Small Stokes Shift and Two‐Site Occupation in the ANb₂O₆:Cr³⁺ (A = Zn/Mg) Phosphors Toward Highly Efficient Ultra‐Broadband Near‐Infrared Emission for Multifunctional Applications

Abstract

The development of the new generation of smart near infrared (NIR) light sources is a problem demanding prompt solution with the increasing role of NIR spectroscopy in security, food, medical treatment, agriculture, and other fields. In this work, Cr3+ doped ANb2O6 (A = Zn/Mg) phosphors are successfully developed, which generate a NIR emission with a peak at 930 nm covering 750–1300 nm under excitation of 515 nm light. Thanks to the small Stokes shift, the internal quantum efficiency (IQE) values of the optimal samples of ZnNb2O6:Cr3+ and MgNb2O6:Cr3+ reach up to 70% and 62%, respectively. This ultra‐broadband NIR emission originates from the simultaneous occupation of [AO6] and [NbO6] octahedrons by Cr3+, which is confirmed by the excitation wavelength‐dependent emission spectra, low‐temperature photoluminescence spectra (77 K), time‐resolved photoluminescence (TRPL) spectra, and density functional theory (DFT) calculation. The thermal quenching mechanism of ANb2O6:Cr3+ (A = Zn/Mg) is revealed from the aspects of thermal cross and thermal ionization. Benefiting from the excellent performance of ANb2O6:Cr3+ (A = Zn/Mg) NIR phosphors, the combination of 520 nm LED chips, and as‐prepared phosphors demonstrate the dramatic potential applications in night vision, non‐destructive testing, biological tissue imaging, and spectral analysis.

Blue light-excited broadband NIR-II-emitting Li2ZnSn3O8:Cr3+,Ni2+ phosphor for multifunctional optical applications

“…The decay curve of Cr 3+ can be fitted using the double exponential function: 7,42 I = I 0 + A 1 exp(− t / τ 1 ) + A 2 exp(− t / τ 2 )where I and I 0 belong to the PL intensities at times t and t = 0, respectively, t is time, A 1 and A 2 are corresponding fitting constants, τ 1 and τ 2 represent two different lifetimes of the exponential components. The following equations are used to estimate the average lifetime ( τ* ) and ET efficiency ( η ′ ET ): 6,43 where τ Cr,Ni and τ Cr represent the decay times of Cr 3+ with and without Ni 2+ , respectively. Typically, two different lifetimes are observed.…”

“…FIR is based on the integral intensity of each emission peak, which denotes the ratio of luminescence intensities between two different emission wavelengths under the same excitation wavelength. 43,48 To study the temperature sensing performance, the following equation can represent the relationship between FIR ( I 959 nm / I 1465 nm ) and temperature: 31 …”