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Visible and infrared absorption and emission spectra of Er3+-doped strontium gadolinium gallate (SrGdGa3O7) single-crystal were measured at room temperature. From the measured fluorescence spectra, the Er3+ emission cross section spectra were calculated at first. Then, by utilizing McCumber relation, the absorption cross section spectra were further calculated. In parallel, the absorption cross section spectra were also calculated from the measured absorption spectra of the crystal, and compared with those spectra calculated from the McCumber relation. The comparison shows that the absorption cross section spectra obtained using the McCumber relation are in reasonable agreement with those deduced from the measured absorption spectrum.

Optical and spectroscopic properties of Er3+/Pr3+-codoped Gd3Ga5O12 single-crystal grown by Czochralski method have been studied. Absorption spectrum of the crystal was measured at room temperature and Er3+ absorption cross-section spectral distributions were calibrated from it. The Er3+ spectroscopic properties were analyzed on the basis of the Judd-Ofelt theory. Fundamental spectroscopic parameters were obtained that include absorption coefficient, cross-section spectral distribution, electronic transition oscillator strength, Judd-Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency as well. Study shows that Pr3+-codoping results in substantial change of Er3+ spectroscopic properties, in qualitative consistent with the previous fluorescence studying result. In addition, refractive index of the crystal was measured at different wavelengths using prism coupling method, and the Sellmeier equation reported previously for Er3+-only doped Gd3Ga5O12 crystal is corrected.

A metamaterial perfect absorber working in the ultraviolet-to-near infrared region is proposed. It consists of a periodic nanoarray of quadrangular frustum pyramids with a homogeneous titanium nitride (TiN) film as the ground. Each unit cell of the nanoarray is composed of alternately stacked TiN and dielectric patches with their width tapered linearly from the bottom to the top. The absorption mechanism was qualitatively explained by analyzing the electric and magnetic field distributions at the resonance wavelengths, and the absorption performance was simulated as a function of its geometric parameters and the angle and polarization of incident beam as well. Optimal geometric parameters are presented. With the optimal parameters, the absorption efficiency at normal incidence is above 99.3% over the entire spectral region from 300 to 2500 nm, and a high average absorption of 99.9% is achieved. The ultrabroadband perfect absorption behaviors are attributed to the localized surface plasmonic resonance effect of the pyramid, the intrinsic loss of the TiN material and the coupling of resonance modes between two adjacent pyramids. In addition, the absorber also shows polarization insensitivity and good angular acceptance capability of oblique incidence up to 70°. The unique and compact structure provides a new way for achieving an ultrabroadband solar absorber, showing great application prospects in the fields of solar energy harvesting and the corresponding (thermo-)photovoltaics.

Gallium-diffused lithium niobate (LiNbO3) channel optical thin-film was fabricated by diffusion of photolithographically patterned gallium-oxide stripes on a Z-cut congruent LiNbO3 substrate. Composition, optical properties of the channel thin-film and gallium diffusion profiles were characterized. The results show that the thin-film is in congruent composition environment, confines single-mode ordinary and extraordinary waves with a loss

Under 980 nm wavelength excitation, 530 and 550 nm green upconversion emission spectra of erbium-doped gadolinium gallium garnet single-crystal were measured in the temperature range of 298–423 K for ratiometric thermometry based on fluorescence intensity ratio (FIR). The crystal shows strong emission intensity, highly efficient ratiometric thermometric performance, as well as thermally stable emission spectral structure, it is thus a promising luminescent material for ratiometric thermometry. A multiple ratiometric thermometry is proposed and demonstrated in comparison with the usually adopted ratiometric thermometry based on integrated emission intensity. The multiple ratiometric thermometry considers six FIRs involving two component peaks of the 530 nm emission band and three component peaks of the 550 nm emission band, which result from an electronic transition from one Stark sublevel of the 2H11/2 or 4S3/2 state to another of the ground state 4I15/2 of Er3+. All the six FIR schemes show highly efficient sensing performances with slightly different temperature characteristics. The temperature is overall determined by the six FIR schemes, largely increasing the reliability of temperature measurement.

Under 980 nm wavelength excitation, green upconversion emission spectra of Er3+ ions in NaYF4 (NYF) micro-crystals were measured in the temperature range of 298–383 K. A multiple ratiometric thermometry is proposed to realize reliable temperature sensing. It considers six luminescence intensity ratios(LIRs) involving two peaks at 530 nm emission band and three peaks at 550 nm emission band, which concern electronic transitions between crystal-field Stark sublevels of Er3+. The six LIR schemes display similar temperature characteristics with high thermometric efficiency. The temperature can be overall determined by the six LIR schemes, largely increasing measurement reliability. The study also shows that the 980 nm excitation power adopted neither induces a detectable temperature change nor has a noticeable effect on the LIR value. In addition, the Er3+-doped NYF phosphor displays intense green emissions and thermally stable spectral structure which are desired for the multiple ratiometric thermometry.

A previous paper [J. Lumin. 177 (2016) 219] has studied Judd-Ofelt spectroscopic properties of Er3+ (0.5 at%)-doped Gd3(Al, Ga)5O12 garnet single-crystal, and reported the Judd-Ofelt intensity parameters Ω2 = 1.47 × 10−20 cm2, Ω4 = 1.38 × 10−20 cm2 and Ω6 = 1.19 × 10−20 cm2. We have performed a re-study on the Judd-Ofelt spectroscopic properties of a similar garnet single-crystal Er3+(20 at%)-doped Gd3(Al0.4Ga0.6)5O12, and obtained quite different values of Judd-Ofelt intensity parameters Ω2 = (0.34 ± 0.11) × 10−20 cm2, Ω4 = (0.48 ± 0.16) × 10−20 cm2 and Ω6 = (1.05 ± 0.17) × 10−20 cm2. The quite different Ωt values given by two studies are mainly due to remarkably different absorption characteristics of Er3+ in the crystals employed in two studies, and factors that lead to quite different absorption characteristics are discussed. Another reason is that the hypersensitive transition at 380 nm was excluded from the Judd-Ofelt calculation in that paper, resulting in deviation of their result. Instead, all of the Er3+ absorption bands were included in our calculation, allowing to obtain more accurate Ωt values. Quite different Ωt values lead to considerable differences of relevant spectroscopic parameters, such as radiative rates and lifetimes of typical Er3+ emissions, for which the difference from each other is as much as three times. In addition, visible, near-infrared and mid-infrared fluorescence spectra and lifetimes of Er3+ in the studied crystal were measured, and the emission characteristics are discussed.

A metamaterial perfect absorber working in the ultraviolet to near-infrared band is proposed based on a triple-layer structure composed of titanium nitride (TiN) periodic nanoarray, dielectric film, and TiN bottom layer. Each unit cell of the nanoarray is a truncated pyramid structure with its width tapered linearly from the bottom to the top. The physical mechanism of the absorber was explained by analyzing the electric field distributions at different wavelengths, and the absorption performance was simulated as a function of its geometric parameters and the angle and polarization of incident light as well. Optimal geometric parameters are presented. The absorber implemented using the optimal parameters would display an excellent performance with almost perfect absorption (above 99%) over the entire spectral region from 300 to 2500 nm. The ultra-broadband perfect absorption behavior is attributed to the localized surface plasmon resonance effect of the TiN pyramid, the intrinsic loss of the TiN material and the coupling of resonance modes between two adjacent pyramids. Besides, the absorber also exhibits a polarization-independent feature at normal incidence and good angular acceptance capability of incident light. The reported ultra-broadband metamaterial absorber shows great application prospects in the solar energy harvesting industry and solar thermophotovoltaic systems.

980-nm-upconverted 530 and 550 nm Er

In the previous paper [J. Alloys Compd. 102 (2019) 873–878], optical and Judd-Ofelt (J-O) spectroscopic properties of Er3+/Pr3+-codoped Gd3Ga5O12 single-crystal have been reported and the J-O study was performed on the basis of measured absorption spectrum of the crystal. Present paper reports corrected absorption spectrum and J-O spectroscopic parameters of the crystal, which include J-O intensity parameters, oscillator strengths, fluorescence branch ratios, radiative rates and radiative lifetimes. Comparison shows that the previous paper erroneously reported almost one order of magnitude larger absorption cross-section, J-O intensity parameters, oscillator strength and radiative rate as well. A further comparison with previously reported results of Er3+-only doped crystal reveals that the Pr3+-codoping causes considerable spectroscopic change in absorption cross-section, J-O intensity parameters, oscillator strength and radiative rate of Er3+ transitions, and the reason of the change is discussed from the viewpoint of Pr3+-codoping and crystal growth procedure effect on ion environment of Er3+. In addition, errors are given for both the J-O parameters and radiative probabilities of several typical Er3+ emissions.

980-nm-upconverted 530 and 550 nm Er3+ green fluorescence spectra of Er3+/Yb3+-codoped NaGd(WO4)2 submicron crystals were measured in the temperature range of 298–383 K. A sextuple ratiometric thermometry is proposed. It is established on the basis of six schemes of fluorescence intensity ratio (FIR) that considers three component peaks of the 530 nm emission band and two component peaks of the 550 nm emission band, which involve electronic transitions between two Stark sublevels of Er3+. The study shows that the phosphor shows strong green fluorescence, which is verified by measured quantum yield, and thermally stable spectral structure desired for the sextuple ratiometric thermometry. All of the six FIR schemes display highly efficient sensing performances with slightly different thermal sensitivities. Each scheme gives a temperature value and the six schemes give an averaged result. In parallel, we have also carried out an ex vivo experimental study on the temperature characteristics of the green fluorescence of the phosphor. Almost same results have been obtained, verifying biological applicability of the phosphor. The ex vivo experimental results also show that the sextuple thermometry increases considerably the accuracy and reliability of temperature measurement in comparison with the conventional intensity integration method.

We have studied thermal effect on filtering feature of electro-optic long period grating (LPG) in Ti-diffused LiNbO3 waveguide, and observed the phenomenon of thermally induced multi-wavelength filtering. At room temperature (20.8 °C), a rejection band due to LPG effect is observed at 1450 nm wavelength regime for a driving voltage of 115 V. As the temperature is increased, the band weakens gradually, and is no longer discernible at 27 °C. Meanwhile, three new dips with similar contrasts and wavelength intervals are resolved at shorter wavelengths 1190, 1265 and 1339 nm. Their contrasts increase with a rise in temperature and have a value of 20 dB at available temperature of 44.5 °C. The positions of these dips change little with the temperature, but red-shift with the increase of driving voltage. These dips are associated with thermally induced multi-mode interference.

We present z-propagation single-mode Ti: Er: Tm: LiNbO 3 strip waveguides on X-Cut congruent LiNbO 3 substrate. The waveguide has been fabricated by a technological process, starting with the preparation of the Er 3+ /Tm 3+ codoped LiNbO 3 plate, followed by the fabrication of 8-μm-wide Ti-diffused strip waveguide. The results of surface refractive indices by employing prism coupling technique shows Er 3+ /Tm 3+ codoped have no effects on the substrate index, and the surface composition was evaluated from the measured indices with the help of Sellmeier equation. We demonstrated the amplified simultaneous emission (ASE) spectra from the waveguide pumped at 980nm and 795nm without optical damage observed. The results shows that the co-doping combines the laser property of both ions, and the emission band around 1.5μm is about 150 nm, as a result, opening up a series of possibilities for stable, broadband amplifier devices by employing pump sources under 980nm and 795nm laser diodes.

Based on inverted surface plasmon resonance (ISPR) a novel biosensor consisting of Ge₂₀Ga₅Sb₁₀S₆₅-palladium-graphene layer-biomolecule layer is proposed. The refractive index of biomolecule layer alters as biomolecule experience interactions, thus leading to a shift of ISPR angle. On this basis, the spectrum output of sensor is derived by transfer matrix method. The sensitivity, the resolution, the dynamic detection range and the signal to noise ratio of the presented sensor are discussed and compared with the performance of traditional sensors. Moreover, the influences of grapheme layer thickness on sensors are analyzed with comparative study. Finally, near infrared is used as the incident light of the presented sensor. The results show that, the best thickness of grapheme layer is monolayer; the peak intensity of the ISPR reflection is about 80%~90% of intensity of incident light, guaranteeing a high signal to noise ratio; In the visible light, when λ = 632.8 nm, the presented sensor is 1.9 times the resolution of the sensor based on SiO₂ coupling inverted surface plasmon resonance, is 3. 5 times the resolution of the sensor based on surface plasmon resonance(SPR), and is 2 times the dynamic detection range of pre-existing biosensor based on SPR. The application of Ge₂₀Ga₅Sb₁₀S65 prism extends the detection light wavelength from the visible region to the near infrared region. When λ = 1,000 nm, the sensor is 3-4 times of the sensor in visible region. The research greatly contributes to the realization and application of biosensor based on inverted surface plasmon resonance.