Visible to near-infrared emissions of Bi₂Mo₂O₉: Pr³⁺ multifunctional phosphors for multi-mode temperature sensing, white LEDs and bioimaging

Research on multifunctional luminous materials has garnered a lot of interest in the fields of optical sensing, biological imaging, white light-emitting diodes illumination, etc. A novel multifunctional phosphor of Pr³⁺-doped Bi₂Mo₂O₉ (BMO: Pr), created via the solid-state method, was investigated in this work. X-ray diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectra, and fluorescence decay curves were employed to analyze the produced phosphors. Typical Pr³⁺ characteristic emissions, such as red and near-infrared (NIR), were found under 450 nm excitation. With the temperature increase, the intensity of different emissions changes significantly and exhibits various change trends. In the temperature range of 303-483 K, a multi-mode temperature sensing measurement of BMO: Pr phosphor was performed via three different temperature sensing modes: thermally coupled energy levels of ³P₀/³P₁, non-thermally coupled energy levels of ¹D₂/³P₀, ³P₁, and fluorescence lifetime. The corresponding maximum relative sensitivities were 1.01 %K^-1 at 303 K, 0.92 %K^-1 at 303 K, and 2.73 %K^-1 at 483 K, respectively. Subsequently, a prototype white LED was assembled by integrating the commercial YAG: Ce and BMO: Pr red phosphors and a 460 nm blue LED chip. The calculated color coordinates, related color temperature, and color rendering index were (0.33, 0.33), 5373 K, and 87, respectively. In addition, biological tissue penetration experiments were conducted to discuss the possible use of NIR emission from BMO: Pr phosphor in biological imaging. All the results indicated that the BMO: Pr phosphors are promising for the fields of multi-mode optical temperature detection, white LED, and bioimaging.