Engineering cation vacancies to improve the luminescence properties of Ca₁₄Al₁₀Zn₆O₃₅: Mn⁴⁺ phosphors for LED plant lamp

Abstract

In the recent years, Mn4+‐doped phosphors for indoor plant cultivation have received extensive concern owing to the far‐red emission that can match well with the absorption spectra of plant pigments. Whereas, many Mn4+‐doped phosphors still face some challenges such as poor light efficiency and low thermal stability. It is an effective way to resolve these problems via cation vacancies engineering. Herein, the Ca14−xAl10Zn6−yO35: Mn4+ phosphors are successfully synthesized by combustion method. The luminescence intensity of Ca14−xAl10Zn6−yO35: Mn4+ phosphor is enhanced through engineering Ca2+ and Zn2+ vacancies according to the charge compensation mechanism. The optimal content of each Ca2+ and Zn2+ vacancy is equal to be 0.3. Furthermore, the defect formation is accompanied with lattice distortion, which plays a vital role in driving the excited phonon traps to reduce the energy loss by non‐radiation transitions. Therefore, the thermal stability of Ca14−xAl10Zn6−yO35: Mn4+ phosphor is also improved via engineering cation vacancies. In addition, the Ca14−xAl10Zn6−yO35: Mn4+ phosphors can be effectively excited by blue light and it exhibits far‐red emission due to the Mn4+ spin‐forbidden 2E → 4A2 transition. The results suggest that the Ca14−xAl10Zn6−yO35: Mn4+ phosphors can have a tremendous potential in indoor plant cultivation.

Fundamental luminescence properties of Mn4+ activated Ca14Al10Zn6O35 phosphor

“…Note that the activation energy DE 1 is equal to that obtained from the temperature-dependent emission intensity by eqn (14), while the smaller activation energy DE 2 is equal to hv 4 . In comparison, eqn (18) shows the best fit to the fluorescence lifetimes, and the fitting yields t 0 = 6.39 ms, tn R = 7.09 Â 10 À7 ms, hv = 0.0365 eV (B295 cm À1 ; hv 6 o hv o hv 4 ) and DE = 0.79 eV. The values of both DE 2 in eqn (15) and hv in eqn (18) are of the same order of magnitude as the lattice vibration energy, and thus can be regarded as a reflection of the contribution from vibration.…”

“…In comparison, eqn (18) shows the best fit to the fluorescence lifetimes, and the fitting yields t 0 = 6.39 ms, tn R = 7.09 Â 10 À7 ms, hv = 0.0365 eV (B295 cm À1 ; hv 6 o hv o hv 4 ) and DE = 0.79 eV. The values of both DE 2 in eqn (15) and hv in eqn (18) are of the same order of magnitude as the lattice vibration energy, and thus can be regarded as a reflection of the contribution from vibration. It is found that the two curves fitted by eqn ( 17) and ( 18) are perfectly coincident below 420 K, which indicates the absolute dominance of the radiation transition.…”

“…16 In addition to the traditional solid-state reaction method, Sol-gel, combustion, and hydrothermal methods have been proposed to enhance the absorption of NUV/blue light and the emission of deep-red light. [17][18][19] (ii) Composition modifications, including isovalent cation substitution (e.g., Ca by Sr, Al by Ga, and Zn by Mg), aliovalent co-doping (e.g., equimolar Mn 4+ and Mg 2+ /Zn 2+ in Al 3+ /Ga 3+ sites, Li + /Na + /K + in Ca 2+ sites while Mn 4+ /Ge 4+ in Al 3+ /Ga 3+ sites, and so on), insufficient Ca 2+ /Zn 2+ or excess Al 3+ on the phase component. 18,[20][21][22][23][24][25][26][27] These strategies can reduce crystal defects, improve crystallinity, or maintain charge neutralization (to stabilize Mn 4+ ), and thereby improve the photoluminescence performances.…”

“…[17][18][19] (ii) Composition modifications, including isovalent cation substitution (e.g., Ca by Sr, Al by Ga, and Zn by Mg), aliovalent co-doping (e.g., equimolar Mn 4+ and Mg 2+ /Zn 2+ in Al 3+ /Ga 3+ sites, Li + /Na + /K + in Ca 2+ sites while Mn 4+ /Ge 4+ in Al 3+ /Ga 3+ sites, and so on), insufficient Ca 2+ /Zn 2+ or excess Al 3+ on the phase component. 18,[20][21][22][23][24][25][26][27] These strategies can reduce crystal defects, improve crystallinity, or maintain charge neutralization (to stabilize Mn 4+ ), and thereby improve the photoluminescence performances. For example, the partial substitution of Ca by Sr in Ca 14 Al 10 Zn 6 O 35 :Mn 4+ leads not only to an increase in emission intensity (by B53%) and QY (from 78% to 83%), but also to a low thermal quenching effect (the emission intensity remains at 98% @ 425 K and 92% @ 500 K relative to that at 300 K) superior to that of the commercial (Sr,Ca)AlSiN 3 :Eu 2+ red phosphors (B93% @ 425 K and 81% @ 500 K of the initial emission intensity at 300 K).…”

“…Despite the extensive research on improving the luminescent properties of CAZO:Mn 4+ and developing its analogues, its fundamental luminescent properties, such as the energy levels (ZPL excitation and emission energy), lattice vibration behavior, and luminescence quenching mechanism, have received little attention, and even the location of the R-line (ZPL emission energy) still remains a dispute. 4,17,18,20,21,24,26,37 The clarification of these inherent characteristics is of great importance for further improving the photoluminescence performances of Mn 4+ -activated CAZO-based phosphors. Therefore, in this work, we fabricated a series of high-quality CAZO:Mn 4+ phosphors and conducted a systematic study on their fundamentals of luminescence.…”