Longjiang Zheng

Short-wavelength upconversion emissions in Ho 3+ /Yb 3+ codoped glass ceramic and the optical thermometry behavior

Ho(3+)/Yb(3+) codoped glass ceramic was prepared by melt-quenching and subsequent thermal treatment. Under a 980 nm diode laser excitation, upconversion emissions from Ho(3+) ions centered at 540, 650, and 750 nm were greatly enhanced compared with those in the precursor glass. Especially, the short-wavelength upconversion emissions centered at 360, 385, 418, 445, and 485 nm were successfully obtained in the glass ceramic. An explanation for this phenomenon is given based on the fluorescence decay curve measurements. In addition, an optical temperature sensor based on the blue upconversion emissions from (5)F(2,3)/(3)K(8)→(5)I(8) and (5)F(1)/(5)G(6)→(5)I(8) transitions in Ho(3+)/Yb(3+) codoped glass ceramic has been developed. It was found that by using fluorescence intensity ratio technique, appreciable sensitivity for temperature measurement can be achieved by using the Ho(3+)/Yb(3+) codoped glass ceramic. This result makes the Ho(3+)/Yb(3+) codoped glass ceramic be a promising candidate for sensitive optical temperature sensor with high resolution and good accuracy.

Optical Thermometry through Green Upconversion Emissions in Er3+/Yb3+-Codoped CaWO4 Phosphor

Under 980 nm excitation, the temperature-dependent green upconversion emissions from Er3+/Yb3+-codoped CaWO4 phosphor were studied at temperatures from 294 to 923 K. By using the fluorescence intensity ratio technique, the maximum sensitivity for temperature measurement achieved here is approximately 0.0092 K-1, which is much higher than previously reported temperature sensors based on the fluorescence of Er3+ ions in other host materials. With the efficient upconversion fluorescence, the Er3+/Yb3+-codoped CaWO4 is a very promising candidate for optical high-temperature sensors with high sensitivity and good accuracy.

Optical temperature sensing based on the near-infrared emissions from Nd 3+ /Yb 3+ codoped CaWO 4

Under a 980 nm diode laser excitation, the near-infrared (NIR) emissions from Nd3+:4F7/2, 4F5/2, and 4F3/2 states in Nd3+/Yb3+ codoped CaWO4 powder were studied at temperatures ranging from 303 to 873 K. As the temperature increased, the NIR luminescence intensity was significantly enhanced and nearly 190-fold enhancement was achieved at 873 K compared with that at 303 K. By using the fluorescence intensity ratio technique, the thermometry behaviors through the NIR emissions were investigated. The results illustrate that the sensitivity and the accuracy achieved here are much higher than temperature sensors based on other rare earth ion doped materials.

Multifunctional nanoparticles based on the Nd³⁺/Yb³⁺ codoped NaYF₄.

Broadband near-infrared luminescence (NIR) from 720 to 950 nm, which is located in the biological window, has been successfully achieved from Nd3+/Yb3+ codoped hexagonal NaYF4 nanoparticles when excited by 980 nm diode laser. Using the fluorescence intensity ratio technique, the temperature sensing behavior of Nd3+ NIR emissions exhibits various advantages over other rare earth ion based nanothermometers. The light-induced thermal loading for the 980 nm excited NaYF4:Nd3+/Yb3+ was also investigated. The results illustrate the multifunctionality of such fluoride nanoparticles, which could simultaneously act as the luminescent nanothermometers and nanoheaters and find potential application in photothermal therapy.

Optical thermometry based on the red upconversion fluorescence of Er 3+ in CaWO 4 :Yb 3+ /Er 3+ polycrystalline powder

Based on the fluorescence intensity ratio method, the temperature-sensing behavior through thermally coupled levels (TCL) of the H_11/22 and S_3/24 states as well as the sub-levels of the F_9/24 state of Er³⁺ has been studied. The thermometry is observed to be dependent on the pump power for the H_11/22 and S_3/24 states, leading to an error of more than 20 K at 478 K. By utilizing the sub-levels of the F_9/24 state, such a problem could be solved. The maximum sensitivity is about 0.15%  K^-1 at 298 K. This will provide guidance on selecting appropriate and practical TCL for precisely sensing the temperature.

Valley-to-peak intensity ratio thermometry based on the red upconversion emission of Er 3+ .

Upon 976 nm diode laser excitation, the temperature dependence of the red upconversion emission of Er³⁺ in CaWO₄:Yb³⁺/Er³⁺ phosphor was studied from 298 to 478 K. The spectrum was verified to consist of two Stark components originating from two Stark sublevels of ⁴F_9/2 excited state to ⁴I_15/2 ground state of Er³⁺. The valley-to-peak intensity ratio (VPR) of this double-peak spectrum was found to increase linearly with the rise of temperature. The maximum relative sensitivity of this VPR method was obtained to be about 0.20% K^-1 at 298 K. Moreover, a study on the power dependence was also performed, suggesting that VPR method is immune to the pump power and is thus suitable for monitoring the temperature.