Development of Multifunctional Materials Based on Heavy Concentration Er³⁺‐Activated Lead‐free Double Perovskite Cs₂NaBiCl₆

Abstract

Lead halide perovskites have been very promising for versatile optoelectronic applications, whereas the inherent toxicity and instability of lead halide restrict its wide application. Herein, a kind of high‐performance multifunctional phosphor is designed based on heavy concentration Er3+‐activated lead‐free double perovskite Cs2NaBiCl6 (CNBC), which realizes the self‐sensitization of Er3+ ions and emits high‐brightness pure green emission upon dual near‐infrared (dual‐NIR) excitation. The luminescence properties can be further optimized by adding sensitizers (Yb3+/Nd3+). Interestingly, the emission intensity of the green region is heightened by 212‐fold after Yb3+ ions doping, which is 40 times higher than that of the current popular phosphors (α‐NaYF4:2%Er3+,18%Yb3+). Meanwhile, the temperature sensing properties of the thermally coupled levels (Er3+:2H11/2,4S3/2) in Cs2NaBiCl6:40%Er3+ are also investigated systematically based on the luminescence intensity ratio principle, and the maximum relative sensitivity is calculated to be as high as 1.27% K‐1 (980 nm) and 1.57% K‐1 (808 nm). Fortunately, the thermal stability and the performance for temperature readout of the studied phosphors are still maintaining a high level after doping sensitizers. The insights provided by this work will broaden the scope of lead‐free halide double perovskites in the fields of luminescence and thermometry.

Lanthanide-doped lead-free double perovskite La2MgTiO6 as ultra-bright multicolour LEDs and novel self-calibrating partition optical thermometer

“…Each sample has the same emission band characteristics, corresponding to the 2 H 11/2 → 4 I 15/2 (534 nm), 4 S 3/2 → 4 I 15/2 (554 nm) and 4 F 9/2 → 4 I 15/2 (662 nm) transitions of Er 3+ ions, respectively. 32 Although the UC luminescence intensity of Er 3+ is proportional to the proportion of Yb 3+ ion doping in Fig. 4a, the impurity La 2 Ti 2 O 7 appears when the doping amount of Yb 3+ ions reaches 6% (Fig.…”

“…35,36 Based on the energy gap law, NR processes will hardly occur if the Δ E in activators is five times higher than that of the vibrational frequency of the host, which explains the extremely weak red emission in the Ho–Yb system. 32…”

Pure Green Upconversion from a Multicolor Downshifting Perovskite Crystal

“…[30] Thanks to the intense green emission, the single crystals could find its application for remote temperature monitor. [19,31] In a proof-of-concept experiment, the two thermally-coupled levels of Er 3+ ( 2 H 11/2 and 4 S 3/2 ) were used in optical thermometry based on their luminescence intensity ratio (LIR). As shown in Figure 5a, the temperature-dependent upconversion spectra of the crystals were collected.…”

“…Recently, many chloride-based double perovskites have emerged as an efficient host for single-band upconversion. [16][17][18][19] Despite these progress on powder samples, single crystal of single-band emission remained elusive.Here, we reported a double perovskite crystal of Cs 2 NaInCl 6 :Yb 3+ ,Er 3+ that was grown in a hydrothermal reactor. Under UV excitation, the multicolor downshifting luminescence featured a set of sharp peaks at 448, 550, and 660 nm, covering a wide color gamut in CIE diagram.…”

“…Recently, many chloride-based double perovskites have emerged as an efficient host for single-band upconversion. [16][17][18][19] Despite these progress on powder samples, single crystal of single-band emission remained elusive.…”