Beyond single-ion doping: K+–Bi3+ synergy enables crop-tailored blue luminescence through crystal field engineering

Abstract

In the pursuit of sustainable and efficient indoor agriculture, the development of advanced lighting technologies tailored to plant growth needs has become imperative. Conventional blue/near-UV LEDs with Eu²⁺/Ce³⁺ phosphors exhibit narrow emission, mismatching broad chlorophyll absorption in the 380–500 nm range and causing low light efficiency. Bi³⁺ phosphors offer broad emission and large Stokes shifts for reduced reabsorption; yet, their excessive bandwidth and poor thermal stability limit their utility. This study introduces an advancement in agricultural lighting technology through the development of a novel Cs₂MgSi₅O₁₂:Bi³⁺ blue-emitting phosphor, precisely regulated via K⁺ ion incorporation. The proposed material exhibits a broad emission band (FWHM = 95 nm) and a large Stokes shift (∼11 550 cm⁻¹), effectively mitigating spectral reabsorption while matching the wide absorption range of the photosynthetic pigment. The introduction of K⁺ ions not only enhances the thermal stability of the phosphor, achieving a thermal activation energy (ΔE) of 0.277 eV, but also enables the continuous tuning of the photoluminescence (PL) peak position between 380 and 405 nm by adjusting K⁺ doping concentrations. This dual modulation approach, combining Bi³⁺ doping with K⁺ regulation, demonstrates exceptional control over the luminescence properties, making the phosphor a promising and adaptable candidate for plant growth lighting requirements. Importantly, when encapsulated in LEDs, this phosphor significantly enhances the phenotypic characteristics of Brassica rapa var. pekinensis, underscoring its immense potential to advance indoor agricultural lighting systems.