Up-conversion Luminescence Of Mn⁴⁺ Sensitized By Rare Earth Ions Under 980nm Excitation

Photon up-conversion is an anti-stokes process in which low-energy photons are converted into high-energy photons via two-photon or multi-photon mechanism.Since the up-conversion（UC）light-emitting mechanism has been reported in the1960s,there are growing interests focused on up-conversion luminescent materials due to their potential applications including infrared displays,temperature sensors and solar spectral converter.Lanthanides such as Er³⁺、Tm³⁺、Ho³⁺,etc.are possible to give efficient up-conversion luminescence when they are doped into a suitable host.However,rare earth ions have fixed emission bands and narrow light emission bandwidth,and usually only a few kinds of fixed up-conversion luminescence can be obtained,which limits the application of up-conversion materials in some unconventional wavelength bands.Thus,it is of great significance to explore new up-conversion materials with novel emission bands to meet various application requirements.In view of this situation,Yb³⁺/Er³⁺/Mn⁴⁺triply-doped NaMgGdTeO₆phosphors and Yb³⁺/Ho³⁺/Mn⁴⁺triply-doped SrLaAlO₄phosphors were synthesized by high temperature solid-state method.The luminescent properties and energy transfer mechanism of the above phosphors were studied.The NaMgGdTeO₆:Yb³⁺/Er³⁺/Mn⁴⁺phosphor show an up-conversion emission band（696 nm）attributed to Mn⁴⁺:²E→⁴A₂under 980 nm laser excitation.In the host NaMgGdTeO₆,the up-conversion luminescence properties of the luminescent material at different concentrations and temperatures are studied in detail through concentration control and temperature tests.Moreover,based on the studies of Yb³⁺、Er³⁺and Mn⁴⁺concentration dependent up-conversion spectra,the optimal doping concentrations are determined to be 0.06、0.08 and 0.002.At the same time,based on the Mn⁴⁺dependent Er³⁺:544 nm emission lifetimes and pumping power dependent up-conversion luminescence intensity,the energy transfer mechanism Yb³⁺→Er³⁺→Mn⁴⁺in NaMgGdTeO₆phosphors is proved.In this system,Yb³⁺is used as a sensitizer,and Er³⁺light-emitting center as an energy donor transfer energy to Mn⁴⁺.However,due to the reverse energy transfer Mn⁴⁺→Er³⁺and Mn⁴⁺→Yb³⁺in the host,the up-conversion intensity of Yb³⁺/Er³⁺/Mn⁴⁺triply-doped NaMgGdTeO₆phosphors is not high.Similarly,the Yb³⁺/Ho³⁺/Mn⁴⁺triply-doped SrLaAlO₄phosphors exhibit an up-conversion emission band（716 nm）which attributed to Mn⁴⁺:²E→⁴A₂,and the transitions under 980 nm laser excitation,the connection of the up-conversion spectra of Mn⁴⁺and Ho³⁺ions leads to the broadband red emission.In the experiment,by further adjusting the doping concentration of Yb³⁺、Ho³⁺and Mn⁴⁺,the optimal up-conversion doping concentration are confirmed to be 0.04、0.01 and 0.004.By studying the crystal structure of the sample,the influence of doping concentration on the up-conversion spectra and lifetimes,and pumping power dependent up-conversion luminescence intensity,the energy transfer mechanism between Yb³⁺、Ho³⁺and Mn⁴⁺is discussed.