Dipankar Das Sarma

Mn ²⁺ doping in hybrid perovskite‐derived two‐dimensional (2D) lead bromide systems exhibits efficient Mn ²⁺ emission and enhanced environmental stability compared to their 3D analogue perovskites. Here, we investigate the sensitization of Mn ²⁺ emission in doped 2D BA ₂ PbBr ₄ (BA = butylammonium) through comprehensive temperature‐dependent PL analyses. We establish a near‐resonant energy transfer from the host excitonic state to the higher‐lying Mn ²⁺ multiplet ( ⁴ T _2g (D)), followed by successive multiphonon‐assisted de‐excitations through the intermediate multiplets of Mn ²⁺ between the originally populated ⁴ T _2g (D) and the first excited multiplet, ⁴ T _1g (G) state. Infrared (IR) spectroscopy identifies the highest‐energy phonon mode at 59.2 meV in BA ₂ PbBr ₄ , more than twice that of the previously analyzed 3D perovskite CsPbCl ₃ nanocrystals, pointing to a significantly more efficient multiphonon relaxation and suppressed phonon bottleneck effects in the 2D case, explaining the efficient Mn ²⁺ emission observed even at low temperatures. The contrasting behaviors are further accentuated by the significantly higher exciton binding energy in the 2D case compared to the 3D ones. We derive temperature‐dependent rate equations to quantitatively explain host‐to‐dopant energy‐transfer dynamics, identifying the role of dark excitonic states in near‐resonant energy‐transfer and back‐transfer processes, establishing a comprehensive understanding of Mn ²⁺ emission in such 2D hybrid lead bromide systems.

Two-dimensional (2D) hybrid lead halide systems have emerged as promising materials for optoelectronic applications due to their remarkable optical properties and enhanced moisture stability. However, photoluminescence (PL) from such 2D samples has been reported to vary substantially across different sample forms and experimental geometries, and the associated recombination dynamics are often inconsistently interpreted in the literature. The incorporation of Mn2+ dopant ions into these 2D systems further complicates the picture by introducing host-to-dopant energy-transfer pathways, highlighting the need for a mechanistic understanding of PL in these materials. Here, we use 2D BA2PbBr4 (BA = butylammonium) as a model system to address these questions by systematically comparing the undoped and Mn2+-doped samples in diverse forms, namely crystals, films, and pellets, through comprehensive spatially resolved, time-resolved, and temperature-dependent PL analyses, together with DFT calculations. Spatial resolution allows us to confirm that the high-energy emission corresponds to interior excitonic recombination, while the secondary low-energy emission arises from edge-related states amplified by waveguiding. The variation in edge-related emission intensity across different samples in a given geometry reflects differences in the amount of edge-related sites present in the volume sampled by the experiment; on the other hand, the dependence on PL collection geometries in a given sample arises from the variations in the fraction of excitonic emission that is waveguided in-plane to the edges prior to detection, thereby preferentially favoring the excitation of edge-related states. These observations resolve the long-standing ambiguity regarding the wide variations in emission spectra reported across different sample forms and measurement geometries. We further show that both interior excitonic and edge-related states transfer energy to the Mn2+ ion, and that variations in host emission across different sample forms do not influence the intrinsic Mn2+ energy-transfer pathways. Finally, we explore the potential of these materials in light-emitting applications.

What qualifies as transformative materials research? In this Viewpoint, we use “transformative” to denote work that forces revision of underlying assumptions, enables generalization across systems, or reveals regimes inaccessible to existing frameworks. The term is widely invoked yet rarely defined with disciplinary precision. Perspectives spanning nanomaterials chemistry, catalysis, soft and bioinspired interfaces, and functional materials suggest that transformation occurs when new reaction mechanisms are uncovered, when structure–property relationships are redefined, and when operation under realistic chemical environments reveals fundamentally new governing mechanisms. Foundational insight, developmental refinement, and industrial realization constitute an interdependent value chain through which transformative discoveries mature into societal impact. Mistaking progress within a single component for a fundamental shift risks blurring the line between incremental refinement and genuine conceptual change. Transformation requires a conceptual discontinuity in at least one stage of this value chain, most commonly through foundational scientific insight, while the remaining stages enable its realization and broader impact. This Viewpoint argues that transformative materials research is defined less by topic than by intellectual pursuit, chemical and structural rigor, and sustained engagement with unexpected observations during mechanism discovery and eventual validation under realistic chemical environments and at scale.

Lead-free metal halide luminophores offer alternatives to toxic lead-based perovskites, yet octahedral [SbCl6]3– antimony(III) systems suffer rapid moisture-induced degradation within hours despite high photoluminescence quantum yields, limiting practical implementation. (BTMA)2(TMA)SbCl6 (BtTmSbCl), a zero-dimensional hybrid synthesized via solvent-free thermal reaction at 433 K, incorporates benzyltrimethylammonium (BTMA+) and in situ–generated trimethylammonium (TMA+) cations, forming a hydrogen-bonding network that stabilizes isolated [SbCl6]3– octahedra. The material exhibits 95% photoluminescence quantum yield with greenish-yellow emission at 565 nm, matching peak human photopic sensitivity. BtTmSbCl retains ∼95% initial PLQY after 30 days ambient air exposure and maintains stability under continuous UV irradiation, thermal stress, and organic solvents. Self-trapped exciton emission with a large Stokes shift (222 nm), a Huang–Rhys factor of 9.14, and 2.59 μs lifetime enables white LED performance (CRI 82, CCT 5171 K) and applications in security inks, fingerprint detection, and flexible electronics. This work demonstrates design principles for environmentally stable [SbCl6]3– luminophores through synthetic control of hydrogen-bonding architectures.

Yb ³⁺ ‐doped CsPbCl ₃ nanocrystals exhibit an exceptionally efficient quantum‐cutting, converting single UV photons into a pair of near‐infrared photons with a photoluminescence quantum yield approaching 200%, offering broad opportunities for optoelectronic and photonic applications. Recent studies highlighted the importance of Yb ³⁺ ‐induced defect states in mediating energy transfer from the host to Yb ³⁺ multiplets. However, the persistent observation of thermally activated Yb ³⁺ emission even when the defect‐state energy lies well above the threshold for quantum‐cutting remains intriguing and unresolved. Based on temperature‐dependent emission measurements, we establish that the thermal activation of Yb ³⁺ emission is universal and introduce temperature‐dependent rate equations that quantitatively reproduce all experimental observations. The detailed analyses demonstrate that the observed thermal activation is the combined effect of the thermally activated defect state population and the presence of 15 phonon‐assisted multiphonon processes, presenting a phonon bottleneck at low temperatures, and thereby suppressing the dissipation of excess energy to lattice phonons. Furthermore, photon‐correlation analyses, performed here for the first time to probe the quantum nature of the Yb ³⁺ emission in CsPbCl ₃ nanocrystals, unambiguously establish the decoherence of the emitted photons due to the large time separations between the cooperative excitation of Yb ³⁺ ions (∼ns) and their long‐lived emission (∼2.7 ms).

Corrigendum to the article by Hegde et al. [(2025). J. Synchrotron Rad. 32 , 757–765].

The integration of inorganic materials in perovskite solar cells (PSCs) is critical for enhancing long‐term operational stability, scalability, and economic viability. Here, we demonstrate the transformational efficacy of using a modified protocol for sputtered nickel oxide as a hole transport layer (HTL) in n–i–p structured PSCs, in conjunction with a thin Spiro‐OMeTAD buffer layer. The introduction of a biased grid and a buffer interface enable us to achieve a soft landing of NiO on the halide perovskite, thereby minimizing process‐induced interfacial damage. Our results indicate that the buffer layer serves solely as an interfacial protection layer, rather than as a functional HTL. Using this approach, we report champion power conversion efficiencies of 23.45% (mean ≈22.2%) on rigid glass substrates and 22.1% (mean ≈21%) on flexible ITO‐coated PET substrates, both employing fully inorganic charge transport layers. These results represent unprecedented enhancements over previously reported highest PCE values (<12%) for n‐i‐p devices using sputtered NiO as the HTL, placing them on par with p‐i‐n architectures that utilize a combination of NiO and organic HTLs. This work demonstrates a scalable, commercially viable pathway toward high‐efficiency, stable perovskite photovoltaics based solely on sputtered inorganic layers, offering a competitive edge for further development.