Although luminescence spectroscopy has been a promising sensing technology with widespread applications in point-of-care diagnostics and chem-bio detection, it fundamentally suffers from low signal collection efficiency, considerable background noise, poor photostability, and intrinsic omnidirectional emission properties. In this regard, surface plasmon-coupled emission, a versatile plasmon-enhanced detection platform with >50% signal collection efficiency, high directionality, and polarization has previously been explored to amplify the limit of detection of desired analytes. However, high Ohmic loss in metal-dependent plasmonic platforms has remained an inevitable challenge. Here, we develop a hybrid nanocavity interface on a template-free and loss-less photonic crystal-coupled emission (PCCE) platform by the quintessential integration of high refractive index dielectric Nd2O3 “Huygens sources” and sharp-edged silver nanoprisms (NPrs). While efficient forward light scattering characteristics of Nd2O3 nanorods (NRs) present 460-fold emission enhancements in PCCE, the tunable localized plasmon resonances of NPrs display high electromagnetic field confinement at sharp nanotips and protrusions, boosting the enhancements 947-fold. The judicious use of silver NPr (AgNPr) metal-Nd2O3 dielectric hybrid resonances in conjugation with surface-trapped Bloch surface waves of the one-dimensional photonic crystal (1DPhC) displayed unprecedented >1300-fold enhancements. The experimental results are validated by excellent correlations with numerical calculations. The multifold hotspots generated by zero and nonzero nanogaps between the coassembly of NPrs, NRs, and 1DPhCs are used for (i) determination of hyper and hypothyroidism levels through monitoring the concentration of iodide (I–) ions and (ii) single-molecule detection (zeptomolar) of the stress hormone, cortisol, through the synthesized cortisol-rhodamine B conjugate obtained using a simple esterification reaction.

A variety of materials such as low dimensional carbon substrates (1D, 2D, and 3D), nanoprisms, nanocubes, proteins, ceramics, and DNA to name a few, have been explored in surface plasmon-coupled emission (SPCE) platform. While these offer new physicochemical insights, investigations have been limited to silver as primary plasmonic material. Although, gold nanoparticles (AuNPs) exhibit robust performance, its intrinsic property to quench the emission from radiating dipoles (at distances < 5 nm) has impeded its utility. Despite the use of metal-dielectric resonances (with Au decorated SiO2 NPs) and sharp nanotips (from Au nanostars) for dequenching the emission, the enhancements obtained has been less than 200-fold in SPCE platform. To address these long-standing challenges, we demonstrate the utility of gold soret colloids (AuSCs) and photonic crystal-coupled emission (PCCE) platform. The soret nano-assemblies synthesized using adiabatic cooling technique presented integrated hotspots when taken with high refractive index Nd2O3 ‘Huygens sources’. The collective and coherent coupling between localized Mie and delocalized Bragg plasmons (of sorets), dielectric plasmons (of Nd2O3), highly confined and intense Bloch surface waves (of PCCE platform) aided in realization of dequenched, as well as amplified > 1500-fold enhancements at the photoplasmonic nanocavity interface, presenting new opportunities for multidisciplinary applications.

The intrinsically lossy nature of plasmonic-based detection platforms necessitates the use of alternative nanophotonic platforms such as one-dimensional photonic crystals (1DPhCs) to exploit properties pertaining to photonic stop band (PSB), Bloch surface waves (BSWs), microcavity, and band-edge modes. We present a highly desirable confinement of internal optical modes (IOMs) and large surface electromagnetic (EM) field due to BSWs on a plasmon-free, metal template-free, photonic crystal-coupled emission (PCCE) platform ensuing 44-fold emission enhancements of the, otherwise, omnidirectionally emitting radiating dipoles. The effect of dielectric thickness in the PCCE platform has also been explored, and the optimized thicknesses for enhanced coupling of both BSWs and IOMs with the radiating dipoles have been obtained. Cavity engineering involving quantum emitters sandwiched in hot spots between 1DPhCs and Ag nanoparticles (AgNPs) has delivered ∼200-fold emission enhancements on account of the improved local density of states (LDOS) via exceptional EM field trapping by BSWs, IOMs, and localized surface plasmon resonance (LSPR) of plasmonic nanoparticles. Experimental results that are in strong agreement with the numerically calculated data validate this augmentation in enhancements due to the amplified coupling between the radiating dipoles and modes supported by 1DPhCs. Moreover, the tightly entrapped optical energy within the hot spots between AgNPs and 1DPhCs was adopted for sensing environmentally hazardous Al 3+ ions at a 0.21 parts per quadrillion (ppq) limit of detection in drinking water samples with reliable and reproducible results, opening new avenues for investigating distinctive photonic crystal nanoarchitectures as a robust, practical, and user-friendly technology for multiplexed diagnostic fluorescence assays.

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Rare earth (RE)-doped silica-based optical fibers with transparent glass ceramic (TGC) core was fabricated through the well-known modified chemical vapor deposition (MCVD) process without going through the commonly used stage of postceramming. The main characteristics of the RE-doped oxide nanoparticles namely, their density and mean diameter in the fibers are dictated by the concentration of alkaline-earth element used as phase-separating agent. Magnesium and erbium co-doped fibers were fabricated. Optical transmission in term of loss due to scattering as well as some spectroscopic characteristics of the erbium ions was studied. For low Mg content, nano-scale particles could be grown with and relatively low scattering losses were obtained, whereas large Mg-content causes the growth of larger particles resulting in much higher loss. However, in the latter case, certain interesting alteration of the spectroscopic properties of the erbium ions were observed. These initial studies should be useful in incorporating new doped materials to realize active optical fibers for constructing lasers and amplifiers.