Below the Earth’s crust, temperatures may reach beyond 600 K, impeding the batteries used to power conventional thermometers. Fluorescence intensity ratio based temperature probes can be used with optical fibers that can withstand these conditions. However, the probes tend to exhibit narrow operating ranges and poor sensitivity above 400 K. In this study, we have investigated single and dual layered YVO 4 : Ln 3+ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) thin films (100–150 nm) for use in fluorescence intensity ratio based temperature sensors in the 300–850 K range. The type of lanthanide emission can be fine-tuned by adjusting the thickness of each layer, and the layered structure allows for emission from otherwise incompatible lanthanide pairs. This novel multi-layered approach enables high sensitivity over a broad temperature range. The highest relative sensitivity was achieved for a dual layered YVO 4 : Eu 3+ /YVO 4 : Dy 3+ sample, exhibiting a maximum sensitivity of 3.6% K −1 at 640 K. The films were successfully deposited on all tested substrates (silicon, iron, aluminum, glass, quartz, and steel), and can be applied homogenously to most surfaces without the use of binders. The films are unaffected by water, enabling non-contact temperature sensing in water, where IR thermometers are not an option.

The effect of the native silicon oxide layer on the passivation properties of Al 2 O 3 on p-type Si surfaces has been investigated. This was done by comparing effective carrier lifetime, surface saturation current density, fixed charge, and density of interface states of samples, where the native oxide was not removed prior to Al 2 O 3 passivation, with samples subjected to a 3 min HF-dip. The sample with the native oxide exhibits excellent surface passivation post-annealing, with a surface saturation current density of 13 fA/cm 2 and significantly longer effective lifetime compared to the sample, where the native oxide was removed. Capacitance-voltage measurements of a sample with the native oxide revealed a remarkably low density of interface states (10 10 eV −1 cm −2 ), almost three times lower than a sample where the native oxide was removed prior to Al 2 O 3 deposition. The results indicate that a thin layer of native oxide improves the Al 2 O 3 surface passivation of silicon.

Thin films of YVO4:Yb3+ exhibiting intense NIR emission have been deposited by atomic layer deposition. The NIR emission is attributed to a quantum splitting process that could be used to enhance the efficiency of solar cells.