Stark sublevels in Tm³⁺–Yb³⁺ codoped Na₂Y₂B₂O₇ nanophosphor for multifunctional applications

Abstract

Phase and crystal structure of the Na 2 Y 2 B 2 O 7 :Tm 3+ -Yb 3+ inorganic phosphor prepared by solution combustion method has been identified by powder X-ray diffraction technique.Surface morphology and particle size has been examined by using the field emission scanning electron microscopy and high resolution transmission electron microscopy characterizations of the prepared materials. No absorption band around 980 nm has been observed in the Tm 3+ doped phosphors, whereas a broad band around 980 nm in the Tm 3+ -Yb 3+ codoped phosphors corresponding to the 2 F 7/2 ← 2 F 5/2 absorption transition of Yb 3+ ion has been detected. The upconversion emission bands have been observed in the UV, visible and NIR regions upon excitation with 980nm laser diode. The temperature sensing behaviour and the concept of nanoheater in the developed nanophosphor has been demonstrated by using the stark sublevels of the 1 G 4 level of Tm 3+ ion, which is responsible for the blue upconversion emission. The maximum sensor sensitivity of about 4.54×10 -3 K -1 at 300 K for the developed multifunctional nanophosphor has been determined. The temperature gain of about ~435 K has been observed at laser power density of 66.88 W/cm 2 and the colour coordinates do not change with the variation of pump power density. For localizing and heating the hyperthermia based cancer cells by using the NIR radiation a very low pump power density of about ~7.0 W/cm 2 has been established. The experimental observations prove the developed material to be used as a multifunctional nanomaterial in optical devices and biological applications.

Thermal and pump power effect in SrMoO4:Er3+-Yb3+ phosphor for thermometry and optical heating

“…2(b)). On further increasing the temperature, the UC emission peaks do not appear clear and becomes noisy due to the thermal quenching effect and hence it becomes difficult to measure the FIR due to the low signal to noise ratio [28,29]. The FIR of two thermally coupled energy levels only depends on energy level separation (energy gap) and temperature of the sample [13,18,30,31].…”

“…Zhang et al reported that the 2 H 11/2 level is also populated from the 4 S 3/2 level by a fast thermalization between these two states [25]. The population transfer from the 4 S 3/2 level to the 2 H 11/2 level is very rapid under the application of external temperature and the transfer of population between two thermally coupled levels is quasi-thermal type [20,28]. Therefore, the well known Boltzmann distribution can be used to describe the thermalization between the two thermally coupled levels by ignoring the effect of self absorption of the fluorescence [33].…”

“…The study on optical induced heating by using the rare earth doped upconverting materials for localization and treatment of hyperthermia based cancer cells has been performed by different researchers [21,22,28,37]. The temperature required for hyperthermia treatment is about 314-318 K. The prepared phosphor is competent to produce heating in the required temperature range via pump and probe scheme that may trigger cell diseases.…”

Multiple Temperature-Sensing Behavior of Green and Red Upconversion Emissions from Stark Sublevels of Er3+

“…In addition to the intrinsic thermally coupled energy levels of rare earth ions, the pair energy levels of Stark sublevels can also be thermally coupled and used to investigate FIR versus temperature characteristics [15,16,17,18]. Baxter et al [17], for example, used the coupled energy levels of 2 F 5/2(a) and 2 F 5/2(b) by Stark split of 2 F 5/2 levels in Yb 3+ ions to study FIR properties of Yb 3+ -doped silica fiber.…”

Effect of crystallinity on the optical thermometry sensitivity of Tm3+/Yb3+ codoped LiNbO3 crystal

“…Typically, upconversion emissions of Tm 3+ ion can be obtained under 980 nm excitation, Yb 3+ ion is usually used as the sensitizer ion to absorb 980 nm photons and transfer the energy to Tm 3+ ion [6,7]. And the thermally coupled energy levels or stark sublevels of Tm 3+ ion are proved to be appropriate for optical thermometry with high sensitivity and good accuracy recently [8][9][10][11].…”