Storage upconversion phosphors for SWIR?

[Stefano]

There's two types of upconversion phosphors: the "direct" ones, that absorb multiple low-energy photons to emit one higher-energy photon, and the "storage" ones, that must be charged with high-energy light (such as UV) and release their stored energy as photons when illuminated by IR light.

 

MaxMax sells both, and below is a video of a comparison between two storage phosphors:

 

 

What I noticed is how bright they are. The laser pointer used in the video is probably also quite powerful, but direct upconversion phosphors are very inefficient. [Edit: in the comments the author of the video says the laser is 980 nm, 100 mW]

 

Andy has experimented with them (read this topic), and he can tell you he needed a lot of light.

 

Of course the problem is that these phosphors need to be charged. If one wants to take video, then one way is to flash the phosphor in the blind times between frames, somehow synchronizing the flashes with the camera sensor (or maybe even continuously illuminating the phosphor and imaging it through a longpass filter that blocks the charging light).

 

The storage phosphors sold by MaxMax (in the video above) are rated to respond between 700 and 1500 nm.

 

To my knowledge, this techique hasn't been tried yet.

[Andy Perrin]

Interesting thought, although I’m not sure you aren’t a few years late on this - the price of InGaAs sensors on ebay has really dropped and I think I would recommend one of those to anyone thinking of getting into SWIR. Ultimately I was unsatisfied by the poor performance (bad contrast and poor sharpness) of projecting an image on a screen, it wasn’t just the intense light required by the upconverting phosphors that pushed me towards the TriWave. 

[Stefano]

Contrast might be improved by making the phosphor layer really thin, to limit the size of the diffusion cone. Sensitivity might suffer though.

[colinbm]

Excellent Stefano, thanks.

[Foxfire]

Thanks for the post, didn't know there are at least two types of upconversion phosphors. Would like to see how these will perform as a screens, but for the "storage" type, maybe this phosphor will dim out before any usable brightness image is recorded..

[Stefano]

Someone should test it to know. Repeated exposures could solve the issue, if present.

[Foxfire]

Yes, my encouragements also. From the vid it's not really well seen how fluorescent they are under UV, but who knows, maybe even a continuous illumination would work. Anyway, it wouldn't be too easy to build. 

 

Have seen some upconversion phosphors in Alibaba, these seemed to be "direct" types (RGB choices)