Transparent perovskite glass-ceramics for visual optical thermometry

Enrichment of anchoring sites by introducing supramolecular halogen bonds for the efficient perovskite nanocrystal LEDs

Considering the multi-functionalization of ligands, it is crucial for ligand molecular design to reveal the landscape of anchoring sites. Here, a typical triphenylphosphine (TPP) ligand was employed to explore its effect on the surface of CsPbI3 perovskite nanocrystals (PNCs). Except for the conventionally considered P-Pb coordination, an P-I supramolecular halogen bonding was also found on the NC surface. The coexistence of the above two types of bonding significantly increased the formation energy of iodine vacancy defects and improved the photoluminescence quantum yield of PNCs up to 93%. Meanwhile, the direct interaction of P and I enhanced the stability of the Pb-I octahedra and dramatically inhibited the migration of I ions. Furthermore, the introduction of additional benzene rings (2-(Diphenylphosphino)-biphenyl (DPB)) increased the delocalized properties of the PNC surface and significantly improved the charge transport of the PNCs. As a result, the DPB passivated CsPbI3 NCs based top-emitting LEDs exhibite a peak external quantum efficiency (EQE) of 22.8%, a maximum luminance of 15, 204 cd m-2, and an extremely low-efficiency roll-off of 2.6% at the current density of 500 mA cm-2.

Highly Sensitive Dual-Mode Optical Thermometry of Er3+/Yb3+ Codoped Lead-Free Double Perovskite Microcrystal

In this Letter, erbium (Er³⁺) and ytterbium (Yb³⁺) codoped perovskite Cs₂Ag_0.6Na_0.4In_0.9Bi_0.1Cl₆ microcrystal (MC) is synthesized and demonstrated systematically to the most prospective optical temperature sensing materials. A dual-mode thermometry based on fluorescence intensity ratio and fluorescence lifetime provides a self-reference and highly sensitive temperature measurement under dual wavelength excitation at a temperature from 300 to 470 K. Combined with the white-light emission derived from self-trapped excitons (STEs), the characteristic emission peak of Er³⁺ ions can be observed under 405 nm laser excitation. The fluorescence intensity ratio (FIR) between perovskite and Er³⁺ is used as temperature-dependent probe signal, of which maximum value for relative and absolute sensitivities reaches to 1.40% K^-1 and 8.20 × 10^-2 K^-1. Moreover, Er³⁺ luminescence becomes stronger with the feeding Yb³⁺ increasing under 980 nm laser excitation. The energy transfer of Er³⁺ and Yb³⁺ is revealed by power-dependent photoluminescence (PL) spectroscopy, and the involved upconversion mechanism pertains to the two-photon excitation process. The results reveal that the Er³⁺/Yb³⁺ codoped lead-free double perovskite MC is a good candidate for a thermometric material for the novel dual-mode design.

Ultrasensitive Temperature Sensing Based on Ligand-Free Alloyed CsPbClx Br3-x Perovskite Nanocrystals Confined in Hollow Mesoporous Silica with High Density of Halide Vacancies

Temperature sensing based on fluorescent semiconductor nanocrystals has recently received immense attention. Enhancing the trap-facilitated thermal quenching of the fluorescence should be an effective approach to achieve high sensitivity for temperature sensing. Compared with conventional semiconductor nanocrystals, the defect-tolerant feature of lead halide perovskite nanocrystals (LHP NCs) endows them with high density of defects. Here, hollow mesoporous silica (h-SiO₂ ) template-assisted ligand-free synthesis and halogen manipulation (chloride-importing) are proposed to fabricate highly defective yet fluorescent CsPbCl_1.2 Br_1.8 NCs confined in h-SiO₂ (CsPbCl_1.2 Br_1.8 NCs@h-SiO₂ ) for ultrasensitive temperature sensing. The trap barrier heights, exciton-phonon scattering, and trap state filling process in the CsPbCl_1.2 Br_1.8 NCs@h-SiO₂ and CsPbBr₃ NCs@h-SiO₂ are studied to illustrate the higher temperature sensitivity of CsPbCl_1.2 Br_1.8 NCs@h-SiO₂ at physiological temperature range. By integrating the thermal-sensitive CsPbCl_1.2 Br_1.8 NCs@h-SiO₂ and thermal-insensitive K₂ SiF₆ :Mn⁴⁺ phosphor into the flexible ethylene-vinyl acetate polymer matrix, ratiometric temperature sensing from 30.0 °C to 45.0 °C is demonstrated with a relative temperature sensitivity up to 13.44% °C^-1 at 37.0 °C. The composite film shows high potential as a thermometer for monitoring the body temperature. This work demonstrates the unparalleled temperature sensing performance of LHP NCs and provides new inspiration on switching the defects into advantages in sensing applications.

Upconversion luminescence and optical thermometry properties of transparent oxyfluoride glass ceramics embedded with Ba4Y3F17: Yb3+, Er3+ nanocrystals

Transparent glass ceramic embedded with Ba₄Y₃F₁₇: Yb³⁺, Er³⁺ nanocrystals can be realised as a promising temperature sensor.