(Luminescence and Display Materials Division Centennial Outstanding Achievement Award) An Investigation of New Sources of Visible Light
Authors: Di Bartolo Baldassare 
Published: February 2020

The investigation of new sources of visible light is an interesting field of research, and has produced relevant results in the past few years. We are presenting a new process whose basic idea has been validated by a patent [1].
What follows is a brief description of this idea. A diode laser emits NIR radiation that excites a nanopowder of an oxide compound. When the intensity of the laser emission exceeds a certain amount, the nanopowder starts emitting a light that is white, with a spectrum similar to that of a black body or a ribbon bulb [2-8].
The following points describe our additional findings:
1. The nanopowder produces white light (WL) even if it is not doped with any optical active (i. e. luminescence producing) ion, but an appropriate dopant may increase the intensity of the WL.
2. In one of our recent investigations we have used a nanopowder of yttrium silicate prepared by the sol-gel procedure and a laser diode emitting radiation at 976 nm. We have found that the threshold intensity of the laser radiation necessary to produce the WL decreases with decreasing the pressure in the chamber where the nanopowder resides or increasing the temperature of the copper nanopowder-holder. Also, we have observed the accompanying effect of gaining WL intensity for a certain laser output power when lowering the pressure or increasing the temperature of the holder.
3. As said above the presence of an appropriate dopant favors the emission of the WL. In our case we have used trivalent ytterbium (Yb) which absorbs in the region where the laser emits. We have found that the presence of this ion lowers the laser power necessary to produce the WL by an amount that is greater for greater concentrations of Yb.
4. We have also tried to characterize more the WL by measuring such parameters as decay pattern following an interruption of the laser excitation and rise pattern following a sudden excitation. These patterns were also measured for different Yb concentrations, laser power, temperature, pressure. I will report on our findings.
References

1) PATENT APPROVED BY US PATENT OFFICE: N.9, 209, 597

Gokhan Bilir and Baldassare Di Bartolo
“Method and Device for Producing White Light from Y2O3 Nano-Powders”

2)G. Bilir and B. Di Bartolo, “Production of Bright, Wideband White Light from Y2O3 Nano-Powders Induced by Laser Diode Emission,” Optical Materials 36, 1357-1360 (2014)

3) G. Bilir, G. Özen, J. Collins, M. Cesaria, and B. Di Bartolo, “Unconventional Production of Bright White Light Emission by Nd-doped and Nominally Un-doped Y2O3 nano-powders”, IEEE Photonics Journal, 6 (4) 8200518 (2014)

4) G. Bilir, G. Özen, M. Bettinelli, F. Piccinelli, M. Cesaria, and B. Di Bartolo “Broadband Visible Light Emission from Nominally Un-doped and Cr3
+ doped Garnet Nano-powders”, IEEE Photonics Journal, 6 (4) 2201211 (2014)

5) G. Bilir, G. Özen, and B. Di Bartolo, “Peculiar Effects Accompanying the Production of White Light by IR Excited Nano-particles”, Optics and Spectroscopy 118, 114-117 (2015)

6) M. Cesaria, G. Bilir, G. Özen, M. Bettinelli, J. Collins, F. Piccinelli, and B. Di Bartolo, “Incandescet Lamp-Like Emission from Doped and Undoped Nanopowders,” in Nanostructures for Optics and Photonics, edited by B. Di Bartolo, J. Collins and L. Silvestri, 273-284, Springer 2015

7) M. Erdem, G. Eryurek, and B. Di Bartolo, “White Light Emission from Sol-gel Derived γ- Y2Si2O7 Nanoparticles”, Journal of Alloys and Compounds, 639, 485-87 (2015)

8) M.Erdem, G. Eryurek, and B. Di Bartolo, “Change of Spectral Output with Pressure and White Light Generation in Nanoscale Yb3+:Y2Si2O,7,” Optical Materials, 49, 90-93 (2015)