Exploring the luminescence and photometric behavior of green emitting NUV excited Er3+ doped Ca9Y(PO4)7 nanophosphor: A promising material for solid-state illumination applications

Abstract

The unparalleled ability of nanosized rare-earth activated phosphors stimulated by near ultraviolet (nUV) light to provide efficient visible emission has garnered huge interest as excellent sources for next-generation solid-state illumination devices. Herein, we have proposed bright green emitting Er³⁺ doped Ca₉Y(PO₄)₇ nanomaterials for application prospects in optoelectronic technology owing to its magnificent down-conversion luminescence. The phase purity and structure, surface morphology, photophysical features (e.g., excitation and emission spectra, concentration quenching, decay curves, optical energy band gap etc.) of Ca₉Y(PO₄)₇: Er³⁺ nanophosphors were investigated systematically. Phase purity and space group (trigonal with R3c(161)) of synthesized nanophosphors Ca₉Y(PO₄)₇: Er³⁺ were confirmed by high quality powder X-ray diffraction data. The scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) images have been captured to examine surface characteristics and crystallite dimensions of Ca₉Y(PO₄)₇: Er³⁺ nanoparticles. Constituent elements of phosphors were determined by EDAX spectroscopy to depict high purity. Ca₉Y(PO₄)₇: Er³⁺ nanophosphors perform bright green emission under NUV excitation of 381 nm. The greenish light emitted at 564 nm is attributed to the transition ⁴S_3/2 → ⁴I_15/2 of Er³⁺ ions. The optimal activator concentration is 10 mol %, beyond which concentration quenching attributed to electric multipolar interactions was observed as studied via Dexter's and Van-Uitert's theoretical model. The conducting performance of the Ca₉Y(PO₄)₇: Er³⁺ nanophosphors is authenticated by their optical energy gap calculation using Kubleka-Munk and Tauc's hypothesis which falls in wide band-gap semiconductor regime. Decay curve and photoluminescent lifespan analysis using Auzel's model established high quantum efficiency of synthesized nanophosphors. The photometric features like CIE color coordinates, CCT suggested the exceptional potential of Ca₉Y(PO₄)₇: Er³⁺ nanophosphors for use as a bright green emitting segment in NUV based cool pc-WLEDs. Such NPs have interesting applications in emerging optoelectronic devices, hence rendering them of profound utility in the near future as promising contenders for near-ultraviolet (NUV) chip-based WLEDs and solid-state lighting surpassing the commercially available traditional light sources.