Room Temperature Photoluminescence (RT-PL)
Semiconductor Materials
Annealing induces defects, leading to the emergence of electronic in-gap states in monolayer MoS 2 , as illustrated in Figure 1a . We utilized PL spectroscopy ( Figure 1b ) and reflectance measurements ( Figure 1c ) to assess the optical properties of monolayer MoS 2 at room temperature. In pristine MoS 2 , the PL spectrum exhibits characteristic peaks, including A − trion/A exciton (A − /A) at 1.90 eV and B exciton at 2.05 eV. The annealed sample shows a low-energy localized emission peak, LXD, originating from defect-induced in-gap states with substantial binding energy of 185 meV. This defect-mediated emission corresponds to transitions between an unoccupied, in-gap defect state and another energy state at the valence band maximum. The binding energy of the defect-mediated emission aligns with the observed 185 meV LXD peak in our PL results. The reflectance spectrum broadens in the defective sample. The deconvoluted room temperature PL spectrum indicates an increased ratio of integrated intensity of A − trion to A exciton (I( A − )/I(A)) from 0.44 in pristine MoS 2 to 1.06 in annealed MoS 2 , signifying enhanced electron doping due to defect creation, as supported by the XPS peak shift in Figure 1c . The reproducibility of our results is demonstrated across 22 samples, as illustrated in the statistical histogram ( Figure 1d )
Reference:
Zhao, W., He, Z. & Tang, BZ Room-temperature phosphorescence from organic aggregates. Nat Rev Mater 5, 869–885 (2020). https://doi.org/10.1038/s41578-020-0223-z
Optoelectronics devices
In this study, the PL spectra of Zn 0.95 Mn 0.05 S (ZMS), Zn 0.94 Mn 0.05 Cu 0.01 S (ZMCS-1), Zn 0.92 Mn 0.05 Cu 0.03 S (ZMCS-2), Zn 0.90 Mn 0.05 Cu 0.05 S (ZMCS-3) and Zn 0.85 Mn 0.05 Cu 0.1 S (ZMCS-4) thin films were obtained at room temperature under 320 nm excitation ( Fig. 2 ). The PL spectra, ranging from 300 to 700 nm, revealed near-band emissions (NBE) at 347, 349, 352, 354, 358, and 369 nm, corresponding to ZnS, ZMS, ZMCS-1, ZMCS-2, ZMCS-3, and ZMCS-4 thin films, respectively. Emissions at 378, 381, 389, 395, 398, and 402 nm were attributed to IS related emissions, while blue emissions at 418, 426, 428, 433, 435, and 442 nm indicated V S related transitions. Green emissions at 525, 530, 532, 540, 540, and 545 nm resulted from the recombination of electrons of sulfur vacancies with interstitial sulfur states. A strong yellow-orange emission peak at 581 nm was attributed to the Mn 2+ 4 T 1 – 6 A 1 transition, indicating successful Mn incorporation into the ZnS host. The PL intensity decreased with increasing Cu substitution, except for 10%, suggesting Cu incorporation into the ZnS matrix, with the highest PL intensity observed at 5% Mn incorporation. This tunable visible emission by Mn/Cu substitutions holds potential for nano-sized light-emitting diodes and photonic devices.
Reference:
Goktas, A. (2020). Role of simultaneous substitution of Cu 2+ and Mn 2+ in ZnS thin films: Defects-induced enhanced room temperature ferromagnetism and photoluminescence. Physica E: Low-dimensional Systems and Nanostructures, 117(), 113828 –. doi:10.1016/j.physe.2019.113828
Light Emitting Diodes
In this research, the focus is on exploring the optical characteristics of lead-free perovskite Cs 2 Zr 1−x Te x Cl 6 microcrystals (MCs). Illustrated in Figure 3a , Cs 2 ZrCl 6 perovskite MCs display strong absorption at 280 nm, extending continuously up to 500 nm. Conversely, Cs 2 Zr 1−x Te x Cl 6 perovskite MCs exhibit notably enhanced absorption in the 330–360 nm and 360–500 nm ranges due to Te 4+ doping, intensifying with higher Te 4+ content ratios. The optical bandgap decreases from 3.74 eV for Cs 2 ZrCl 6 to 3.01 eV for Cs 2 Zr 0.9 Te 0.1 Cl 6 , indicating a reduction in bandgap with increased Te 4+ content, implying the replacement of Zr 4+ by Te 4 + . The photoluminescence (PL) emission spectra (excitation at 325 nm) of Cs 2 Zr 1−x Te x Cl 6 perovskite MCs, depicted in Figure 3c , reveal a wide emission peak at 570 nm with a FWHM of approximately 105 nm and a substantial Stokes shift of around 130 nm, attributed to minimal Te content. Additionally, the PL spectra exhibit a slight red shift with rising Te content ratios. Examining Figure 3d , Cs 2 Zr 1−x Te x Cl 6 perovskite MCs display two excitonic absorptions around 340 and 425 nm corresponding to 1 S 0 → 3 P 2 and 1 S 0 → 3 P 1 , respectively, with the long-wavelength 1 S 0 → 3 P 1 dominating the excitation absorption. This dominance confirms the prevalence of [ TeCl 6 ] 2− octahedrons in the excitation absorption of Cs 2 Zr 1−x Te x Cl 6 perovskite MCs. Further insights into luminescent properties are gained from PL lifetimes. The PL decay curves of Cs 2 ZrCl 6 perovskite MCs, as presented in Figure 3e, exhibit a double exponential model with short and long PL lifetimes of 19.4 μs and 148.8 μs, respectively, consistent with prior reported results.Figure 3f reveals the PL lifetime of Cs 2 Zr 0.99 Te 0.01 Cl 6 perovskite MCs as 3.93 and 43.4 μs, respectively. Noteworthy, the short and long lifetimes correspond to 3 P 1 → 1 S 0 and 3 P 0 → 1 S 0 pathways , respectively, as known for the ground state of an S 2 ion.
Reference:
Zhilin Li, Zhihui Rao, Qiaoqiao Li, Liujiang Zhou, Xiujian Zhao, Xiao Gong. Cs 2 Zr 1−x Te x Cl 6 Perovskite Microcrystals with Ultrahigh Photoluminescence Quantum Efficiency of 79.46% for High Light Efficiency White Light Emitting Diodes. Adv. Optical Mater. 2021, 2100804. https://onlinelibrary.wiley.com/doi/full/10.1002/adom.202100804
Ceramics
Figure 4a shows the room temperature photoluminescence (PL) spectra of BLT and BLT 0.95 Nb 0.04 ceramics. When excited by a laser with an energy of 2.54 eV, the spectra exhibit a wide band of emissions covering a large portion of the visible spectrum, as well as a band in the near-infrared region. By analyzing the spectra using a Gaussian profile, it is possible to identify five distinct peaks. For BLT as shown in Fig. 4b , these peaks correspond to wavelengths of 479 nm (blue), 540 nm (green), 591 nm (orange), 690 nm (red), and 827 nm (near-infrared). In the case of BLT 0.95 Nb 0.04 , the peaks are observed at higher wavelengths, with peaks at 575 nm ( green-yellow), 591 nm and 614 nm (orange), 699 nm (red), and 827 nm (near-infrared) ( Fig. 4c ). Interestingly, the width at half height of the peaks is narrower for BLT 0.95 Nb 0.04 compared to pure BLT.
Reference:
Jebli, M., Hamdaoui, N., Smiri, B. et al. Raman spectra, photoluminescence, and low-frequency dielectric properties of Ba 0.97 La 0.02 Ti 1−x Nb 4x/5 O 3 (x = 0.00, 0.05) ceramics at room temperature. J Mater Sci: Mater Electron 31, 15296–15307 (2020). https://doi.org/10.1007/s10854-020-04094-z