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The second near-infrared (NIR II) response photon up-conversion (UC) materials show great application prospects in the fields of biology and optical communication. However, it is still an enormous challenge to obtain efficient NIR II response materials. Herein, we develop a series of Er 3+ doped ternary sulfides phosphors with highly efficient UC emissions under 1532 nm irradiation. β-NaYS 2 :Er 3+ achieves a visible UC efficiency as high as 2.6%, along with high brightness, spectral stability of lights illumination and temperature. Such efficient UC is dominated by excited state absorption, accompanied by the advantage of long lifetimes ( 4 I 9/2 , 9.24 ms; 4 I 13/2 , 30.27 ms) of excited state levels of Er 3+ , instead of the well-recognized energy transfer UC between sensitizer and activator. NaYS 2 :Er 3+ phosphors are further developed for high-performance underwater communication and narrowband NIR photodetectors. Our findings suggest a novel approach for developing NIR II response UC materials, and simulate new applications, eg., simultaneous NIR and visible optical communication. Development of efficient upconversion (UC) phosphors that emit under irradiation in the NIR II region is challenging - most UC materials rely on the presence of sensitizers absorbing at shorter wavelengths. Here, authors synthesize Er 3+ doped ternary sulfides phosphors with visible UC efficiency up to 2.6% and long emission lifetimes under 1532 nm irradiation, via an excited state absorption mechanism.

Plasmonic metal nanostructures have been widely used to enhance the upconversion efficiency of the near‐infrared (NIR) photons into the visible region via the localized surface plasmon resonance (LSPR) effect. However, the direct utilization of low‐cost nonmetallic semiconductors to both concentrate and transfer the NIR‐plasmonic energy in the upconversion system remains a significant challenge. Here, a fascinating process of NIR‐plasmonic energy upconversion in Yb3+/Er3+‐doped NaYF4 nanoparticles (NaYF4:Yb‐Er NPs)/W18O49 nanowires (NWs) heterostructures, which can selectively enhance the upconversion luminescence by two orders of magnitude, is demonstrated. Combined with theoretical calculations, it is proposed that the NIR‐excited LSPR of W18O49 NWs is the primary reason for the enhanced upconversion luminescence of NaYF4:Yb‐Er NPs. Meanwhile, this plasmon‐enhanced upconversion luminescence can be partly absorbed by the W18O49 NWs to re‐excite its higher energy LSPR, thus leading to the selective enhancement of upconversion luminescence for the NaYF4:Yb‐Er/W18O49 heterostructures. More importantly, based on this process of plasmonic energy transfer, an NIR‐driven catalyst of NaYF4:Yb‐Er NPs@W18O49 NWs quasi‐core/shell heterostructure, which exhibits a ≈35‐fold increase in the catalytic H2 evolution from ammonia borane (BH3NH3) is designed and synthesized. This work provides insight on the development of nonmetallic plasmon‐sensitized optical materials that can potentially be applied in photocatalysis, optoelectronic, and photovoltaic devices. Nonmetallic plasmon‐induced selective enhancement of upconversion luminescence is observed in a layer‐structured NaYF4:Yb‐Er/W18O49 film due to the near‐infrared‐plasmonic energy upconversion. Based on this photonics process, an infrared‐driven plasmonic catalyst of NaYF4:Yb‐Er@W18O49 heterostructures is designed and synthesized, which exhibits a ≈35‐fold increase in catalytic H2 evolution upon IR excitation.

Upconversion luminescence properties from the emissions of Stark sublevels of Er3+ were investigated in Er3+-Yb3+-Mo6+-codoped TiO2 phosphors in this study. According to the energy levels split from Er3+, green and red emissions from the transitions of four coupled energy levels, 2H11/2(I)/2H11/2(II), 4S3/2(I)/4S3/2(II), 4F9/2(I)/4F9/2(II), and 2H11/2(I) + 2H11/2(II)/4S3/2(I) + 4S3/2(II), were observed under 976 nm laser diode excitation. By utilizing the fluorescence intensity ratio (FIR) technique, temperature-dependent upconversion emissions from these four coupled energy levels were analyzed at length. The optical temperature-sensing behaviors of sensing sensitivity, measurement error, and operating temperature for the four coupled energy levels are discussed, all of which are closely related to the energy gap of the coupled energy levels, FIR value, and luminescence intensity. Experimental results suggest that Er3+-Yb3+-Mo6+-codoped TiO2 phosphor with four pairs of energy levels coupled by Stark sublevels provides a new and effective route to realize multiple optical temperature-sensing through a wide range of temperatures in an independent system.

Hydrogenated microcrystalline silicon （mc-Si：H） thin films were deposited by inductively coupled plasma assistant magnetron sputtering （ICP-MS） in an Ar-H2 gas mixture. The role of ion bombardment in the growth of mc-Si：H films was studied with increasing negative bias voltages on the substrate holder from 0 to -100 V. Raman scattering, X-ray diffraction （XRD）, Fourier transform infrared （FTIR） spectroscopy and transmission electron microscopy （TEM） were performed to investigate the microstructure changes of deposited Si films. Raman scattering showed that the high energy ion bombardment resulted in crystalline degradation of Si films. The XRD results showed the decrease and even elimination of preferential growth orientation of crystalline Si films with ion bombardment energy increase. The SiH bonding configuration changes and the increase of bonded hydrogen concentration were determined with the analysis of FTIR spectra. Furthermore, the dramatic evolution of cross-sectional morphology of Si thin films was detected by TEM observation.

Infrared to green up-conversion emissions centered at the wavelengths of about 524 and 550 nm of the Er 3+ -Yb 3+ codoped borosilicate glass are recorded, using a 978 nm semiconductor laser diode (LD) as an excitation source. The fluorescence intensity ratio (FIR) of the green up-conversion emissions at about 524 and 550 nm in the Er 3+ -Yb 3+ codoped borosilicate glass has been studied as a function of temperature over the temperature range of 295–873 K. The maximum sensitivity and the temperature resolution derived from the FIR of the green up-conversion emissions are approximately 0.0038 K −1 and 0.2 K, respectively. It is demonstrated that the prototype optical temperature sensor based on the FIR technique from the green up-conversion emissions in the Er 3+ -Yb 3+ codoped borosilicate glass plays a major role in temperature measurement.

The Er3+-Yb3+ codoped Al2O3 nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The green and red up-conversion emissions centered at about 526, 547 and 677 nm, corresponding respectively to the 2H11/2→4I15/2, 4S3/2→4I15/2 and 4 F9/2→4I15/2 transitions of Er3+, were detected by a 978-nm semiconductor laser diode excitation. The Annealing has evident effect on the up-conversion emissions of the samples: The red up-conversion emission is noticeable before annealing; however, the green up-conversion emission becomes predominant after annealing. The mixture of (Er,Yb)3Al5O12 and α-(Al,Er,Yb)2O3 phases is more favorable for green up-conversion emissions due to an enhancement of the ESA (I) of 4I11/2+a photon→4F7/2 and ET (III) of 2F5/2(Yb3+)+4I11/2(Er3+)→2F7/2(Yb3+)+4F7/2(Er3+) processes. The two-photon absorption up-conversion process is involved in the green and red up-conversion emissions. The results have proved that arc discharge synthesis is a new promising preparation technology for optical materials.

Upconversion luminescence properties from the emissions of Stark sublevels of Er(3+) were investigated in Er(3+)-Yb(3+)-Mo(6+)-codoped TiO₂ phosphors in this study. According to the energy levels split from Er(3+), green and red emissions from the transitions of four coupled energy levels, ²H11/2(I)/²H11/2(II), ⁴S3/2(I)/⁴S3/2(II), ⁴F9/2(I)/⁴F9/2(II), and ²H11/2(I) + ²H11/2(II)/⁴S3/2(I) + ⁴S3/2(II), were observed under 976 nm laser diode excitation. By utilizing the fluorescence intensity ratio (FIR) technique, temperature-dependent upconversion emissions from these four coupled energy levels were analyzed at length. The optical temperature-sensing behaviors of sensing sensitivity, measurement error, and operating temperature for the four coupled energy levels are discussed, all of which are closely related to the energy gap of the coupled energy levels, FIR value, and luminescence intensity. Experimental results suggest that Er(3+)-Yb(3+)-Mo(6+)-codoped TiO₂ phosphor with four pairs of energy levels coupled by Stark sublevels provides a new and effective route to realize multiple optical temperature-sensing through a wide range of temperatures in an independent system.

The second near-infrared (NIR II) response photon up-conversion (UC) materials show great application prospects in the fields of biology and optical communication. However, it is still an enormous challenge to obtain efficient NIR II response materials. Herein, we develop a series of Er doped ternary sulfides phosphors with highly efficient UC emissions under 1532 nm irradiation. β-NaYS :Er achieves a visible UC efficiency as high as 2.6%, along with high brightness, spectral stability of lights illumination and temperature. Such efficient UC is dominated by excited state absorption, accompanied by the advantage of long lifetimes ( I , 9.24 ms; I , 30.27 ms) of excited state levels of Er , instead of the well-recognized energy transfer UC between sensitizer and activator. NaYS :Er phosphors are further developed for high-performance underwater communication and narrowband NIR photodetectors. Our findings suggest a novel approach for developing NIR II response UC materials, and simulate new applications, eg., simultaneous NIR and visible optical communication.