Effect of Cr3+ occupying an extremely weak crystal field on down-conversion of β-PbF2:Er3+/Yb3+/Cr3+ glass–ceramic composites

The influence of Cr³⁺ on the down-conversion luminescence (DCL) of β-PbF₂:Er³⁺/Yb³⁺/Cr³⁺ glass–ceramic composites was studied. Under the excitation of a 378 nm xenon lamp, β-PbF₂:Er³⁺/Yb³⁺/Cr³⁺ glass–ceramic composites exhibit bright DCL with a spectral width ranging from 480 nm to 720 nm, which is reported for the first time. As the doping concentration of Cr³⁺ ions increases, emission intensity with a spectral width ranging from 480 nm to 620 nm also continues to increase, resulting in CIE chromaticity coordinates of β-PbF₂:Er³⁺/Yb³⁺/Cr³⁺ glass–ceramic composites changing from near single red to yellow-green. The broad spectrum from 480 nm to 620 nm originating from radiative transition from ⁴T₁, ²T₁, and ²E to ⁴A₂ energy states of Cr³⁺ ions has been reported for the first time. Cr³⁺ ions enter the F⁻ ions sublattice via interstitial doping and soccupy an extremely weak octahedral crystal field, and the energy state of Cr³⁺ in β-PbF₂ is determined. By combining the energy state structures and DCL spectra of Cr³⁺ and Er³⁺, the DCL process of β-PbF₂:Er³⁺/Yb³⁺/Cr³⁺ glass–ceramic composites and the energy transfer process between Cr³⁺ and Er³⁺ ions are also clarified. The β-PbF₂:Er³⁺/Yb³⁺/Cr³⁺ glass–ceramic composites with a wide range of adjustable colors of DCL presents potential applications in the fields of full spectrum lighting and display.