Energy Transfer Mechanisms and Optical Thermometry of BaMgF₄:Yb³⁺,Er³⁺ Phosphor

Abstract

Motivated from our previous studies on the upconversion properties of BaMgF:Yb,Tb phosphor, here we investigated the upconversion properties of BaMgF:Yb,Er phosphor. We demonstrate a two-way versatile approach for the fine-tuning of emission from green to the red region, by varying the dopant concentration and adjusting the pulse width of an infrared laser. The mechanism involved in tuning the emission color by laser power and pulse width variation was illustrated in detail. The temperature dependent upconversion spectra were studied by analyzing the fluorescence intensity ratio of the thermally coupled levels. The maximum sensitivity obtained is 83.29 × 10 K at 583 K, which is much higher than the temperature sensitivity reported for other fluoride based materials. Moreover, the influence of the excitation power density on the ability of the phosphor for temperature sensing was also investigated. We obtained a maximum (∼415 K) temperature detection at 2563 mW laser power. The obtained results illustrate the potential use of BaMgF:Yb,Er phosphor in an optical thermometer due to its highly sensitive temperature detection ability.

Origin of visible and near IR upconversion in Yb3+-Tm3+-Er3+ doped BaMgF4 phosphor through energy transfer and cross-relaxation processes

“…Based on the obtained results we proposed the use of this phosphor as a solar spectrum convertor in perovskite solar cells [13]. We also showed that the same host doped with Yb 3þ -Er 3þ pair can be used in optical thermometry [14]. The rare-earth ion doped UC phosphors are remarkably efficient in transferring the excited state energy of the sensitizer (Yb 3þ ) to the neighboring activators (Tm 3þ or Er 3þ ) which gives rise to an efficient UC emission by the non-linear anti-stokes process [15].…”

“…Recently, we studied the UC properties of BaMgF 4 doped with Yb 3þ , Tb 3þ13 and Yb 3þ , Er 3þ [14]. In both these phosphors we obtained a characteristic emission of Tb 3þ and Er 3þ .…”

Phase evolution, structure, and up‐/down‐conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho, Er, Tm)

“…10 As no power threshold was observed in the range of this study, the PA mechanism can be neglected. With the energy diagram constructed in Figure 6C, the process of UC luminescence may be described as follows: (1) The Yb 3+ electrons are excited from 2 F 7/2 ground state to 2 , and the other part decays to the 5 F 5 state via nonradiative relaxation (NR; 5 F 4 / 5 S 2 ~ 5 F 5 ), followed by radiative relaxation to the 5 I 8 ground state to generate the ~ 654 nm red emission ( 5 F 5 → 5 I 8 ). The very weak red luminescence ( Figure 6A) may indicate that the probability of 5 F 4 / 5 S 2 ~ 5 F 5 NR is rather low.…”

“…Upconversion (UC) luminescence attracted considerable attention during the past decades and is now being applied in the various fields of optical imaging, temperature sensing, solid state lasers, photodynamic therapy, in vitro/in vivo bioimaging, biological labels, photovoltaics and photocatalysis . Trivalent rare‐earth ions (RE 3+ , except for Ce 3+ ) generally exhibit weak electron‐phonon coupling and sharp f‐f transitions due to the shielding effect of neighboring 5s 2 and 5p 6 subshells .…”

“…Fluoride and oxide are the most frequently used hosts in the UC field, since the former has the advantages of high luminescence efficiency, multicolor tunability and high sensitivity in temperature sensing, while the latter has the superiorities of desirable chemical stability and high feasibility of commercial production via simple synthesis. Among oxides, the garnet‐type compounds have received enormous interest due to their favorable chemical, physical, structural, and optical properties.…”