Absorption and upconversion light emission properties of Er3+ and Yb3+/Er3+ codoped NaYS2

Towards highly efficient NIR II response up-conversion phosphor enabled by long lifetimes of Er3

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 (⁴I_9/2, 9.24 ms; ⁴I_13/2, 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.

Tellurium Doping and the Structural, Electronic, and Optical Properties of NaYS2(1-x)Te2x Alloys

New ternary and quaternary NaYS_2(1-x)Te_2x alloys (with x = 0, 0.33, 0.67, and 1) are proposed as promising candidates for photon energy conversion in photovoltaic applications. The effects of Te doping on crystal, spectral, and optical properties are studied within the framework of periodic density functional theory. Increasing Te content decreases the band gap (E _g) considerably (from 3.96 (x = 0) to 1.62 eV (x = 0.67)) and fits a quadratic model (E _g(x) = 3.96-6.78x + 4.70x ², (r ² = 0.96, n = 4)). The band gap of 1.62 eV makes the NaYS_0.67Te_1.33 alloy ideal for photovoltaic applications for their ability to absorb in the visible segment of the sunlight spectrum. The calculated exciton binding energies are 9.78 meV for NaYS_1.33Te_0.67 and 6.06 meV for NaYS_0.67Te_1.33. These values of the order of the thermal energy at room temperature suggest an easily dissociable hole-electron pair. The family of NaYS_2(1-x)Te_2x alloys are, therefore, promising candidates for visible photocatalytic devices and worthy of further experimental and theoretical investigations.

A Selective Cation Exchange Strategy for the Synthesis of Colloidal Yb3+-Doped Chalcogenide Nanocrystals with Strong Broadband Visible Absorption and Long-Lived Near-Infrared Emission

Doping lanthanide ions into colloidal semiconductor nanocrystals is a promising strategy for combining their sharp and efficient 4f-4f emission with the strong broadband absorption and low-phonon-energy crystalline environment of semiconductors to make new solution-processable spectral-conversion nanophosphors, but synthesis of this class of materials has proven extraordinarily challenging because of fundamental chemical incompatibilities between lanthanides and most intermediate-gap semiconductors. Here, we present a new strategy for accessing lanthanide-doped visible-light-absorbing semiconductor nanocrystals by demonstrating selective cation exchange to convert precursor Yb³⁺-doped NaInS₂ nanocrystals into Yb³⁺-doped PbIn₂S₄ nanocrystals. Excitation spectra and time-resolved photoluminescence measurements confirm that Yb³⁺ is both incorporated within the PbIn₂S₄ nanocrystals and sensitized by visible-light photoexcitation of these nanocrystals. This combination of strong broadband visible absorption, sharp near-infrared emission, and long (>400 μs) emission lifetimes in a colloidal nanocrystal system opens promising new opportunities for both fundamental-science and next-generation spectral-conversion applications such as luminescent solar concentrators.

Preparation of Gd2O2S:Er3+,Yb3+ phosphor and its multi-wavelength sensitive upconversion luminescence mechanism

Er³⁺–Yb³⁺ codoped Gd₂O₂S infrared upconversion phosphor has been prepared via a coprecipitation–solid state reaction process.