light range. [1] Significant progress has been made in photocatalysis, [2] hydrogen evolution, [3] light-emitting diodes (LEDs), [4] luminescent solar concentrators (LSCs), [5] solar cells, [6] and other fields. [7] The past seven years have witnessed a rapid growth of metal halide perovskite materials for LEDs with external quantum efficiency larger than 20%. [8] However, the poor stability and high toxicity hinder the commercial applications of perovskite. Therefore, fabrication of new lead-free perovskite materials with stable PL and high efficiency is still a great challenge. [9] Generally, the traditional Pb 2+ is usually replaced by other metal atoms in the similar outermost electron distribution, such as Sn 2+ and Ge 2+ . [10] Nevertheless, owning to the reducibility, they are easy to be oxidized into a tetravalent state. Afterward, other metal atoms with the same valence as Pb 2+ have been applied to form perovskite structure (AB II X 3 , B II = Mn 2+ , Co 2+ , Cu 2+ , Fe 2+ , etc.). [11] In addition, the ways including heterovalent Recently, lead-free materials with stable photoluminescence (PL) at room temperature, such as vacancy-ordered double perovskites have drawn wide attention. Herein, Te 4+ -doped all-inorganic lead-free Cs 2 Zr 1−x Te x Cl 6 perovskite microcrystals (MCs) are reported. The obtained pure Cs 2 ZrCl 6 perovskite MCs exhibit a blue emission, while Cs 2 Zr 1−x Te x Cl 6 perovskite MCs show a broad and strong yellow emission with ultrahigh photoluminescence quantum yield (PLQY) up to 79.46% at room temperature. The structure and optical properties of perovskite MCs are investigated in detail by experiments and theoretical calculations. The mechanism that 3 P 1 of Te can be partially frozen at the low temperature regarding Cs 2 Zr 1−x Te x Cl 6 perovskite MCs is proposed. White light emitting diodes (WLEDs) with a color coordinate of (0.344, 0.333), a correlated color temperature of 4959 K, a color rendering index (Ra) of 74.8, and a high light efficiency of 91.16 lm W −1 , are fabricated by the prepared Cs 2 Zr 1−x Te x Cl 6 perovskite MCs powder with a commercial near-UV LED (NUV-LED) chip (450 nm). The results suggest that Te 4+ -doped all-inorganic lead-free perovskite MCs show great potential in the next-generation solidstate lightings.
Fluorescence intensity ratio (FIR) thermometry, a new contactless temperature measurement, can achieve accurate measurements in a harsh environment. In this work, all-inorganic lead-free Cs 2 AgInCl 6 : Er−Yb and Cs 2 AgBiCl 6 : Er−Yb microcrystals emit bright green up-conversion emission, which are synthesized by precipitation at a low temperature (80 °C). In up-conversion emission, FIR of the 2 H 11/2 → 4 I 15/2 band to the 4 S 3/2 → 4 I 15/2 band exhibits temperature dependence, which can be used as the temperature measurement parameter, so-called FIR thermometry. Moreover, the theoretically accurate measurement range is from 100 to 600 K, achieving maximum absolute sensitivities from 0.0130 to 0.0113 K −1 , respectively. The principle of up-conversion and high sensitivity is well explained by calculating the partial density of states. Compared to the reported thermometry materials based on the FIR method, the prepared all-inorganic lead-free Cs 2 AgInCl 6 : Er−Yb and Cs 2 AgBiCl 6 : Er−Yb microcrystals show outstanding temperature measurement width and sensitivity, becoming a potential candidate for high-sensitivity optical temperature sensors.
Low-dimension perovskite materials have attracted wide attention due to their excellent optical properties and stability. Herein, Sb 3+ -doped Cs 2 ZrCl 6 crystals are synthesized by a coprecipitation method in which Sb 3+ ions partially replace Zr 4+ ions. The Cs 2 ZrCl 6 :xSb 3+ powder shows blue and orange−red emissions under a 254 and 365 nm light, respectively, due to the [ZrCl 6 ] 2− octahedron and [SbCl 6 ] 3− octahedron. The photoluminescence quantum yield (PLQY) of Cs 2 ZrCl 6 :xSb 3+ (x = 0.1) crystals is up to 52.5%. According to experimental and computational results, the emission mechanism of the Cs 2 ZrCl 6 :xSb 3+ crystals is proposed. On the one hand, a wide blue emission with a large Stokes shift is caused by the self-trapping excitons of [ZrCl 6 ] 2− octahedra under a 260 nm excitation. On the other hand, the luminescence mechanism of [SbCl 6 ] 3− octahedron is divided into two parts: 1 P 1 → 1 S 0 (490 nm) and 3 P 1 → 1 S 0 (625 nm). The broad-band emission, high PLQY, and excellent stability endow the Cs 2 ZrCl 6 :xSb 3+ powders with the potential for the fabrication of white light-emitting diodes (WLEDs). A WLED device is fabricated using a commercial 310 nm NUV chip, which shows a high color rendering index of 89.7 and a correlated color temperature of 5333 K. In addition, the synthesized Cs 2 ZrCl 6 :xSb 3+ crystals can be also successfully used for information encryption. Our work will provide a deep understanding of the photophysical properties of Sb 3+ -doped perovskites and facilitate the development of Cs 2 ZrCl 6 :xSb 3+ crystals in encrypting multilevel optical codes and WLEDs.
Due to the toxicity and instability issues of lead halide perovskites, lead-free perovskites have recently emerged as a viable alternative. However, significant optical band gaps of lead-free perovskites exert influence on their luminescent properties. Fortunately, the addition of dopants becomes an efficacious solution. The current widely utilized methods for synthesizing perovskites almost require high temperatures, a long period, and atmosphere protection, which cost more energy and resources. In this paper, we report that Rb2ZrCl6:xSb3+ perovskite phosphors can be easily prepared by a wet grinding approach at room temperature, which is a more efficient and facile process. Due to the self-trapped excitons of the host structure and Sb3+ ions, the produced samples display blue-white and orange fluorescence under UV lamp irradiation at 254 and 365 nm, respectively. In the photoluminescence spectrum, the doped perovskite exhibits an emission peak at 630 nm under excitation at 365 nm. Importantly, the prepared phosphors have tunable emissions related to the excitation wavelength. In addition, our produced powders show remarkable stability at room temperature, laying the foundations for this approach to be widely used in perovskite production.
Ratio-metric luminescence thermometer based on trivalent erbium ions is a noninvasive remote sensing technique with high spatial and temporal resolution. The thermal coupling between two adjacent energy levels follows the...
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