We have carried out a systematic study of optical emission in Yb-doped fiber glass materials which can be used for fiber laser applications. The stimulated emission crosssections of these materials have been calculated. The wavelength dependence of emission of these materials has been studied. The peak emission cross section in Yb-doped silica glass is 2.6 pm2 and the peak wavelength is at 974 nm. The codopants do not significantly alter the emission cross section or the peak wavelength of this cross section.

Photothermal therapy (PTT) has been widely used for the treatment of various medical conditions due to their noninvasive and cost-effective advantages. However, the light absorption and scattering of the biosystem limit the deep tissue applications of conventional PTT probes. In this paper, we proposed the sub-10 nm NaNdF 4 nanocrystals with both incident and emission wavelengths located at the optical window. Under 800 nm laser excitation, the maximum light-to-heat conversion efficiency of these ultrasmall photothermal agents is evaluated to be 85%. In addition, the conversion efficiency can be further adjusted through varying the doping concentration, changing the probe size, and coating the inert shell. Meanwhile, temperature feedback on the basis of the Nd 3+ luminescence signal validates the precise temperature manipulating inside the biological tissue, evidencing the feasibility of the proposed probes for PTT treatment. Beneficial from the efficient photothermal conversion and low energy loss of excitation/ emission photons in organic tissue, the effective treatment depth of the nanoprobes goes to 6 mm with the actual laser power density only ∼0.2 W/cm 2 . Finally, based on the rapid heating response of the formed nanoprobes, fast ablation treatment of a 1.5 cm pork tissue is achieved using pulsed laser.

Lifetime of lanthanide luminescence basically decreases with increasing the ambient temperature. In this work, we developed NaErF4 core–shell nanocrystals with compensation of the lifetime variation with temperature. Upconversion lifetime of various emissions remains substantially unchanged as increasing the ambient temperature, upon 980/1530 nm excitation. The concentrated dopants, leading to extremely strong interactions between them, are responsible for the unique temperature-independent lifetime. Besides, upconversion mechanisms of NaErF4 core-only and core–shell nanocrystals under 980 and 1530 nm excitations were comparatively investigated. On the basis of luminescent ratiometric method, we demonstrated the optical thermometry using non-thermally coupled 4F9/2 and 4I9/2 emissions upon 1530 nm excitation, favoring the temperature monitoring in vivo due to both excitation and emissions fall in the biological window. The formed NaErF4 core–shell nanocrystals with ultra-small particle size, highly efficient upconversion luminescence, unique temperature-independent lifetimes, and thermometry operated in a biological window, are versatile in applications such as anti-counterfeiting, time-domain manipulation, and biological thermal probes.

Lanthanide-ion-based thermometers have been widely researched and utilized as contactless temperature sensing materials. Cooperating with the unique optical and excellent physical properties of transparent ceramics, Er 3+ /Yb 3+ co-doped Y 2 Zr 2 O 7 transparent ceramics were successfully fabricated as temperature sensing window materials. Homogeneous distribution of elements inside samples together with high transmittance (nearly 73%) makes it possible as an observing window. Upon excitation at 980 nm, room-temperature luminescent performance was systemically researched for explaining the energy transfer mechanism between Yb 3+ and Er 3+ ions. The FIR method was introduced for thermally coupled energy levels to realize temperature sensing ability. Detecting sensitivity at different temperatures was also calculated (1.24% K −1 at 303 K), suggesting that Yb 3+ , Er 3+ :Y 2 Zr 2 O 7 are adequate for high sensitivity temperature detecting application. It is also investigated that the concentration of Yb 3+ ions not only affects the emission color at room-temperature but also has influence on the sensitivity of temperature and 10 mol % Yb 3+ , 2 mol % Er 3+ :Y 2 Zr 2 O 7 was found to be the most sensitive one. A demonstration experiment was also carried out to validate its application as a smart temperature sensing window. These results suggested that Yb 3+ , Er 3+ :Y 2 Zr 2 O 7 transparent ceramics can have potential for temperature monitoring applications, especially as novel window materials under extreme circumstances.

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