Cr³⁺‐Doped Sc‐Based Fluoride Enabling Highly Efficient Near Infrared Luminescence: A Case Study of K₂NaScF₆:Cr³⁺

Abstract

The development of highly efficient and thermally stable broadband near‐infrared (NIR) luminescence materials is a great challenge to advance the next‐generation smart NIR light source. Benefitting from the low phonon energy and relatively weak electron phonon coupling effect of the fluoride, K2NaScF6:Cr3+ phosphor is designed and obtained, which demonstrates a full width at half maximum of 100 nm peaking at ≈765 nm. Upon blue light excitation, the phosphor exhibits a high quantum efficiency of 74% and its emission intensity at 150 °C can keep 89.6% of the initial value at 25 °C. An NIR output power of 159.72 mW (input electric power, 1094 mW) with a high photoelectric conversion efficiency of ≈14.60%, light‐emitting diode (LED) device is presented based on this K2NaScF6:Cr3+ phosphor. Furthermore, applying the high‐power NIR phosphor‐converted LED device as lighting source, clear and quick veins imaging and recognition in fingers, palm, wrist, and arm of the human hand are first realized, suggesting K2NaScF6:Cr3+ phosphor has high promise in practical applications.

A General Ammonium Salt Assisted Synthesis Strategy for Cr3+‐Doped Hexafluorides with Highly Efficient Near Infrared Emissions

“…The IQE value of this phosphor is much higher than that of the previously reported hexafluoride phosphors Cs 2 NaAlF 6 :Cr 3+ (≈70%), [ 38 ] Na 3 AlF 6 :Cr 3+ (75%), [ 39 ] and K 2 NaScF 6 :Cr 3+ (74%). [ 43 ] Although this IQE value is somewhat lower than that of the oxide phosphor Gd 3 Sc 2 Ga 3 O 12 :0.01Cr 3+ ,0.5Al 3+ (98.6%), [ 31 ] and Ca 3 ScSi 3 O 12 :0.06Cr 3+ (92.3%), [ 32 ] the EQE value of Na 3 ScF 6 :35.96%Cr 3+ is much higher than theirs (EQE ≈ 23%/25.5%). The relatively high AE value (44.61%) of Na 3 ScF 6 :35.96% Cr 3+ is mainly ascribed to the high optimal Cr 3+ concentration (35.96%) in this phosphor.…”

“…Although the use of Cr 3+ ‐doped hexafluoride materials for lasers or LEDs has been reported in previous studies, their IQE values have not exceed 80%. [ 38–43 ] Moreover, it is difficult to synthesize these phosphors through a universal and convenient strategy owing to the complex chemical reaction processes in the solution. Herein, pre‐synthesized (NH 4 ) 3 ScF 6 ((NH 4 ) 3 CrF 6 ) is used to replace the ionic Sc 3+ (Cr 3+ ) source, thereby increasing the doping efficiency of activator Cr 3+ into the host lattice Na 3 ScF 6 , as well as effectively preventing the appearance of extra phases.…”

Cr3+ Activated Garnet Phosphor with Efficient Blue to Far‐Red Conversion for pc‐LED

“…Thus, numerous studies have been conducted to develop efficient FR phosphors and pc‐LEDs in recent three years. [ 6–26 ]…”

The hydrothermally synthesis of K3AlF6:Cr3+ NIR phosphor and its performance optimization based on phase control

“…It is noted that fluoride substrates can also provide a suitable coordination environment for Cr 3+ , which has a simple preparation process and a low sintering temperature. [40][41][42] For instance, K 3 AlF 6 :Cr 3+ (KAF:Cr 3+ ) phosphors show a broadband NIR emission from 650 to 900 nm and can be obtained by a coprecipitation method. 43 However, the internal quantum efficiency (IQE: ~25%) of KAF:Cr 3+ in pc-NIR-LED device is still need to be improved.…”

“…The synthesis of these phosphors requires calcination at a temperature of 800‐1600°C, which results in high production costs. It is noted that fluoride substrates can also provide a suitable coordination environment for Cr 3+ , which has a simple preparation process and a low sintering temperature 40‐42 . For instance, K 3 AlF 6 :Cr 3+ (KAF:Cr 3+ ) phosphors show a broadband NIR emission from 650 to 900 nm and can be obtained by a coprecipitation method 43 .…”