LED (360–400 nm) or blue LED chips (450–480 nm) based on GaN semiconductor. K3RE(VO4)2 could be suggested to be a potential candidate to give further investigations for the application on near-UV excited white LEDs.

Synthesis and efficient blue-emitting of Eu2+-activated borate fluoride BaAlBO3F2

Eu2+-doped borate fluoride BaAlBO3F2 was synthesized by the conventional high temperature solid state reaction. The crystal phase formations were confirmed by X-ray powder diffraction (XRD) measurements and the structure refinement. The photoluminescence (PL) excitation and emission spectra, and the decay curves were investigated. Eu2+-doped BaAlBO3F2 phosphor can be efficiently excited by near-UV light and presents narrow blue luminescence band centered at 450nm. The maximum absolute quantum efficiency (QE) of BaAlBO3F2:0.05Eu2+ phosphor was measured to be 76% excited at 398nm light at 300K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability with high thermal activation-energy on temperature quenching effects because of the rigid crystal lattices.

Higher than 60% internal quantum efficiency of photoluminescence from amorphous silicon oxynitride thin films at wavelength of 470 nm

We reported the study on the photoluminescence internal quantum efficiency (PL IQE) and external quantum efficiency (PL EQE) from the amorphous silicon oxynitride (a-SiNO) films, which were fabricated by plasma-enhanced chemical vapor deposition followed by in situ plasma oxidation. We employed the direct measurement of absolute quantum efficiency within a calibrated integration sphere to obtain the PL EQE. Then, we calculated the PL IQE by combing the measured EQE and optical parameters of light extraction factor, reflectivity, and transmittance of the a-SiNO thin films. We also derived the PL QE through investigating the characteristic of the temperature dependent PL. These results show that the PL IQE as high as 60% has been achieved at peak wavelength of about 470 nm, which is much higher than that of Si nanocrystal embedded thin films.

Photoluminescence Properties of Eu3+-Doped Glaserite-Type Orthovanadates CsK2Gd[VO4]2

Undoped and Eu(3+)-doped glaserite-type orthovanadates CsK2Gd1-xEux[VO4]2 with various Eu(3+) concentrations of x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 were synthesized via the solid-state reaction. The formation of a single phase compound was verified through the X-ray diffraction studies. The photoluminescence (PL) and PL excitation (PLE) spectra, PL decay curves, and absolute quantum efficiency (QE) were investigated. Unlike the conventional Eu(3+)-doped vanadates, these Eu(3+)-doped samples showed not only several sharp emission lines due to Eu(3+) but also a broad emission band with a maximum at 530 nm due to the [VO4](3-) host. The intensities of the host and Eu(3+) emissions increased when the Eu(3+) concentration was increased from x = 0 to x = 0.6 and decreased above x = 0.6. Similar concentration dependence was observed for QE. The host emission, even if in the Eu(3+)-condensed host of CsK2Eu(VO4), was never quenched indicating inefficient energy transfer from the host [VO4](3-) to Eu(3+). This inefficient energy transfer is understood by suppression of the energy transfer by the V-O-Eu bond angle deviated from 180° and the separation of Eu(3+) ions at the Gd(3+) site from [VO4](3-). Like the 530 nm charge transfer [VO4](3-) emission, two broad and intense PLE bands with maxima at 330 and 312 nm were observed for the Eu(3+) emission. A maximum QE of 38.5% was obtained from CsK2Gd1-xEux[VO4]2 (x = 0.6). A white-colored emission was obtained by the combination of the broad 530 nm emission band and the intense sharp lines due to Eu(3+) at 590-620 nm.

Influence of Gd doping on the absolute quantum efficiency and lifetime of EuxGd1−x(TTA)3phens

Absolute quantum yield (Φ) is one of the most important parameters to evaluate the potential of novel materials. Lanthanide complexes EuxGd1−x(TTA)3phens are synthesized with the ratio of Gd3+ dopant concentration ranging from 10% to 90% to improve the absolute quantum yield. EuxGd1−x(TTA)3phens possess similar infrared and ultraviolet spectra, showing that they have similar molecular structures. The absolute emission quantum yields of EuxGd1−x(TTA)3phens are determined using a fluoromax-4 spectrofluorometer equipped with an integrating sphere. The fluorescence lifetimes of the EuxGd1−x(TTA)3phens are measured in the same experiment. It was found that both absolute quantum yields and fluorescence lifetimes of EuxGd1−x(TTA)3phens are of quasi-periodic variation with the change of the Gd3+ dopant concentrations. The absolute quantum efficiency and fluorescence lifetime vary with respect to the Gd content in an opposite fashion, indicating that the rate of energy absorption by the EuxGd1−x(TTA)3phens and the conversion to light energy is critical for the absolute quantum efficiency. The radiative rate constant Kr and non-radiative rate constant Knr are calculated. The dependence of Kr and Knr on the Gd3+ dopant concentrations is very similar to that of absolute quantum efficiency. The radiation rate constant Kr and absolute quantum efficiency have a linear relationship.

NIR Detector Nonlinearity and Quantum Efficiency

A study was performed to investigate the experimental conditions and systematic uncertainties that need to be considered in order to precisely characterize quantum efficiency (QE). Measurements were performed on a HAWAII-2RG1.7 μm detector but the methodology of characterization is applicable to other detectors as well and may be useful in characterization of detectors used in future ground and space based surveys. For this study the detector QE as a function of illumination intensity, total integrated signal, and temperature was measured. A 3% relative systematic uncertainty on the measured QE value was achieved at wavelengths longer than 800 nm but the total uncertainty in the determination of absolute QE is dominated by the uncertainty in the conversion gain, which adds an additional 3.4% scale uncertainty. It was found that the measured detector QE depends on illumination intensity and that temperature dependence of QE can, at least in part, be attributed to reciprocity failure. Well-chosen detector bias voltages can reduce integrated signal nonlinearity.

Monochromatic Near-Infrared to Near-Infrared Upconversion Nanoparticles for High-Contrast Fluorescence Imaging

To develop a fluorescent bioprobe for high-contrast deep tissue fluorescence imaging, monochromatic 800 nm upconversion emissions based on NaYF4: Yb3+, Tm3+ upconversion nanoparticles are investigated. The ratio of I800 to I470, which is used to describe the monochromaticity, showing exponential growth with the increase of Tm3+ doping concentration in NaYF4: Yb3+, Tm3+ nanoparticles, can reach as high as 757 at 4% Tm3+. At such a doping level, the absolute quantum efficiency can reach 3.9 × 10–3 as measured by a calibrated integrating sphere, which is sufficient for fluorescence imaging. High-contrast fluorescence phantom imaging was obtained by adjusting monochromaticity of 800 nm upconversion emission under the excitation of a 980 nm diode laser.