ZnGa_2–yAl_yO₄:Mn²⁺,Mn⁴⁺ Thermochromic Phosphors: Valence State Control and Optical Temperature Sensing

Abstract

Dual-emitting and thermochromic manganese ion single doped ZnGa 2−y Al y O 4 phosphors were prepared by solid-state reaction. The regulation of the valence state and the luminescent properties, especially the luminescent thermal stability of manganese ions in ZnGa 2−y Al y O 4 , are discussed in detail. When excited by ultraviolet (UV) light, the emission spectra of ZnGa 2 O 4 :Mn 2+ ,Mn 4+ present an ultranarrow green emission band at 503 nm with a fwhm of 22 nm, which derives from the Mn 2+ ions formed by the self-reduction of doped Mn 4+ , and a red emission band of the Mn 4+ ions at 669 nm. In addition, a ZnGa 2−y Al y O 4 :Mn 2+ ,Mn 4+ solid solution was designed and synthesized by Al 3+ replacing Ga 3+ . The doping of Al 3+ effectively inhibited the degree of Mn 4+ self-reduction to Mn 2+ , thus realizing the regulation of valence state of manganese ions. Interestingly, the thermal stability of luminescence shows that the response of Mn 2+ and Mn 4+ to temperature is obviously different in ZnGa 2−y Al y O 4 , implying the potential of the prepared phosphors as optical thermometers. Subsequently, three kinds of optical thermometers with superior color discrimination and high relative sensitivity (S r ) based on the fluorescence intensity ratio (FIR) technique were realized in 100−475 K. The S r value of ZGO:0.005Mn/ZGA 0.5 O:0.005Mn/ZGAO:0.005Mn phosphors can be as high as 4.345%/4.001%/3.488% K −1 (at 350/325/400 K), reflecting the great potential of ZnGa 2 O 4 :Mn 2+ ,Mn 4+ for optical thermometry applications.

Multiple-Valence and Visible to Near-Infrared Photoluminescence of Manganese in ZnGa2O4: A First-Principles Study

“…The [GaO 6 ] octahedrons connect each other by edge sharing and are vertex-sharing with [ZnO 4 ] tetrahedrons, while [ZnO 4 ] tetrahedrons are isolated from each other by [GaO 6 ] octahedrons. 34 The band structures are calculated by the GGA + U, HSE06, and PBE0(α) methods, which are plotted in Figure S1. The conduction band minimum (CBM) is located at the Γ-point, and the valence band maximum (VBM) is located along the K−Γ line.…”

Efficient red and broadband near‐infrared luminescence in Mn2+/Yb3+‐doped phosphate phosphor

“…The collection methods of X-ray diffraction (XRD) data, Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometer (EDS) elemental mapping images, photoluminescence excitation (PLE), and emission (PL) spectra, decay curves, and the emission spectra at different temperatures are detailed in the previous report. 50 1A, all diffraction peaks of the prepared phosphors can be assigned to Li 3 Sc 2 (PO 4 ) 3 phase, and no diffraction peak of impurity phase was detected, proving the pure phase of the synthesized sample. To obtain more information regarding the crystal structure, the LSPO:0.008Mn 2+ , LSPO:0.02Yb 3+ , and LSPO:0.008Mn 2+ ,0.02Yb 3+ phosphors were refined by Rietveld method.…”

“…The collection methods of X‐ray diffraction (XRD) data, X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy‐dispersive X‐ray spectrometer (EDS) elemental mapping images, photoluminescence excitation (PLE), and emission (PL) spectra, decay curves, and the emission spectra at different temperatures are detailed in the previous report 50,51 …”

Energy transfer-triggered multicolor emissions in Tb3+/Eu3+-coactivated Y2Mo3O12 negative thermal expansion microparticles for dual-channel tunable luminescent thermometers

“…To explore the feasibility of the developed samples for ratiometric thermometry, their thermometric behaviors should be evaluated by studying the temperature-dependent sensitivity (i.e., S a and S r ). Herein, the exact S a and S r values are able to be estimated by utilizing the following functions: 13,17 (9…”

“…12 Based on the diverse thermal quenching behaviors of Mn 2+ and Mn 4+ ions in ZnGa 2-y Al y O 4 , You et al, reported that the studied samples exhibited a high maximum S r values of 4.345% K -1 . 13 Apart from these, this above technique was also employed to investigate the temperature sensing capacity of other compounds, such as LiTaO 3 :Ti 4+ /Eu 3+ (S a = 0.671 K -1 ; S r = 5.425% K -1 ), Lu 3 Al 5 O 12 :Ce 3+ /Mn 4+ (S r = 4.37% K -1 ), SrGdLiTeO 6 :Mn 4+ /Eu 3+ (S r = 4.9% K -1 ), NaLuF 4 :Eu 3+ @g-C 3 N 4 (S a = 0.0057 K -1 ; S r = 0.455% K -1 ), etc. [14][15][16][17] Notably, when the FIR strategy based on dual-emitting centers is adopted, one obtains superior S a and S r values in rare-earth ions coactivated luminescent materials, implying that the adoption of the various thermal responses of dual-emitting centers is an efficient route to achieve high thermometric properties.…”