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Rare-earth doped oxysulfides have gained considerable attention as a luminescence host material owing to its good chemical stability and high efficiency. In this study, Er3+-sensitized La2O2S nanoparticles are prepared by the high-temperature co-precipitation method. La2O2S:2%Er3+ is selected to construct La2O2S:Er3+@La2O2S core/shell structures through epitaxial growth, and the luminescence properties are studied. The surface defects of La2O2S:Er3+ are repaired by the inert protective shell, and the luminescence intensity of the core/shell nanocrystals is increased by 9.6 times. Finally, MAPbI3 is spin-coated over the La2O2S:Er3+@La2O2S film to construct narrow band near-infrared photodetectors. Under 1550 nm excitation, the response rate is 23 mA W−1, detection rate is 2.57 × 108 Jones, and response time is 220 ms. [ABSTRACT FROM AUTHOR]

Lanthanide ion-doped up-conversion (UC) luminescent materials are highly coveted for their utility in diverse applications such as anti-counterfeiting, fluorescence labeling, and temperature sensing. Here, we attempt to adopt SrY2S4 as a novel host lattice for UC luminescence and high-sensitive optical thermometry under near-infrared irradiation. The results show that the single Er3+-doped SrY2S4 samples present their main emissions in green and red regions under 1550 and 980 nm excitations, which correspond to the H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The green to red intensity ratio increases with the Er3+ concentration under both 980 and 1550 nm excitations. The mechanisms of UC luminescence and energy transfer are further systematically investigated by UC spectra and fluorescence decay dynamics. Furthermore, the non-contact temperature sensing performance of the SrY2S4:10%Er3+ sample is explored via employing fluorescence intensity ratio (FIR) technology. At an excitation of 980 nm, the maximum absolute sensitivity (SA) reaches 7.5 × 10−3 K−1 at 480 K. By utilizing a much safer excitation laser of 1550 nm, the maximum SA achieves 8.4 × 10−3 K−1 at 450 K, with a high and stable SA of more than 7.9 × 10−3 K−1 over a broad temperature range of 360–570 K. The relative sensitivity is 1.06% and 1.01% K−1 under 980 and 1550 nm excitations, respectively. These results indicate that the ternary sulfide SrY2S4 can be adopted as a novel host to achieve promising UC luminescence and thermal sensing performance. [ABSTRACT FROM AUTHOR]

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy3+,Tm3+ single-doped or co-doped K3Y(PO4)2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy3+,Tm3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm3+ and Dy3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm3+ to Dy3+, the emission of Dy3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy3+,Tm3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10−3 K−1, which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K3Y(PO4)2:Tm3+,Dy3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields. [ABSTRACT FROM AUTHOR]

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 Er3+ doped ternary sulfides phosphors with highly efficient UC emissions under 1532 nm irradiation. β-NaYS2:Er3+ 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 (4I9/2, 9.24 ms; 4I13/2, 30.27 ms) of excited state levels of Er3+, instead of the well-recognized energy transfer UC between sensitizer and activator. NaYS2:Er3+ 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 Er3+ 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. [ABSTRACT FROM AUTHOR]