Multifunctional Ca9Na 1-y Li y Y2/3(PO4)7-Based Phosphors: Li+/Na+ Substitution-Regulated Site-Related Eu2+ Emission and Eu2+→Mn2+ Energy Transfer

Abstract Activator-ion coordination in multisite inorganic hosts is key to luminescence modulation and multifunctional integration. However, most phosphor studies address limited functions, and single-host multiscenario platforms remain scarce. Herein, we report a β-Ca3(PO4)2-type Ca9NaY2/3(PO4)7-based single-host phosphor platform for anticounterfeiting, ratiometric optical thermometry, white-light-emitting diodes (WLEDs), and plant-growth LEDs. Based on excitation-dependent spectroscopy, wavenumber-domain Gaussian deconvolution, time-resolved photoluminescence (PL) measurements, and crystal-chemical analysis, the high-, intermediate-, and low-energy Eu2+ emission components are associated with Ca3-related, Ca1/Ca2-related, and Na-related low-coordination environments, respectively. We constructed Ca9Na1-yLiyY2/3(PO4)7:0.02Eu2+ to elucidate how isovalent Li+/Na+ substitution modulates multisite Eu2+ emission contributions via local polyhedral rearrangement; Ca9Na0.2Li0.8Y2/3(PO4)7 (CNLYP) was selected as the host. Mn2+ incorporation enabled Eu2+→Mn2+ nonradiative energy transfer, sensitizing 660 nm red emission with maximum efficiencies of 75.78% and 74.33%. Accordingly, the CNLYP platform was extended to anticounterfeiting and thermometry (Sr,max = 1.34% K–1), single-phosphor WLEDs with a color rendering index (CRI) of 81.8 and a correlated color temperature (CCT) of 5968 K, and plant-growth LEDs with spectral similarity ratios of 87.17% and 91.36% for chlorophyll a and b. This work proposes a phosphate phosphor design strategy coupling local polyhedral rearrangement with energy transfer to regulate multisite luminescent centers for single-host, multiscenario applications.