One Phosphor, Many Possibilities: A Nonlanthanoid Host for Optical Thermometry, Plasmon-Enhanced Upconversion Luminescence, and Stable Photoswitching Performance

Engineering a single phosphor for multiple objectives is challenging and essential for innovative technology, enriching productivity and flexibility, lowering cost, minimizing power intake, etc. In this study, a Yb3+,Er3+-activated NaBiF4 nanophosphor synthesized via a thermolysis approach provided significant opportunity to explore the potential of single phosphor in diverse fields including contactless thermometry, plasmon-enhanced upconversion luminescence (UCL), solid-state lighting, and photoswitching probes. The phosphor has been characterized using several standard techniques to unveil the phase, crystal structure, associated functional groups, morphology, crystalline nature, and optical properties. A 5-fold enhancement in UCL intensity was observed from Yb3+,Er3+:NaBiF4@SiO2@Ag. Upconversion luminescence thermometry of Yb3+,Er3+:NaBiF4 based on thermally coupled energy levels (TCELs) 2H11/2 and 4S3/2 was studied via the fluorescence intensity ratio (FIR) technique. Thermometric parameters based on the ratio of Er3+ transitions (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2) results in ln I520/I540 = 3.88–1086.83/T and ΔE∼ 755.34 cm–1. Results revealed ΔT = 0.4 K at 297 K, and maximum relative sensitivity (Sr) and absolute sensitivity (Sa) values are 1.23% K–1 (at 297K) and 0.173% K–1 (at 397K), respectively. The energy transfer and thermal quenching process were demonstrated mechanistically. The Commission Internationale de l’Éclairage (CIE) chromaticity diagram confirms the suitability of this material as a green light emitter. The unprecedented photostability and photoswitching behavior has been addressed by a photoelectrochemical cell experiment under light and dark conditions. Results suggest that Yb3+,Er3+-activated NaBiF4 is the most promising high-quality luminescent nanophosphor, reflecting the realm of scientific evolution and providing applications in luminescent thermometers, plasmon-enhanced UC luminescence, solid-state lighting, and fast switching photodetectors.